2476 JOURNAL OF APPLIED METEOROLOGY AND CLIMATOLOGY VOLUME 52 Real-Time Track Prediction of Tropical Cyclones over the North Indian Ocean Using the ARW Model KRISHNA K. OSURI AND U. C. MOHANTY School of Earth, Ocean and Climate Sciences, Indian Institute of Technology Bhubaneswar, Odisha, India A. ROUTRAY National Centre for Medium Range Weather Forecasting, Noida, India M. MOHAPATRA India Meteorological Department, New Delhi, India DEV NIYOGI Purdue University, West Lafayette, Indiana (Manuscript received 18 November 2012, in final form 9 July 2013) ABSTRACT The performance of the Advanced Research version of the Weather Research and Forecasting (ARW) model in real-time prediction of tropical cyclones (TCs) over the north Indian Ocean (NIO) at 27-km res- olution is evaluated on the basis of 100 forecasts for 17 TCs during 2007–11. The analyses are carried out with respect to 1) basins of formation, 2) straight-moving and recurving TCs, 3) TC intensity at model initialization, and 4) season of occurrence. The impact of high resolution (18 and 9 km) on TC prediction is also studied. Model results at 27-km resolution indicate that the mean track forecast errors (skill with reference to per- sistence track) over the NIO were found to vary from 113 to 375 km (7%–51%) for a 12–72-h forecast. The model showed a right/eastward and slow bias in TC movement. The model is more skillful in track prediction when initialized at the intensity stage of severe cyclone or greater than at the intensity stage of cyclone or lower. The model is more efficient in predicting landfall location than landfall time. The higher-resolution (18 and 9 km) predictions yield an improvement in mean track error for the NIO Basin by about 4%–10% and 8%–24%, respectively. The 9-km predictions were found to be more accurate for recurving TC track pre- dictions by ;13%–28% and 5%–15% when compared with the 27- and 18-km runs, respectively. The 9-km runs improve the intensity prediction by 15%–40% over the 18-km predictions. This study highlights the capabilities of the operational ARW model over the Indian monsoon region and the continued need for operational forecasts from high-resolution models. 1. Introduction the premonsoon season (April–early June). Because of growing population and development, damage from The north Indian Ocean (NIO), including the Bay of landfalling TCs over the NIO has shown a steady in- Bengal (BoB) and the Arabian Sea (AS), experiences crease. For disaster warnings and mitigation efforts, two tropical-cyclone (TC) seasons, with a primary maxi- forecasting TC tracks is a critical component; track mum in TC frequency during the postmonsoon season forecast errors over the NIO are high relative to those (October–December) and a secondary maximum during over the Atlantic and Pacific Oceans (Mohapatra et al. 2013b). It is evident that synoptic and statistical methods have limitations in predicting track and intensity beyond Corresponding author address: Prof. U. C. Mohanty, School of Earth, Ocean and Climate Sciences, Indian Institute of Technology 24 h over the NIO (Mohanty and Gupta 1997; Gupta Bhubaneswar, Satya Nagar, Bhubaneswar–751 007, India. 2006). With advancements in resolution, physics, and E-mail: [email protected] initializations, global and mesoscale models have the DOI: 10.1175/JAMC-D-12-0313.1 Ó 2013 American Meteorological Society Unauthenticated | Downloaded 09/30/21 10:54 PM UTC NOVEMBER 2013 O S U R I E T A L . 2477 potential to provide forecast guidance for TC genesis, baseline for mesoscale modeling capability over this re- intensity, and movement for a period of 72 h for disaster gion. A semioperational effort of this kind may provide mitigation and warning systems. a basis for improving track and intensity prediction skills The Advanced Research version of the Weather Re- in this region. This semioperational effort with ARW search and Forecasting system (ARW), developed at the shall become the benchmark for evaluating any future National Center for Atmospheric Research (NCAR), is developments over the NIO region for TC predictions. one of the two distinct dynamical cores of the Weather Research and Forecasting (WRF) model. The other 2. Modeling system and configuration core version, the Nonhydrostatic Mesoscale Model (NMM), was developed at the Environmental Modeling The model configuration including domain and physi- Center of the National Centers for Environmental cal parameterization schemes follows the sensitivity study Prediction (NCEP). Over the Indian monsoon region, of Osuri et al. (2012a). The initial and lateral boundary and indeed globally, the ARW model is being widely conditions for the ARW model are obtained from the used for the simulation of a variety of weather events, analysis and forecast fields of the NCEP GFS. The lateral such as heavy rainfall (Niyogi et al. 2006; Routray et al. boundary conditions are updated in 6-h intervals with 2010; Dodla and Ratna 2010; Hong and Lee 2009) and a fixed sea surface temperature throughout the model TCs (Osuri et al. 2012a; Pattanaik and Rama Rao 2009; integration, with no regional data assimilation used in this Davis et al. 2008). The ARW model has been used for study. The land surface boundary conditions are taken real-time TC forecasting since 2007. The application of from the U.S. Geological Survey with a horizontal grid such mesoscale models for TC forecasting over the NIO spacing of 10 min. A single experimental domain is fixed is a recent development. Osuri et al. (2012a) demon- between 778 and 1028Eandbetween38 and 288Noverthe strated the promising ability of the ARW model for real- BoB, and between 488 and 788E and between 58 and 308N time prediction of TC track and intensity over the NIO over the AS, with 51 vertical layers and 27-km horizontal during the 2008 season. This study also demonstrated grid resolution with an Arakawa C grid. This study used that the performance of the ARW model was reasonably a time step of 90 s with the Kain–Fritsch cumulus pa- good in comparison with other global models. The current rameterization scheme, the slab model for the land sur- TC operational model in use at the India Meteorological face representation, the WRF single-moment 3-class Department (IMD), New Delhi, is the Quasi-Lagrangian microphysics scheme, and the Yonsei University plane- Model (QLM), apart from global and regional models tary boundary layer scheme. Details of the model equa- like the Global Forecast System (GFS) and the ARW. tions, physics, and dynamics are available in Skamarock The QLM has shown little skill over the NIO Basin be- et al. (2005; see also online at http://wrf-model.org). cause it runs at 40-km horizontal resolution with 16 ver- tical levels (see online at http://www.imd.gov.in/section/ 3. Method nhac/dynamic/RSMC-2011.pdf; Roy Bhowmik and Kotal 2010; Kotal and Roy Bhowmik 2011). As compared with On the basis of criteria adopted by the IMD, a TC is other operational centers, NCEP in the United States designated as a cyclonic storm if the associated maxi- uses the high-resolution hurricane WRF (HWRF) mum sustained surface wind (MSW) is 34–47 kt (1 kt ’ 2 model, which is based on the NMM dynamical core of 0.51 m s 1), as a severe cyclonic storm if it has MSW of WRF; operating at cloud-permitting (3 km) resolution, 48–63 kt, as a very severe cyclonic storm if it has MSW of it has achieved significant skill in hurricane track and 64–119 kt, and as a supercyclonic storm if it has MSW intensity forecasts (Gopalakrishnan et al. 2006, 2012; of 120 kt or more (IMD 2011). It is considered a de- Tallapragada et al. 2008) over the Atlantic and Pacific pression if the MSW is 17–33 kt. Seventeen TCs during Ocean basins. The recent case studies by Mohanty et al. 2007–11 over the NIO are considered in this study. Of (2013) and Pattanayak et al. (2012) reported better re- these 17 TCs, 13 were formed over the BoB and 4 formed sults using the HWRF model for BoB cyclones as well. over the AS. A real-time TC forecast up to 120 h was The prime objective of this study is to evaluate the performed 2 times per day (0000 and 1200 UTC) performance of the ARW model for track predictions throughout the TC life with effects from the genesis over the NIO on the basis of 100 forecast cases involving stage (formation of depression). Table 1 shows the period 17 TCs that occurred over the NIO between 2007 and of simulations as well as the time of landfall for each 2011. Note that this 5-yr period considered is comparable TC. The numerical simulations result in 100 prediction to the period typically used in other operating centers ‘‘cases.’’ The details of synoptic situations and best- such as NCEP. This is an effort to document prediction track data of the 17 TCs were obtained from the IMD skills over the NIO, because there is no well-established Regional Specialized Meteorological Centre (RSMC) Unauthenticated | Downloaded 09/30/21 10:54 PM UTC 2478 JOURNAL OF APPLIED METEOROLOGY AND CLIMATOLOGY VOLUME 52 TABLE 1. Details of the model simulations and observed landfall time of each TC. For intensity, CS 5 cyclonic storms, SCS 5 severe cyclonic storms, VSCS 5 very severe cyclonic storms, and SuCS 5 supercyclonic storms. For nature, SM 5 straight-moving TCs and RC 5 recurving TCs. Different TC name No. of forecasts TC categories (intensity) Simulation period in 12-h intervals Obs landfall (LF) (nature) Arabian Gonu (SuCS) 0000 UTC 2–1200 UTC 5 Jun 2007 0300 UTC 6 Jun (over Oman) 8 (SM) Sea cyclones Yemyin (CS) 0000 and 1200 UTC 25 Jun 2007 0300 UTC 26 Jun 2 (SM) Phyan