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Special Issue on Severe Weather About the Cover HKMetS BULLETIN, Volume 4, Number 1, 1994 HONG KONG METEOROLOGICAL SOCIETY Special Issue on Severe Weather About the cover The cover picture shows a GMS4-IR image of Typhoon Ira, then a tropical storm, making landfall near Yangjiang at 1500Z on 4 November, 1993. During the next several hours Ira brought heavy rainstorms, particularly over the west of the territory. More details on this and other severe rainfall events which affected Hong Kong in 1993 can be found in several articles in this issue. The Hong Kong Meteorological Society EDITOR-in-CHIEF Bulletin is the official organ of the Society, devoted to editorials, articles, Bill Kyle news, activities and announcements of the Society. EDITORIAL BOARD Members are encouraged to send any articles, media items or information for Johnny C.L. Chan publication in the Bulletin. Y.K. Chan WL. Chang For guidance see the "INFORMATION Edwin S. T. Lai FOR CONTRIBUTORS" in the inside back cover. The Bulletin is copyright. Views expressed in articles or correspondence are those of the Permission to use figures, tables, and authors and do not necessarily brief extracts from this publication in represent those of the Society. any scientific and educational work is hereby granted provided that the source The mention of specific products is properly acknowledged. Any other or companies does not imply any use of the material requires the prior endorsement by the Hong Kong written permission of the Hong Kong Meteorological Society or its Meteorological Society. office bearers in preference to others which are not mentioned. Published by The Hong Kong Meteorological Society c/o Royal Observatory, 134A Nathan Road, Kowloon, Hong Kong. HKMetS BULLET~N, Vol. 4, Numbe, t 1994 HONG KONG METEOROLOGICAL SOCIETY BULLETIN CONTENTS Special Issue on Severe Weather II Editorial 2 Rainstorm in Hong Kong on 16 June 1993 3 Part I: Synoptic and Mesoscale Aspects M.K. Song Rainstorm in Hong Kong on 16 June 1993 13 Part II: Nowcasting Aspects c.Y. Lam A Late-Season Tropical Cyclone 20 Related Rainstorm in Hong Kong C.M. Tam & C.M. Cheng Three Heavy Rain Occasions Severely 32 Affecting Hong Kong in 1993 B.Y. Lee, C.C. Chan & C.M. Cheng 1993 Tropical Cyclone Summary for the 52 Western North Pacific Ocean Bill Kyle News and Announcements 71 Hong Kong Weather Reviews 79 Meeting Reviews 87 Editorial A brief look at the contents page of this issue of of Typhoon Dot, which dumped more than 300 the Bulletin will alert the reader to the fact that it mm of rain on the northern part of the NT. This is almost entirely dedicated to severe weather paper seeks to find common factors associated phenomena. In Hong Kong 1993 was remarkable with the onset of heavy rain in the three events because of three heavy rainfall events which from the perspective of the weather forecaster. severely affected the territory. Not surprisingly these events have been analyzed from a variety of The second of the series of annual tropical perspectives in order to help us better understand cyclone summaries, the 1993 Tropical Cyclone these severe weather events. Hence there is a Summary for the ~stern Nortb Pacific Ocean preponderance of papers on this subject. We (wet of 180 degrees) continues the theme of hope these will stimulate further ideas and work weather hazards in this issue. It documents all on this extremely important subject as far as the 1993 season tropical cyclones occurring in the territory is concerned. Western North Pacific Ocean and includes tracks for all storms affecting Hong Kong as well as The first two papers, by M.K. Song and CY, satellite imagery of major storms. Lam respectively, both of the Royal Observatory Hong Kong, deal with different aspects of the The remainder of the Bulletin contains the now severe rainstorm on 16 June 1993 which brought regular features News and Announcements, over 280 mm of rain to Sai Kung. In the first, Hong Kong ~ather Reviews, and Meeting Ms. Song provides an account of the synoptic Reviews. The News and Announcements section background during the event and then examines includes the verifications of the 1993 Atlantic the mesoscale aspects in some detail. C.Y. Hurricane Season Activity and Sahel Rainfall Lam then concentrates on nowcasting aspects of forecasts made by Colorado State University the event in the second paper which should help meteorologists included in Bulletin 3(2). The provide insights for forecasters charged with extended range forecasts for 1994 are also forecasting localized heavy rain within very short presented courtesy of Chris Landsea. As before time frames. it is the intention to follow up on the verifications of these forecasts in the next issue. In the third paper C.M. Tam & C.M. Cheng, both of the Royal Observatory Hong Kong, The Editorial Board would like to express their examine the rainstorm of 5 November associated thanks to all the contributors and hope that the with the proximity of T.S.lra. This event also good response will encourage others to submit produced extremely localized heavy rain with items related to their research and work. We Tung Chung on Lantau receiving over 750 mm hope you find this issue interesting and useful. of rain. It was also unusual in bringing so much Your support for future issues is always sought heavy rain in an otherwise normally dry month. in the form of contributions of either papers or correspondence. The fourth paper, by RY. Lee, C.C. Chan and C.M. Cheng, all of the Royal Observatory Hong ~~ Kong, also examines these two events as well .-/ that on 26 September, associated with the passage Bill Kyle, Editor-in-chief 2 HKMetS BUUETIN Vol. 4, No. I, 1994 Sandy M.K. Song Royal Observatory Hong Kong Rainstorm in Hong Kong on 16 June 1993: Part I Synoptic and Mesoscale Aspects RAINFALL Introduction mm A severe rainstorm occurred in Hong Kong on 16 June 1993. Heavy rain first fell over eastern 50 Hong Kong, and then over the whole territory. A daily total of 153 mm of rainfall was recorded at the Royal Observatory and the heaviest downpour was confined to a short 3-hour period from 10 a.m. to 1 p.m. HKT (Figure 1.1). The maximum instantaneous rainfall intensity at King's Park reached 203 mm per hour at 12:24 p.m. The worst hit areas were Sai Kung and 30 Tsuen Wan where daily rainfall over 250 mm and 200 mm were recorded respectively (Figure 1.2). For ease of reference, local place names mentioned in the text are shown in Figure 4 20 from part II (Lam, 1994). Although rain gradual­ ly eased off during the afternoon, the consequences of the rainstorm were serious. There were 268 cases of flooding and over 56 10 reports of landslips during the period. A woman was killed and five others were injured in a mudslip in Tsuen Wan. About 67 hectares of y 1{ IITr •••• Tr farmland and 14 fish ponds were damaged in the e 9 '0 " 12 13 14 15 " " 18 19 20 21 22 23 24 New Territories. HONG KONG TIME Figure 1.1 Hourly raitifa/l recorded at the Royal Observatory Looking further afield, the rainfall distribution Hong Kong on 16 June 1993. (Tr -trace) in southern China over the 12-hour period from 8 a.m. to 8 p.m. on 16 June, derived from 1966 (Chen, 1969) and June 1972 (Cheng and synoptic data, is given in Figure 1.3. The Yerg, 1979). Warm moist air from the Indian very localized nature of the heavy rain in Hong Ocean constitutes the prevailing south-westerly Kong is strikingly illustrated. flow at the 850 hPa level. At higher levels, the background flow is basically westerly up to 300 An account of the synoptic background during hPa. Divergence associated with a narrow ridge the event is given in the following sections. of high pressure is also quite common at 200 hPa level. The synoptic background of the rain­ Synoptic Situation storm on 16 June 1993 generally conforms to this pattern. With moist southwest monsoon, June is normally the wettest month in a year. Indeed, the worst A southwest monsoon dominated over the rainstorms in recent memory occurred in June south of China on 16June 1993 (Figure 2.1a). IlKMetS BUllETIN Vol. 4, No. I, 1994 3 -~- ~ '. (J "-"---150 100 Figure 1.2 (a) &l'lfall (mm) In Hong Kong between 10 a.m. to 1 p.",. 011 16 JUlie 1993. (b) Daily ral'lfall (mm) in HOllg KOllg Oil 16 JUlie 1993. (RO stands fo« Royal ObsenaJory) 4 HKMelS BUUET1N Vol.4. No.1, 1994 25' N 20'N 105· E \I O· E 11S' E 120' E Figure 1.3 Roin/alJ (111111) in smuhem Chino, aa.11I. - ap.11I. on 16 June 1993. Despite the influence of the southwest monsoon, Hong Kong just ahead of the trough. From the the previous few days went by with just a few satellite picture and streamline chart at 8 a.m. on morning showers interspersed with sunny 16 June 1993 (Figure 2.4b and Figure 2.1 c), periods. it can be seen that the 500 hPa trough seemed to split into two, the northern part north of 25°N The upper air conditions over Hong Kong at 8 and the southern part south of 25°N. The cloud a.m. 16 June 1993 are shown in Figure 2.2. mass associated with the northern part of the The atmosphere was potentially unstable: the wet trough continued to move eastward, whereas . bulb potential temperature was around 26 degrees the convection associated with the southern end Celsius in the lowest part of the atmosphere and still lingered near Hong Kong.
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