Hong Kong Hot Days Caused by Outer Subsiding Air of Tropical Cyclones: Statistical Analyses on Favorable Cyclone Locations and Rapid Onsets

As a densely populated city, Hong Kong (HK) faces a growing threat from hot weather under global warming. Previous studies noticed that HK hot weather is sometimes linked to outer subsiding air of a TC, and provided rough locations where TC can drive hot weather in HK. Here, we find 40%–80% of HK annual hottest days are linked to TCs. We perform a grid cell-based analysis and find that TC east of HK, around Taiwan or northwest of Luzon Island, is conducive to HK hot weather. These 85 1°×1° grid cells take up 9% TC occurrences but 32% extreme hot days. Defining TC-related hot days based on TC location, we find that northerly downslope winds contribute to TC-related hot days and that TC-related hot weather strengthens and decays around 30% faster than TC-unrelated ones. The rapid onset of TC-related hot weather makes it challenging to adapt to. Hot weather–conducive TC locations identified in this study help predicting such extreme hot days, and lays important quantitative foundation for future studies.