Report on Cyclonic Disturbances Over North Indian Ocean

World Meteorological Organisation India Meteorological Department RSMC-Tropical Cyclones Report No…/2013

REPORT ON CYCLONIC DISTURBANCES OVER NORTH INDIAN OCEAN

DURING 2012

SATELLITE AND DWR IMAGERIES OF CYCLONIC STORM NILAM

RSMC-TROPICAL CYCLONES, NEW DELHI March 2013

WMO

INDIA METEOROLOGICAL DEPARTMENT

RSMC- TROPICAL CYCLONES, NEW DELHI MARCH 2013

INDIA METEOROLOGICAL DEPARTMENT

DOCUMENT AND DATA CONTROL SHEET

1. Document title Report on cyclonic disturbances over the north Indian Ocean during 2012 2. Document Technical Report type 3. Issue No. RSMC- Tropical Cyclone Report No. 02/2012 4. Issue date March-2013 5. Security Unclassified Classification 6. Control Status Uncontrolled 7. Document Scientific Report type 8. No. of Pages 209 9. No. of Figures - 10. No. of Tables - 11. No. of - reference 12. Distribution Unrestricted 13. Language English 14. Authors RSMC-Tropical Cyclones, New Delhi 15. Originating RSMC-Tropical Cyclones, New Delhi Division/Group 16. Reviewing Director General of Meteorology, India Meteorological and Department Approving Authority 17. End users Operational Forecaster, NWP Modeler, Disaster Manager and Researcher 18. Abstract The activities of Regional Specialised Meteorological Centre (RSMC) – Tropical Cyclone New Delhi are briefly presented alongwith the current state of art for monitoring and prediction of cyclonic disturbances over the north Indian Ocean. This report further describes the characteristics of cyclonic disturbances formed over the north Indian Ocean during 2012. The special emphasis has been given on the features associated with genesis, intensification, movement, landfall and associated adverse weather like heavy rain, strong wind and storm surge. The performance of the forecasts issued by RSMC, New Delhi with respect to tropical cyclones are verified and discussed. Also the performance of various dynamical and statistical models for cyclone forecasting has been evaluated and discussed. 19. Key words Cyclogenesis, intensity, track, landfall, NWP model, forecast verification

CONTENTS

Page No

INTRODUCTION 1

CHAPTER- I 22

ACTIVITIES OF REGIONAL SPECIALISED METEOROLOGICAL CENTRE, NEW DELHI

CHAPTER –II 23-157

CYCLONIC ACTIVITIES OVER NORTH INDIAN OCEAN DURING 2012

CHAPTER – III 158-194

PERFORMANCE OF STATISTICAL AND DYNAMICAL NWP MODELS DURING 2012

CHAPTER – IV 195-209

PERFORMANCE OF TRACK AND INTENSITY PREDICTION OF CYCLONES BY IMD DURING 2012

INTRODUCTION

Regional Specialized Meteorological Centre (RSMC) - Tropical Cyclones, New Delhi, which is co-located with Cyclone Warning Division has the responsibility of issuing Tropical Weather Outlook and Tropical Cyclone Advisories for the benefit of the countries in the World Meteorological Organization (WMO)/ Economic and Social Co- operation for Asia and the Pacific (ESCAP) Panel region bordering the Bay of Bengal and the Arabian Sea, namely, Bangladesh, Maldives, Myanmar, Pakistan, Sultanate of Oman, Sri Lanka and Thailand. It has also the responsibilities as a Tropical Cyclone Advisory Centre (TCAC) to provide Tropical Cyclone Advisories to the designated International Airports as per requirement of International Civil Aviation Organization (ICAO).

The broad functions of RSMC- Tropical Cyclones, New Delhi are as follows:

 Round the clock watch on weather situations over the entire north Indian Ocean.  Analysis and processing of global meteorological data for diagnostic and prediction purposes.  Detection, tracking and prediction of cyclonic disturbances in the Bay of Bengal and the Arabian Sea.  Running of numerical weather prediction models for tropical cyclone track and storm surge predictions.  Interaction with National Disaster Management Authority and National Disaster Management, Ministry of Home Affairs, Govt. of India to provide timely information and warnings for emergency support services. RSMC-New Delhi also coordinates with National Institute of Disaster Management (NIDM) for sharing the information related to cyclone warning.  Implementation of the Regional Cyclone Operational Plan of WMO/ESCAP Panel.  Issue of Tropical Weather Outlook and Tropical Cyclone Advisories to the Panel countries in general.  Issue of Tropical Cyclone advisories to International airports in the neighbouring countries for International aviation.  Collection, processing and archival of all data pertaining to cyclonic disturbances viz. wind, storm surge, pressure, rainfall, damage report, satellite and Radar derived information etc. and their exchange with Panel member countries.  Preparation of comprehensive annual reports on cyclonic disturbances formed over North Indian Ocean every year.  Preparation of annual review report on various activities including meteorological, hydrological and disaster preparedness and prevention activities of panel member countries.  Research on storm surge, track and intensity prediction techniques.

CHAPTER-I

ACTIVITIES OF REGIONAL SPECIALIZED METEOROLOGICAL CENTRE – TROPICAL CYCLONES, NEW DELHI

1.1 Area of Responsibility

The area of responsibility of RSMC- New Delhi covers Sea areas of north Indian Ocean, north of equator between 450 E and 1000 E and includes the member countries of WMO/ESCAP Panel on Tropical Cyclones viz, Bangladesh, India, Maldives, Myanmar, Pakistan, Sri Lanka, Sultanate of Oman and Thailand as shown in Fig. 1.1.

Fig. 1.1 Area of responsibility of RSMC- Tropical Cyclone, New Delhi

1.2 Naming of tropical cyclones over north Indian Ocean:

The WMO/ESCAP Panel on Tropical Cyclones at its twenty-seventh Session held in 2000 in Muscat, Sultanate of Oman agreed in principle to assign names to the tropical cyclones in the Bay of Bengal and Arabian Sea. After long deliberations among the member countries, the naming of the tropical cyclones over north Indian Ocean commenced from September 2004. RSMC New Delhi is continuing the naming of Tropical Cyclones formed over North Indian Ocean since October 2004. The first name was „ONIL‟ which developed over the Arabian Sea (30 September to 03 October, 2004). According to approved principle, a list of 64 names in eight columns has been prepared. The name has

been contributed by Panel members. The RSMC-tropical cyclones New Delhi gives a tropical cyclone an identification name from the above name list. The Panel member‟s name is listed alphabetically country-wise in each column. The names are used sequentially column-wise. The first name starts from the first row of column one and continues sequentially to the last row in column eight. The identification system covers both the Arabian Sea and the Bay of Bengal. These lists are used sequentially, and they are not rotated every few years unlike the Atlantic and Eastern Pacific lists. Out of 64 approved names, 30 names have been utilized till the end of year 2012.

1.3 Observational System

A brief description of different types of observational network of India Meteorological Department (IMD) and observations collected from networks are given below.

1.3.1 Surface Observatories

IMD has a good network of surface observatories satisfying the requirement of World Meteorological Organization. There are 559 surface observatories in IMD. The data from these stations are used on real time basis for operational forecasting. The surface observatory network of IMD is shown in fig 1.2

Fig.1.2. Surface Observatory Network of IMD

20 moored ocean buoys including Meteorological Buoy (MB), Shallow Water (SW), Deep Sea (DS) and Ocean Thermal (OT) buoys have been deployed over the Indian Sea, under the National Data Buoy Programme (NDBP)

of the Ministry of Earth Sciences, Government of India. Out of 14 Meteorological buoys 11 are active and 3 are under maintenance.

A number of Automated Weather Stations (AWS) are also in operation and provide surface observations on hourly basis which are utilized in cyclone monitoring and forecasting. The AWS network of IMD is shown in fig 1.3

Fig.1.3. IMD’s network of 675 AWS (125 old+550 new AWS)

High Wind Speed Recorder (HWSR) system has been installed and operational at 13 coastal stations. These are Digha, Visakhapatnam, Chennai, Nellore, Machilipatnam, Karaikal, Puri, Balasore, Gopalpur, Paradip, Mumbai (Colaba), Veraval & Dwarka.

1.3.2. Upper Air Observatories

There are at present 62 Pilot Balloon Observatories (PBO), 37 Radiosonde/Radio wind (RS/RW) observatories and 02 Radio sonde Observatories. The upper air meteorological data collected all over the country

are used on real time basis for operational forecasting. The PBO network and RS/RW observatory network of IMD is shown in fig 1.4 & 1.5 respectively.

Upper Air Network -62

Fig.1.4. Pilot balloon observatory network of IMD

Fig.1.5. RS/RW observatory (including 10 GPS stations) network of IMD

A Wind Profiler/Radio Acoustics Sounding System has been installed at Pashan, Pune in collaboration with M/S SAMEER, Mumbai and IITM, Pune. The instrument is capable of recording upper air temperature up to 3 km and upper wind up to 9 km above Sea level.

1.3.3. Cyclone Detection Radars

1.3.3.1 Current status:.

There are 7 S-Band Radars which are operational for cyclone detection at coastal stations. Out of these, 5 Doppler Weather Radars are operational at Chennai, Kolkata, Machilipatnam, Visakhapatnam and Sriharikota. 2 analogue radars are working at Kochi, Karaikal. In first Phase of modernization plan of IMD Radar network, 12 Nos of DWRs procured from M/s Metstar China for installation at Delhi (Palam), Hyderabad, Agartala, Nagpur, Patna, Mohanbari, Patiala, Lucknow, Bhopal, Goa, Paradip, and Karaikal. Out of these DWRs, 8 have already been commissioned. DWR at Bhopal is under installation and likely to be commissioned by the end of March, 2013. Remaining 3 Nos are likely to be installed at Goa, Paradip, and Karaikal. IMD has procured two nos. of indigenous DWRs under an ongoing scheme and are installed at Bhuj and Mumbai. IMD has also procured 2 C-band dual polarized DWRs and are installed and commissioned at Delhi (HQ), Mausam Bhawan and at Jaipur.

Fig. 1.6. S-Band Cyclone Detection Radar Network

Doppler Weather Radars Provide vital informations on radial velocity and spectral width in addition to reflectivity. Reflectivity estimates obtained from these radars are more accurate in comparison to those from conventional radars as the Doppler Weather Radars have capability for correcting the values for clutters, bright band etc. Surface Rainfall Intensity (second level product derived from reflectivity) and other hydrological products like Precipitation Accumulation

(PAC), Vertical Integrated Liquid (VIL) is very important for issuing warnings for heavy rain, flash flood and hail. The algorithms for generation of these products employ some adaptable parameters which depends on drop size distribution (DSD) present in the precipitation (DSD is different for different season, geographical location and type of precipitation).

1.3.3.2 Future Plan:- In the phase-II of modernization of IMD Radar network, more DWRs will be procured and inducted in the radar network to bring entire country under Weather Radar coverage. The project comprises of sustenance of existing radar network and commissioning of state-of-art technology based radars all over the country and on priority at coastal regions. The program of installation of these DWRs is expected to be completed in Five year plan 2012-2017.

Outcome of the project in terms of level of improvement in the weather forecasting service is given below:

(i) Early detection of tropical cyclones and better prediction of their movement and landfall. This will allow more focused mitigation actions. More accurate predictions of landfall will help in identifying damage prone areas for evacuation of people. Dissemination of forecasts and products at district level, particularly for use by the farming community.

(ii) Monitoring and warnings for severe weather events like flash floods, thunderstorms, dust storms, heavy rainfall, Gale winds, hail etc. Timely warnings of these severe weather events can save more lives and minimize the damages to properties.

1.3.4 Satellite Monitoring

1.3.4.1 Current status:

At present IMD is receiving and processing meteorological data from two Indian satellites namely Kalpana-1 and INSAT-3A. Kalpana-1 was launched on 12th September, 2002 and is located at 740 E. INSAT-3A was launched on 10 April, 2003 and is located at 93.50 E. Kalpana-1 and INSAT-3A both have pay load of Very High Resolution Radiometer (VHRR) for imaging the earth in three channels viz. Visible (0.55-0.75 µm), Infra-Red (10.5-12.5µm) and Water vapour (5.7-7.1µm) having resolution of 2X2 km in visible and 8X8 km in Water vapour (WV) and Infra red (IR) channels. In addition, the INSAT-3A has a three channel Charge Coupled Device (CCD) payload for imaging the earth in Visible (0.62- 0.69um), Near IR (0.77-0.86µm) and Short Wave IR (1.55-1.77µm) bands of Spectrum. The Resolution of CCD payload in all the three channels is 1KmX 1 Km. At Present about 48 nos. of satellite images are taken daily from Kalpana-1 which is the main operational satellite and approximately 20 images are taken from INSAT-3A. Imaging from CCD is done 5 times during daytime only. All the

received data from the satellite are processed and archived in National Satellite Data Centre (NSDC), New Delhi.

Indian Meteorological Data Processing System (IMDPS) is processing meteorological data from INSAT VHRR and CCD data and supports all operational activities of the Satellite Meteorology Division on round the clock basis. Cloud Imagery Data are processed and transmitted to forecasting offices of the IMD as well as to the other users in India and foreign countries.

Apart from generating half hourly cloud imagery, IMDPS produces derived products from the processed data as follows:  Cloud Motion Vectors (CMV) are derived half hourly using Visible & IR images from the operational Kalpana-I Satellite.  Water Vapour Winds (WVWs) are derived half hourly using IR & Water vapour images from the operational Kalpana-I Satellite.  Sea Surface Temperatures (SST) are computed at 10 x 10 grid intervals from all Kalpana-I data on half hourly /daily /weekly/monthly basis.  Outgoing Longwave Radiation (OLR) are computed at 0.250 x 0.250 grid intervals from all Kalpana-I data on half hourly /daily /weekly/monthly basis.  Quantitative Precipitation Estimation (QPE) is generated at 10 x 10 Grid from Kalpana-1 imagery on half hourly/daily/weekly/monthly basis.  Upper Tropospheric Humidity (UTH). At present Dvorak technique is widely used but manually applied. Recently efforts have been made for automation of this technique. Automated Dvorak technique is running in experimental mode at Synoptic Application Unit, Satellite Meteorology Division. Satellite Application Unit is also using Microwave imageries operationally from NOAA, Metops, DMSP satellites for locating the tropical systems.

Satellite Application Unit issues three hourly bulletins in general and hourly and half hourly bulletins in case of tropical cyclones and other severe weather events. The unit has modified these bulletins in 2013.

With the Web Archival System developed at IMD, KALPANA/INSAT3A data products and imageries are being archived since January 2009. Satellite bulletins are archived since 2012. The automatic script is being used to keep and update the images/products on the website for 1 month. These are available to all users.

On 23rd Sept 09, polar orbiting satellite OCEANSAT–II has been launched by Indian Space Research Organisation (ISRO) which carries a ku band pencil beam scatterometer to provide ocean surface winds at 10 m height for early detection of tropical cyclones. Winds from this satellite are used regularly for locating the centre and intensity of the tropical systems in the formative stage.

Space Application Centre (SAC), ISRO Ahmedabad has developed a technique to predict the formation of tropical cyclones over north Indian Ocean (Bay of Bengal & Arabian Sea) before 24-96 hrs lead time based on OCEANSAT-II Scatterometer wind. Satellite Division of IMD has acquired the software and validating the technique before making it operational.

On 12th October, 2011 another Polar orbiting satellite MEGHA TROPIQUES has been launched which covers the area 20º N to 20º S. MEGHA TROPIQUES has three payloads: 1. MADRAS: a microwave imager aimed mainly at studying precipitation and clouds properties, 2. SAPHIR: a 6 channels microwave radiometer for the retrieval of water vapour vertical profiles and horizontal distribution, 3. SCARAB: a radiometer devoted to the measurement of outgoing radiative fluxes at the top of the atmosphere. 4. The basic principles of the MEGHA-TROPIQUES mission are to provide simultaneous measurements of several elements of the atmospheric water cycle, water vapour, clouds, condensed water in clouds, precipitation and evaporation, measure the corresponding radiative budget at the top of the atmosphere, ensure high temporal sampling in order to characterise the life cycle of the convective system and to obtain significant statistics.

1.3.4.2. Digital Meteorological Data Dissemination:

IMD transmits processed imagery, meteorological data and facsimile weather charts to field forecasting offices distributed over the country using the Digital Meteorological Data Dissemination (DMDD) facility, through INSAT in broadcast mode. The bulletins providing description of the cloud organization and coverage are also sent as advisory to forecasting offices every synoptic hour. When cyclones are detected in satellite imagery, these bulletins are sent every hour. Such advisories are also transmitted to the neighbouring countries.

Processed satellite imagery, analyzed weather charts and conventional synoptic data are up-linked to the satellite in C-band. Satellite broadcasts these data to DMDD receiving stations in S-band. DMDD receiving stations analyze weather imagery and other data to generate required forecast. There are 37 no. of DMDD stations installed in India. Three DMDD receiving stations are also operating in neighbouring SAARC countries at Sri Lanka, Nepal and Maldives. These stations are receiving direct broadcast of cloud imagery, weather facsimile charts and meteorological data on an operational basis. The frequency of transmission from ground to satellite (uplink) is 5886 MHz and that of downlink is 2586 MHz.

1.3.4.3 Future Plan:

Under INSAT-3D programme, a new Geostationary Meteorological Satellite, INSAT-3D is being designed by ISRO. It will have an advanced imager with six imagery channels (VIS, SWIR, MIR, TIR-1, TIR-2, & WV) and a nineteen channel sounder (18 IR &1 Visible) for derivation of atmospheric temperature and moisture profiles. It will provide 1 km. resolution imagery in visible band, 4 km resolution in IR band and 8 km in water vapour channel. This new satellite is scheduled for launch in 2013 and will provide much improved capabilities to the meteorological community and users. In preparation for the reception and processing of this data, SAC-ISRO has installed a data reception and processing system to process the data. After full commissioning, the system will be able to receive and process the data from all the above three satellites on real time mode and produce the following products with respect to cyclone monitoring:

1. Outgoing Long wave Radiation (OLR) 2. Quantitative Precipitation Estimation ( QPE) 3. Sea Surface Temperature (SST) 4. Cloud Motion Vector (CMV) 5. Water Vapor Wind (WVW) 6. Upper Tropospheric Humidity (UTH) 7. Temperature, Humidity profile 8. Value added parameters from sounder products a. Geo-potential Height b. Layer Perceptible Water c. Total Perceptible Water d. Lifted Index e. Dry Microburst Index f. Maximum Vertical Theta-E Differential g. Wind Index 9. Flash Flood Analyzer

1.4. Analysis and Prediction system

Cloud imageries from Geostationary Meteorological Satellites INSAT-3A and METSAT (KALPANA-1) are the main sources of information for the analysis of tropical cyclones over the data-sparse region of north Indian Ocean. Data from Oceansat & scatteometry based satellites like ASCAT & WINDSAT and Ocean buoys also provide vital information. Ship observations are also used critically during the cyclonic disturbance period. When the system comes closer to the coastline, the system location and intensity are determined based on hourly observations from Radar as well as from coastal observatories. The AWS stations along coast are also very useful as they provide hourly observations on real time basis. The Water Vapor based Wind Vector (WVWV) and Cloud Motion Vectors (CMV) in addition to the conventional wind vectors observed by Radio Wind (RW) instruments are very useful for monitoring and prediction of cyclonic

disturbance, especially over the Sea region. The direction and speed of the movement of a tropical cyclone are determined primarily from the three hourly displacement vectors of the centre of the system and by analyzing satellite imageries. The analysis of synoptic and asynoptic observations is performed four times daily at 00, 06, 12, and 18 UTC. During cyclonic disturbance (depression and above intensity), synoptic charts are prepared and analysed every three hour to monitor the tropical cyclones over the north Indian Ocean. Various strategies have been adopted in recent years for improvement of analysis and prediction of cyclone. The tropical cyclone analysis, prediction and decision-making process is made by blending scientifically based conceptual models, dynamical & statistical models, meteorological datasets, technology and expertise. Conventional observational network, automatic weather stations (AWS), buoy & ship observations, cyclone detection radars and satellites are used for this purpose. A new weather analysis and forecasting system in a digital environment is used to plot and analyse different weather parameters, satellite, Radar and Numerical Weather Prediction (NWP) model products. An integrated fully automated forecasting environment facility is thus available for this purpose.

In this hybrid system, synoptic method could be overlaid on NWP models supported by modern graphical and GIS applications to produce • high quality analyses • Ensemble of forecasts from NWP models at different scales - global, regional and mesoscale A schematic representation of the monitoring and analysis, forecast and warning procedure is given in Fig.1.7.

Initial conditions Action (Observations) Synopic Synoptic analysis Satellite Radar Forecaster NWP Users* Model Runs of different Models, Consecutive runs from the same model, Ensemble runs Numerical End ("choosing the forecasts forecast best member")

*Central / State Govt/ Media/ Public

Fig.1.7. Strategy adopted for cyclone analysis and forecasting

The Tropical Cyclone Module installed in this forecasting system has the following facilities.

 Analysis of all synoptic, satellite and NWP model products for genesis, intensity and track monitoring and prediction  Preparation of past and forecast tracks upto 120 hrs  Depiction of uncertainty in track forecast  Depiction of observed and forecast winds in different quadrants of cyclone.

All the available data and products form various national and international sources are systematically considered for analysis and prediction of cyclones. Various data and products utilized for this purpose are as follows.

 Data and analysis Products through digitized system as mentioned above.  Radar data and products from IMD‟s radar network and neighbouring countries  Satellite imageries and products from IMD and international centres  Data analysis and Dynamical & statistical Model products from various national and international centres

1.5. NWP Models in operational use during the year 2012

1.5.1. Global Forecast System

The Global Forecast System (GFS), adopted from National Centre for Environmental Prediction (NCEP), at T382L64 (~ 35 km in horizontal) resolution (incorporating Grid point Statistical Interpolation (GSI) scheme as the global data assimilation for the forecast up to 7 days) was implemented at New Delhi on IBM based High Power Computing Systems (HPCS) in May 2010. The GFS T382L64 has been replaced by the upgraded version GFS T574L64 (GSI 3.0.0 and GSM 9.1.0) model (~ 25 km in horizontal over the tropics) in April 2012. The model is run twice in a day (00 UTC and 12 UTC). The real-time outputs are made available to the national web site of IMD (www.imd.gov.in).

1.5.2. Regional Forecast System

IMD operationally runs three regional models WRFDA-WRFARW(v3.2), HWRF and Quasi-Lagrangian Model (QLM) for short-range prediction during cyclone condition.

1.5.2.1. Non-hydrostatic mesoscale modeling system WRFDA-WRF-ARW

The mesoscale forecast system Weather Research and Forecast WRF (version 3.2) with 3DVAR data assimilation is being operated daily twice to generate mesoscale analysis at 27 km and 9 km horizontal resolutions using IMD

GFS-T574L64 analysis/forecast as first guess. Using initial and boundary conditions from the WRFDA, the WRF (ARW) is run for the forecast up to 3 days with double nested configuration with horizontal resolution of 27 km and 9 km and 38 Eta levels in the vertical. The model mother domain covers the area between lat. 25º S to 45º N long 40º E to 120º E and child covers whole India. The performance of the model is found to be reasonably skilful for cyclone genesis and track prediction. At ten other regional centres, very high resolution mesoscale models (WRF at 3 km resolution) are also operational with their respective regional setup/configurations.

1.5.2.2. Quasi-Lagrangian Model (QLM)

The QLM, a multilevel fine-mesh primitive equation model with a horizontal resolution of 40 km and 16 sigma levels in the vertical, is being used for tropical cyclone track prediction in IMD. The integration domain consists of 111x111 grid points centred over the initial position of the cyclone. The model includes parameterization of basic physical and dynamical processes associated with the development and movement of a tropical cyclone. The two special attributes of the QLM are: (i) merging of an idealized vortex into the initial analysis to represent a storm in the QLM initial state and (ii) imposition of a steering current over the vortex area with the use of a dipole. The initial fields and lateral boundary conditions are taken from the IMD GFS T574L64. The model is run twice a day based on 00 UTC and 12 UTC initial conditions to provide 6 hourly track forecasts valid up to 72 hours. The track forecast products are disseminated as a World Weather Watch (WWW) activity of RSMC, New Delhi.

1.5.2.3. Hurricane WRF (HWRF) Model

Recently under Indo-US joint collaborative program, IMD adapted Hurricane-WRF (HWRF) model for Tropical Cyclone track and intensity forecast for North Indian Ocean region for its operational requirements. The basic version of the model HWRFV (3.2+) which was operational at EMC, NCEP, USA was ported on IMD IBM P-6/575 machine with nested domain of 27 km and 9 km horizontal resolution and 42 vertical levels with outer domain covering the area of 800x800 and inner domain 60x60 with centre of the system adjusted to the centre of the observed cyclonic storm. The outer domain covers most of the North Indian Ocean including the Arabian Sea and Bay of Bengal and the inner domain mainly covering the cyclonic vortex which moves along the movement of the system. The model has special features such as vortex initialization, coupled with Ocean model to take into account the changes in SST during the model integration, tracker and diagnostic software to provide the graphic and text information on track and intensity prediction for real-time operational requirement.

As part of model validation, case studies were undertaken to test the ability of the model for the cyclonic storms formed during the year 2010 and model forecasts are produced upto 5 days during the 2011 cyclone season as an experimental forecast in real-time. In these runs only the atmospheric model (HWRF) has been tested. The model has been run on real time twice a day (started from cyclone season 2012) based on 00 UTC and 12 UTC initial conditions to provide 6 hourly track and intensity forecasts valid up to 72 hours. The model uses IMD GFS-T574L64 analysis/forecast as first guess.The Ocean Model (POM-TC) and Ocean coupler requires the customization of Ocean Model for Indian Seas. In this regards, IMD is expecting to work in collaboration with Indian National Centre for Ocean Information Services (INCOIS), Hyderabad which is running the Ocean Models (POM)/Hybrid co-ordinate ocean model (HYCOM) to support in porting the Ocean Model with Indian Ocean climatology and real time data of SST over Indian Seas.

1.5.3. Genesis Potential Parameter (GPP)

A cyclone genesis parameter, termed the genesis potential parameter (GPP), for the North Indian Ocean is developed. The parameter is defined as the product of four variables, namely vorticity at 850 hPa, middle tropospheric relative humidity, middle tropospheric instability, and the inverse of vertical wind shear. The parameter is operationally used for distinction between non- developing and developing systems at their early development stages. The composite GPP value is found to be around three to five times greater for developing systems than for non-developing systems. The analysis of the parameter at early development stage of a cyclonic storm is found to provide a useful predictive signal for intensification of the system.

The grid point analysis and forecast of the genesis parameter up to seven days is also generated on real time (available at http://www.imd.gov.in/section/nhac/dynamic/Analysis.htm). Higher value of the GPP over a region indicates higher potential of genesis over the region. Region with GPP value equal or greater than 30 is found to be high potential zone for cyclogenesis. The analysis of the parameter and its effectiveness during cyclonic disturbances in 2012 affirm its usefulness as a predictive signal (4-5 days in advance) for cyclogenesis over the North Indian Ocean.

1.5.4. Statistical Dynamical model for Cyclone Intensity Prediction (SCIP)

A statistical-dynamical model SCIP has been implemented for real time forecasting of 12 hourly intensity up to 72 hours. The model parameters are derived based on model analysis fields of past cyclones. The parameters selected as predictors are: Initial storm intensity, Intensity changes during past 12 hours, Storm motion speed, initial storm latitude position, vertical wind shear averaged along the storm track, vorticity at 850 hPa, divergence at 200 hPa and SST. For the real-time forecasting, model parameters are derived based on the

forecast fields of ECMWF model. The method is found to provide useful guidance for the operational cyclone forecasting.

1.5.5. Multi-model ensemble (MME) technique

The multi model ensemble (MME) technique is based on a statistical linear regression approach. The predictors selected for the ensemble technique are forecasts latitude and longitude positions at 12-hour interval up to 72-hour of five operational NWP models. In the MME method, forecast latitude and longitude position of the member models are linearly regressed against the observed latitude and longitude position for each forecast time at 12-hours intervals for the forecast up to 72-hour. The outputs at 12 hours forecast intervals of these models are first post-processed using GRIB decoder. The 12 hourly predicted cyclone tracks are then determined from the respective mean sea level pressure fields using a cyclone tracking software. Multiple linear regression technique is used to generate weights (regression coefficients) for each model for each forecast hour (12hr, 24hr, 36 hr, 48hr, 60hr, 72hr) based on the past data. These coefficients are then used as weights for the ensemble forecasts. 12-hourly forecast latitude (LATf) and longitude (LONf) positions are defined by multiple linear regression technique. In the updated version, MM5 model in the ensemble member is replaced by IMD WRF model and also included IMD GFS T574L64. A collective bias correction is applied in the MME by applying multiple linear regression based minimization principle for the member models viz., WRF(ARW), QLM, GFS(IMD), GFS(NCEP), ECMWF and JMA. All these NWP products are routinely made available in real time on the IMD web site www.imd.gov.in. IMD also makes use of NWP products prepared by some other operational NWP Centres like, ECMWF (European Centre for Medium Range Weather Forecasting), GFS (NCEP), JMA (Japan Meteorological Agency), UKMO etc.

1.5.6. Rapid Intensification (RI) Index

A rapid intensification (RI) index has been developed for tropical cyclones over the Bay of Bengal (Kotal and Roy Bhowmik, 2013). The RI index uses large- scale characteristics of tropical cyclones to estimate the probability of RI over the subsequent 24-h. The RI is defined as an increase of intensity by 30 kt (15.4 ms- 1) during 24-h. The RI index technique is developed by combining threshold (index) values of the eight variables for which statistically signiﬁcant differences are found between the RI and non-RI cases. The variables are : storm latitude position, previous 12-h intensity change, initial storm intensity, vorticity at 850 hPa, divergence at 200 hPa, vertical wind shear, lower tropospheric relative humidity, and storm motion speed. The probability of RI is found to increase from 0% to 100% when the total number of parameters satisfying the conditions increases from zero to eight. As part of validation, case studies were undertaken to test the ability of the RI index for the cyclonic storms formed during the cyclone season, 2011-2012 as an experimental mode. Although forecasts were not available to operational

forecaster in real time, the results of 2012 are presented in chapter-III, section 3.7. The forecast will be made available in real time from 2013.

1.5.7. Tropical Cyclone Ensemble Forecast based on Global Models Ensemble (TIGGE) Data

As part of WMO Program to provide a guidance of tropical cyclone (TC) forecasts in near real-time for the WMO/ESCAP Panel Member Countries based on the TIGGE cyclone XML (CXML) data, IMD implemented JMA supported software for real-time forecast over north Indian Ocean during 2011.

The Ensemble and deterministic forecast products from ECMWF (50+1 Members), NCEP (20+1 Members), UKMO (23+1 Members) and MSC (20+1 Members) are available near real-time for north Indian Ocean region for named cyclones. These Products includes: Deterministic and Ensemble track forecasts, strike probability maps, strike probability of cities within the range of 120 kms 4 days in advance. The JMA provided software to prepare Web page to provide guidance of tropical cyclone forecasts in near real-time for the WMO/ESCAP Panel Members. The forecast products are made available in real time.

1.5.8. NCMRWF GEFS

 At NCMRWF the Global ensemble forecasting system (GEFS) configuration consists of four cycles corresponding to 00Z, 06Z, 12Z 18Z and 10-day forecasts are made using the 00Z initial condition.  A T190L28 control that is started with T574L64 analysis and run out to 10 days  20 perturbed forecasts each run out to 10 days at T190L28 horizontal and vertical resolution. The initial perturbations are generated using Ensemble Transform with Rescaling (ETR) method.

1.5.8.1.The Ensemble Mean and Spread The ensemble spread is a measure of the difference between the members and is represented by the standard deviation (Std) with respect to the ensemble mean (EM). On average, small (high) spread indicates a high (low) forecast accuracy.  The ensemble spread is flow-dependent and varies for different parameters.  It usually increases with the forecast range, but there can be cases when the spread is larger at shorter forecast ranges than at longer ranges. This might happen when the initial days are characterized by strong synoptic systems with complex structures but are followed by large-scale "fair weather" high pressure systems.

1.5.8.2. Probabilistic forecasts of quantitative precipitation

 In these charts, the probability that 24-hour precipitation amounts over a 2.5x2.5 lat-lon grid box will exceed certain threshold values is given. The forecast probability is estimated directly from the 20-member global ensemble.  At each grid point the number of ensemble members having a 24-hour precipitation amount within a specified range (e.g. 1-2cm, 2-5cm etc) is counted (M) and the probability is expressed as 100*(M/20).

1.6. Products Generated By RSMC, New Delhi

RSMC, New Delhi prepares and disseminates the following bulletins.

1.6.1. Tropical Weather Outlook

Tropical Weather Outlook is issued daily at 0600 UTC based on 0300 UTC observations in normal weather for use of the member countries of WMO/ESCAP Panel. This contains description of synoptic systems (low pressure area) over north Indian Ocean along with information on significant cloud systems as seen in satellite imageries and ridge line at 200 hPa level over Indian region. The Special Tropical Weather Outlook is issued twice a day when a low pressure area concentrates into a depression. It is issued at 0600 UTC basd on 0300 UTC and 1500 UTC based on 1200 UTC observations. The Special Tropical Weather Outlook indicates discussion on various diagnostic and prognostic parameters apart from the 72 hours track and intensity forecast. The track and intensity forecast are issued in digital form for +06, +12, +18, +24, +36, +48, +60 and +72 hours when the depression intensifies into a deep depression. It also includes the description of current location & intensity, past movement and description of satellite imageries. The time of issue of this bulletin is HH+03 hours. The cone of uncertainty in the track forecast is also included in the graphical presentation of the bulletin.

Tropical weather outlooks are transmitted to panel member countries through global telecommunication system (GTS) and are also made available on real time basis through internet at IMD's website: http://www.imd.gov.in. RSMC, New Delhi can also be contacted through e-mail at [email protected] for any real time information on cyclonic disturbances over north Indian Ocean.

1.6.2. Tropical Cyclone Advisories

Tropical Cyclone Advisory bulletin is issued when a deep depression intensifies into a tropical cyclone (surface wind speed= 34 knots or more). It replaces the „Special Tropical Weather Outlook‟ bulletin.

Tropical cyclone advisories are issued at 3 hourly intervals based on 00, 03, 06, 09, 12, 15, 18 and 21 UTC observations. The time of issue is HH+03 hrs. These bulletins contain the current position and intensity, past movement, central pressure of the cyclone, description of satellite cloud imageries, expected direction and speed of movement, expected track and intensity of the system upto 72 hours like that in special tropical weather outlook. The expected point and time of landfall, forecast winds, squally weather and state of the Sea in and around the system are also mentioned. Storm surge guidance is provided in the bulletin as when required. Tropical cyclone advisories are transmitted to panel member Countries through GTS and are also made available on real time basis through internet at IMD's website: http://www.imd.gov.in . RSMC, New Delhi can also be contacted through e-mail at [email protected] for any real time information on cyclonic disturbances over north Indian Ocean.

1.6.3. Global Maritime Distress Safety System (GMDSS)

Under Global Maritime Distress Safety System (GMDSS) Scheme, India has been designated as one of the 16 services in the world for issuing Sea area bulletins for broadcast through GMDSS for MET AREA VIII (N), which covers a large portion of north Indian Ocean. As a routine, two GMDSS bulletins are issued at 0900 and 1800 UTC. During cyclonic situations, additional bulletins (up to 4) are issued for GMDSS broadcast. In addition, coastal weather and warning bulletins are also issued for broadcast through NAVTEX transmitting stations located at Mumbai and Chennai.

1.6.4. Tropical Cyclone Advisories for Aviation

Tropical Cyclone Advisories for aviation are issued by TCAC, New Delhi for international aviation as soon as any disturbance over the north Indian Ocean attains or likely to attain the intensity of cyclonic storm (sustained surface wind speed ≥ 34 knots) within next six hours. These bulletins are issued at six hourly intervals based on 00, 06, 12, 18 UTC synoptic charts and the time of issue is HH+03 hrs. These bulletins contain present location of cyclone in lat./long., maximum sustained surface wind (in knots), direction of past movement and estimated central pressure, forecast position in Lat./Long. and forecast winds in knots valid at HH+6, HH+12, HH+18 and HH+24 hrs in coded form. The tropical cyclone advisories are transmitted on real time basis through GTS and AFTN channels to designated International Airports of the region prescribed by ICAO.

1.6.5. Bulletin for India coast

These bulletins are issued from the stage of depression onwards during the stage of depression/deep depression; it is issued based on 00, 03, 06, 12, and 18 UTC observations. When the system intensifies into a cyclonic storm over north Indian Ocean, these bulletins are issued at 00, 03, 06, 09, 12, 15, 18 and 21 UTC

(every three hourly interval) based on previous observations. This bulletin contains present status of the system i.e. location, intensity; past movement and forecast intensity & movement for next 72 hours or till the system weaken into a low pressure area, likely landfall point & time and likely adverse weather including heavy rain, gale wind & storm surge. Expected damage and action suggested are also included in the bulletins. This bulletin is completely meant for national users and these are disseminated through various modes of communication including All India Radio, Telephone/Fax, Print and electronic media. It is also posted on cyclone page of IMD website.

1.6.6. Wind forecast for different quadrants

The forecast of maximum wind in four quadrants of a cyclone commenced with effect from cyclone, GIRI during October 2010. In this forecast, the radius of 34, 50 and 64 knot winds are given for various forecast periods like +06, +12, +18, +24, +36, +48, +60 and +72 hrs. This quadrant wind forecast bulletin is issued as bulletin from the deep depression stage onwards to various users through GTS. It is also given to NWP Division of IMD, IIT, Delhi and NCMRWF for their use in creating the synthetic vortex.

1.6.7. Warning Graphics 1.6.8. The warnings in the form of graphics are issued for tropical cyclones track, intensity, cone of uncertainty and radii of winds in different threshold in four quadrants of a tropical cyclone. The TCAC bulletin is also issued in graphical format. The examples of these products are shown in fig. 1.8-1.10.

Fig.1.8. A typical graphical presentation of wind forecast during cyclonic storm ‘NILAM’

Fig.1.9. A typical example of observed and forecast track of cyclonic storm ‘NILAM’

Fig.1.10. A typical example of TCAC Bulletin issued during cyclonic storm ‘NILAM’

1.7. Cyclone Warning Dissemination

Cyclone warnings are disseminated to various users through telephone, fax, e-mail and GTS, All India Radio, Television, the print & electronic media. These warnings/advisories are also put in the website (www.imd.gov.in) of IMD.

Also cyclone warning bulletins are disseminated by SMS to state and national disaster management authorities. In addition to these, TCAC bulletin is sent to Aviation Disaster Risk Reduction Centre, Honkong (ADRR) through ftp. Another means to transmit warning is IVRS (Interactive Voice Response system). The requests for weather information and forecasts from general public are automatically answered by this system. For this purpose, the person has to dial a toll free number “18001801717” from anywhere in the country. This system has been installed at 26 Meteorological Centres/ Regional Meteorological Centres. High Speed Data Terminals (HSDT) installed at cyclone warning centres are capable of sending short warning message as SMS and the whole warning message as email.

In addition to the above network, for quick dissemination of warning against impending disaster from approaching cyclones, IMD has installed specially designed receivers within the vulnerable coastal areas for transmission of warnings to the concerned officials and people using broadcast capacity of INSAT satellite. This is a direct broadcast service of cyclone warning in the regional languages meant for the areas affected or likely to be affected by the cyclone. There are 352 Cyclone Warning Dissemination System (CWDS) stations along the Indian coast; out of these 101 digital CWDS are located along Andhra coast. The IMD‟s Area Cyclone Warning Centres (ACWCs) at Chennai, Mumbai & Kolkata and Cyclone Warning Centre (CWCs) at Bhubaneswar, Visakhapatnam & Ahmedabad are responsible for originating and disseminating the cyclone warnings through CWDS. The bulletins are generated and transmitted every hour in three languages viz English, Hindi and regional language. The cyclone warning bulletin is up-linked to the INSAT in C band. For this service, the frequency of transmission from ground to satellite (uplink) is 5859.225 MHz and downlink is at 2559.225 MHz. The warning is selective and will be received only by the affected or likely to be affected stations. The service is unique in the world and helps the public in general and the administration, in particular, during the cyclone season. It is a very useful system and has saved millions of lives and enormous amount of property from the fury of cyclones. The digital CWDS have shown good results and working satisfactorily. This CWDS network will be replaced shortly by 500 new CWDS, which are modern and easy to maintain. Efforts are on to replace the network of CWDS/DCWDS by the ISRO developed direct to home (DTH) modified type CWDS. An MOU has been signed among ISRO, IMD and official television (Doordarshan) for replacement of the existing network of CWDS by new DTH modified type CWDS designed by ISRO.

1.8. Forecast Demonstration Project (FDP) on Landfalling Tropical Cyclones over the Bay of Bengal

A Forecast Demonstration Project (FDP) on landfalling tropical cyclones over the Bay of Bengal has been taken up. It will help us in minimizing the error in prediction of tropical cyclone track and intensity forecasts.

During pilot phase (15 Oct- 30 Nov. 2012), several national institutions participated for joint observational, communicational & NWP activities, like during 2008-2011. However there was improved observational campaign with the observation from Buoys, Oceansat-II and microwave satellites. There was intense observation period for 06 days during the field phase 2012. The daily reports prepared during this period will be helpful to find out the characteristics of genesis, intensification and movement of the systems as well as environmental features over the Bay of Bengal during 15 Oct. to 30 Nov., 2012.

1.9. Modernised Forecast and Warning System of IMD

India Meteorological Department has completed phase-I of an extensive modernisation programme with. The phase II of the programme will be taken up in 12th five year plan commencing from 2013.

CHAPTER–II

CYCLONIC ACTIVITIES OVER NORTH INDIAN OCEAN DURING 2012

The north Indian Ocean and adjoining land surface witnessed the formation of five cyclonic disturbances during the year, 2012. Out of five disturbances three formed over the Bay of Bengal and two over the Arabian Sea. Out of the three cyclonic disturbances over the Bay of Bengal, one intensified upto the stage of cyclonic storm, NILAM, two upto the stage of deep depression. Out of two cyclonic disturbances formed over the Arabian Sea, one intensified upto the stage of cyclonic storm, MURJAN and one upto the stage of deep depression. Tracks of the cyclonic disturbances formed over the north Indian Ocean during the period are shown in Fig 2.1.

The salient features of the cyclonic disturbances during 2012 were as follows:

 The number of total cyclonic disturbances (depression and above) during the year was significantly below normal, as only five cyclonic disturbances formed during 2012 against the normal of 13. Similarly only two cyclones formed during the year against the normal of about 5.  Both the cyclones made landfall .While cyclonic storm ‗MURJAN‘ made landfall over Somalia, the cyclonic storm, ‗NILAM‘ made landfall over Tamilnadu and Puducherry coast.  The track of the cyclonic storm, ‗NILAM‘ was rare in nature as it initially moved westwards, came closer to Srilanka coast and remained stationary for about a day and then moved north-northwestwards to cross Tamilnadu coast.  There were no cyclonic disturbances formed over the north Indian Ocean and adjoining land surface during monsoon season (June-Sep.) against the normal of 7 cyclonic disturbances. There were no cyclonic disturbances over the north Indian Ocean during the pre-monsoon season (March-May), 2012 also.

(a) Cyclonic Storm, “MURJAN” over the Arabian Sea (23-26 October, 2012.)

(i) It was the first cyclonic storm to hit Somalia after 1994. A severe cyclonic storm crossed Somalia coast on 19th November 1994 near lat. 8.00N.

(ii) The cyclonic storm, Murjan caused heavy rainfall and strong wind over Somalia and Ethiopia. (iii) Though predicted by most of the NWP models to gradually weaken before landfall, it maintained its cyclonic storm intensity till landfall.

(b) Cyclonic Storm, „NILAM‟ over the Bay of Bengal (28 October- 1 November)

A cyclonic storm, NILAM crossed Tamilnadu coast near Mahabalipuram (south of Chennai) in the evening of 31st October 2012 with a sustained maximum wind speed of 70-80 knots. The salient features of this storm are as follows.

(i) It followed a unique track with many rapid changes in direction of movement. It initially moved westwards, remained practically stationary for quite some time near Sri Lanka coast and then moved north-northwestwards till landfall. It moved west-northwestwards initially over land upto south interior Karnataka and then moved northwest and northwards. The remnant low pressure area moved northeastwards (ii) It moved very fast on the day of landfall, i.e. 31st October 2012. (iii) Over the land surface, the cloud mass was significantly sheared to the northeast of system centre during its dissipation stage leading to heavy rainfall activity over entire Andhra Pradesh and adjoining Odisha (iv) Maximum rainfall occurred over southwest sector of the system centre at the time of landfall and heavy to very heavy rainfall extended upto 300 km.

The statistics of the cyclonic disturbances formed during 2012 are given in Table 2.1. The characteristic features of these disturbances are given in Table 2.2. The intraseasonal variation in frequency of genesis, intensification and life period of the disturbances is shown in Table 2.3. The interannual variation of genesis and intensity is shown in Table 2.4.

Table 2.1: Cyclonic disturbances formed over north Indian Ocean and adjoining land areas during 2012

1. Deep Depression over Bay of Bengal, 10-11 October 2012 2. Cyclonic storm ‗MURJAN‘ over Arabian Sea, 23-26 October 2012 3. Cyclonic storm ‗NILAM‘ over Bay of Bengal, 28 October- 1 November 2012 4. Deep Depression over Bay of Bengal, 17-19 November 2012 5 Deep Depression over Arabian Sea, 22-25 December 2012

Table 2.2 Some Characteristic features of cyclonic disturbances formed over north Indian Ocean and adjoining region during 2012 Cyclonic Storm Date, Time Date, Time (UTC) Estimated Estimated Max. / Depression & Place of place (Lat./Long.) lowest central Maximum T.No. genesis of landfall pressure, wind speed Attaine (Lat.0N/ Time & Date (kt), Date & d Long.0E) (UTC) & latoN / Time longoE Deep 10 October Crossed 1002 hPa at 30 knots at T-2.0 Depression 2012 at Bangladesh coast 1800 UTC of 1800 UTC of over the Bay of 1200 UTC near Hatia 10 October 10 October Bengal (10-11 over between 0000- 2012 near 2012 October 2012) northeast 0100 UTC of 11 22.0/91.0 Bay of October 2012 Bengal near 21.0/91.0 Cyclonic Storm 23 October Crossed Somalia 1000 hPa at 40 Knots at T-2.5 ‗MURJAN‘ over 2012 over coast near 1200 UTC of 1800 UTC of Arabian Sea southeast latitude 24 October 24 October (23-26 October Arabian 9.50N/longitude 2012 near 2012 2012) Sea near 50.80E) between 10.5/56.5 11.0/65.0 1700-1800 UTC of 25 October 2012 Cyclonic Storm 28 October Crossed Tamil 990 hPa at 45 knots at T-3.0 ‗NILAM‘ over at 0600 Nadu coast Near 0000 UTC of 0000 UTC of Bay of Bengal UTC over Mahabalipuram 31 October 31 October (28 October- 1 southeast (near latitude 2012 near 2012 November Bay of 12.60N/longitude 10.5/811.5 2012) Bengal 80.20E) between near 1030-1130 UTC 9.5/86.0 of 31 October 2012 Deep 17 Weakened into a 1002 hPa at 30 Knots at T-2.0 Depression November Well Marked Low 1200 UTC of 1200 UTC of over the Bay of 2012 at Pressure area 17 November 17 November Bengal (17-19 0600 UTC over west central 2012 near 2012 November near Bay of Bengal at 16.0/89.0 2012) 15.5/90.0 1500 UTC of 19 November 2012

Deep 22 Weakened into a 1002 hPa at 30 knots at T-2.0 Depression December Well Marked Low 0000 UTC of 0000 UTC of over Arabian 2012 at Pressure area 23 december 23 December sea (22-25 0900 UTC over southwest 2012 near 2012 December near Arabian sea off 9.0/60.5 2012) 9.0/63.0 Somalia coast

Table 2.3: Statistical data relating to cyclonic disturbances over the north Indian Ocean during 2012

A) Monthly frequencies of cyclonic disturbances (CI  1.5)

S.N Type Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 1. D 2. DD    CS  3.   Peak intensity of the system

B) Life time of cyclonic disturbances during 2012 at different stages of intensity

S. No. Type Life Time in (Days)

1. D 5.2 2. DD 5.9 3. CS 2.9 4. SCS 0 5. VSCS 0 6. SuCS 0

Total Life Time in (Days) 14.0

C) Frequency distribution of cyclonic disturbances with different intensities based on satellite assessment

CI No. 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

No. of 5 5 2 1 0 0 0 0 disturbances

D) Basin-wise distribution of cyclonic disturbances

Number of cyclonic disturbances Basin Bay of Bengal 3 Arabian Sea 2 Land depression 0

Table 2.4. Cyclonic disturbances formed over the north Indian Ocean and land areas of India during 1997-2012

Year Basin D DD CS SCS VSCS SuCS Total

BOB 1 4 1 1 1 0 8 ARB 1 0 0 0 0 0 1 1997 Land 0 0 0 0 0 0 0 Total 9 BOB 0 3 0 1 2 0 6 ARB 0 1 1 1 1 0 4 1998 Land 1 0 0 0 0 0 1 Total 11 BOB 2 2 1 0 1 1 7 ARB 0 0 0 0 1 0 1 1999 Land 1 0 0 0 0 0 1 Total 9 BOB 1 1 2 -- 2 0 6 ARB 0 0 0 0 0 0 0 2000 Land 1 0 0 0 0 0 1 Total 7 BOB 2 0 1 0 0 0 3 ARB 0 0 2 0 1 0 3 2001 Land 0 0 0 0 0 0 0 Total 6 BOB 1 1 2 1 0 0 5 ARB 0 0 0 0 0 0 1 2002 Land 0 0 0 0 0 0 0 Total 6 BOB 2 2 0 1 1 0 6 ARB 0 0 0 1 0 0 1 2003 Land 0 0 0 0 0 0 0 Total 7 BOB 2 0 0 0 1 0 3 ARB 0 2 0 3 0 0 5 2004 LAND 2 0 0 0 0 0 2 Total 10 27

BOB 2 3 4 0 0 0 9 ARB 2 0 0 0 0 0 2 2005 LAND 1 0 0 0 0 0 1 Total 12 BOB 5 2 1 0 1 0 9 ARB 0 1 0 1 0 0 2 2006 LAND 1 0 0 0 0 0 1 Total 12 BOB 3 4 1 0 1 0 9 ARB 0 1 1 0 0 1 3 2007 Land 0 0 0 0 0 0 0 Total 12 BOB 1 2 3 0 1 0 7 ARB 1 1 0 0 0 0 2 2008 LAND 1 0 0 0 0 0 1 Total 10 BOB 0 2 2 1 0 0 5 ARB 2 0 1 0 0 0 3 2009 LAND 0 0 0 0 0 0 0 Total 8 BOB 2 1 0 2 1 0 6 ARB 0 0- 1 0 1 0 2 2010 LAND 0 0 0 0 0 0 0 Total 8 BOB 2 2 0 0 1 0 5 ARB 1 2 1 0 0 4 2011 LAND 1 0 0 0 0 0 1 Total 10 BOB 0 2 1 0 0 0 3 ARB 0 1 1 0 0 0 2 2012 LAND 0 0 0 0 0 0 0 Total 5

D: Depression DD: Deep Depression, CS: Cyclonic Storm, SCS: Severe Cyclonic Storm, VSCS: Very Severe Cyclonic Storm, SuCS: super Cyclonic Storm BOB: Bay of Bengal, ARB: Arabian Sea

Fig. 2.1 Tracks of the cyclonic disturbances formed over the north Indian Ocean during the year, 2012

2.1 Deep Depression over the Bay of Bengal (10-11 October, 2012)

2.1.1 Introduction

A deep depression formed over northeast Bay of Bengal in the evening of 10th October, 2012. It moved northward and crossed Bangladesh coast near Hatia during 11th morning and then moved northeastwards across Bangladesh. It weakened into a well marked low pressure area at 0600 UTC of 11th October, 2012 over Tripura 29

and adjoining Bangladesh and Mizoram. It caused the death of about 43 persons and left several injured in southeastern part of Bangladesh. The salient features of this deep depression were as follows. (i) It formed from a remnant from the south China Sea which moved across Vietnam and Myanmar and emerged into the northeast and adjoining eastcentral Arabian Sea. (ii) It was short lived with the life period of about 15 hrs (iii) It intensified into a deep depression before landfall, though it was lying very close to coast.

2.1.2 Monitoring of depression

As the deep depression formed over northeast Bay of Bengal close to Bangladesh and Myanmar coasts, it could be monitored with INSAT imageries, microwave imageries from Polar Orbiting Satellites, Doppler Weather Radars (DWR) at Khepupara, Cox‘s Bazar (Bangladesh) and Agartala. The DWR imageries of Khepupara and Cox‘s Bazar and coastal surface observations from Bangladesh were received from Bangladesh Meteorological Department. These products were very helpful for monitoring and prediction of this deep depression. Though the surface observations from Bangladesh could not be received on real time due to problem in Global Telecommunication System (GTS), these data were received through e-mail in late mode. These data were very helpful in reanalysis of the system.

2.1.3 Genesis, intensification and movement

A remnant of a tropical storm over south China Sea moved westwards across Vietnam and Myanmar and emerged into northeast and adjoining east central Bay of Bengal as an upper air cyclonic circulation on 9th October 2012. It moved northwestwards and was seen as a low pressure area at 0300 UTC of 10th October, 2012. It concentrated into a depression and lay centred at 1200 UTC of 10th October, 2012 over northeast Bay of Bengal near latitude 21.00N and longitude 91.00E. Track of the system is shown in Fig.2.1.Sustained maximum surface wind speed was estimated to be about 25 knots gusting to 35 knots around system centre. The state of the sea was rough to very rough around the system centre. The estimated central pressure was about 1003 hPa with outer most closed isobar as 1006 hPa. The 24 hrs pressure tendency was negative and about 1 hPa along Bangladesh coast. The best track parameters are shown in Table 1

Table 2.1.1 The best rack position and other parameters of deep depression over the Bay of Bengal during 10-11 October, 2012 Date Time Centre C.I. Estimate Estimated Estimated Grade (UTC) lat.0 N/ NO. d Central Maximum Pressure long. 0 E Pressure Sustained drop at the (hPa) Surface Wind Centre (hPa) (kt) 1200 21.0/91.0 1.5 1003 25 3 D 10.10.12 1500 21.5/91.0 1.5 1003 25 4 D 1800 22.0/91.0 2.0 1002 30 5 DD 0000 22.5/91.3 2.0 1002 30 5 DD Deep Depression crossed near Hatia (Bangladesh ) between 0000-0100 UTC 11.10.12 0300 23.0/91.5 1.5 1006 20 3 D 0600 Weakened into a well marked low pressure area over Tripura & adjoining Bangladesh and Mizoram

In association with favourable environmental conditions like low to moderate wind shear, increase in convergence and vorticity in lower levels, increase in upper level divergence and its location near the upper tropospheric steering ridge, the depression moved northward and intensified into a deep depression 1800 UTC of 10th October. It then moved north-northeastwards as the system lay close to the north of the upper tropospheric ridge. The deep depression crossed Bangladesh coast near Hatia between 0000-0100 UTC of 11th October, 2012. The associated sustained maximum wind speed at the time of landfall was about 30 knots. After the landfall, the deep depression continued to move north- northeastwards, weakened into a depression and lay centred at 0300 UTC over Bangladesh and adjoining Tripura near latitude 23.00N and longitude 91.50E, about 100 km south of Agartala. It then continued to move northeastwards and further weakened into a well marked low pressure area over Tripura and adjoining Bangladesh and Mizoram at 0600 UTC of 11th October, 2012. It further weakened and moved away northeastwards towards Myanmar on 12th October, 2012 morning. There was rapid weakening of the system after the landfall, as it interacted with the hilly land surface and was cut-off from moisture alongwith feeding of cold and dry wind at middle tropospheric level over the northeast in association with the mid- latitude trough in westerlies over the region.

2.1.4 Synoptic features

The reanalyzed synoptic charts based on 1200, 1500, 1800 UTC of 10th and 0000, 0300 and 0600 UTC of 11th October are shown in Fig. 2.1.1. It indicates that the lowest Estimated Central Pressure (ECP) was 1002 hPa during 1800 UTC of 10th to 0000 UTC of 11th October, 2012. The maximum pressure drop at the centre during this period was 5 hPa. The pressure gradient was more towards Bangladesh coast. Considering the 24 hr pressure changes in every three hourly interval, the maximum pressure fall of 3.6 hPa was reported by Hatia (Bangladesh) at 1800 UTC 31

of 10th October with mean sea level pressure (MSLP) of 1004.8 hPa. Thereafter, the pressure increased over this station. The lowest pressure of 1002 hPa has been reported by Chittagong at 0000UTC of 11th October 2012, when the deep depression was lying west of this station. The pressure over Chittagong increased thereafter becoming 1006hPa at 0300 UTC of 11th, when the system weakened into a depression and lay to the north-northwest of Chittagong.

2.1.5 Features observed through satellite imageries

The system was monitored with Kalpana-1 imageries and products during 10th and 11th October 2012. The satellite Division of IMD assigned T1.0 as per Dvorak‘s classification to the vortex at 0300UTC of 10th October. As per reanalysis by Satellite Division of IMD, the vortex lat centred near lat. 19.50N and long. 91.50E at 0300 UTC, near 21.00N and long. 91.00E at 1200 UTC, near 21.50N and long. 91.00E at 1700 UTC, near 22.00N and long. 91.00E at 2100 UTC of 10th and near lat. 22.50N and long. 91.50E at 0000UTC of 11th October 2012. It lay centred over land near lat. 23.00N and long. 91.50E at 0300 UTC of 11th October. Hence, according to satellite reanalysis, the vortex initially moved northwestwards during 0300 to 0600 UTC of 10th and then it moved northwards till 0000 UTC of 11th October. It then moved north-northeastwards. It continued as T1.0 during 0300UTC to 0900UTC of 10th and was assigned as T1.5 at 0900 UTC and T2.0 at 1500 UTC of 10th. It was downgraded to T 1.5 at 0000UTC of 11th October. As per satellite imageries, the convective clouds started disorganising at 0300UTC of 11th and further disorganization took place at 0600UTC of 11th while moving north-northeastwards.

(a) (b)

Fig. 2.1.1 (a-d) Mean sea level pressure analyses of 10th October 2012 (a)1200UTC, (b) 1500 UTC, (c) 1800 UTC and (d) 2100 UTC.

(e) (f)

(b) (a) 0000UT 0600UTC C

(g)

Fig. 2.1.1 (e-g) Mean sea level pressure analyses of 11th October 2012 (e)0000UTC, (f) 0300 UTC, (g) 0600 UTC.

The typical satellite imageries are shown in Fig. 2.1.2 during the life period of the deep depression. These imageries clearly indicated the convective cloud bands in association with the system. The lowest cloud top temperature (CTT) of about - 800C was recorded during 10th night. However, it increased and was about -700C at 0000 UTC of 11th. As a result, the depth of convection was less during the landfall and hence led to relatively less intense rainfall. The maximum amount of rainfall was about 11 cm as shown on the realized weather section below. The IR imageries with CTTs during 10th and 11th October 2012 are shown in Fig. 2.1.3. The satellite based intensity and cloud top temperatures (CTT) are shown in Table 2.1.2.

(a) Formation of Vortex (T1.0) (b)Intensified into Depression (T1.5)

0300 UTC, 10.10.2012 0900 UTC, 10.10.2012

1500 UTC, 10.10.2012 0000 UTC, 11.10.2012

Fig. 2.1.2(a-d): Satellite imageries of depression at (a) 03, (b) 09, (c) 15 UTC of 10th October, 2012 and (d) 00 UTC of 11th October 2012

(e) Landfall (f) Oceansat-II based surface wind

0300 UTC, 11.10.2012 2311 UTC, 09.10.2012

Fig. 2.1.2(e-f) (e) Satellite imagery of depression at 03UTC of 11th October 2012 showing landfall and (f) Oceansat-II based surface wind at 2311 UTC of 09th October, 2012 indicating emergence of the remnant into Bay of Bengal.

Table 2.1.2 Satellite observations of Deep Depression over Bay of Bengal (10- 11 October, 2012)

Date Time (UTC) Lat (N) Long (E) T No CTT (°C) 0000 LLC -80 0300 19.5 91.5 1.0 -76 0600 20.0 91.0 1.0 -73 0900 20.5 91.0 1.5 -65 1200 21.0 91.0 1.5 -70 1500 21.2 91.0 2.0 -62 1800 21.5 91.0 2.0 -72 10.10.2012 2100 22.0 91.0 2.0 -72 0000 22.5 91.5 1.5 -65 11.10.2012 0300 23.0 91.5 Overland -65

Fig. 2.1.3 (a). IR imageries with Cloud Top Temperature (CTT) at 0000, 0300, 0600, 0900, 1200, 1500 and 2100 UTC of 10th October, 2012

Fig. 2.1.3 (b). IR imageries of Cloud Top Temperature (CTT) for 0000, 0300, 0600, 0900, 1200, 1500 and 2100 UTC of 11th October, 2012

2.1.6 Features observed through DWR imageries

The deep depression was monitored with the DWR at Khepupara, Cox‘s Bazar and Agartala as mentioned earlier. The typical DWR imageries from these DWRs are shown in Fig. 2.1.4. These imageries clearly indicated the convective cloud bands in association with the system.

Fig. 2.1.4 (a) Radar imageries of deep depression over Bay of Bengal at 1145 UTC and 1230 UTC, 1715 JST, and 2100 JST of 10th October and 0000 JST and 0215 UTC of 11th October, 2012 from Cox‟s Bazar and Khepupara respectively

Fig. 2.1.4 (b) DWR, Agartala MAX(Z) imageries during 0100 to 0330 UTC of 11th October, 2012

Fig. 2.1.4(b) (Contd) DWR, Agartala MAX(Z) imageries during 0350 to 0630 UTC of 11th October.

As per DWR imageries, the reflectivity of the convective clouds was relatively less (50DB). As a result, the intensity of rainfall due to the system was limited to about 10 cm per hours. The centred determined by DWR imageries are in agreement with the centres mentioned in the best track (Table 2.1.1).

Fig. 2.1.5 DWR, Agartala PPI-V imageries at elevation of 0.20 during 0100 to 0230 UTC of 11th October 2012.

The PPI-V imageries from DWR, Agartala are shown in Fig. 2.1.5. for the period of 0100 to 0230 UTC at the interval of half an hour. It indicates that the wind speed was higher in the southeastern quadrant of the deep depression at the time of landfall. The wind speed gradually decreased as the deep depression moved over land surface in the north-northeast direction. The radial wind of about 25-30 meter per second (48-58 knots) has been report by DWR, Agartala in the southeast direction at a distance of about 130 km and with an elevation angle of 0.20. As there is no conversion formula available in the literature for conversion of radial wind

measured by a DWR at a certain elevation to the surface wind, the conversion method used for conversion of flight level wind of reconnaissance aircraft to the surface wind (James Franklin, 2000) has been used to calculate the surface wind. As per this method, the radial wind speed of 25-30 meter per second at a height of 1 km is equivalent to 36-44 knots at surface level.

Fig. 2.1.6 Wind observed over Agartala as per DWR, Agartala during 0100 to 0330 UTC of 11th October 2012.

The wind reported over Agartala as observed through DWR, Agartala is shown in in Fig. 2.1.6 It indicates that Agartala experienced 15-20 knots wind at the surface level during 0100-0300 UTC. The wind backed over time indicating north- northeastward movement of the system. The wind speed gradually decreased and became about 5 knots around 0600 UTC.

2.1.7 Dynamical features

The low level convergence as well as upper level divergence and lower level relative vorticity had increased on 10th October. The vertical wind shear between 200 and 850 hpa levels was low to moderate (10-20 knots) around system centre. However, it increased towards Bangladesh coast. The upper tropospheric ridge lay along 200 N and hence close to system centre. This ridge moved northward alongwith the movement of the system. Helce, it helped in northward movement of the system. However, at 0000 UTC of 11th the system lay close to the north of the system centre. Further, a trough in mid-tropospheric westerlies roughly ran along 800E to the north of 180N. Under these conditions, the system moved north- northeastwards and weakened over the land surface. The Meteosat-7 satellite based derived products, viz., middle and upper tropospheric water vapour derived wind vectors, lower level cloud motion vectors, vertical wind shear of horizontal wind, lower level convergence and relative vorticity and upper level divergence at 1200 UTC of 10th October 2012 are shown in Fig. 2.1.7 to illustrate the above facts.

Fig. 2.1.7(a) Meteosat-7 satellite based lower level relative vorticity at 1200 UTC of 10th Oct. 2012

(b) (c)

(d) (e)

(f) (g)

Fig. 2.1.7(b-g) Meteosat-7 satellite based derived products (b) middle and upper tropospheric water vapour derived wind vectors, (c) lower level cloud motion vectors, (d) vertical wind shear of horizontal wind, (e) 24 hr tendency of vertical wind shear (f) lower level convergence and (g) upper level divergence at 1200 UTC of 10th October 2012.

2.1.8 Large scale features

Considering the environmental features, the Madden Julian Oscillation Index lay over phase 6 with amplitude of 1 on 10th October, 2012. As per statistical and NWP model predictions, it was expected to lie in phase 7 during next 2-3 days with decrease in amplitude. Hence it was not favourable for intensification. The sea surface temperature was about 29-300C over north Bay of Bengal. The ocean thermal energy was 50 - 60 KJ/cm2 around the system centre. It decreased towards Bangladesh coast. Hence it was also not favourable for further intensification into cyclonic storm. The deep depression did not intensify further as it lay over the area with less Ocean thermal energy and increased vertical wind shear near Bangladesh coast. The interaction with land also did not favour further intensification.

2.1.9 NWP Guidance

The NWP guidance from global models like IMD GFS, NCEP GFS, ECMWF, NCMRWF Unified model, UKMO, mesoscale models like IMD WRF model and ensemble forecast system like NCMRWF global ensemble forecast system (GEFS) were utilised for monitoring and prediction of track and intensity of deep depression. In the analysis field, the ECMWF model, Unified model and Meteo-France model could detect the genesis in their analysis fields of both pressure and wind. However, the maximum intensity of the system was depression as per these models. IMD GFS and NCMRWF-GEFS could not detect the system. However, these models showed maximum intensity of a low pressure area.

Considering the NWP model guidance, the genesis of the depression could be predicted by ECMWF, Meteo-France and Unified models based on the initial conditions of 1200 UTC of 9th October and 0000 UTC of 10th October, 2012. IMD GFS and WRF models predicted a low pressure area based on these initial conditions. Above mentioned global models did not suggest further intensification of the system limiting the maximum intensification upto depression stage. Most of the models suggested northward movement and landfall over Bangladesh coast near 910 E by 11th October morning and further northeastward movement.

The IMDGFS, ECMWF, NCMRWF Unified Model and GEFS analysis and forecast products for 24 & 48 hr forecast period based on initial conditions of 0000 and 1200 UTC of 10th and 11th October, 2012 are shown in Fig. 2.1.8 - 2.1.13.

To summarise the performance of the NWP models, though the track could be predicted well by most of the NWP models, the genesis and intensity of the system could not be well predicted by many models. The intensity remained under-predicted by all the models with ECMWF and unified model being closer to realized intensity of the system.

Fig. 2.1.8 (a) IMD GFS pressure and wind analysis (850, 500 & 200 hPa) based on 0000 UTC of 10th October, 2012.

Fig. 2.1.8 (b) IMD GFS pressure and wind analysis (850, 500 & 200 hPa) based on 1200 UTC of 10th October, 2012.

Fig. 2.1.8 (c) IMD GFS pressure and wind analysis (850, 500 & 200 hPa) based on 0000 UTC of 11th October, 2012.

Fig. 2.1.8 (d) IMD GFS pressure and wind analysis (850, 500 & 200 hPa) based on 1200 UTC of 11th October, 2012.

Fig.2.1.9 (a) IMD GFS pressure and 850 hPa wind forecasts for 24hr and 48 hr period based on 0000 UTC of 10th October, 2012

Fig. 2.1.9(b) IMD GFS pressure and 850 hPa wind forecast for 24 and 48 hr period based on 1200 UTC of 10th October, 2012.

Fig. 2.1.9 (c) IMD GFS pressure and wind (850 hPa) forecast for 24 and 48 hr period based on 0000 UTC of 11th October, 2012.

Fig. 2.1.10(a) ECMWF analysis of MSLP and Winds at 850, 500 & 200 hPa

levels based on 0000 UTC of 10th October, 2012

Fig. 2.1.10 (b). ECMWF analysis of MSLP and Winds at 850, 500 & 200 hPa levels based on 1200 UTC of 10th October, 2012

Fig. 2.1.10 (c) ECMWF analysis of MSLP and Winds at 850, 500 & 200 hPa levels based on 0000 UTC of 11th October, 2012

Fig. 2.1.10 (d) ECMWF analysis of MSLP and Winds at 850, 500 & 200 hPa levels based on 1200 UTC of 11th October, 2012

Fig. 2.1.11 (a). ECMWF forecast for 24 & 48 hr forecast period based on initial conditions of 0000 UTC of 10th October, 2012.

Fig. 2.1.11 (b). ECMWF forecast for 24 & 48 hr forecast period based on initial conditions of 1200 UTC of 10th October, 2012.

Fig. 2.1.11 (c). ECMWF forecast for 24 & 48 hr forecast period based on initial conditions of 0000 UTC of 11th October, 2012.

Fig. 2.1.12(a) NCMRWF Global Ensemble Forecast System (GEFS) mean MSLP and 850 hPa wind analysis and 24 & 48 hr forecasts based on 0000 UTC of 10th October 2012 59

Fig. 2.1.12(b) NCMRWF Global Ensemble Forecast System (GEFS) mean MSLP and 850 hPa wind analysis and 24hr forecasts based on 0000 UTC of 11th October 2012

Fig. 2.1.12(c) NCMRWF Global Ensemble Forecast System (GEFS) mean 500 and 200 hPa wind analysis and 24 & 48 hr forecasts based on 0000 UTC of 10th October 2012

Fig. 2.1.13(a) NCMRWF Unified Model (Global) MSLP analysis and 24 & 48 hr forecasts based on 0000 UTC of 10th October 2012

Fig. 2.1.13(b) NCMRWF Unified Model (Global) MSLP analysis and 24 hr forecasts based on 0000 UTC of 11th October 2012

Fig. 2.1.13(c) NCMRWF Unified Model (Global) 850 hPa wind and contour analysis and 24 & 48 hr forecasts based on 0000 UTC of 10th October 2012

Fig. 2.1.13(d) NCMRWF Unified Model (Global) 850 hPa wind and contour analysis and 24 hr forecasts based on 0000 UTC of 11th October 2012

Fig. 2.1.13(e) NCMRWF Unified Model (Global) 500 and 200 hPa wind and contour analysis and 24 & 48 hr forecasts based on 0000 UTC of 10th October 2012

Fig. 2.1.14 DWR, Agartala based hourly rainfall rate during 0100 to 0600 UTC of 11th Oct.

2.1.10 Realised Weather

India:

Fairly widespread rainfall with isolated heavy falls occurred over Nagaland, Manipur, Mizoram and Tripura on 10th and 11th October, 2012. Fairly widespread rainfall also occurred over Assam, Meghalaya and Arunachal Pradesh on 10th and th 11 October, 2012. Chief amounts of 24 hrs cumulative rainfall ( ≥ 5 cm) ending at 0300 UTC of 11th and 12th October, 2012 are given below :- 11.10.2012 : Meghalaya: Cherrapunjee, Barapani-5 cm each. Assam: Chouldhowaghat and Jia Bharali N T Road Xing-5 cm each. Tripura: Belonia-9 cm, Bagafa-7 cm and Amarpur-6 cm.

12.10.2012 Mizoram: Lengpui -9 cm and Llowngtlai – 5 cm Manipur: Imphal – 6 cm and Thoubal – 5 cm Assam: Matizuri- 9 cm, Kajalgaon (AWS) – 7 cm and Badarpurghat – 6 cm

Bangladesh:

Bangladesh reported sustained maximum surface wind of 22 knots over Hatia, 25 kts over Sandip and 32 knots over Chittagong at the time of landfall. Widespread rainfall occurred over Bangladesh on 10th and 11th October, 2012. Chief th amounts of 24 hrs cumulative rainfall ( ≥ 5 cm) ending at 0300 UTC of 11 October, 2012 are given below:

Cox‘s Bazar- 10.6 cm, Kutubdia- 10 cm, Hatia- 9 cm, Sandip- 6.5 cm, Rangamati- 6 cm and Chittagong- 6 cm.

Hourly rainfall rates as observed through DWR, Agartala during 0100 to 0600 UTC of 11th October 2012 are shown in Fig.2.14. It indicated that the maximum rainfall rate was observed around 0200 UTC and it decreased gradually thereafter.

2.1.11 Damage The deep depression brought high winds and heavy rains over Bangladesh, causing extensive damage. 43 people were killed and dozens injured when powerful deep depression lashed several upzillas of Noakhali, Bhola, Chittagong and Feni districts during early hours of 11th October 2012. Over 200 thatched cottages in Hatia were damaged. Scores of trees along the Subarnachar and Hatia were uprooted, several fishermen with their fishing trawlers remained missing. Squalls destroyed mosques and educational institutions. A few damage photographs are shown in Fig.2.15.

Fig.2.1.15 Photographs showing damage in coastal areas of Bangladesh

2.2. Cyclonic Storm „MURJAN‟ over Arabian Sea (23-26 October, 2012)

2.2.1 Introduction

The cyclonic storm, Murjan formed over the south Arabian Sea in association with an active inter tropical convergence zone during last week of October 2012. It was the first cyclone over the north Indian Ocean during this year. Moving west- southwestwards, it crossed Somalia coast between 1700 and 1800 UTC of 25th October near lat. 9.80N and long. 50.80E. The salient features of this cyclone are given below. (i) It was the first cyclonic storm to hit Somalia after 1994. A severe cyclonic storm crossed Somalia coast on 19th November 1994 near lat. 8.00N. (ii) The cyclonic storm, Murjan caused heavy rainfall and strong wind over Somalia and Ethiopia. (iii) Though predicted by most of the numerical weather prediction (NWP) models to gradually weaken before landfall, it maintained its cyclonic storm intensity till landfall.

2.2.2 Monitoring and prediction

The cyclonic storm was mainly monitored by satellite. The half hourly INSAT/ Kalpana imageries and products were used for monitoring of cyclonic storm. Various NWP and dynamical-statistical models including IMD‘s global and meso-scale models were utilized to predict the track and intensity of the storm. Recently installed Tropical Cyclone Module in the digitized forecasting system of IMD was utilized for analysis and comparison of various NWP models and decision making process. The brief history of the genesis, intensification and movement of this storm are discussed below.

2.2.3 Genesis

Under the influence of an active inter-tropical convergence zone, a low pressure area formed over the south Bay of Bengal on 18th October 2012. It moved westwards across Sri Lanka and Palk straight and emerged into southeast Arabian Sea, near Lakshadweep area on 21st October. It continued to move westwards and intensified into a depression over southeast and adjoining southwest and central Arabian Sea near lat. 11.00N and long. 65.00E, about 800 km west of Amini Divi at 0300 UTC of 23rd October, 2012.

During the genesis phase, the Madden Julian Oscillation index lay in phase 2 with amplitude greater than one. The phase 2 is favourable for genesis and intensification of the cyclonic disturbances over the Arabian Sea. The sea surface temperature (SST) over the southeast Arabian Sea and adjoining areas was 29-30 degree C. The Ocean heat content (OHC) was 80-100 KJ/cm2 over the area. The

lower level convergence and relative vorticity as well as upper level divergence increased from 22nd to 23rd October. The upper tropospheric ridge lay along 150N and hence provided the upper level divergence for intensification. The vertical wind shear between 200 and 850 hPa levels was moderate (10-20 knots) around the system centre on 22nd and 23rd October.

2.2.4 Intensification and movement

As the depression lay to the south of the upper tropospheric ridge and the steering winds at middle and upper tropospheric levels were east-southeasterly, the system initially moved west- northwestwards and intensified into a deep depression at 1500 UTC of 23rd October under the favourable conditions as mentioned in previous section.

Thereafter, the convection increased in the southwest sector with increase in low level relative vorticity in this sector and the steering ridge to the north weakened leading to west-southwestward movement. However, the low to moderate wind shear continued to prevail over the region. Under these circumstances, the deep depression moved west-southwestwards and intensified into a cyclonic storm, ‗MURJAN‘ at 1200 UTC of 24th October. It then continued to move west- southwestwards and crossed Somalia coast near lat. 9.50 N between 1700 and 1800 hrs. UTC of 25th October, 2012. Though the Ocean Heat Content was less over the southwest Arabian Sea (50-80 KJ/cm2) and further less near Somalia coast (less than 50 KJ/cm2) as well as SST (26-280C), the system could maintain its intensity of cyclonic storm till landfall, basically due to low to moderate vertical wind shear.

Table 2.2.1 Best track positions and other parameters of the Cyclone „MURJAN‟ over the Arabian Sea during 23-26 October, 2012 Date Time Centre lat.0 C.I. Estimated Estimated Estimated Grade (UTC) N/ long. 0 E NO. Central Maximum Pressure drop at Pressure Sustained the Centre (hPa) (hPa) Surface Wind (kt)

0300 11.0/65.0 1.5 1004 25 3 D 23-10-2012 1200 11.5/64.0 1.5 1003 25 3 D 1500 11.5/63.5 2.0 1002 30 4 DD 0300 11.0/59.0 2.0 1002 30 5 DD 24-10-2012 1200 10.5/56.5 2.5 1000 35 6 CS 1800 10.5/55.5 2.5 1000 40 8 CS 0000 10.5/54.0 2.5 1000 35 6 CS 0600 10.0/53.0 2.5 1000 35 6 CS 25-10-2012 1200 9.5/51.5 2.5 1000 35 6 CS The system crossed Somalia coast near 9.50N and 50.80E between 1700-1800 UTC 1800 9.5/50.5 - 1001 30 4 DD 0000 9.5/49.5 - 1002 25 3 D 26-10-2012 0300 9.5/48.5 - 1002 25 3 D 1200 Weakened into a well marked low pressure area over Somalia and neighbourhood

After the landfall, due to land interaction, it weakened into a deep depression over coastal Somalia at 1800 UTC of 25th October. It further weakened into a depression over Somalia in the morning of 26th October while moving west- southwest wards. It further weakened into a well marked low pressure area over Somalia and neighbourhood in the evening of 26th October, 2012. The track of the system is shown in Fig. 2.1. The best track parameters are shown in Table 2.2.1. Formation of Vortex Intensification of the system (T1.5)

1200 UTC, 22.11.2012 2100 UTC, 22.10.2012 Further intensification (T2.0) Intensification into cyclonic storm (T2.5)

1700 UTC, 23.10.2012 1200 UTC, 24.10.2012 Landfall

1600 UTC, 25.10.2012 Fig. 2.2.1. Typical satellite imagery of cyclone, Murjan at different stages of its evolution and landfall.

2.2.5 Satellite observations

According to satellite observations, a low level circulation developed over Tamilnadu and neighbourhood on 19th October at 0600UTC. It moved westward and intensified into a vortex with intensity T1.0 and centered near 10.00N/68.00E on 22nd October at 1200 UTC. It moved in west-northwestwards and intensified with intensity T1.5 at 2100 UTC of 22nd. The centre of the system at this time was located near 10.80N/66.50E. The system intensified further with intensity T2.0 at 1700 UTC of 23rd with centre at 11.30N/63.30E. and into a cyclonic storm with intensity T2.5 with centre at 10.50N/56.50E. The system was of shear pattern till 0600UTC UTC of 23rd. Then it changed into curved band pattern till landfall of the system. The typical satellite imagery of cyclone, Murjan at various stages are shown in Fig. 2.2.1. Satellite based position and intensity are shown in Table 2.2.2.

Table 2.2.2 Position & Intensity of cyclone, Murjan according to satellite observations of IMD DATE TIME(UTC) LAT(0N) LONG (0E) INTENSITY T No. CTT (0C) 21.10.12 0000 - - LLC - 22.10.12 1200 10.0 68.0 1.0 -73 1500 10.5 67.5 1.0 -76 1700 10.8 67.5 1.0 -76 2100 10.8 66.5 1.5 -71 23.10.12 0000 10.8 66.0 1.5 -62 0300 11.2 65.0 1.5 -65 0600 11.2 65.0 1.5 -76 0900 11.3 64.5 1.5 -84 1200 11.3 64.0 1.5 -80 1500 11.3 63.5 1.5 -80 1700 11.3 63.3 2.0 -84 2100 11.3 62.5 2.0 -76 24.10.12 0000 11.3 62.0 2.0 -69 0600 10.5 58.0 2.0 -79 0900 10.5 57.4 2.0 -81 1200 10.5 56.5 2.5 -78 1500 10.5 56.0 2.5 -75 1700 10.5 55.4 2.5 -77 2100 10.5 54.2 2.5 -68 25.10.12 0000 10.5 53.8 2.5 -75 0300 10.5 53.5 2.5 -79 0600 10.1 52.9 2.5 -77 0900 9.7 52.7 2.5 -75 1200 9.5 51.6 2.5 -72 1500 9.5 51.0 2.5 -69 1600 9.5 50.6 Overland -69

2.2.6 Realised Weather

As estimated by satellite imagery and products, the sustained maximum wind of 65-75 kmph prevailed along and off Somalia coast at the time of landfall. There was no meteorological observation available from Somalia.

There were reports of large scale flooding in Bosaso city in Somalia. The storm brought strong winds and heavy but beneficial rains within the areas of Bari region (Bossasso, Ishkushban and Bandar Beyla) according to Somalia Water and Land Information Management, as reported in the media.

2.2.7 NWP Guidance

The genesis, track and intensity of the cyclone, Murjan was reasonably captured by most of the models. The NWP model analyses of pressure and wind at 850, 500 and 200 hPa levels based on 0000 UTC of 23-26 October 2012 for ECMWF, UKMO and IMD GFS models are shown in Fig. 2.2.2- 2.2.4.

Fig. 2.2.2 (a) ECMWF analysis of MSLP and winds at 850, 500 and 200 hPa levels based on 0000 UTC of 23rd October, 2012

Fig. 2.2.2(b) ECMWF analysis of MSLP and winds at 850, 500 and 200 hPa

levels based on 1200 UTC of 23rd October, 2012

Fig. 2.2.2(c) ECMWF analysis of MSLP and winds at 850, 500 and 200 hPa levels based on 0000 UTC of 24th October, 2012

Fig. 2.2.2(e) ECMWF analysis of MSLP76 and winds at 850, 500 and 200 hPa levels based on 0000 UTC of 25th October, 2012

Fig. 2.2.2(f) ECMWF analysis of MSLP and winds at 850, 500 and 200 hPa th levels based on 1200 UTC of 25 October, 2012

Fig. 2.2.2(g) ECMWF analysis OF MSLP and winds at 850, 500 and 200 hPa levels based on 0000 UTC of 26th October, 2012

Fig. 2.2.2(h). ECMWF analysis of MSLP and Winds at 850, 500 and 200 hPa levels based on 1200 UTC of 26th October, 2012

Fig. 2.2.3(a) UKMO analysis MSLP and wind at 850,500 & 200 hPa based on 0000 UTC of 23 October, 2012

Fig. 2.2.3(b) UKMO analysis of MSLP and wind at 850, 500 & 200 hPa levels based on 0000 UTC of 24 October, 2012

Fig. 2.2.3(c) UKMO analysis of MSLP and wind at 850, 500 & 200 hPa.

levels based on 0000 UTC of 25 October, 2012

Fig. 2.2.3(d) UKMO analysis of MSLP and wind at 850, 500 & 200 hPa. levels based on 0000 UTC of 26 October, 2012

Fig. 2.2.4(a) NCMRWF GFS 574L64 analysis of MSLP and wind at 850, 500 & 200 hPa based on 0000 UTC of 23 October, 2012

Fig. 2.2.4(b) NCMRWF GFS 574L64 analysis of MSLP and wind at 850,500 & 200 hPa

levels based on 0000 UTC of 24 October, 2012

Fig. 2.2.4(c) NCMRWF GFS 574L64 analysis of MSLP and wind at 850, 500 & 200 hPa levels based on 0000 UTC of 25 October, 2012

2.2.7.Damage

Fig. 2.2.4(d) NCMRWF GFS 574L64 analysis of MSLP and wind at 850, 500 & 200 hPa levels based on 0000 UTC of 26 October, 2012

2.3 Cyclonic Storm, NILAM over Bay of Bengal (28 October- 01 November, 2012)

2.3.1 Introduction

A cyclonic storm, NILAM crossed Tamilnadu coast near Mahabalipuram (south of Chennai) in the evening of 31st October 2012 with a sustained maximum wind speed of about 80 kmph. The salient features of this storm are as follows.

(i) It followed a unique track with many rapid changes in direction of movement. It initially moved westwards, remained practically stationary for quite some time near Sri Lanka coast and then moved north- northwestwards till landfall. It moved west-northwestwards initially over land upto south interior Karnataka and then moved northwest and northwards. The remnant low pressure area moved northeastwards across Andhra Pradesh (ii) It moved very fast on the day of landfall, i.e. 31st October 2012. (iii) Maximum rainfall occurred over southwest sector of the system centre and heavy to very heavy rainfall extended upto 300 km during landfall. (iv) Over the land surface, the cloud mass was significantly sheared to the northeast of system centre during its dissipation stage leading to heavy rainfall activity over entire Andhra Pradesh and adjoining Odisha.

2.3.2 Monitoring and Prediction

The cyclonic storm, NILAM was monitored mainly with satellite supported by meteorological buoys and coastal and island observations. It was monitored by Doppler Weather Radar (DWR), Chennai and Sriharikota from the night of 29th October, when the cyclonic storm was at about 500 km southeast of Chennai. While coastal surface observations were taken on hourly basis, the half hourly INSAT/ Kalpana imageries and every 10 minutes DWR imageries and products were used for monitoring of cyclonic storm.

Various NWP and dynamical-statistical models including IMD‘s global and meso-scale models were utilized to predict the track and intensity of the storm. Recently installed Tropical Cyclone Module in the digitized forecasting system of IMD was utilized for analysis and comparison of various NWP models and decision making process.

2.3.3 Genesis:

A remnant cyclonic circulation from the south China Sea entered into south Andaman Sea on 25th October 2012 across the Gulf of Thailand. It gradually moved westwards and concentrated into a low pressure area in the early hours of 27th October. It further concentrated into a depression over southeast and adjoining

southwest Bay of Bengal at 0600 UTC of 28th October 2012 near latitude 9.50N and longitude 86.00E. Considering the satellite observations, the convection increased gradually in terms of its height and organization from 27th to 28th October. The lowest cloud top temperature (CTT) was about -700C at the time of formation of depression, i.e. at 0600 UTC of 28th October 2012.

Considering the environmental features, the sea surface temperature on the day of genesis was 29-300C over south Bay of Bengal and the Ocean thermal energy was about 50-80 KJ/cm2 around the area of genesis. The Madden Julian Oscillation (MJO) index lay over phase 2, which is favourable for cyclogenesis. The upper tropospheric ridge at 200 hPa level ran along 130N and provided required upper level divergence for intensification of the system. The lower level convergence and the vorticity also increased from 27th to 28th October. The vertical wind shear between 200 and 850 hPa levels was low to moderate (10-20 knots) over the region, which was also favourable for genesis and intensification.

The best track parameters of the system is shown in Table 2.3.1. The best track is shown in Fig.2.1.

Table 2.3.1 Best track positions and other parameters of the Cyclone, „Nilam‟ over the Bay of Bengal during 28 October-01 November, 2012 Date Time Centre C.I. Estimate Estimated Estimated Grade (UTC) lat.0 N/ NO. d Central Maximum Pressure drop long. 0 E Pressure Sustained at the (hPa) Surface Wind Centre (hPa) (kt) 0600 9.5/86.0 1.5 1004 25 3 D 28-10-2012 1200 9.5/85.0 1.5 1003 25 3 D 1800 9.5/84.5 1.5 1002 25 4 D 0000 9.5/84.0 2.0 1000 30 4 DD 0300 9.5/83.5 2.0 1000 30 4 DD 29-10-2012 0600 9.0/83.0 2.0 1000 30 4 DD 1200 9.0/82.5 2.0 1000 30 5 DD 1800 9.0/82.0 2.0 1000 30 5 DD 0000 9.0/82.0 2.0 999 30 5 DD 0300 9.0/82.0 2.5 998 35 6 CS 0600 9.0/82.0 2.5 996 35 6 CS 30-10-2012 0900 9.5/82.0 2.5 996 35 6 CS 1200 9.5/82.0 2.5 994 40 8 CS 1500 9.5/82.0 2.5 994 40 8 CS 1800 10.0/82.0 2.5 992 40 8 CS 2100 10.0/82.0 2.5 990 40 10 CS 0000 10.5.81.5 3.0 988 45 12 CS 31-10-2012 0300 11.0/81.0 3.0 987 45 13 CS 0600 11.5/81.0 3.0 987 45 13 CS 89

0900 12.3/80.5 3.0 987 45 13 CS The system crossed north Tamilnadu coast near Mahabalipuram, south of Chennai (near latitude 12.50N and longitude 80.20E) between 1030 and 1130 UTC 1200 12.7/79.8 991 35 8 CS 1500 13.0/79.5 996 35 7 CS 1800 13.0/78.5 998 30 5 DD 0000 13.0/77.5 999 20 4 D 0300 13.5/77.0 1002 20 3 D 01-11-2012 0600 13.5/77.0 1002 20 3 D 1200 14.0/77.0 1002 20 3 D 1800 14.5/77.0 1004 20 3 D 0000 Weakened into a well marked low pressure area over Rayalaseema and 02-11-2012 neighbourhood D : Depression, DD : Deep Depression, CS : Cyclonic storm

2.3.4 Intensification and movement

Similar favourable environmental conditions continued on 29th and 30th October. As a result, the deep depression further intensified into a cyclonic storm Nilam and lay centred at 0300 UTC of 30th over southwest Bay of Bengal near Lat. 9.00N / Long. 82.00E, about 500 km south–southeast of Chennai. Further, it moved northwards and lay centred at 1200 UTC of 30th near Lat. 9.50N/ Long. 82.00E, about 450 km south-southeast of Chennai. The cyclonic storm moved very slowly during 0000 UTC of 29th to 1200 UTC of 30th, remaining almost stationary.It then moved northwestwards and lay centred at 0300 UTC of 31st over southwest Bay of Bengal near Lat. 11.00N/Long. 81.00E, about 260 km south-southeast of Chennai. Moving north-northwestwards, it crossed north Tamil Nadu coast near Lat. 12.50N / Long. 80.20E, south of Chennai, near Mahabalipuram between 1030 and 1130 UTC of 31 and lay centred at 1200 UTC of 31st near Lat. 12.70N/Long. 79.80E, about 50 km south–southwest of Chennai. It moved west-northwestwards and weakened into a deep depression and lay centred over north Tamil Nadu and adjoining areas of Rayalaseema and interior Karnataka at 1800 UTC of 31st October, near Lat. 13.00N/

Long. 78.50E, about 180 km west–northwest of Chennai. It further moved west- northwestwards and weakened into a depression over Rayalaseema and adjoining areas of south interior Karnataka and lay centred at 0000 UTC of 1st November 2012 near Lat. 13.00N / Long. 77.50E, about 75 km, south of Anantpur and at 0300 UTC over south Interior Karnataka, near Lat. 13.50N / Long. 77.00E, close to Chitradurga. It moved further northward and lay centred at 1200 UTC near Lat. 14.00N/ Long. 77.00E and at 1800 UTC of 1st November 2012 near Lat. 14.5° N/ Long. 77.0° E. It further weakened into a well marked low pressure area over Rayalaseema and neighbourhood in the morning of 2nd November. It further weakened into a low Pressure area over Telangana and neighbourhood on 3rd and over North coastal Andhra Pradesh and neighbourhood on 4th November. It became less marked on 5th November.

According to survey report, ―NILAM‖ crossed North Tamil Nadu coast, south of Kalpakkam and north of Koovathur, a small coastal village situated close to river Palar Estuary (landfall near 120 27‘ and 800 09‘) between 1040 and 1110 hrs UTC of 31st October 2012. The crucial observations showing the landfall point and time of cyclone, Nilam are shown in Fig.2.3.1

Fig.2.3.1 Hourly surface observations indicating landfall point and time of Nilam.

2.3.5 Lowest pressure and maximum wind

The lowest estimated central pressure (ECP) was 986 hPa (post cyclone survey report). The lowest observed pressure was 987.8 hPa at 1040 UTC of 31st October at Kalpakkam (ISRO-AWS) located south of Chennai The maximum estimated mean wind speed was 45 knots. Maximum sustained wind speed of 74 kmph (40 kts) has been reported over Chennai (Nungambakkam) at 1110 UTC of 31. The high wind speed recorder (HWSR) at Karaikal reported maximum wind speed of westerly/37 kts on 31st October. The lowest pressure and maximum wind

reported by a few coastal stations at the time of landfall are shown in Table 2.3.2 and 2.3.3

Table 2.3.2. Lowest mean sea level pressure reported by coastal observatories at the time of landfall

Table 2.3.3 Maximum sustained surface wind reported by coastal observatories at the time of landfall

The pressure and wind observations from the Kalpakkam observatory which is nearest to landfall point are shown in Fig.2.3.2. It indicates clearly the landfall time of the cyclone

Fig. 2.3.2 Kalpakkam Pressure & Wind data on 31st Oct. (Time in hrs IST)

2.3.6 Satellite observations

The system was monitored mainly with satellite supported by meteorological buoys, coastal and island observations during genesis phase and its intensification into cyclonic storm on 29th October. Typical satellite imageries of the system are shown in Fig.2.3.3.

According to satellite observations, a low level circulation developed over south-east Bay of Bengal around 1200 UTC of 25th October 2012, which organized into vortex (T1.0) on next day (26th October 2012) at 1500 UTC centered near 12.00N/91.50E. It intensified upto T3.0. The system was of curved band pattern till 1800 UTC of 30th October. Then it changed into central dense overcast (CDO) pattern. The satellite based T number and CTT are shown in Table 2.3.4.

Table 2.3.4. Satellite based observations of cyclone, Nilam Time Date (UTC) Lat (E) Long (E) T. No. C.T.T (C) 25.10.12 1200 - - LLC - 1500 12.0 91.5 1.0 -75 26.10.12 1700 12.0 91.5 1.0 -71 2100 12.2 91.5 1.0 -81 0000 12.2 91.5 1.0 -80 0300 12.0 91.0 1.0 -79 0600 12.0 91.0 1.0 -79 0900 12.0 90.5 1.0 -76 27.10.12 1200 12.0 90.0 1.0 -79 1500 12.0 90.0 1.0 -85 1700 12.0 89.5 1.0 -87 2100 11.5 88.5 1.0 -88 0000 11.0 87.5 1.0 -91 0300 10.0 87.5 1.0 -87 0600 9.5 87.0 1.5 -84 0900 9.5 86.0 1.5 -83 28.10.12 1200 9.5 85.0 1.5 -86 1500 9.5 84.5 1.5 -83 1700 9.5 84.5 1.5 -91 2100 9.5 84.5 1.5 -91 0000 9.5 84.0 2.0 -86 0300 9.3 83.3 2.0 -80 0600 8.9 82.8 2.0 -81 0900 8.7 82.5 2.0 -85 29.10.12 1200 8.7 82.5 2.0 -84 1500 8.7 82.3 2.0 -79 1700 8.7 82.2 2.0 -83 2300 8.7 82.0 2.0 -84 0000 8.7 82.0 2.0 -83 0300 9.0 82.0 2.5 -85 0600 9.2 82.0 2.5 -82 0900 9.3 82.0 2.5 -85 30.10.12 1200 9.5 81.9 2.5 -88 1500 9.5 81.9 2.5 -89 1700 9.6 81.8 2.5 -93 2100 10.2 81.8 2.5 -94 0000 10.4 81.7 3.0 -96 0300 10.5 81.1 3.0 -85 31.10.12 0600 11.0 80.9 3.0 -84 0900 11.7 80.3 3.0 -86 1200 12.5 80.0 Overland -85 94

Formation of vortex Intensified into Depression

26.10.12, 1500 UTC (T1.0) 28.10.12, 0600UTC (T1.5) Intensified into Deep Depression Intensified into Cyclonic storm

29.10.12, 0000UTC (T2.0) 30.10.12, 0300UTC (T2.5)

Fig. 2.3.3 IR Imageries based on 15 UTC of 26th Oct., 06 UTC of 28th Oct., 00 UTC of 29th Oct. and 03 UTC of 30th Oct.,2012 in association with different stages of cyclonic storm, NILAM over Bay of Bengal

Intensified further to T3.0 Landfall of the system

31.10.12, 0000UTC (T3.0) 31.10.2012, 1200 UTC (T3.0)

Oceansat-II based surface wind

30.10.12, 1812UTC

Fig. 2.3.3(Contd.) IR Imageries based on 00 and 12 UTC of 31st Oct. and Oceansat II based surface wind at 1812 UTC of 30th October 2012.

2.3.7 Radar observations

The cyclonic storm, NILAM was monitored was also monitored by DWR Chennai and Sriharikota and conventional S-band RADAR, Karaikal. DWR Chennai monitored the system from the night of 29th October, when the cyclonic storm was about 500 km southeast of Chennai. The DWR performance during the cyclone surveillance period had been very good with optimum power output, sensitivity and stability without any trouble except during the period from 0615 to 0710 UTC (Radome door inter lock switch opened due to strong wind). Prominent features of eye could not be seen persistently. Radar-echoes in some parts of spiral bands were stronger than the eye-wall echoes on many occasions. Maximum observed reflectivity was around 55 dBZ. The wind field was less symmetric to the eye. Maximum velocity of about 30 mps observed in the cyclone field was associated with the spiral band. The typical radar imageries of the system from DWR, Chennai are shown in Fig.2.3.4. Features observed through radar are also shown in Table 2.3.5

Table 2.3.5. Features observed through DWR, Chennai

Fig. 2.3.4(a) DWR Chennai imageries based on 17, 18 & 21 UTC of 30th and 01 UTC of 31st Oct 2012 during Cyclonic Storm, NILAM over Bay of Bengal.

Fig. 2.3.4(b) DWR Chennai imageries based on 03, 06, 09 & 10 UTC of 31st Oct 2012 during Cyclonic Storm, NILAM over Bay of Bengal

Fig. 2.3.4(c) DWR SHAR PPI_V imageries based on 06 UTC of 28th, 03 UTC of 29th and 03, 06, 09 & 12 UTC of 30th Oct. 2012

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Fig. 2.3.4(d) DWR SHAR PPI_V imageries based on 03, 06 09, 10 & 11 UTC of 31st Oct. and 06 UTC of 1st Nov. 2012

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2.3.8. Features observed through NWP model analyses

The mean sea level pressure analysis, 850 hPa, 500 hPa and 200 hPa wind analyses of various models are shown in Fig.2.3.5-2.3.8. The performance of various models for detection and prediction of this system showed large scale variation with respect to genesis, track and intensification. However, the models guidance converged to each other, as the system came closer to coast. Detailed verification of NWP guidance are given in Chapter III.

Fig. 2.3.5(a) ECMWF MSLP and 850, 500 & 200 hPa levels wind analysis based on 00 UTC of 28th Oct. 2012

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Fig. 2.3.5(b) ECMWF MSLP and 850, 500 & 200 hPa levels wind analysis based on 00 UTC of 29th Oct. 2012

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Fig. 2.3.5 (c) ECMWF MSLP and 850, 500 & 200 hPa levels wind analysis based on 00 UTC of 30th Oct. 2012

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Fig. 2.3.5(d) ECMWF MSLP and 850, 500 & 200 hPa levels wind analysis based on 00 UTC of 31st Oct. 2012

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Fig. 2.3.5(e) ECMWF MSLP and 850, 500 & 200 hPa levels wind analysis based on 00 UTC of 1st Nov. 2012

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Fig. 2.3.5(f) ECMWF MSLP and 850, 500 & 200 hPa levels wind analysis based on 00 UTC of 2nd Nov. 2012

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Fig. 2.3.5(g) ECMWF MSLP and 850, 500 & 200 hPa levels wind analysis based on 00 UTC of 3rd Nov. 2012

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Fig. 2.3.6(a) IMD GFS MSLP, 10m wind and winds at 850, 500 & 200 hPa levels analysis based on 00 UTC of 28th Oct. 2012

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Fig. 2.3.6(b) IMD GFS MSLP, 10m wind and winds at 850, 500 & 200 hPa levels analysis based on 00 UTC of 29th Oct. 2012

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Fig. 2.3.6(c) IMD GFS MSLP, 10m wind and winds at 850, 500 & 200 hPa levels analysis based on 00 UTC of 30th Oct. 2012

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Fig. 2.3.6(d) IMD GFS MSLP, 10m wind and winds at 850, 500 & 200 hPa levels analysis based on 00 UTC of 31st Oct. 2012

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Fig. 2.3.6(e) IMD GFS MSLP, 10m wind and winds at 850, 500 & 200 hPa levels analysis based on 00 UTC of 1st Nov. 2012

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Fig. 2.3.6(f) IMD GFS MSLP, 10m wind and winds at 850, 500 & 200 hPa levels analysis based on 00 UTC of 2nd Nov. 2012

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Fig. 2.3.6(g) IMD GFS MSLP, 10m wind and winds at 850, 500 & 200 hPa levels analysis based on 00 UTC of 3rd Nov. 2012

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Fig. 2.3.7(a) NCMRWF GFS T-574 model MSLP, 850, 500 and 200 hPa wind analysis based on 00 UTC of 28th Oct. 2012

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Fig. 2.3.7(b) NCMRWF GFS T-574 model MSLP, 850, 500 and 200 hPa wind analysis based on 00 UTC of 29th Oct. 2012

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Fig. 2.3.7(c) NCMRWF GFS T-574 model MSLP, 850, 500 and 200 hPa wind analysis based on 00 UTC of 30th Oct. 2012

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Fig. 2.3.7(d) NCMRWF GFS T-574 model MSLP, 850, 500 and 200 hPa wind analysis based on 00 UTC of 31st Oct. 2012

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Fig. 2.3.8(a) UKMO model MSLP, 850, 500 and 200 hPa wind analysis based on 00 UTC of 28th Oct. 2012

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Fig. 2.3.8(b) UKMO model MSLP, 850, 500 and 200 hPa wind analysis based on 00 UTC of 29th Oct. 2012

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Fig. 2.3.8(c) UKMO model MSLP, 850, 500 and 200 hPa wind analysis based on 00 UTC of 30th Oct. 2012

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Fig. 2.3.8(d) UKMO model MSLP, 850, 500 and 200 hPa wind analysis based on 00 UTC of 30th Oct. 2012

2.3.9. Realized Weather

Under its influence gale wind speed reaching 70-80 kmph prevailed along and off north coastal Tamil Nadu, Puducherry and adjoining south Andhra Pradesh coast Available observations from meteorological observatories indicate that the maximum wind speed of 75 kmph has been reported over Chennai & 65 kmph over Kalpakkam at the time of landfall.

Rainfall at most places with scattered heavy to very heavy rainfall occurred over north coastal Tamil Nadu. Rainfall at most places with isolated heavy to very heavy rainfall also occurred over north interior Tamil Nadu on 31st October and 1st November 2012. During weakening phase as a low over Andhra Pradesh, it caused

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rainfall at most places with scattered heavy to very heavy rainfall and isolated extremely heavy rainfall over coastal Andhra Pradesh and isolated heavy to very heavy rainfall over Telengana, Rayalaseema and south Odisha during 2nd to 5th November 2012. Chief amounts of 24 hrs rainfall (7 cm or more) ending at 0300 UTC of 31st Oct-3rd Nov 2012 are given below.

Tamil Nadu and Puducherry: 31. 10. 2012 Vedaranyam (Nagapattinam Dist) and Mahabalipuram (Kancheepuram Dist) 13 each, Trangambadi (Nagapattinam Dist) 10, Ennore AWS (Tiruvallur Dist), Chennai Nungambakkam (Chennai Dist), Nagapattinam (Nagapattinam Dist), Kalpakkam (Kancheepuram Dist) and Tiruvarur (Tiruvarur Dist) 9 each, Madavaram AWS (Tiruvallur Dist), Thiruthuraipoondi and Nannilam (both Tiruvarur Dist), Kelambakkam and Chennai Airport (both Kancheepuram Dist), Karaikal (Karaikal Dist) and Anna University (Chennai Dist) 8 each, Tambaram (Kancheepuram Dist), Sirkali and Mayiladuthurai (both Nagapattinam Dist), Kodavasal and Muthupet (both Tiruvarur Dist), Marakkanam and Vanur (both Villupuram Dist), Chengalpattu (Kancheepuram Dist), Cholavaram (Tiruvallur Dist), Puducherry (Puducherry Dist) and DGP office (Chennai Dist) 7 each,

01. 11. 2012 Yercaud (Salem Dist) 24, Alangayam (Vellore Dist) 20, Vandavasi (Tiruvannamalai Dist) 19, Tirukoilur (Villupuram Dist) 14, Vanur and Tindivanam (both Villupuram Dist) 13 each, Gingee, Villupuram and Mylam AWS (all Villupuram Dist), Ambur and Tirupattur (both Vellore Dist) and Valangaiman (Tiruvarur Dist) 11 each, Sirkali (Nagapattinam Dist), Kodavasal (Tiruvarur Dist), Polur (Tiruvannamalai Dist), Sethiathope and Tozhudur (both Cuddalore Dist), Thali (Krishnagiri Dist), Melalathur (Vellore Dist) and Naduvattam (Nilgiris Dist) 10 each, Parangipettai (Cuddalore Dist), Trangambadi and Kollidam (both Nagapattinam Dist), Penucondapuram (Krishnagiri Dist), Needamangalam (Tiruvarur Dist) and Arani (Tiruvannamalai Dist) 9 each, Chengam and Tiruvannamalai (both Tiruvannamalai Dist), Mayiladuthurai (Nagapattinam Dist), Mannargudi (Tiruvarur Dist), Colachel (Kanyakumari Dist), Chidambaram and Cuddalore (both Cuddalore Dist), Pallipattu (Tiruvallur Dist) and Tirukattupalli (Thanjavur Dist) 8 each, Aravakurichi (Karur Dist), Barur, Hosur, Denkanikottai, Krishnagiri, Uthangarai and Pochampalli (all Krishnagiri Dist), Kattumannarkoil, Chidambaram AWS and Neyveli AWS (all Cuddalore Dist), Thanjavur, Thiruvidaimaruthur, Kumbakonam, Madukkur, Vallam, Aduthurai AWS and Grand anaicut (all Thanjavur Dist), Sankarapuram (Villupuram Dist), Nannilam and Thiruthuraipoondi (both Tiruvarur Dist), Vaniaymbadi (Vellore Dist), Puducherry (Puducherry Dist), Pappireddipatti and Dharamapuri (both Dharmapuri Dist), Thuvakudi and Pullambadi (both Trichy Dist), Eraniel (Kanyakumari Dist)a nd Kothagiri (Nilgiris Dist) 7 each,

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Karnataka: 01.11.2012 Bagepalli (Chikaballapura dt) 14, Koratagere (Tumkur dt) 11, Kolar, Rayalpadu (Kolar dt), GKVK (Bengaluru Urban dt), Hoskote (Bengaluru Rural dt) 10 each, Srinivaspura (Kolar dt), Doddaballapura (Bengaluru Rural dt), Nayakanahatti (Chitradurga dt), CN Halli, Madhugiri (Tumkur dt), Thondebhavi, Gudibande (both Chikaballapura dt) 9 each, MM Hills (Chamarajanagar dt), Mulbagal, Bangarpet (both Kolar dt), Bengaluru City, Bengaluru HAL AP, Nelamangala (Bengaluru Rural dt), Hiriyur (Chitradurga dt), Kibbanahalli, Kunigal, Bargur (all Tumkur dt), Chintamani, Gowribidanur (both Chikaballapura dt) 8 each, Panchanahalli, Kadur (both Chikmagalur dt), Arasikere (Hassan dt), Bandipura (Chamarajanagar dt), Maddur (Mandya dt), Malur (Kolar dt), TG Halli (Bengaluru Urban dt), Devanahalli (Bengaluru Rural dt), Jagalur (Davangere dt), Hosanagara (Chitradurga dt), Chitradurga, Gubbi, Sira (both Tumkur dt), Sidlaghatta (Chikaballapura dt), Magadi, Channapatna, Kanakapura (all Ramanagara dt), Ramanagara 7 each,

Coastal Andhra Pradesh 01.11.2012: Distt. Nellore: Vinjamur-16, Kavali-13, Rapur- 12, Kavali(a)- 11, Venkatagiri Town- 11, Udayagiri-10, Atmakur-8, Gudur-8, Nellore- 8, Seetharampuram-7. Distt. Prakasam: Ongole-15, Darsi-14, Addanki-13, Darsi(a)-13, Cumbam-13, Podili-12. Distt. Krishna: Avanigadda- 10,. Distt. East Godavari: Kakinada –7. Distt. Vishakhapatnam: Bhimunipatnam-12,

02.11.2012: Distt. Prakasam: Addanki-9, Darsi(a)-9, Ongole-8, Podili-7. Distt. Guntur: Sathenapalli- 14, Atchempet-10, Lam(a)-8, Bapatla- 8, Guntur- 7, Bapatla(a)-7, Macharla-7, Tenali-7. Distt. Krishna: Vijayawada (AP)-13, Nandigama- 11, Nuzvidu- 11, Gudivada-10, Vuyyuru(a)-9, Tiruvuru-8, Avanigadda-8, Kaikalur-7. Distt. West Godavari: Koderu-10, Tanuku-8, Eluru-7. Distt. East Godavari: Prathipadu-11, Tuni-9, Kakinada-8. Distt. Vishakhapatnam: Chintapalli-8, Araku Valley-8, Yellamanchili-7. Distt. Vizianagaram: Salur-14, Bobbili- 10, Vijayanagaram- 9, Gajapathinagaram- 9, Srungavarapukota-9, Cheepurupalli-7, Parvatipuram-7. Distt. Srikakulam: Palasa-8.

03.11.2012: Distt. Guntur: Mangalgiri-18, Bapatla-14, Bapatla(a)-13, Rapalle-12, Tenali-11, Guntur-9, Lam(a)-8. Distt. Krishna: Tiruvuru-21, Gudivada-15, Vuyyuru(a)-13, Avanigadda-11, Nuzvidu- 9, Nandigama-8, Kaikalur-7.

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Distt. West Godavari: Chintalapudi-17, Bhimavaram-14, Tanuku-13, Eluru-13, Tadepalligudem-13, Polavaram-10, Bhimadole-9, Koyyalagudem-8. Distt. East Godavari: Rajahmundry-8. Distt. Vishakhapatnam: Chintapalli-15, Chodavaram-9, Narsipatnam-8, Araku Valley-7. Distt. Vizianagaram: Srungavarapukota-18, Therlam-8, Parvatipuram-7, Salur-7, Gajapathinagaram-7. Distt. Srikakulam: Sompeta-8, Itchapuram-7.

04.11.2012: Distt. West Godavari: Narasapur(a)-31, Koderu-23, Tanuku-17, Tadepalligudem- 16, Narsapuram-16, Bhimavaram-14, Polavaram-12. Distt. East Godavari: Amalapuram-27, Rajahmundry-25, Kakinada-20, Tuni-19, Peddapuram-17, Prathipadu-15. Distt. Vishakhapatnam: Yelamanchili(a)-25, Chodavaram-22, Narsipatnam-21, Yellamanchili-18, Anakapalli-18, Anakapalle(a)-17, Visakhapatnam Ap-17, Bhimunipatnam-17, Visakhapatnam-15, Paderu-9, Araku Valley-7. Distt. Vizianagaram: Vijayanagaram-19, Srungavarapukota-16, Cheepurupalli-9, Therlam-9, Gajapathinagaram-9, Salur-7. Distt. Srikakulam: Ranasthalam-16, Gudivada-10, Palakonda-7, Kaikalur-7.

05.11.2012: Distt. Vishakhapatnam: Narsipatnam-9, Bhimunipatnam-8. Distt. Srikakulam: Kalingapatnam-26, Tekkali-11, Pathapatnam-9, Palasa-8.

Rayalseema

31.10.2012: Distt. Chittoor: Srikalahasthi-11, Tirumalla(a)-8, Chittoor-7.

01.11.2012: Distt. Chittoor: Tirumalla(a)-15, Venkatagirikota-11, Chittoor-9, Thambalapalli-8, Arogyavaram-8, Srikalahasthi-7, Punganur-7, Puttur-7. Distt. Cuddapah: Rajampet-9. Distt. Anantapur: Madakasira-8, Amarapuram-7, Penukonda-7, Kadiri-7.

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(02-04).11.2012: Nil

05.11.2012: Distt. Chittoor: Chittoor-8.

Telangana

02.11.2012: Distt. Khammam: Khammam-9, Madhira-9.

03.11.2012: Distt. Khammam: Dummugudem-15, Aswaraopet(a)-14, Venkatapuram-9, Yellandu-7. Distt. Warangal: Eturnagaram-13. Distt. Medak: Ramayampet-9. The spatial distribution of rainfall activity associated with this weather system on different days from 1st to 6th November is shown in Fig. 2.3.9. It shows north- northeast ward movement of rainfall activity associated with the system. Associated with the system, heavy to very heavy rainfall was reported over Coastal Andhra Pradesh and adjoining area from 2nd to 5th November.

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Fig.2.3.9. Spatial distribution of rainfall (mm) activity during 1st to 6th November 2012. The shading is based on IMD classification of rainfall like very light, light, moderate, rather heavy, heavy, very heavy and extremely heavy rainfall

2.3.10. Damage:

Tamil Nadu In Tamil Nadu the incessant heavy rains caused flash floods leading to extensive damage. 17 people were killed and loss of live stock was 298. Paddy crop of 4646 hectares was submerged in Tiruvarur district due to heavy rains. About 5000 electric poles were damaged during the storm period. 415 huts were fully damaged and 3283 were partially damaged. 242 km of roads and 3 bridges were damaged by its impact. Samaanthipuram bridge was washed away in the flash floods in the upper reaches of Eastern Ghats. Damage photographs due to CS NILAM are shown in Fig. 2.3.9.

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In Samanthipuram (Lat 12039‘ N and Lon 7906‘ E) village situated under foothills of Eastern Ghat in Tiruvannamalai district a bridge of length 100 m was washed away in the flash floods which occurred in the upper reaches of Eastern Ghat. This Samaanthipuram Bridge is vital road link for neighboring three tribal villages. The flood water reaching Shenbahathope Dam breached near river sluice in the dam causing flash flood in KamandalaNaga Nadi- a tributary of Palar river.

Andhra Pradesh In Prakasham district there was severe flooding. On November 1, more than 200 boats ran aground due to strong winds. As Nilam weakened, heavy rainfall continued affecting south coastal Andhra Pradesh, Rayalaseema and Telangana with heavy rains and flash flooding. The Kandaleru-Poondi part of the Telugu Ganga project near Gudur, overflowed cutting transportation across the river. Several villages in and around Ongole were inundated by floodwater. Severe flooding had blocked transportation between Ongole and the villages, stranding the villagers. Heavy rains in Visakhapatnam district led to a train derailment in Araku Valley. In East Godavari district, floodwater overflew a railway bridge. Around 500,000 hectares of cropland was ruined while 68,000 people were evacuated and taken to flood relief camps. A total of around 495 km (308 mi) of roads, 406 km (252 mi) of drains, 107 km (66 mi) of water supply lines, 10,882 street lights and 36 municipal buildings were left in ruins, after the storm. A total of 44 people were confirmed dead and the state suffered economic losses worth 200 crore.

Sri Lanka The storm brought torrential rains to Sri Lanka. The Puttalam — Mannar road had come under about a meter of water near Eluwankulama due to the overflowing of the Kala Oya river. About 1,000 houses were damaged by the storm. Across Sri Lanka, ten people were killed in events related to Cyclone Nilam.

Fig.2.3.9 Photographs showing damage due to cyclonic storm, NILAM in Tamil Nadu

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2.4 Deep depression over Bay of Bengal (17-19 November 2012)

2.4.1 Introduction:

A depression formed over the eastcentral Bay of Bengal from a remnant low pressure system of South China Sea, which emerged into Bay of Bengal across Thailand. It initially moved northwestwards and then westwards during 17th and 18th November. On 19th, it started moving west-southwestwards over the westcentral Bay of Bengal. Due to entrainment of cold air from the Indian mainland in middle tropospheric levels and relatively colder sea, the deep depression weakened gradually to a low pressure area over southwest and adjoining west central Bay of Bengal off north Tamil Nadu and south Andhra Pradesh coast on 22nd November and became less marked on 23rd. It caused isolated heavy rainfall over south coastal Andhra Pradesh and Rayalaseema on 22nd November. The salient features of this system are given below.

(i) It moved westwards initially and then west-southwestwards under the influence of the middle tropospheric steering ridge. (ii) It weakened over the sea due to entrainment of cold and dry air from Indian main land in middle tropospheric level. (iii) There existed a well defined low level circulation centre with banding features though the convection was significantly sheared to northeast under the influence of high wind shear on 18th and 19th November.

2.4.2 Monitoring of depression:

As the system was formed over deep sea (east central Bay), the system was mainly monitored by Satellite. The half hourly INSAT/ Kalpana imageries and products, Oceansat observations and microwave products from polar orbiting satellites were used for monitoring the location and intensity of the system. However, the available buoy and island observations helped in improving the satellite estimates of location and intensity. Various NWP and dynamical-statistical models including IMD‘s global and meso-scale models were utilised to predict the track and intensity of the system.

2.4.3 Genesis:

In association with an active inter-tropical convergence zone (ITCZ), a low pressure area formed over southeast Bay of Bengal on 15th November 2012. It moved west-northwestwards and became well marked over southeast and adjoining eastcentral Bay of Bengal on 16th November. It concentrated into a depression over east central Bay of Bengal at 0600 UTC of 17 November 2012 near latitude 15.50N and longitude 90.00E.

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Considering the environmental features, the favourable features for cyclogenesis included warmer sea surface temperature (SST), which was about 28- 300C over south and central Bay of Bengal. The Ocean heat content was about 50- 80 kJ/cm2 over southeast and adjoining east central Bay of Bengal, i.e. around the system centre. The upper tropospheric ridge ran along latitude 160N and hence provided poleward outflow which is favourable for intensification of the system. The low level convergence and upper level divergence increased with increase in low level relative vorticity from 15th to 17th November. The vertical wind shear of horizontal wind was moderate (10-20 knots) in the morning of 17th.

Table 2.4.1: Best track positions and other parameters of Deep Depression over the Bay of Bengal during 17-19 November, 2012 Date Time Centre C.I. Estimated Estimated Estimated Grade (UTC) lat.0 N/ NO. Central Maximum Pressure long. 0 E Pressure Sustained drop at the (hPa) Surface Wind (kt) Centre (hPa) 0600 11.5/90.0 1.5 1004 25 3 D 17.11.2012 1200 16.0/89.0 2.0 1002 30 5 DD 1800 16.0/89.0 2.0 1002 30 5 DD 18.11.2012 0000 16.0/88.5 2.0 1002 30 5 DD 0300 16.0/88.5 2.0 1002 30 5 DD 0600 16.0/88.0 2.0 1002 30 5 DD 1200 16.0/87.5 2.0 1002 30 5 DD 1800 16.0/87.5 2.0 1002 30 5 DD 0000 15.5/87.0 1.5 1004 25 3 D 0300 15.0/86.5 1.5 1004 25 3 D 0600 15.0/86.5 1.5 1004 25 3 D 19.11.2012 1200 15.0/86.0 1.5 1005 20 3 D 1500 Weakened into a well marked low pressure area over west central Bay of Bengal

2.4.4 Intensification and Movement:

The favourable conditions of 17th November morning, as mentioned in the previous section continued in the evening of the same day. In their association, the depression moved initially west-northwestwards and intensified into deep depression at 1200 UTC of 17th November over east central Bay of Bengal near latitude 16.00N and longitude 89.00E. However, as it was lying very close to the upper tropospheric ridge, the movement of the deep depression became slow thereafter. It moved westwards under the influence of the middle tropospheric steering ridge upto 1200 UTC of 18th. After remaining stationary for some time, it then moved west-southwestward and weakened into a Depression at 0000 UTC of 19th. It further weakened into a well marked low pressure over west central Bay of

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Bengal at 1500 UTC of 19th. As a low pressure area, t moved west-southwestwards close to north Tamil Nadu coast during 19th to 24th Nov, 2012.

The weakening of the system could be attributed to (i) entrainment of dry and cold air into the system from the Indian land mass in the lower and middle tropospheric levels, (ii) gradual increase in the vertical wind shear resulting in the northeastward shearing of convection from the low level circulation centre.

The track of this deep depression is shown below in Fig.2.1. The best track parameters are shown in Table 2.4.1. The crucial observations supporting the best track are given in Table 2.4.2.

Table 2.4.2. Crucial surface observations over Bay of Bengal during Deep Depression (17-19 November 2012) Observational Time (UTC) Position of Observastion Tool Buoy Buoy 171200 16.50N/88.00E MSLP: 1004.2 hPa 24 hours Pressure fall: 2.9 hPa Wind: 050/25 kts 180600 16.50N/88.00E MSLP: 1005.4 hPa Wind: 070/27 kts 180900 16.50N/88.00E Wind: 090/30 kts

181200 16.50N/88.00E Wind: 100/25 kts

190300 16.50N/88.00E MSLP: 1008.4 hPa

Wind: 070/18 kts

191200 16.50N/88.00E MSLP: 1007.6hPa

Wind: 110/14 kts 0 13.5 N/84.00E Wind: 340/16 kts Microwave 191138 F-16 Wind: 20-15 kts imagery

Table 2.4.3. Satellite observations of deep depression (14-22 November 2012) Intensity (T CTT No/ Date Time (UTC) Lat (N) Long (E) CI No) 14.11.12 0900 - - LLC - 0300 14.5 91.0 1.0 -71 0600 14.5 91.0 1.0 -73 0900 14.5 91.0 1.0 -69 16.11.12 1200 14.5 91.0 1.0 -68 1500 14.5 90.5 1.0 -73 1800 14.5 90.5 1.0 -79 2100 14.5 90.5 1.0 -82 132

0000 14.5 90.5 1.0 -84 0300 14.5 90.0 1.0 -77 0600 15.5 90.0 1.5 -77 0900 15.5 89.5 2.0 -75 17.11.12 1200 15.9 89.2 2.0 -71 1500 16.1 89.0 2.0 -77 1800 16.1 88.9 2.0 -79 2100 16.1 88.9 2.0 -79 0000 16.1 88.8 2.0 -75 0300 16.1 88.5 2.0 -75 0600 16.1 88.2 2.0 -64 18.11.12 0900 16.1 88.0 1.5/2.0 -59 1500 16.0 87.8 1.5/2.0 -52 1800 15.8 87.5 1.5/2.0 -52 2100 15.4 87.1 1.5/2.0 -50 0000 15.3 86.9 1.5/2.0 -50 0300 15.1 86.8 1.5/2.0 -36 0600 15.1 86.6 1.5/2.0 -34 0900 15.0 86.4 1.5/2.0 -37 19.11.12 1200 15.0 86.2 1.5/2.0 -45 1500 15.0 86.0 1.0/1.5 -60 1800 15.0 86.0 1.0/1.5 -68 2100 15.0 85.5 1.0/1.5 -68 0000 15.0 85.0 1.0/1.5 -67 0300 15.0 85.0 1.0/1.5 -68 0600 15.0 85.0 1.0/1.5 -60 0900 15.0 84.5 1.0/1.5 -68 20.11.12 1200 14.9 84.5 1.0/1.5 -68 1500 14.9 84.3 1.0/1.5 -70 1800 14.7 84.0 1.0/1.5 -81 2100 14.5 83.8 1.0/1.5 -85 0000 14.5 83.5 1.0/1.5 -87 0300 14.0 83.5 1.0/1.5 -79 0600 14.0 83.0 1.0/1.5 -68 0900 14.0 83.0 1.0/1.5 -75 21.11.12 1200 14.0 83.0 1.0/1.5 -75 1500 14.0 82.8 1.0/1.5 -50 1800 14.0 82.6 1.0/1.5 -50 2100 13.9 82.4 1.0/1.5 -67 0000 13.9 82.4 1.0/1.5 -70 22.11.12 0300 13.0 82.5 1.0 -64 0600 - - LLC -

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2.4.5 Estimated central pressure (ECP) and maximum sustained surface wind (MSW)

The estimated central pressure (ECP) of the system decreased from 1004 hPa at genesis stage to 1002 hPa at the stage of deep depression. The maximum sustained surface wind (MSW) reached upto 30 knots during 1200 UTC of 17th to 1800 UTC of 18th November 2012. The MSW was also supported by available scatterometry wind observations from various satellites including Oceansat-II.

2.4.6 Satellite observations

A low level circulation developed over east-central (EC) Bay of Bengal on 14th November at 0900UTC which intensified into a vortex with intensity T1.0 centered near 100N/910E at 0300 UTC of 16th November. The system remained stationary till 1200 UTC then moved westward till 0300 UTC of 17th. At 0600 UTC of 17th, the system intensified into T1.5 with centre at 15.50N/90.00E, it further intensified into T2.0 at 0900 UTC of 17th with centre near 15.50N/89.50E and started moving northwestward. The intensity of the system decreased to T1.5 at 0900 UTC of 18th when its position was 16.10N/88.00E. Intensity further decreased to T1.0 at 1500 UTC of 19th. It became less marked at 0600 UTC of 22nd and remained as low level circulation near 13.00N/82.50E. Formation of vortex(T1.0) Intensified into Depression (T1.5)

16.11.2012, 0300 UTC 17.11.2012, 0600 UTC Intensified into Deep Depression (T2.0) Weakened into Depression (T1.5)

17.11.2012, 0900 UTC 18.11.2012, 0900 UTC Fig.2.4.1 . Typical satellite imageries showing genesis, intensification, movement of the deep depression (16-18 November 2012) 134

Weakened into LLC (T1.0) Microwave image

19.11.2012, 1500 UTC 19.11.2012 2307 UTC

Fig.2.4.1(contd.) Typical satellite imageries showing weakening of the deep depression on 19th November 2012

Oceansat- II Wind Wind shear

18.11.2012, 1723 UTC 17.11.2012, 0300 UTC

Fig.2.4.2. Typical Oceansat-II based surface wind at 1723 UTC of 18th Nov 2012 and Meteosat based vertical wind shear at 0300 UTC of 17th Nov 2012

The convective cloud clusters got organized gradually and also there was in deep convection. The lowest cloud top temperature(CTT) was about -750C in the morning of 17th. The Madden Julian Oscillation (MJO) index lay over phase 5 with amplitude greater than 1. The MJO index at phase 5 is favourable for cyclogenesis over the Bay of Bengal. The typical satellite imageries of the system are shown in Fig.2.4.1. Detailed satellite observations are shown in Table 2.4.3.

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2.4.7. NWP model performance

The analysis and forecast fields of MSLP and wind at 850, 500 and 200 hPa levels based on ECMWF and IMD GFS models for the period of deep depression are shown in Fig.2.4.3. The genesis, intensity and movement of the deep depression could be reasonably predicted by these two models. The circulation pattern further indicates that the system was steered by the middle tropospheric flow pattern.

Fig.2.4.3(a). ECMWF model analyses of MSLP and wind/geopotential height at 850, 500 and 200 hPa levels based on 0000 UTC of 17th November 2012.

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Fig.2.4.3(b) IMD GFS model analyses of MSLP and wind at 850, 500 and 200 hPa levels based on 0000 UTC of 17 th November 2012.

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Fig.2.4.3(c) ECMWF model analyses of MSLP and wind at 850, 500 and 200 hPa levels based on 0000 UTC of 18 th November 2012.

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Fig.2.4.3(d). IMD GFS model analyses of MSLP and wind at 850, 500 and 200 hPa levels based on 0000 UTC of 18 th November 2012.

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Fig.2.4.3(e). ECMWF model analyses of MSLP and wind at 850, 500 and 200 hPa levels based on 0000 UTC of 19 th November 2012.

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Fig.2.4.3(f). IMD GFS model analyses of MSLP and wind at 850, 500 and 200 hPa levels based on 0000 UTC of 19 th November 2012.

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2.4.7. Realised Weather

Heavy rainfall occurred over Andhra Pradesh, Puducherry and Tamil Nadu due the remnant low pressure area of this depression. The chief amount of 24 hrs cumulative rainfall (5 cm or more) ending at 0300 UTC of date are given below.

22 November 2012

Tamil Nadu & Puducherry: Sathanur Dam-10, Padalur-6, Sankarapuram-5

23 November 2012

Coastal Andhra Pradesh: Tada-7 Rayalaseema: Tirupati (AP)-14, Perumallapalli and Puttur-7 each, Tirupati and Rajampet-6 each, Pakala-5 Tamil Nadu & Puducherry: Pallipattu-6

24 November 2012

Tamil Nadu & Puducherry: Chengalpattu-14, Watrap and Tuticorin-10 each, Usilampatti, Bodinaickanur, Virudachalam-7 each, Coonoor-6, Viralimalai, Maduranthagam, Kothagiri, Ulundurpet, Vellore, Sirkali and Keeranur-5 each

25 November 2012

Tamil Nadu & Puducherry: Manimutharu-14, Thenkasi-12, Shencottah and Maniyachi-6 each, Illuppur-5.

2.4.8. Damage :

There was no damage due to the deep depression as, it weakened over the sea.

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2.5 Deep Depression over Arabian Sea (22-25 December, 2012)

2.5.1 Introduction

A depression formed over the south Arabian Sea in association with an active inter tropical convergence zone on 22nd December 2012. It moved initially westwards and intensified into a deep depression on 23rd December 2012. However, as it moved west-southwestwards towards Somalia coast, it weakened into a depression in the evening of 24th December and further into a low pressure area in the morning of 25th December 2012 over the southwest Arabian Sea off Somalia coast. The salient features of this cyclone are given below. (i) It moved west-southwest wards and weakened over the sea (ii) It was the first cyclonic disturbance in the month of December after 1992, which affected Somalia coast. The last cyclonic disturbance with a maximum intensity of a depression crossed Somalia coast on 24th December 1992.

2.5.2 Monitoring and prediction

The cyclonic storm was mainly monitored by satellite. The half hourly INSAT/ Kalpana imageries and products were used for monitoring of the system. Various NWP and dynamical-statistical models including IMD‘s global and meso-scale models were utilized to predict the track and intensity of the system.

2.5.3 Climatological characteristics

Considering the data during 1891-2011, only one cyclonic disturbance upto a maximum intensity of depression has crossed Somalia coast in the month of December. The deep depression during 22nd-25th December, 2012 was the first cyclonic disturbance in the month of December after 1992, which affected Somalia coast. The last cyclonic disturbance with a maximum intensity of a depression crossed Somalia coast on 24th December 1992. The cyclonic disturbances formed over the Arabian Sea during December for the period of 1891-2011 are shown in Fig.2.5.1. The brief history of the genesis, intensification and movement of this storm are discussed in following sections.

2.5.4 Genesis

Under the influence of an active inter-tropical convergence zone, a low pressure area formed over the Comorin area on 18th December 2012. It moved westwards and lay over Lakshadweep area on 19th and over southeast Arabian Sea on 20th December. Continuing to move westwards, it concentrated into a depression at 0900 UTC of 22nd December 2012 and lay centred over southeast and adjoining southwest Arabian Sea near lat. 9.00N and long. 63.00E, about 100 km west- southwest of Amini Divi.

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During the genesis phase, the Madden Julian Oscillation index lay in phase 2 with amplitude less than one. The phase 2 is favourable for genesis and intensification of the cyclonic disturbances over the Arabian Sea. The sea surface temperature (SST) over the southeast Arabian Sea and adjoining areas was 28-30 0C. The Ocean heat content (OHC) was 50-80 KJ/cm2 over the area. The lower level convergence and relative vorticity as well as upper level divergence increased from 22nd to 23rd October. The upper tropospheric ridge lay along 130N and hence provided the upper level divergence for intensification. The vertical wind shear between 200 and 850 hPa levels was low to moderate (05-15 knots) around the system centre on 22nd and 23rd December. Considering all these, the environmental parameters were favourable for genesis and intensification of the system. However, most of the NWP models could not detect/predict the genesis of this depression. The track of the system is shown in Fig.2.1. The best track parameters are shown in Table 2.5.1.

Fig. 2.5.1 Tracks of cyclonic disturbances formed over the Arabian Sea during the month of December over the period of 1891-2011.

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Table 2.5.1: Best track positions and other parameters of the deep depression over the Arabian Sea during 22-25 December, 2012

Date Time Centre C.I. Estimated Estimated Estimated Grade (UTC) lat.0 N/ NO. Central Maximum Pressure long. 0 E Pressure Sustained drop at the (hPa) Surface Centre Wind (kt) (hPa) 22-12-2012 0900 9.0/63.0 1.5 1004 25 3 D 1200 9.0/62.5 1.5 1003 25 4 D 0000 9.0/60.5 2.0 1002 30 5 DD 23-12-2012 0300 9.0/60.0 2.0 1002 30 5 DD 1200 8.5/57.0 2.0 1002 30 5 DD 0300 8.0/54.0 2.0 1002 30 5 DD 24-12-2012 1200 7.0/52.0 1.5 1004 25 3 D 0000 6.5/50.0 1.5 1005 20 3 D 25-12-2012 0300 Weakened into a low pressure area over southwest Arabian Sea off Somalia coast

2.5.5 Intensification and movement

As the depression lay to the south of the upper tropospheric ridge and the steering winds at middle and upper tropospheric levels were easterly to east- northeasterly, the system initially moved westwards and then west-southwestwards. It intensified into a deep depression and lay centred at 0300 UTC of 23rd December 2012 over southwest Arabian Sea near lat. 9.00N and long. 60.00E, about 1000 km east-southeast of Ras Binnah, Somalia as the favourable environmental conditions as mentioned in the previous section continued on 23rd December 2012.

On 23rd December, the convection increased in the southwest sector with increase in low level relative vorticity in this sector and the steering ridge to the north weakened leading to west-southwestward movement. However, the low to moderate wind shear continued to prevail over the region. Under these circumstances, the deep depression moved west-southwest wards and maintained its intensity, though the system was moving over a relatively colder sea area. On 24th December, as the system came closer to Somalia coast, it experienced further colder sea with Ocean thermal energy of < 40 KJ/cm2 and sea surface temperature of 26-280C. The vertical wind shear of horizontal wind increased and became high (about 25 knots) around the system centre. It also interacted with land surface as it lay close to Somalia coast and there was cold and dry air incursion over the area from Arabia and Africa. Under these circumstances, the deep depression weakened into a depression and lay centred at 1200 UTC of 24th December 2012 over southwest Arabian Sea near lat. 7.00N and long. 52.00E, close to Somalia coast. The dynamical statistical models of IMD indicated the system to attain the intensity of marginal cyclone and most of

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the NWP models indicated gradual weakening of the system. The system crossed Somalia coast as a low pressure area and became less marked.

2.5.6 Satellite observations

A low level circulation developed over southeast Arabian Sea on 19th December 2012 at 0900 UTC which intensified into a vortex with intensity T1.0 centered near 9.00N/65.00E at 0300 UTC of 22nd December. The system further intensified into T1.5 at 0600 UTC of the same day. At 0000 UTC of 23rd, the system intensified into T2.0 near 9.00N/60.50E and continued to move westward with little southerly component till 0600 UTC of 24th. Thereafter the system started moving southwesterly. The system was of shear pattern at this time. The wind shear at 0000 UTC of 24th was 20-30 Kts. At 1300 UTC of 24th the intensity of the system reduced to T1.5 when its position was at 7.00N/51.80E. The intensity further reduced to T1.0 at 0300 UTC of 25th December and ultimately became a low level circulation at 0900 UTC of same day. The vertical wind shear based on Meteosat-7 are shown in Fig.2.5.1.The typical satellite imagery of deep depression over Somalia coast is shown in Fig.2.5.2(a-b). The CTT imageries are shown in Fig.2.5.3. The detailed satellite observations are shown in Table 2.5.2.

0300 UTC, 22.12.2.12 00000000 UTC, 24.12.2.1224.12.2.12

Fig.2.5.1 Typical Satellite imagery of deep depression over Arabian Sea (22-25 December 2012) with vertical wind shear based on Meteosat-7

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Table 2.5.2 Satellite observation of Deep Depression

DATE TIME (UTC) LAT (0N) LONG (0E) INTENSITY CI No. CTT (0C) 19.12.12 0900 - - LLC - 0300 9.0 65.0 1.0 -80 0600 9.0 64.0 1.5 -77 0930 9.0 63.5 1.5 -77 22.12.12 1200 9.0 62.5 1.5 -70 1500 9.0 62.0 1.5 -75 1800 9.0 61.5 1.5 -78 2100 9.0 61.0 1.5 -79 0000 9.0 60.5 2.0 -75 0200 9.0 60.0 2.0 -78 0600 9.0 58.7 2.0 -76 0900 8.5 57.7 2.0 -71 23.12.12 1230 8.5 57.1 2.0 -62 1500 8.5 56.9 2.0 -71 1800 8.5 56.6 2.0 -75 2100 8.5 55.8 2.0 -75 0000 8.5 55.1 2.0 -78 0300 8.5 54.1 2.0 -75 0600 8.5 53.2 2.0 -60 0900 7.5 52.6 2.0 -55 24.12.12 1200 7.0 52.0 2.0 -61 1500 7.0 51.6 1.5/2.0 -56 1800 6.9 51.2 1.5/2.0 -52 2100 6.8 50.6 1.5/2.0 -57 0000 6.6 49.9 1.5 -50 0300 6.5 49.5 1.0 -52 25.12.12 0600 6.0 49.3 1.0 -39 0900 5.2 49.1 LLC

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Formation of vortex (T1.0) Intensified to Depression (T1.5) 0300 UTC, 22.12.2012 0600 UTC, 22.12.2012

Intensified to Deep Depression (T2.0) Weakened to Depression (T1.5) 0000 UTC, 23.12.2012 1300 UTC, 24.12.2012

Further weakening (T1.0) Microwave Image 0300 UTC, 25.12.2012 2124 UTC, 22.12.2012

Fig. 2.5.2 Typical satellite imagery of deep depression over Arabian Sea (22-25 December, 2012) 148

Fig. 2.5.3 Typical satellite imagery of deep depression over Arabian Sea (22-25 December, 2012) with cloud top temperatures

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2.5.7 NWP Guidance

The genesis, track and intensity of the deep depression were reasonably captured by most of the models. The NWP model MSLP analysis and wind at 850, 500 and 200 hPa levels based on 0000UTC of 22nd -25th October 2012 for ECMWF and IMD-GFS models are shown in Fig.2.5.4 (a-h).

Fig. 2.5.4 (a) ECMWF MSLP & Winds at 850, 500 and 200, hPa levels based on 0000 UTC of 22nd December, 2012

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Fig. 2.5.4 (b) IMD-GFS MSLP Analysis & Winds at 850 and 500 hPa levels based on 0000 UTC of 22nd December, 2012

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Fig. 2.5.4 (c) ECMWF MSLP & Winds at 850, 500 and 200, hPa levels based on UTC of 23rd December, 2012

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Fig. 2.5.4 (d) IMD-GFS MSLP Analysis & Winds at 850 and 500 hPa levels based on 0000 UTC of 23rd December, 2012

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Fig. 2.5.4 (e) ECMWF MSLP & Winds at 850, 500 and 200, hPa levels based on UTC of 24th December, 2012

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Fig. 2.5.4 (f) IMD-GFS MSLP Analysis & Winds at 850 and 500 hPa levels based on 0000 UTC of 24th December, 2012

155

Fig. 2.5.4 (g) ECMWF MSLP & Winds at 850, 500 and 200, hPa levels based on UTC of 25th December, 2012

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Fig. 2.5.4 (h) IMD-GFS MSLP Analysis & Winds at 850 and 500 hPa levels based on 0000 UTC of 25th December, 2012

2.5.8. Realised Weather

As estimated by satellite imagery and products, the sustained maximum wind of 15- 20 knots prevailed along and off Somalia coast, when the depression lay close to this coast. There was no meteorological observations available from Somalia to estimate the actual intensity of the system near this coast.

2.5.9. Damage

No damage report has been received from Somalia.

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CHAPTER-III

Performance of operational NWP models for forecasting tropical cyclones over the North Indian Ocean during the year 2012

3.1 Introduction:

India Meteorological Department (IMD) operationally runs two regional models, WRF and Quasi-Lagrangian Model (QLM) for short-range prediction and one Global model T574L64 for medium range prediction (7 days). The WRF-Var model is run at the horizontal resolution of 27 km, 9 km and 3 km with 38 Eta levels in the vertical and the integration is carried up to 72 hours over three domains covering the area between lat. 25o S to 45o N long 40o E to 120o E. Initial and boundary conditions are obtained from the IMD Global Forecast System (IMD-GFS) at the resolution of 23 km. The boundary conditions are updated at every six hours interval. The QLM model (resolution 40 km) is used for cyclone track prediction in case of cyclone situation in the north Indian Ocean. IMD also makes use of NWP products prepared by some other operational NWP Centres like, ECMWF (European Centre for Medium Range Weather Forecasting), GFS (NCEP), JMA (Japan Meteorological Agency). A multi-model ensemble (MME) for predicting the track of tropical cyclones for the Indian Seas is developed. The MME is developed applying multiple linear regression technique using the member models IMD- GFS, IMD-WRF, QLM, GFS (NCEP), ECMWF and JMA. In addition to the above NWP models, IMD also run operationally the Statistical Cyclone Intensity Prediction (SCIP) model for 12 hourly intensity predictions up to 72-h and Genesis potential parameter (GPP) for potential of cyclogenesis and forecast for potential cyclogenesis zone. In this report performance of these individual models, MME forecasts, SCIP and GPP for cyclones during 2012 are presented and discussed.

Recently the Hurricane WRF (HWRF) model and Ensemble prediction system (EPS) has been implemented at the NWP Division of the IMD for operational forecasting of cyclones and a rapid intensification index (RII) is developed for the probability forecast of rapid intensification (RI). The performances of these models for cyclones during 2012 are also presented.

3.2 Cyclonic storm “MURJAN” (24-26 October, 2012)

3.2.1 Genesis

Analysis of Genesis GPP values computed (Kotal et al, 2009) for cyclone „MURJAN‟ on the basis of real time model analysis fields along with the GPP values for Developing Systems and Non-Developing Systems are shown in Table 3.2.1 The higher GPP values (> 8.0, the threshold value) at early stages of development (T.No. 2.0) have clearly indicated that the cyclone “MURJAN” had enough potential to intensify into a developing system (>35 knots).

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Table 3.2.1 GPP (x10-5) for Developing System, Non-Developing System and Cyclone “MURJAN”

24.10.2012 Date/Time 0000 UTC T.No.  2.0 Developing 13.3 Non-Developing 4.6 MURJAN 27.2

3.2.2 Grid point analysis of GPP

The grid point analysis and forecast of tropical cyclone genesis potential parameter (GPP) for the cyclone MURJAN over the Arabian Sea is shown in Fig 3.2.1.

Fig. 3.2.1 Grid point analysis of GPP (x10-5) for Cyclone “MURJAN”

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Region with GPP value equal or greater than 30 is high potential zone for cyclogenesis. The analysis and forecast of the parameter clearly indicated the cyclogenesis zone and its intensification (3-4 days in advance) over the Arabian Sea at the early stages of development.

3.2.3 Track Observed and forecast tracks of cyclone „MURJAN‟ are shown in fig. 3.2.2.

Fig. 3.2.2(a) Observed track of cyclone MURJAN over the Arabian Sea (24 -26 Oct. 2012)

Fig. 3.2.2(b) Forecast tracks of cyclone „MURJAN‟ based on 00 UTC of 24th Oct 2012

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Fig. 3.2.2(b)(contd) Forecast tracks of cyclone „MURJAN‟ based on 00 UTC of 24th Oct 2012

Fig. 3.2.2.(c) Forecast tracks of cyclone „MURJAN‟ based on 00 UTC of 25th Oct 2012

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Fig. 3.2.2(c)(contd.) Forecast tracks of cyclone „MURJAN‟ based on 00 UTC of 25th Oct 2012

Table 3.2.2 Average Track forecast errors (Direct position error in Km) for TC MURJAN (24 October-25 November 2012):

Lead time → Models 12 hr 24 hr 36 hr 48 hr ECMWF 71 (2) 130 (2) 110 (1) 186 (1) GFS 125 (2) 203 (2) 78 (1) 283 (1) (NCEP) JMA-25 87 (2) 176 (2) 164 (1) 379 (1) QLM (IMD) 247 (1) 277 (1) - - MME (IMD) 97 (2) 114 (2) 64 (1) 194 (1) GFS (IMD) 87 (2) 192 (2) 56 (1) 229 (1) WRF(IMD) 99 (2) 96 (2) 40 (1) 300 (1) The figures in parantheses indicate number of forecasts verified

It is observed that 24hr forecast errors were less than 150 km (Table 3.2.2.) for all models except GFS (NCEP), JMA-25, QLM (IMD) and GFS (IMD). It was minimum for WRF (IMD) followed by MME (IMD) and ECMWF. Similarly 48 hr forecast was minimum for ECMWF followed by MME (IMD).

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3.2.3 Intensity

From table 3.2.3, it is observed that SCIP model has the error of 10 kts for 24 hr forecast period. Table 3.2.3 SCIP model performance based on 0000 UTC of 25.10.2012

Forecasts hours 00 hr 12 hr 24 hr → Observed (knots) 35 38 35 Forecasts (knots) 35 35 25 Error (knots) 0 -3 -10

3.2.4 Landfall

The landfall position and time forecast errors in case of cyclone „MURJAN‟ are shown in Table 3.2.4 and 3.2.5 respectively.

Table 3.2.4 Landfall forecast error (km) Model 12hr forecast 36hr forecast based on 00 UTC of based on 00 UTC of 25.10.2012 24.10.2012 ECMWF At landfall 78 NCEP-GFS 188 323 JMA-25 139 105 IMD-QLM 146 - IMD-MME 65 196 IMD-T574 105 279 IMD-ARW- 16 322 WRF-VAR

Table 3.2.5 Landfall time error (in Hour Min.). (E- Early; D- Delay)

Model 12hr forecast 36hr forecast based on 00 UTC of based on 00 UTC of 25.10.2012 24.10.2012 ECMWF 06:30 D 18:30 D NCEP-GFS 00:30 D 07:30 D JMA-25 11:30 D 09:30 D IMD-QLM 11:30 D - IMD-MME 03:30 D 07:30 D IMD-T574 00:30 E 07:30 D WRF-VAR 01:30 E 07:30 D

It is found that landfall point forecast error was minimum for ECMWF model for both 12 and 36 hrs in advance of landfall.

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3.2.5 Performance of IIT, Delhi WRF model

TC Murjan was tracked in real-time at IIT Delhi during its period from 23 – 26 October 2012 using ARW model at 27 km horizontal resolution. And the forecast was issued at 00 and 12 UTC of each day. The statistics of track and intensity forecast of TC Murjan is given below.

3.2.5.1 Track prediction

The ARW model produced better track forecast at all the initial times and showed consistent landfall of the system over the Somalia Coast. The track errors for this system is below 200 km for 72 hour forecast.(Fig. 3.2.4)

Mean track error (km) for TC MURJAN

200

161

153 146

150 136

130

129

127

119

114 114 112

103 100

50 40

Mean(km) trackerror 0 0 12 24 36 48 60 72 Forecast length (hour)

Fig. 3.2.4 Observed and forecast tracks and mean track forecast error for cyclone, „MURJAN‟

3.2.5.2 Intensity prediction:

The results of intensity forecast verification are shown in Figure 3.2.5. While the model initially under estimated the intensity, it became nearer to observed intensity based on 00 UTC of 25th. It could not predict the peak intensity i.e. the cyclone storm intensity but predicted the intensity at the time of landfall.

1010 Murjan MSLP Verification 25 Murjan Intensity - 10m wind (m/s) 1008 1006 20 1004 15 1002

1000 10 MSLP(hPa) 998 OBS-IMD IC-2300 IC-2312 5 OBS-IMD IC-2300 IC-2312 996 IC-2400 IC-2412 IC-2500 (m/s) max.wind 10-m IC-2400 IC-2412 IC-2500 994 0

2303 2312 2315 2403 2412 2418 2500 2506 2512 2518 2600 2603 2303 2312 2315 2403 2412 2418 2500 2506 2512 2518 2600 2603 TIME (DayHour) of Oct 2012 TIME (DayHour) of Oct 2012

Fig. 3.2.5 Intensity forecast error of IITD WRF (ARW) model for cyclone, „MURJAN‟

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3.3 Cyclonic storm “NILAM” (28 October-01 November, 2012)

3.3.1 Genesis

Analysis of GPP values computed (Kotal et al, 2009) for cyclone „NILAM‟ on the basis of real time model analysis fields along with the GPP values for Developing Systems and Non-Developing Systems are shown in Table 3.3.1. The higher GPP values (> 8.0, the threshold value) at early stages of development (T.No. 1.0, 2.0) have clearly indicated that the cyclone “NILAM” had enough potential to intensify into a developing system (>35 knots).

Table 3.3.1 GPP (x10-5) for Developing System, Non-Developing System and Cyclone “NILAM” 27.10.2012 28.10.2012 29.10.2012 Date/Time 0000 UTC 0000 UTC 0000 UTC T.No.  1.0 1.0 2.0 Developing 11.1 11.1 13.3 Non-Developing 3.4 3.4 4.6 NILAM 17.7 20.5 19.2

3.3.1.1 Grid point analysis of GPP

The grid point analysis and forecast of tropical cyclone genesis potential parameter (GPP) for the cyclone NILAM over the Bay of Bengal is shown in Fig 3.4.1. The analysis and forecast of the parameter clearly indicated the cyclogenesis zone (GPP≥30) and its intensification (3-4 days in advance) over the Bay of Bengal at the early stages of development.

Fig. 3.3.1 Grid point analysis of GPP (x10 -5) for Cyclone “NILAM” based on 00 UTC of 24th Oct. valid for 00, 24, 48 and 72hr forecast period

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Fig. 3.3.1 (contd) Grid point analysis of GPP (x10-5) for Cyclone „NILAM‟ based on 00 UTC of 24th Oct. valid for 96, 120, 144 and 168 hr forecast period

3.3.2 Track Observed and forecast tracks of cyclone „NILAM‟ are shown in Fig.3.3.2. and 3.3.3.

Fig. 3.3.2(a) Observed track of cyclone „NILAM‟ over the Bay of Bengal (28 October-01 November, 2012)

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Fig. 3.3.2(b) Forecast tracks of cyclone „NILAM‟ over the Bay of Bengal based on 00 UTC of 28th Oct 2012

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Fig. 3.3.2(c) Forecast tracks of cyclone „NILAM‟ over the Bay of Bengal based on 00 UTC of 29th Oct 2012

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Fig. 3.3.2(d) Forecast tracks of cyclone „NILAM‟ over the Bay of Bengal based on 00 UTC of 30th Oct 2012

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Fig. 3.3.2(e) Forecast tracks of cyclone „NILAM‟ over the Bay of Bengal based on 00 UTC of 31st Oct 2012

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HWRF Forecast for TC, NILAM are shown in Fig. 3.3.3.

th Fig. 3.3.3(a) HWRF forecast of track, Vmax and Pmin based on 1200 UTC of 29 Oct 2012

th Fig. 3.3.3(b) HWRF forecast of track, Vmax and Pmin based on 0000 UTC of 30 Oct 2012

th Fig. 3.3.3(c) HWRF forecast of track, Vmax and Pmin based on 1200 UTC of 30 Oct 2012

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Fig. 3.3.3(d) HWRF forecast of track, Vmax , Pmin and 24hr forecast of 10m max. st wind based on 0000 UTC of 3 1 Oct 2012

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The average track forecast errors of NWP models run in IMD in case of cyclone, NILAM are shown in Table 3.3.2. The average 24 hr forecast error was less than 150 km for most models except QLM (IMD), GFS (IMD) and WRF (IMD). It was minimum for HWRF followed by MME (IMD). The 48 hr forecast error was minimum for MME (IMD) and ECMWF and 72 hr forecast error was minimum for MME (IMD) followed by GFS (NCEP) and ECMWF model.

Table 3.3.2 Average Track forecast errors (Direct position error in km) (28 October-01 November 2012): NILAM Lead time → Models 12 hr 24 hr 36 hr 48 hr 60 hr 72 hr ECMWF 87 (4) 109 (4) 110 (3) 113 (3) 105 (2) 171 (2) GFS (NCEP) 127 (4) 110 (4) 74 (3) 135 (3) 146 (3) 137 (2) JMA-25 119 (4) 105 (4) 114 (3) 186 (3) 224 (3) 206 (2) QLM (IMD) 130 (3) 182 (3) 180 (2) 319 (2) 269 (2) - MME (IMD) 97 (4) 99 (4) 72 (3) 113 (3) 97 (3) 130 (2) GFS (IMD) 117 (4) 168 (4) 118 (3) 129 (3) 186 (3) 233 (2) WRF(IMD) 113 (4) 193 (4) 118 (3) 225 (3) 232 (3) 353 (2) HWRF 41 (4) 96 (4) 150 (3) 206 (1) - -

3.3.3 Intensity

The intensity forecast error for cyclone, NILAM by SCIP model and HWRF model are shown in table 3.3.3 and 3.3.4 respectively. The average absolute error was less than 10 kts for all forecast times by SCIP model. However, the error was significantly higher by HWRF model for 12 and 24 hr forecasts due to over estimation by the model.

Table 3.3.3 Average Absolute Error (SCIP) for TC Nilam Forecasts hours → 12 24 36 48 60 72 hr hr hr hr hr hr NILAM 00/28.10.12 Error -1 -2 +6 +9 +5 +6 00/29.10.12 Error(knots) +5 +8 -4 -7 -5 - 00/30.10.12 Error(knots) -5 -7 -5 - - - 00/31.10.12 Error(knots) +14 +11 - - - - (kts) Average Absolute Error(AAE) (kts) 6.3 7.0 5.0 8.0 5.0 6.0

Table 3.3.4. Average Absolute Error (HWRF) for TC Nilam

Forecasts hours → 12 hr 24 hr 36 hr 48 hr 60 hr NILAM 00/29.10.12 Error +17 +14 +5 -4 -1 00/30.10.12 Error(knots) +18 +20 +7 +9 - 12/30.10.12 Error(knots) +32 +16 +15 - - 00/31.10.12 Error(knots) (kts) +27 +8 - - - Average Absolute Error(AAE) (kts) 23.5 14.5 9.0 6.5 1.0

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3.3.4 Landfall forecast error

The landfall point and time forecast errors by various NWP models are shown in Table 3.3.5 and 3.3.6 respectively. The landfall point forecast errors were less than 100 km for all models except IMD (QLM) and ECMWF for 36 hrs before landfall and it was less than 200 km for all models except IMD (WRF) and HWRF models for 60 hrs before landfall. Table 3.3.5 Landfall point forecast error (km) Model 12 (11:00) based 36 (35:00) based 60 (59:00) based on 31.10.2012 on 30.10.2012 on 29.10.2012 F/C F/C F/C ECMWF 11 156 156 NCEP-GFS 95 16 183 JMA-25 At L/F Point At L/F Point 95 IMD-QLM 167 267 139 IMD-MME At L/F Point 16 95 IMD-T574 16 16 No L/F IMD-WRF 16 16 358 HWRF 55 49 236 (based on 29.10.12/1200UTC) F/C-Forecast; L/F-Landfall

Table 3.3.6 Landfall time forecast error (in Hour Min.)

Model 12 (11:00) based 36 (35:00) based 60 (59:00) based on 31.10.2012 on 30.10.2012 on 29.10.2012

F/C F/C F/C ECMWF at L/F Time 02:00D 08:00D NCEP-GFS 02:00E 01:00E 10:00E

JMA-25 06:00D 07:00D 08:00D IMD-QLM 01:00D 22:00D 11:00E

IMD-MME 03:00D 02:00D 03:30E IMD-T574 03:00D 00:30D No L/F

IMD- WRF 01:00D at L/F Time 03:00E

HWRF 01:00D 07:30E 11:00E(based on 29.10.12/1200UTC)

(E- Early; D- Delay; F/C-Forecast)

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3.3.5 ENSEMBLE (EPS) FORECAST FOR TC NILAM

The ensemble forecasts for TC NILAM are shown in Fig. 3.3.4.

UKMO EPS

Fig.3.3.4(a) EPS Forecasts for TC, NILAM based on 1200 UTC of 29th October 2012.

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NCMRWF(Ind

NCMRWF (India) GEFS guidance

UKMO EPS

Fig.3.3.4(b) EPS Forecasts for TC, NILAM based on 0000 UTC of 30th October 2012.

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Fig.3.3.4(c) EPS Forecasts for TC, NILAM based on 0000 UTC of 31st October 2012.

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3.3.6 Performance of IIT, Delhi WRF model

TC Nilam forecast was given at 00 and 12 UTC of each day TC period using same ARW model at 27 km resolution. The track and intensity forecast verification is done to see the performance of ARW model. Results are shown in Fig.3.3.5 and 3.3.6 respectively. The track and intensity forecast errors were quite reasonable by the IITD WRF (ARW) model.

Mean track error (km) for TC NILAM

200 186 153

154 136

150 134

126

120 116

115

105

95 94

100 93 72

51 50

Mean(km) trackerror 0 0 12 24 36 48 60 72 84 Forecast length (hour)

Fig.3.3.5 Track prediction of TC, NILAM by IITD WRF model

1010 NILAM intensity - MSLP (hPa) 40 35 NILAM intensity: 10-m wind (m/s) 1000 30 990 25 980 20 970 15 MSLP(hPa) OBS-IMD IC-2812 IC-2900 OBS-IMD IC-2812 IC-2900

10-m wind (m/s) wind 10-m 10 960 IC-2912 IC-3000 IC-3012 5 IC-2912 IC-3000 IC-3012 IC-3100 IC-3100 950 0

106 106 2812 2821 2906 2915 3000 3009 3018 3103 3112 3121 2812 2821 2906 2915 3000 3009 3018 3103 3112 3121 Time (DateHour) of Oct 2012 Time (DateHour) of Oct 2012

Fig.3.3.6 Intensity prediction of TC, NILAM by IITD WRF model

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3.4 Deep Depression (17-19 November, 2012)

3.4.1 Genesis

Analysis of GPP values computed (Kotal et al, 2009) for Depression on the basis of real time model analysis fields along with the GPP values for Developing Systems and Non-Developing Systems are shown in Table 3.5.1. Although the higher GPP values (> 8.0, the threshold value) at early stages of development at 0000 UTC of 17.11.2012 (T.No. 1.0) have indicated that the Depression had potential to intensify into a developing system (>35 knots) but on subsequent hours at 0000 UTC of 18.11.2012 and 19.11.2012 clearly indicated weakening of the system, as GPP was less than the threshold value 8.0. Table 3.4.1 GPP (x10-5) for Developing System, Non-Developing System and the Depression 17.11.2012 18.11.2012 19.11.2012 Date/Time 0000 UTC 0000 UTC 0000 UTC T.No.  1.0 2.0 1.5 Developing 11.1 13.3 11.1 Non-Developing 3.4 4.6 3.4 Depression 13.7 6.6 3.7

3.4.1.1 Grid point analysis of GPP

The grid point analysis and forecast of tropical cyclone GPP for the Deep Depression over the Bay of Bengal is shown in Fig 3.4.1. The analysis and forecast of the parameter clearly indicated the formation of cyclogenesis zone (GPP≥30) over the Bay of Bengal.

Fig. 3.4.1 Grid point analysis of GPP (x10-5) for Deep Depression (17-19 Nov. 2012)

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Fig. 3.4.1(contd.) Grid point analysis of GPP (x10-5) for Deep Depression (17-19 Nov. 2012)

3.4.2 Track

Observed and forecast tracks of the system based on NWP models are shown in Fig. 3.4.2 and 3.4.3 The track forecast errors of various models used in IMD are shown in Table 3.4.2

Fig.3.4.2(a) Observed track of deep depression (17-19 Nov. 2012)

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Fig.3.4.2(b) Forecast tracks of deep depression (17-19 Nov. 2012) based on 00UTC of 18th Nov 2012

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Fig.3.4.2(c) Forecast tracks of deep depression (17-19 Nov. 2012) based on 00UTC of 19th Nov 2012

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The 24 hr forecast errors have been less than 150 km for all the models. It was minimum for GFS (NCEP) and GFS (IMD) followed by MME (IMD).

Table 3.4.2 Average track forecast errors (Direct Position Error in km) for deep depression (17-19 Nov 2012):

Lead time → Models 12 hr 24 hr 36 hr ECMWF 69 (2) 133 (1) 131 (1) GFS(NCEP) 27 (2) 56 (1) 111 (1) JMA-25 46 (2) 116 (1) 140 (1) QLM (IMD) - - - MME (IMD) 20 (2) 70 (1) 86 (1) GFS (IMD) 1 (2) 56 (1) 56 (1) WRF(IMD) 32 (2) 139 (1) 216 (1) HWRF 63(2) 135(1) 177(1)

Fig 3.4.3 (a) HWRF forecast of track, Pmin and Vmax for the deep depression based on 0000 UTC of 18th Nov 2012

Fig 3.4.3 (b) HWRF forecast of track, Pmin and Vmax for the deep depression based on 0000 UTC of 19th Nov 2012

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3.4.3 Intensity

The average absolute error based on SCIP and HWRF model are shown in Table 3.4.3 and 3.4.4 respectively.

Table 3.4.3 Average absolute error (SCIP) for deep depression (17-19 Nov 2012) Forecasts hours → 12 hr 24 hr 36 hr Deep 00/18.11.12 Error 0 +1 +3 Depression 00/19.11.12 Error(knots) +5 - - (knots) Average Absolute Error(AAE) (knots) 2.5 1.0 3.0

Table 3.4.4 Average absolute error (HWRF) for deep depression (17-19 Nov 2012) Forecasts hours → 12 hr 24 hr 36 hr Deep 00/18.11.12 Error +5 +5 +13 Depression 00/19.11.12 Error(knots) +6 - - (knots) Average Absolute Error(AAE) (knots) 5.5 5.0 13.0

3.4.4 Ensemble Prediction System (EPS) guidance: The EPS guidance from different NWP models is shown in Fig.3.4.4.

Fig.3.4.4(a) EPS guidance based on 0000 UTC of 18th Nov. 2012

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Fig.3.4.4(b) EPS guidance based on 0000 UTC of 19th Nov. 2012

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3.5 Deep Depression over Arabian Sea (22-25 December 2012)

3.5.1 Genesis

Analysis of GPP values computed (Kotal et al, 2009) for Deep Depression on the basis of real time model analysis fields along with the GPP values for Developing Systems and Non-Developing Systems are shown in Table 3.5.1. Although the higher GPP values (> 8.0, the threshold value) at early stages of development (T.No. 1.0, 2.0) have indicated that the Deep Depression had potential to intensify into a developing system (>35 knots) but subsequently 12 hourly forecast GPP up to 24-h based on 0000 UTC of 24.11.2012 showed weakening of the system due to significant decrease of moisture in the middle troposphere as shown in the Table 3.5.2.

Table 3.5.1. GPP (x10-5) for Developing System, Non-Developing System and the Depression 22.12.2012 23.12.2012 24.12.2012 Date/Time 0000 UTC 0000 UTC 0000 UTC T.No.  1.0 2.0 2.0 Developing 11.1 13.3 13.3 Non-Developing 3.4 4.6 4.6 Depression 16.6 14.1 10.4

Table 3.5.2 GPP (x10-5) genesis potential parameter (GPP) based on 0000 UTC of 20121224 ------Hr V M I S GPP ------0 7.82 1.42 22.13 23.68 10.4 12 5.79 1.27 22.77 24.09 6.9 24 4.18 0.82 21.42 16.94 4.3 ------

3.5.1.1 Grid point analysis of GPP

The grid point analysis and forecast of tropical cyclone genesis potential parameter (GPP) for the Deep Depression over the Bay of Bengal is shown in Fig 3.5.1. The analysis and forecast of the parameter clearly indicated the formation of cyclogenesis zone (GPP≥30) over the Arabian Sea.

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Fig. 3.5.1 Grid point analysis of GPP (x10-5) for Deep Depression over Arabian Sea (22-25 Dec. 2012)

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3.5.2 Track

Observed and forecast tracks of deep depression over the Arabian Sea during 22-25 Dec 2012 are shown in Fig.3.5.2. and Fig.3.5.3. The track forecast errors are shown in Table 3.5.3. It is found that 24hr forecast error is minimum for MME (IMD) followed by ECMWF and WRF (IMD) model.

Table 3.5.3 Average track forecast errors (Direct position error in km) (22 24 Dec 2012) Lead time → Models 12 hr 24 hr 36 hr 48 hr 60 hr ECMWF 154(3) 239(2) 201(2) 116(1) 175(1) GFS (NCEP) 137(3) 161(2) 106(2) 124(1) 222(1) JMA-25 366(3) 420(2) 505(2) 494(1) 570(1) QLM (IMD) 305(1) 416(1) 531(1) - - MME (IMD) 128(3) 173(2) 161(2) 94(1) 144(1) GFS (IMD) 83(3) 149(2) 149(2) 123(1) 229(1) WRF(IMD) 96(2) 89(2) 122(2) 119(1) 126(1) HWRF 60(1) 154(1) 123(1) - -

Fig.3.5.2(a) Observed track of Deep Depression over the Bay of Bengal (22-24 Dec. 2012)

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Fig. 3.5.2(b) Forecast tracks of deep depression over Arabian Sea based on 0000 UTC of 22 Dec 2012

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Fig. 3.5.2(c) Forecast tracks of deep depression over Arabian Sea based on 0000 UTC of 23 Dec 2012

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Fig. 3.5.2(d) Forecast tracks of deep depression over Arabian Sea based on 0000 UTC of 24 Dec 2012

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Fig.3.5.3 HWRF model forecasts of the deep depression over Arabian Sea based on 0000 UTC of 23rd Dec 2012

3.5.3 Intensity

The intensity forecast errors by SCIP and HWRF model are shown in Table 3.5.4 and 3.5.5 respectively.

Table 3.5.4 Average Absolute Error (SCIP) for Deep Depression (22-24 Dec 2012) Forecasts hours → 12 hr 24 hr 36 hr DEEP 00/23.12.12 Error +7 +14 +3 DEPRESSION (knots) 00/24.12.12 Error +3 - - (knots) Average Absolute Error(AAE) (knots) → +5 +14 +3

Table 3.5.5 HWRF Model performance based on 0000 UTC of 23.12.2012

Forecasts hours 12 hr 24 hr 36 hr → Observed (knots) 30 30 25 Forecasts (knots) 47 45 44 Error (knots) 17 15 19

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3.6 Rapid Intensification (RI) Index

A rapid intensification index (RII) is developed for tropical cyclones over the Bay of Bengal (Kotal and Roy Bhowmik, 2013). The RII uses large-scale characteristics of tropical cyclones to estimate the probability of rapid intensification (RI) over the subsequent 24-h. The RI is defined as an increase of intensity by 30 kt (15.4 ms-1) during 24-h. The RII technique is developed by combining threshold (index) values of the eight variables. The probability of RI is found to increase from 0% to 100% when the total number of satisfied indices increases from zero to eight.

Case studies were undertaken to test the ability of the model for the cyclonic storms formed during the cyclone season 2011-2012 as an experimental mode. Although forecasts were not available to operational forecaster in real time, the results of 2012 are presented in this section. The RII computed based on this study clearly indicated (Table 3.6.1) the less probability of RI. The product is expected to be made available in real time during cyclone period of 2013.

Table. 3.7 Probability forecasts of rapid intensification (RI) for cyclonic storms in 2012 No. of Cyclonic Forecast RI- Indices Probability(%) Storms Based on satisfied of RI MURJAN 24.10.12/00UTC 5 21.95 25.10.12/00 MURJAN UTC 2 2.56 28.10.12/00 NILAM UTC 3 5.22 29.10.12/00 NILAM UTC 2 2.56 30.10.12/00 NILAM UTC 3 5.22 31.10.12/00 NILAM UTC 4 9.37 18.11.12/00 DD UTC 3 5.22 19.11.12/00 DD UTC 3 5.22 22.12.12/00 DD UTC 4 9.37 23.12.12/00 DD UTC 4 9.37 24.12.12/00 DD UTC 1 0

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3.7 Annual average track forecast errors during 2012

3.7.1 Track

The annual average track forecast errors of various models for the year 2012 are shown in Table 3.7.1. The 24 hr track forecast errors has been less than 150 km for all the models except QLM (IMD), GFS (IMD), JMA (25). For 48 hr forecasts, it has been less than 150 km for all the models except GFS (NCEP), JMA (25), QLM (IMD), WRF (IMD) and HWRF. It is minimum for MME (IMD) followed by ECMWF. Table 3.7.1 Annual average track forecast errors during 2012.

Models Lead time → 12 hr 24 hr 36 hr 48 hr 60 hr 72 hr ECMWF 99 145 138 128 129 172 GFS (NCEP) 111 136 89 163 165 137 JMA-25 167 192 237 286 310 206 QLM (IMD) 189 248 297 319 269 - MME (IMD) 91 115 98 126 109 130 GFS (IMD) 81 157 109 148 195 233 WRF(IMD) 90 142 122 219 205 354 HWRF 50 112 150 207 - -

3.7.2 Intensity

The annual average intensity forecast errors are shown in Table 3.7.2 for SCIP and HWRF models. While it is less than 10 kts for all forecast times by SCIP model, the error for 12-36 hr forecasts is more than 10 kts by HWRF model.

Table 3.7.2 Annual average intensity forecast errors (kts) during 2012

Lead time → 12 hr 24 hr 36 hr 48 hr 60 hr 72 hr AAE OF SCIP 4.8 7.6 4.2 8.0 5.0 6.0 AAE OF HWRF 17.4 13.0 11.8 6.5 1.0 -

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CHAPTER-IV

PERFORMANCE OF OPERATIONAL FORECAST OF CYCLONES BY RSMC, NEW DELHI DURING 2012

4.1 Introduction

The Cyclone Warning Division/ Regional Specialised Meteorological Centre (RSMC)-Tropical Cyclone, IMD, New Delhi mobilised all its resources for monitoring and prediction of cyclonic disturbances over the north Indian Ocean during 2012. It issued 3 hourly warning/advisory bulletins to national disaster management agencies. It issued forecast and warning bulletins to various national and international disaster management agencies including National Disaster Management (NDM), Ministry of Home Affairs (MHA), concerned state Govts. and other users in regular intervals. It also issued advisories to World Meteorological Organisation (WMO)/Economic and Social Cooperation for Asia and the Pacific (ESCAP) Panel member countries including Bangladesh, Myanmar, Thailand, Pakistan, Oman, Srilanka and Maldives during cyclone period. As tropical cyclone advisory centre (TCAC), it also issued tropical cyclone advisories with effect from the stage of cyclone for international civil aviation purpose as per the requirement of international civil aviation organization (ICAO).

IMD continuously monitored, predicted and issued bulletins containing track & intensity forecast at +06, +12, +18, +24, +36, +48, +60 and +72 hrs or till the system weakened into a low pressure area. The above structured track and intensity forecasts were issued from the stage of deep depression onwards. The cone of uncertainty in the track forecast was also given for all cyclones. The radius of maximum wind and radius of ≥34 knots, ≥50 knots and ≥64 knots wind in four quadrants of cyclone was also issued for every six hours. The graphical display of the observed and forecast track with cone of uncertainty and the wind forecast for different quadrants were uploaded in the IMD's website regularly. The storm surge guidance was provided as and when required to the member countries of WMO/ESCAP Panel as per the recommendation of last meeting of Panel on Tropical Cyclone (PTC) held during March, 2009 at Muscat, Oman based on IITD model. The prognostics and diagnostics of the systems were described in the special tropical weather outlook and tropical cyclone advisory bulletins since 2008. The TCAC bulletin was also sent to Aviation Disaster Risk reduction (ADRR) centre of WMO at Honkong like previous year. Tropical cyclone vitals were prepared every six hourly from deep depression stage onwards and sent to various NWP modeling groups in India for bogusing purpose.

The statistics of bulletins issued by IMD, New Delhi with respect to cyclonic disturbances is presented in Sec.4.2. The performance of RSMC-New Delhi in track

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and intensity prediction of the cyclones during 2012 are analysed and discussed in Sec.4.3.

4.2 Bulletins issued by IMD

The following are the statistics of bulletins issued by IMD in association with the cyclonic disturbances during 2011

Bulletins issued during 'MURJAN' Bulletins for national disaster management agencies : 07 Bulletin for WMO/ESCAP Panel counties: 17 (Special Tropical Weather Outlook and Tropical Cyclone Advisory) : Tropical cyclone advisory for international civil aviation: 06

Bulletins issued during 'NILAM' Bulletins for national disaster management agencies : 27 Bulletin for WMO/ESCAP Panel counties (Special Tropical Weather Outlook and Tropical Cyclone Advisory) : 20 Tropical cyclone advisory for international civil aviation: 08

Bulletins issued for all cyclones during 2012 Bulletins for Indian coast 34 RSMC bulletin for WMO/ESCAP Panel member countries 37 (Special Tropical Weather Outlook and Tropical Cyclone Advisory) TCAC bulletin for international civil aviation 14

Bulletins issued for all cyclonic disturbances (depression and above) during 2012 Bulletins for Indian coast 59 RSMC bulletin for WMO/ESCAP Panel member countries : 58 (Special Tropical Weather Outlook and Tropical Cyclone Advisory) TCAC bulletin for international civil aviation 14

4.3 Performance of Operational Track, Intensity and landfall forecast

The performance of operational genesis, track and intensity forecasts issued by IMD, New Delhi for two cyclones and three deep depressions during 2012 are described below. 4.3.1 Deep Depression over Bay of Bengal (10-11 October 2012)

The landfall, track, intensity and associated weather forecasts issued in connection with the deep depression over Bay of Bengal (10-11 October 2012) have been verified and the results are shown in the Table 4.1

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Table 4.1 Forecast verification in connection with deep depression over Bay of Bengal (10-11 October 2012) Parameter Base Date/Time Forecast Actual (UTC) Track, 10.10.2012/ Depression likely to Depression moved intensity & 1500 intensify further, move northward, intensified landfall northward and cross into a deep depression Bangladesh coast near and crossed Hatia in the morning of Bangladesh coast near 11th October. Hatia between 0000- 0100 UTC (0530-0630 hrs IST) of 11th October. Rainfall 10.10.2012/1500 Fairly widespread and Fairly widespread isolated heavy rainfall rainfall with isolated during next 48 hrs over heavy falls (Sec.5) Assam, Meghalaya, Nagaland, Manipur, Mizoram and Tripura Surface 10.10.2012/1500 25 knots gusting to 35 Chittagong- 32 kts in Wind knots. gustiness at 2330 UTC, Hatia-22kts at 2045 UTC and Sandip-25 kts at 2250 UTC of 10th October.

4.3.2 Cyclone ‘MURJAN’ over the Arabian Sea (23-26 October, 2012)

The landfall and track forecast errors for various lead time periods are shown in Table 4.2 and 4.3 respectively. Landfall point error was 23,12 & 14 km with time error of about 1.5, 5.5 & 1 hour respectively in the forecast issued 36, 24 & 12 hrs in advance of the landfall. Average 12, 24 and 36 hr track forecast error were 76, 92 & 112 km respectively. The average intensity forecast error is shown in Table 4.4. Both the average absolute error and root mean squire (RMS) error have been less than 10 kts for different forecast times.

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Table 4.2 Landfall point and time error of Cyclone ‘MURJAN’ over the Arabian Sea (23-26 October, 2012) Lead time hours (Landfall point error in km.) Landfall time error (in hrs.) Hours F/C Actual Error F/C(UTC) Actual(UTC) Error (km) 12 9.640N /50.840E 9.520N 14 251830 251730 1 hour /50.790E early 24 9.410N /50.760E 9.520N 12 252300 251730 5.5 hours /50.790E early 36 9.720E /50.86 9.520E 251900 251730 1.5 hr /50.790E 23 early Table 4.3 Average track forecast errors (Direct position error in Km) Lead time (hours) Direct position error (Km) Number of forecasts verified 12 76 5 24 92 3 36 112 1

Table 4.4 Average Intensity forecast error of cyclone, MURJAN.

Lead Period of Intensity Error No. of Forecasts forecast (knots) verified Average RMS absolute 12 5.9 6.9 6 24 6.0 6.3 4 36 4.7 5.4 2

4.3.3 Cyclone ‘NILAM’ over the Bay of Bengal (28 October-1 November, 2012)

The landfall forecast error, the average track and intensity forecast errors for various lead time periods are shown in Table 4.5, 4.6 and 4.7 respectively. Rainfall forecast verification is given in the Table 4.8. The gale wind forecast and storm surge forecast errors are shown in Table.4.9 and 4.10 respectively.

Landfall point errors are 45 & 11 km with time error of 1 & 2 hours for the lead period 48 and 24 hrs respectively which is significantly less than the long period average. Average track forecast error is 114, 186 and 240 km for the lead period 24, 48 and 72 hrs respectively. This error is significantly less than the average forecast errors in last five years. The average absolute and RMS error is less than 10 kts for almost different lead periods. The realized wind speed at the time of landfall was about 70-80 kmph as recorded by meteorological observatories against the forecast of 80-90 kmph gusting to 100 kmph. 198

Table 4.5 Landfall point and time error of Cyclone ‘NILAM’ over the Bay of Bengal (28 October-1 November, 2012) Landfall Forecast Error of Cyclonic Storm, Nilam Lead Period (hrs) of forecast Landfall Point Landfall Time Forecast from the time of landfall Forecast Error (km) Error (hr) 12 16 1.5 24 11 2.0 36 74 3.0 48 45 1.0 60 11 3.0 72 It was predicted that the system would move towards north Srilanka and Tamil Nadu Coast. Table 4.6 Average track forecast errors (Direct position error in Km)

Lead time (hours) Direct position error (Km) Number of forecasts verified 12 70 11 24 114 10 36 174 9 48 186 7 60 197 5 72 240 3

Table 4.7 Average Intensity forecast error Lead Period of Intensity Error No. of Forecasts forecast (knots) verified Average RMS 12 5.7 6.9 11 24 7.8 9.2 10 36 6.8 8.4 9 48 8.6 11.7 7 60 7.9 8.5 5 72 6.7 7.8 3

Table 4.8 Rainfall Forecast Verification

Heavy rainfall warning issued for Tamil Nadu, Andhra Pradesh and Puducherry Tamil Nadu Synoptic System Forecast issued Forecast Realised and Puducherry 28 October Depression over Widespread with Widespread with 1500 hrs IST southeast Bay of isolated heavy to scattered heavy to Bengal. very heavy rainfall to very heavy rainfall It is likely to intensify commence from 29th over north coastal further and move over north coastal Tamil Nadu and 199

towards Tamil Nadu Tamil Nadu and Puducherry, isolated coast during next 72 hrs Puducherry heavy to very heavy 29 October Deep Depression over Widespread with rainfall over south 0830 hrs IST southwest Bay of isolated heavy to coastal Andhra Bengal. very heavy rainfall to Pradesh, It is likely to intensify commence from 29th Rayalaseema and into a cyclonic storm over north coastal north Tamil Nadu and cross north Tamil Tamil Nadu and Nadu and south Andhra Puducherry Pradesh coast between Nagapattinam and Nellore by 31st Oct evening/night 30 October Cyclonic storm over Widespread with 0830 hrs IST southwest Bay of isolated heavy to Bengal. very heavy rainfall It is likely to intensify during next 12 hrs. further and cross north Intensity will increase Tamil Nadu and south with scattered heavy Andhra Pradesh coast to very heavy and between Nagapattinam isolated extremely and Nellore by 31st Oct heavy falls these evening after. Isolated heavy rainfall would occur over south coastal Andhra Pradesh and Rayalaseema during next 48 hrs 31 October Cyclonic storm over Widespread with 0830 hrs IST southwest Bay of scattered heavy to Bengal. It is likely to very heavy rainfall cross coast between and isolated Cuddalore and Nellore, extremely heavy near Chennai by 31st rainfall during next 24 evening hrs. Rainfall at most places with isolated heavy to very heavy rainfall over south coastal Andhra Pradesh, Rayalaseema and north interior Tamil Nadu

Rainfall status over Coastal Andhra Pradesh for the period 1st November to 5th

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November,2012

Coastal Synoptic System Forecast issued Forecast Realised Andhra Pradesh 31st October The cyclonic storm Widespread with Widespread with “Nilam” crossed Tamil isolated heavy to scattered heavy to Nadu coast near very heavy rainfall very heavy rainfall Mahabalipuram (south over south coastal of Chennai) in the Andhra Pradesh evening of 31st October,2012 1st November The cyclonic storm Fairly widespread Widespread with “Nilam” weakened in to with isolated heavy scattered heavy to a deep depression and rainfall over coastal very heavy rainfall lay centred near Andhra Pradesh and Chitradurga (lat 14.0 Telangana deg north, long.76.5 deg east). The system would move northwest wards and weakens further into a low pressure area. 2nd The depression Fairly widespread Widespread with November weakened in to a well with isolated heavy scattered heavy to marked low pressure rainfall over coastal very heavy rainfall area and now lies over Andhra Pradesh and north interior Karnataka Telangana and adjoining Rayalaseema . 3rd November A low pressure area lies Fairly widespread Widespread with over Telangana and with isolated heavy isolated heavy to very neighbourhood. rainfall over coastal heavy rainfall Andhra Pradesh and Telangana 4th November The low pressure area Widespread over Scattered with lies over north coastal coastal Andhra isolated Heavy to Andhra Pradesh and Pradesh fairly very heavy rainfall neighbourhood . widespread over Telangana with isolated heavy to very heavy rainfall over the same region

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Table 4.9 Gale wind Forecast Verification Date and time Gale wind Realised Gale wind speed (kmph) Error (kmph) (UTC) F/C(kmph) 12 85 1. Chennai (Nungambakam) 74 11 24 85 2. Kalpakam 50-55 11 36 85 3.Puducherry 62 11 48 70 4. Mylam AWS 38 04 60 75 01 Table 4.10 Storm Surge Forecast Verification Lead period Storm Surge Forecast (meter) Realised Storm in hrs Surge (meter) 12 Storm surge of 1-1.5 meter over Chennai, 1.3 Kanchipuram, Tiruvallur and Nellore district 24 Storm surge of 1 meter over Chennai, Kanchipuram, 1.3 Tiruvallur and Nellore district

4.3.4 Deep Depression over the Bay of Bengal (17-19 November, 2012)

The average track forecast and intensity forecast errors for various lead time periods are shown in Table 4.11 and 4.12 respectively. The track forecast error of 12, 24, 36 and 48 hours are 55, 66, 80 & 55 kms respectively which is significantly less than the average forecast errors in last five years. The average absolute error was about 15 kts & 10 kts for 24 & 48 hours forecast respectively.

Table 4.11 Average track forecast errors (Direct position error in km) for deep depression over Bay of Bengal (17-19 Nov. 2012)

Lead time (hours) Direct position error (km) Number of forecasts verified 12 55 6 24 66 5 36 80 3 48 55 1

Table 4.12 Average Intensity forecast error for deep depression over Bay of Bengal (17-19 Nov. 2012)

Lead Period of Intensity Error No. of forecasts forecast (knots) verified Average RMS 12 16.4 18.4 6 24 14.9 16.3 5 36 9.1 9.4 3 48 9.7 9.7 1

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4.3.5 Deep Depression over the Bay of Bengal (22-25 Dec, 2012)

The average track forecast and intensity forecast errors for various lead time periods are shown in Table 4.13 and 4.14 respectively. Average track forecast error is 121 and 201 for the lead period 12 and 24 hours. Average absolute intensity error and RMS are around 13 & 23 km respectively.

4.13 Average track forecast errors (Direct position error in Km)

Lead time Direct position error Number of forecasts (hours) (Km) verified 12 55 5 24 121 4 36 167 6 48 201 2 4.14 Average Intensity forecast error

Lead Period of forecast Intensity Error (knots) No. of Average RMS forecasts verified 12 10.0 10.4 5 24 13.0 13.2 4 36 17.2 17.3 6 48 23.0 23.1 2

4.4 Annual Performance cyclone landfall, Track and intensity forecast

4.4.1 Landfall

Based on two cyclones formed during 2012, the average landfall forecast point errors are about 12 km & 45 km for 24 & 48 hr forecasts and time error is around 4 and 1 hour respectively. The landfall forecast errors for the systems during 2012 are shown in Table 4.15. and 4.16. The 72 hr forecasts for these two cyclones could not be issued quantitatively due to shorter life period of the systems.

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Table 4.15 Annual average landfall point forecast error (km) of cyclones by IMD Name of the System Lead Period (hrs) 12 24 36 48 60 72 Nilam 16 11 74 45 11 It was predicted that the system will move towards north Sri Lanka and Tamil Nadu coast Murjan 14 13 23 - - - Average 2012 (km) 15 12 49 45 11 - Average(2003-11) (km) 73 132 142 145 128 180

Table 4.16 Annual average landfall time forecast error (hrs) of cyclones by IMD

Name of the System Lead Period (hrs) 12 24 36 48 60 72 Nilam 1.5 2.0 3.0 1.0 3.0 1.5 Murjan 1.0 5.5 1.5 - - 1.0 Average 2012 (hrs) 1.3 3.8 2.2 1.0 3.0 1.3 Average(2003-11) (hrs) 4.0 8.6 8.5 7.3 2.2 1.2

4.4.2 Track forecast and skill

Annual average cyclone track forecast error of the year 2012 are 109,186 & 240 Km for the lead period 24, 48 & 72 hrs respectively.. Annual average track forecast error and track forecast skill are given in the Table 4.17 and 4.18 respectively.

Table 4.17 Annual average tropical cyclone track forecast errors (km) of IMD during 2012 Tropical cyclone Lead period in hours 12 24 36 48 60 72 Murjan 76(5) 92(3) 112(1) - - - Nilam 70(11) 114(10) 174(9) 186(7) 197(5) 240(3) Average 2012 72(16) 109(13) 168(10) 186(7) 197(5) 240(3) Average 2003-2011 86 148 193 262 320 386

(Figures in parenthesis indicates the number of six hourly forecasts verified)

The skill score has been calculated by comparing the IMD’s forecast track errors with the forecast difficulty level. For this purpose, the IMD’s forecast error has been compared with the CLIPER (climatology + persistence) model error, which is the international practice. The gain in skill in relation to CLIPER, is quantified in percentage terms by;

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Gain in skill= (CLIPER DPE - DPE) Х 100% CLIPER DPE DPE: Direct Position Error = Distance between forecast and actual point of the track.

Table 4.18 Annual tropical cyclone track forecast skill (%)-2012 Tropical cyclone Lead period in hours 12 24 36 48 60 72 Murjan 5.8 (5) 35.3 (3) 99.4 (1) - - - Nilam 46.6 (11) 59.9 (10) 59.8 (9) 62.5 (7) 59 (5) 52.5 (3) Average(2012) 37.6 (16) 56.7 (13) 92.1 (10) 62.5 (7) 59 (5) 52.5 (3) Average (2003-2011) 9.5 22.7 30.4 39.1 46.5 49.9

4.4.3 Intensity forecast and skill

Annual average cyclone absolute intensity forecast errors are 7.3, 8.6 & 6.7 and root mean square errors are 8.5, 11.7 & 7.8 kts for the lead period 24, 48 and 72 hrs respectively (Table 4.19).

The skill score has been calculated by comparing the IMD’s absolute intensity forecast errors with the forecast difficulty level. For this purpose, the IMD’s absolute intensity forecast error has been compared with the absolute persistence forecast error, which is the international practice. The gain in skill in relation to persistence is quantified in percentage terms by; Gain in skill= (AEpersistence - AEoperational) Х 100% ______AEpersistence The results are shown in Table 4.20.

Table 4.19 Average Intensity forecast error (kts) during 2012 Tropical Intensity Error cyclone Absolute Error Root Mean Squire(RMS) Error Lead period in hours Lead period in hours 12 24 36 48 60 72 12 24 36 48 60 72 Murjan 5.9 6 4.7 - - - 7.2 6.3 5.4 - - - (6) (4) (2) Nilam 5.7(11) 7.8 6.8 8.6 7.9 6.7 6.9 9.2 8.4 11.7 8.5 7.8 (10) (9) (7) (5) (3) Average 6.1 7.3 6. 8.6 7.9 6.7 7 8.5 7.9 11.7 8.5 7.8 (2012) (17) (14) (11) (7) (5) (3) Average 7.6 12.2 13.4 14.0 14.0 20.2 10.2 15.2 17.1 18.5 16.1 25.7 (2003- 2011) (Figures in parenthesis indicates the number of forecast verified)

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Table 4.20 Annual tropical cyclone intensity forecast skill (%) during 2012 with respect to AE Tropical cyclone Lead period in hours 12 24 36 48 60 72 Murjan 19.7 64.6 87.6 - - - Nilam 13.7 50.2 67.8 54.3 62.4 83.8 Average 16.0 54.6 73.5 54.3 62.4 83.8

4.4.4 Trend in forecast performance

The trends in forecast performance during 2003-12 are analysed and presented in following sections

4.4.4.1 Landfall

The landfall forecast errors (landfall point and time errors) are presented in Fig. 4.1. The landfall point forecast error has reduced significantly in recent years. The 12 and 24 hr landfall point forecast errors have decreased at the rate of about 16 and 34 km per year respectively during 2003-2012. However, the rate of decrease is relatively less in case of landfall time forecast error.

(a) Landfall point forecast error (km)

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(b) Landfall time forecast error (hr)

Fig.4.1 Landfall point and time forecast errors of IMD during 2003-12

4.4.4.2 Track

(a)Track forecast error (km)

(b)Track forecast skill (%)

Fig.4.2. (a) Average tropical cyclone track forecast error and (b) track forecast skill during 2003-2012.

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The annual average tropical cyclone track forecast errors and skills during 2003-2012 are presented in Fig.4.2. The track forecast error has decreased at the rate of about 5.1 km/year and 7.2 km/year during 2003-12 for 12 and 24 hr forecasts respectively. The 36-72 hrs forecast errors also have decreased as shown in Fig.4.2. The skill in tropical cyclone track forecast has increased at the rate of 8.2% and 4.1% for 12 and 24 hr forecasts respectively during 2003-2012. There is also significant increase in skill of 36-72 hr track forecasts as shown in the Fig.4.2.

4.4.4.3 Intensity

Fig.4.3. (a) Absolute error and (b) root mean square (RMS) error in tropical cyclone maximum sustained surface wind forecasts by IMD

The average absolute error and (b) root mean square (RMS) error in tropical cyclone maximum sustained surface wind forecasts by IMD during 2005-12 are is shown in Fig.4.3. Comparing Fig.4.2 and 4.3 the rate of decrease in intensity error has been less than that of track error. The annual intensity (wind) forecast error has decreased at the rate of 0.3 knots and 1.2 knots in case of absolute error and 0.5 knots and 1.2 knots in case of RMS error for 12 and 24 hr forecasts respectively. The skill of intensity forecast based on absolute error compared to persistence forecast error during 2005-12 is shown in Fig.4.4. It is found that the skill has increased at the rate of 3.3% per year and 8.3% per year for 12 and 24 hr forecasts respectively during 2005-12.

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Fig.4.4 Skill of intensity forecast based on absolute error compared to persistence forecast error during 2005-12

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DAMAGE DUE TO DEEP DEPRESSION (10-11 OCT. 2012)

DAMAGE DUE TO CYCLONIC STORM NILAM (28 OCT.-01 NOV. 2012)