Compound Tropical Cyclone Heat (TC-Heat) Hazard in Hong Kong: Amplifying Urban Heat Extremes With Storm Position-Driven Peripheral Warming and Urban Footprint

Compound hazards involving tropical cyclones and extreme heat (“TC-heat”) have rarely been examined in prior research. Peripheral subsidence associated with cyclones can warm an area to varying degrees, depending on the cyclone's strength and position. Meanwhile, the peripheral airflow also overwhelmed the land-sea breeze circulation system in coastal cities and favored downwind urbanized heat advection on the Southern China coastline. Here, we systematically applied ERA5 global reanalysis data, local surface-level observations, MODIS-based land-cover data and HYSPLIT backward trajectories to evaluate how the position of distant TCs may divert the monsoon system and foster the surface heat advection from upwind urban agglomerate amplifying air temperature in downwind coastline. The analysis suggests when a distant TC is situated in a favorable area (the vicinity of Taiwan and Luzon Strait) at roughly 500–1,250 km to the east of Hong Kong, it forms a unique meteorological condition which allows the surface heat transport from the Greater Bay Area to Hong Kong, reflecting that regional build-up of heat could be an important mechanism for producing local heat extremes.