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Bulletin American Meteorological Society BULLETIN OF THE AMERICAN METEOROLOGICAL SOCIETY Entered as second class matter at the Post Office, Worcester, Massachusetts, under Act of Aug. 24, 1912. Issued monthly except July and August. Annual subscription, $3.50 ; single copies of this issue, 35c. Address contributions to the Bulletin, and correspondence relating thereto, to ROBERT G. STONE, Editor Dept. of Meteorology, New York University, University Heights, N. Y. Vol. 23 FEBRUARY, 1942 No. 2 Some Features of a Typhoon G. S. P. HEYWOOD Royal Observatory, Hong Kong N THE AFTERNOON of November Luzon or over the Pacific to the east O 23rd, 1939, the central calm of of Formosa. Fr. Gherzi explains the a typhoon passed directly over sudden recurvature of the typhoon as the Royal Observatory, Hong Kong, follows:— for the first time on record. Although " If we consider the synop- the typhoon was fortunately not a tic weather charts of the preceding very intense one, it showed several days and the one of the 23rd, we find unusual features, and a full account that the Trade Wind air mass which, of it was published by the present before the arrival of the typhoon to writer in the Meteorological Results the SE of Hainan, was absent on the of the Observatory for 1939 (6). surface, appeared suddenly as a Fr. E. Gherzi, S.J., of Zi-Ka^Wei strong spur extending from, the Bonin Observatory, Shanghai, has summar- Islands as far as the Loochoos. Mean- ized this account in his annual report while a powerful Siberian anticyclone on typhoons (5), and has drawn some had been invading China SSE'ward. very interesting conclusions regarding " To this advance of the the structure of the typhoon. As his Trade Wind air mass, we would at- opinions differ in several respects tribute the sudden recurving of the from those put forward in the origi- typhoon which was, so to say, taken nal account, it may perhaps be of in- and carried away by the anticyclonic terest to discuss the various points circulation of that high pressure raised. area. ." I am indebted to the Director of the Royal Observatory for permission to Although there was undoubtedly an reproduce the accompanying figures incursion of Trade Wind air over the from the original publication. Loochoos on the 21st, there does not seem to have been any significant TRACK change in the north-easterly air- The track of the typhoon, which is stream over the northern part of the illustrated in fig. 1, was an unusual China Sea at this time, and forecast- one; it is exceptional at any time of ers in Hong Kong expected that the year for a typhoon to recurve in the typhoon would either fill up or move western part of the China Sea and westward, owing to the influence of approach Hong Kong from the south- the anticyclone which was invading west; the majority of November ty- China from the north. Instead the phoons either follow a westerly track typhoon recurved sharply and passed in low latitudes, or recurve near N. directly over Hong Kong, illustrating FIGURE 1. once more the difficulty of forecasting no lengthy pilot-balloon flights could the track from a consideration of the be made at Hong Kong during the surface pressure-distribution alone. approach of the typhoon, but westerly It is more probable that the move- winds were found above about 5,000 ments of tropical cyclones are gov- feet over northern Indo China on the erned by the upper winds in their 23rd, and there were strong westerlies environment, as has been found by above 9,000 feet over Hong Kong on Dyke in the case of West Indian hur- the afternoon of the 24th, when the ricanes (3). Over Hong Kong an typhoon was moving away past For- upper westerly wind prevails through- mosa. It seems reasonable to assume out the winter at heights above 5,000- that this upper westerly current had 10,000 feet, and a typhoon has never forced the typhoon to recurve and been known to approach the Colony was driving it away to the eastward, from an easterly direction when this a conclusion which is also reached by opposing upper current is blowing. Un- Deppermann, who has studied the fortunately, owing to cloudy weather, movements of this typhoon (2). .
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