Review of Operational Practices and Implications for Bangladesh / A Public Disclosure Authorized Improving Lead Time for Tropical Cyclone Forecasting Review of Operational Public Disclosure Authorized Practices and Implications for Bangladesh Public Disclosure Authorized Public Disclosure Authorized Cover photo: Typhoon Nargis over the Bay of Bengal. Credit: NASA Improving Lead Time for Tropical Cyclone Forecasting Review of Operational Practices and Implications for Bangladesh ©2018 The World Bank The International Bank for Reconstruction and Development 1818 H Street, NW Washington, DC 20433, USA Disclaimer This report is a product of the staff of the World Bank with external contributions. The findings, interpre- tations, and conclusions expressed in this volume do not necessarily reflect the views of the World Bank, its Board of Executive Directors, or the governments they represent. The World Bank does not guarantee the accuracy of the data included in this work. Questions regarding figures used in this report should be directed to persons indicated in the source. Rights and Permissions The material in this work is subject to copyright. Because The World Bank encourages dissemination of its knowledge, this work may be reproduced, in whole or in part, for noncommercial purposes as long as full attribution to this work is given. Any queries on rights and licenses, including subsidiary rights, should be addressed to the Office of the Publisher, The World Bank, 1818 H Street NW, Washington, DC 20433, USA; fax: 202-522-2422; e-mail: [email protected]. III Preface his report was published in June 2015. In republishing cyclones.” Since this development is highly germane, the the report, an in-depth follow-up study to determine in above statement is no longer correct. The conclusions have detail what may have changed since then has not been been revised accordingly, as follows: “Starting this year, done. However, to the best of the team’s understanding, NHC has the option to issue advisories, track and intensity Tthe descriptions of both the science of forecasting and the forecasts, watches, and warnings for disturbances that are operational practices at the institutions involved remain not yet a tropical cyclone, but which pose the threat of bringing largely accurate, with one substantive exception. tropical storm or hurricane conditions to land areas within 48 hours.” Details are available at https://noaanhc.wordpress. In the original conclusions section, the possibility of com/2017/06/29/potential-tropical-cyclones-fitting-the- cyclone track and intensity forecasts being produced bill-for-more-timely-warnings/. While these products are before cyclogenesis has occurred was discussed. The 2015 issued only in the limited circumstances described—for lead report stated that while such forecasts had been produced times less than 48 hours, not for the 10-15 day lead times by numerical weather prediction centers and a university group, “there is no evidence of a national center that has described in the report—this is clearly a substantive change, actual responsibility for issuing forecasts for any country and indicates that the state of the art as practiced by national actually issuing official forecasts of this type yet, although the centers is evolving. National Hurricane Center (NHC) has begun experimenting with such products internally.” In 2017 the NHC did, in fact, Beyond this, only minor facts that have changed, such as begin issuing such products to the public. These forecast titles or affiliations of individuals mentioned in the report products are issued for what the NHC calls “potential tropical (including some of those listed in the acknowledgments). Dhaka. Photo by Meinzahn/Thinkstock.com V Contents Acknowledgments ........................................................................................................................................................ viii Acronyms .................................................................................................................................................................. ix Executive Summary ..................................................................................................................................................... xi Objectives ............................................................................................................................................................ xiii Approach .............................................................................................................................................................. xiii Key findings ......................................................................................................................................................... xiv Forecasting at the BMD ...................................................................................................................................... xv Recommendations ............................................................................................................................................... xvi Chapter 1 Introduction: Tropical Cyclones in the Bay of Bengal .............................................................. 1 Objectives .................................................................................................................................................................. 2 Approach and methodology ......................................................................................................................................... 3 Organization of the report ........................................................................................................................................... 3 Chapter 2 Forecasting: Analysis of Operational Practices ............................................................................ 5 Tropical cyclone forecast .............................................................................................................................................. 5 What is a tropical cyclone forecast? ............................................................................................................................. 6 Forecasting existing storms .......................................................................................................................................... 7 Forecasting genesis ....................................................................................................................................................... 10 What types of observations are used? .......................................................................................................................... 11 What types of models are used? ................................................................................................................................... 12 The forecast process ...................................................................................................................................................... 15 Currently available skills and recent developments .................................................................................................... 20 Storm surge forecasting ................................................................................................................................................ 23 What types of observations are used? .......................................................................................................................... 23 What types of models are used? ................................................................................................................................... 24 The forecast process ...................................................................................................................................................... 25 Treatment of uncertainty............................................................................................................................................... 26 The CIFDP Approach ..................................................................................................................................................... 27 Big picture .................................................................................................................................................................. 28 VI Chapter 3 Tropical Cyclone and Storm Surge Forecasting in Bangladesh ........................................... 33 Characteristics of Tropical Cyclones in the Bay of Bengal ........................................................................................... 34 Regional context for tropical cyclone forecasting in Bangladesh ............................................................................... 37 The Bangladesh Meteorological Department ............................................................................................................... 37 Data available at BMD ................................................................................................................................................... 37 BMD forecasts ................................................................................................................................................................ 38 Factors constraining BMD’s forecast practices ............................................................................................................ 40 Other physical systems needs ......................................................................................................................................