A Review of the Storm Characteristics of Typhoon Kalmaegi (1415) and Related Forecasting Considerations in Hong Kong

ABSTRACT 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.