A DISCUSSION OF THE MOST INTENSE TROPICAL CYCLONES IN THE WESTERN NORTH PACIFIC FROM 1978 TO 2013

This study examines a number of very intense tropical cyclones(TCs) in the western North Pacific(WNP) since 1978 as depicted by the best track data from the four main weather agencies in the WNP, namely the Hong Kong Observatory, China Meteorological Administration, Regional Specialized Meteorological Centre Tokyo and Joint Typhoon Warning Centre, and the Advanced Dvorak Technique–Hurricane Satellite dataset prepared by the University of Wisconsin/NOAA National Climatic Data Center to identify the most intense TCs in the western North Pacific. Comparison analysis reveals that there are very large differences in the ranking of maximum sustained wind speed(MSW) among these datasets, probably due to data inhomogeneity issues and the discrepancies in TC intensity assessment among these centres. Re-assessment of the MSW of potential candidates suggests that, within uncertainty range of the analysis, Tip(1979) and Haiyan(2013) are the most intense TCs in the WNP during the period. Among the potential candidates, eight of them made landfall during their lifetime. Satellite pattern comparison and the best track dataset analysis of these typhoons show that Haiyan(2013) has the highest estimated MSW right before landfalling, making it the most intense TC making landfall in the WNP during the period 1978-2013.

Assessment of the damages and direct economic loss in Hong Kong due to Super Typhoon Mangkhut in 2018

Super Typhoon Mangkhut hit Hong Kong on September 16,2018,necessitating the issuance of the highest tropical cyclone warning signal,No.10 Hurricane Signal.Packing ferocious winds and record-breaking storm surge,Mangkhut brought the most serious and widespread destruction to the territory in the recent three decades.A series of post event information search,field visits and damage surveys has been conducted by the Hong Kong Observatory(HKO)and the findings on the damages and impacts caused by Mangkhut in different parts of the territory are documented in this paper.Moreover,by analyzing the economic loss data reported by various government departments,public utilities and organizations in Hong Kong and the statistics on insurance claims from the Hong Kong Federation of Insurers(HKFI),the estimated direct economic loss due to Mangkhut in Hong Kong is about HK$4.60 billion,which is about 3.8 times to that of Super Typhoon Hato in 2017.On the contrary,in the Guangdong-Hong Kong-Macao Greater Bay Area,the estimated direct economic loss due to Hato is significantly higher than that of Mangkhut.This could be attributed to the early and effective warnings for Mangkhut,increased public awareness and typhoon preparedness for Mangkhut in 2018 since the fierce attack of Hato in 2017,and infrastructure enhancement of the major impact areas.

A REVIEW OF THE STORM CHARACTERISTICS OF TYPHOON KALMAEGI (1415) AND RELATED FORECASTING CONSIDER ATIONS IN HONG KONG

Kalmaegi(1415)required the issuance of Gale or Storm Wind Signal No.8 in Hong Kong in 2014,even though it passed by at a distance of 370 km from Hong Kong during its closest approach.Storm surges triggered by Kalmaegi caused backflow of sea water in some low lying areas in both Hong Kong and Macao.This paper reviews the use of observational data in monitoring the cyclone characteristics and studies the synoptic factors leading to its fast movement and extensive circulation.The combined analysis of multi-platform satellite wind retrieval,in-situ surface observations and aircraft reconnaissance data over the northern part of the South China Sea is found to be useful in depicting the cyclone structure.Synoptic analysis suggests that the relatively large size of Kalmaegi may be attributed to monsoon shear pattern during its formation stage and the subsequent strengthening of southwesterlies over the northern part of the South China Sea.A strong subtropical ridge north of Kalmaegi not only provides strong steering and thus its high translational speed,but also leads to extensive gale force wind distribution over its northern semi-circle.The performance of various numerical prediction models in forecasting the movement,intensity change and wind structure of Kalmaegi,as well as the storm surge triggered,is assessed and presented.

PROGRESS IN HONG KONG'S TROPICAL CYCLONE FORECASTING AND WARNING SERVICES IN RECENT DECADES

With modern infrastructures and effective warning systems,casualties,damages and losses due to tropicalcyclones(TCs)have been significantly reduced over the years in Hong Kong.Nevertheless,densely populated coastal cities like Hong Kong will need to continuously enhance its resilience to high winds,heavy rain and storm surges brought by TCs,especially with the growing concern of the challenges induced by climate change and sea level rise.By embracing the advance of remote sensing,communication and numerical modelling technology,the Hong Kong Observatory(HKO)continues to improve its TC monitoring and forecasting techniques as well as forecasting and warning services to meet the needs of the society.This paper concisely reviews the major development and achievement of TC-related operation and services of HKO in recent decades,in aspects such as Numerical Weather Prediction(NWP)models,nowcasting techniques,warning communication and public education.Future thrusts on TC forecasting and warning services of HKO will also be discussed.