南海北部热带气旋移动路径突然右折的预报研究

南海北部北邻华南沿海，当热带气旋以西或西北路径移至南海北部时突然右折，将很快登陆或严重影响华南地区，此时，如预报稍有失误，就会使整个防台减灾布置工作非常被动，甚至带来生命财产的巨大损失。本文利用８５－９０６－０５－０３攻关资料，对此类热带气旋移动路径突然右折的天气学原因进行研究，结果发现：（１）移向突变前４８～７２小时，在距热带气旋８－１０伟距的西北方位高层（２００ｈＰａ）出现大范围的西到西南气流

ON THE FORECASTING TECHNOLOGY OF ABRUPT CLOCKWISE TURNING TROPICAL CYCLONES OVER THE NORTHERN SOUTH CHINA SEA (SUMMARY)

Most of the abrupt clockwise-turning tropical cyclones (TC)over the northern South China Sea may contiuously move and approach or even land the coast of South China and cause serious damage especially were the operation TC warning not accurate and prompt enough.Based on detailed synoptic analysis on such special category TC cases by using the relevant data of the National Research Project(No 85-906-05-03),the following meaningful conclusions are resulted: (1)48-72 hours prior to the abrupt-turning over this sea region,a wide belt of W-SW current in front of a cold trough will appear at 200hPa level within 8-10 Lat 0 distance to the northwest of the TC centre.This stream will gradually extend eastward to meet the TC's west peripheral circulation. (2)The upper trough will gradually propagate from 200hPa downward to 500 and 700hPa levels. (3)When the TC left the original steering easterly current and is moving to the west edge of the weakening and backward withdrawing South China Sea,and the above mentioned upper W-SW Stream has just contacted the west sphere of the TC,the situation or even stagnation may be favourable to result a deceleration or even stagnation of the oringinally westward moving TC.Blocked by the upper W-SW current,the TC will thereafter suddenly turn right and acclerate toward north to northeast.