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World Meteorological Organization WORLD METEOROLOGICAL ORGANIZATION WMO TROPICAL METEOROLOGY RESEARCH PROGRAMME (TMRP) COMMISSION FOR ATMOSPHERIC SCIENCES (CAS) TOPIC CHAIRMAN AND RAPPORTEUR REPORTS OF THE FOURTH WMO INTERNATIONAL WORKSHOP ON TROPICAL CYCLONES (IWTC-IV) HAIKOU, CHINA 21-30 APRIL 1998 WMO/TD - No. 875 Secretariat of the World Meteorological Organization Geneva, Switzerland 1998 NOTE The designations employed and the presentation of the material in this publication do not imply the expression of any opinion whatsoever on the part of the Secretariat of the World Meteorological Organization concerning the legal status of any country, territory, city or area, or of its authorities, or concerning the delimitation of its frontiers or boundaries. This report has been produced without editorial supervision by the WMO Secretariat. lt is not an official WMO publication and its distribution in this form does not imply endorsement by the Organization of the ideas expressed. Foreword This is the fourth in a series of very successful workshops organized through the World Meteorological Organization's Tropical Meteorology Programme. The concept of bringing together researchers and operational forecasters from all parts of the globe for discussion and interaction has proved to be enormously successful. The previous three meetings have produced significant tangible outcomes in the form of publications and forecaster guidance, and have recommended directions for organizations to pursue with respect to tropical cyclones. There are also a number of intangibles surrounding these workshops that may be equally significant in the longer term. The broadening of links between individuals and organizations, the cross-fertilisation of ideas and the raising of awareness about exciting advances that are taking place around the world are all contributing towards the amelioration of the impact of tropical cyclones. My thanks go to the topic chairs, the rapporteurs and the working group members who compiled the following reports. The information represents the current state of knowledge on tropical cyclones and stands on the shoulders of previous IWTC-inspired publications such as A Global View of Tropical Cyclones, Global Guide to Tropical Cyclone Forecasting, and Global Perspectives on Tropical Cyclones. Participants in IWTC-IV should familiarize themselves with the contents of this report. It is the starting point of the Workshop. May it serve to stimulate discussion, ideas and directions. Gary Foley Chairman, ICTC TABLE OF CONTENTS 1. LANDFALLING PROCESSES OF TROPICAL CYCLONES 1.0 Report of the Topic Chairman F. Marks 1.1 The USWRP Landfalling Tropical Cyclone Research Program F. Marks 1.2 Wind Transients, Vertical Structure and Gust Factors in Tropical Cyclones P. Black 1.3 Ocean Processes excited by Tropical Cyclones L. Shay 1.4 Modification of Track at Landfall E. Rappaport 1.5 Rainfall D. Renqing 1.6 Decay after Landfall F. Marks 1.6 Decay after Landfall L. Chen 2. TROPICAL CYCLONE INTENSITY AND STRUCTURE 2.0 Report of the Topic Chairman G. Holland 2.1 Air-Sea Interaction J. Lighthill 2.2 Environmental Interaction (Intensity) J. Molinari 2.3 Tropical Cyclone Maximum Intensity Theory K. Emanual 2.4 Tropical Cyclone Formation W. Frank 2.5 Small and Mesoscale Interactions (TC structure and intensity) L. Ritchie 3. TROPICAL CYCLONE MOTION 3.0 Report of the Topic Chairman R. Elsberry 3.1 Environmental Interaction J.C.L. Chan 3.2 Baroclinic Processes B. Wang 3.3 Barotropic Processes (TC Motion) R. Smith 3.4 Small Scale Interactions (motion) M. Lander 4. TROPICAL CYCLONE PREDICTION 4.0 Report of the Topic Chairman M. Andrews 4.1 Observational Issues S. Ready 4.2 Analysis F. Wells 4.3 Parametric Wind Fields B. Harper 4.4 Track Prediction Techniques L. Carr 4.5 Intensity Prediction Techniques C. Guard 4.6 Seasonal p-rediction Techniques W. M. Gray 4.7 Rainfall Prediction Techniques X. Xiangde 4.8 Upgrade to the Forecasters Guide to Tropical Cyclone Forecasting G. Holland 5. TROPICAL CYCLONE IMPACTS 5.0 Report of the Topic Chairman R. Pielke + K. McGuffie 5.1 Economic Impacts K. McGuffie 5.2 Societallmpacts R. Pielke 5.3 The Warning Processes L. Avilia 5.4 Information Issues C.Landsea Table of Contents TOPIC ONE LANDFALLING PROCESSES OF TROPICAL CYCLONES 1.0 Report of the Topic Chairman F. Marks (USA) 1.1 The USWRP Landfalling Tropical Cyclone Research Program Rapporteur: F. Marks (USA) 1.2 Wind Transients. Vertical Structure and Gust Factors in Tropical Cyclones Rapporteur: P. Black (USA) 1.3 Ocean Processes excited by Tropical Cyclones Rapporteur: L. Shay (USA) 1.4 Modification of Track at Landfall Rapporteur: E. Rappaport (USA) 1.5 Rainfall Rapporteur: D. Renqing 1.6 Decay after Landfall Rapporteur: F. Marks (USA) 1.6 Decay after Landfall Rapporteur: L. Chen (China) Topic 1. 0/1.1 Chairman's Report/ US WRP landfalling tropical cyclone research program Rapporteur: Frank D. Marks, Jr. NOANAOML Hurricane Research Division Miami, FL 33149 email: [email protected] Fax (1) 305-361-4402 Working Group: R. Elsberry, G. Holland, R. Carbone, F. delSol, K. Abe 1.1.1 Introduction The U. S. Weather Research Program (USWRP) (Emanuel et al1995) effort on tropical cyclone (TC) landfall (Marks and Shay 1998) is focused on what the meteorological research community can contribute to a reduction in the disastrous impacts on the nation. With the continuing shift of population and commerce to the U.S. coastal areas from Texas to Maine, the threat is continually rising. Although some ofthe losses from disruptions to industry, commerce, and transportation are not avoidable, better warnings for longer periods in advance of the landfall would allow time for more damage prevention activities. Both science and technology opportunities are described in a five-year (2000-2004) research plan (Elsberry and Marks 1998) that has as its ultimate goal to produce better guidance for hurricane forecasters. A new facet of research is proposed whereby the meteorological community works with the public and private sector to learn what improvements will have the greatest socio-economic impact. One may categorize studies ofTCs into three periods: pre-landfall, landfall, and post­ landfall. These periods are artificial, but they demonstrate that different aspects of the TC forecast problem are paramount at different times. Pre-landfall commences when a storm is within 120 h of a forecast landfall. One key forecast challenge during pre-landfall is to specify the precise coastal location and time at which the 34-kt (17 m s -1) isotach will cross the coast, because the local emergency managers want all disaster preparedness activities to be completed by that time in the warned area. Thus, the outer wind structure that determines the radius of 34-kt winds must be forecast along with the track. In addition, an accurate forecast of at least 24 h of the inner core wind structure is also needed as the storm surge inundation areas and evacuation plans are linked to the intensity (maximum wind). Improved track forecasts are achievable with more accurate specification of the initial conditions of both the large-scale environment and the wind fields of the TC itself. Application of the new NOAA Gulfstream IV (G-IV), deployment of the Global Positioning System(GPS) dropsondes (GPS sondes),identification of the most fruitful adaptive sampling strategies, validation of current -1.1.1- model forecasts, and the development of ensemble forecasting are all likely to improve track forecasts. Once the tropical cyclone is within 72 h of landfall the radius of the 34-kt wind speeds and rapid intensity change become vital issues. The landfall period is declared when wind speeds reach 34 kt; this is a practical consideration as the arrival of 34-kt winds causes most meaningful preparation to cease and it is when all those that should have been evacuated are out of harm's way. During landfall, the key forecasts are of the inner wind structure and precipitation. The inner wind structure, which is modified in complex ways while passing from open ocean to coastal water and then to land is the primary determinant of localized wind damage, tornadoes, storm surge, ocean surface wave run-up, and evenprecipitation during landfall (see section 1.2 below for more details). Our knowledge ofTC structure changes at landfall is in its infancy, as there are little hard data that survive the harsh conditions. The WSR- 88D radars, making standard wind measuring systems more robust, and the application of new sensors such as portable Doppler, wind profilers, and the deployment of expendable sondes all provide an opportunity to learn much about the evolution of a TC as it makes landfall. Theoretical work that addresses TC intensity is needed to speed progress. Precipitation forecasting requires special considerations and will be treated as a separate topic. Post-landfall begins once the TC has lost its warm core. Precipitation forecasting moves to the fore followed by tornado genesis within the region influenced by TC wind shears and stability (see sections 1.5 and 1.6 below for more details). Development of non-hydrostatic cloud resolving models and case studies that take full advantage of the WSR-88D radars are two fruitful avenues worthy of pursuit. For the purpose of prioritizing the research objectives and observational opportunities, the topics are organized into track and wind structure forecasts during pre-landfall, and the inner wind structure and precipitation forecasts during landfall. A fourth focus area is the socio-economic aspects ofTC landfall, which were considered in setting the priorities. 1.1.2 Pre-landfall objectives Two goals for the pre-landfall track are to: (i) increase the preparation lead-time by at least 12 h via an improvement in forecasts of the location and timing of the TC landfall approach point, and by providing forecast guidance to 96 h with the same accuracy as the present 72-h guidance; and (ii) provide more accurate forecast guidance with confidence measures that will allow the U.S.
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