Abstract
On 23 August, 2017, Typhoon Hato rapidly intensified by 10 kt within 3 h just prior to landfall in the city of Macau along the South China coast. Hato’s surface winds in excess of 50 m s−1 devastated the city, causing unprecedented damage and social impact. This study reveals that anomalously warm ocean conditions in the nearshore shallow water (depth < 30 m) likely played a key role in Hato’s fast intensification. In particular, cooling of the sea surface temperature (SST) generated by Hato at the critical landfall point was estimated to be only 0.1–0.5 °C. The results from both a simple ocean mixing scheme and full dynamical ocean model indicate that SST cooling was minimized in the shallow coastal waters due to a lack of cool water at depth. Given the nearly invariant SST in the coastal waters, we estimate a large amount of heat flux, i.e., 1.9k W m−2, during the landfall period. Experiments indicate that in the absence of shallow bathymetry, and thus, if nominal cool water had been available for vertical mixing, the SST cooling would have been enhanced from 0.1 °C to 1.4 °C, and sea to air heat flux reduced by about a quarter. Numerical simulations with an atmospheric model suggest that the intensity of Hato was very sensitive to air-sea heat flux in the coastal region, indicating the critical importance of coastal ocean hydrography.
Highlights
Typhoon Hato rapidly intensified to a category-3 intense typhoon just before making landfall in Macau along the South China coast on 23 August 2017
Due to small sea surface temperature (SST) cooling over the shallow water and increasing wind speed, the total heat flux increased to 1203 W m−2 at P2 when Hato entered the shelf water at 00Z 23 August
On 23 August, 2017, Typhoon Hato rapidly intensified by 10 kt within 3 h before making landfall in Macau, where it caused unprecedented damage
Summary
Typhoon Hato rapidly intensified to a category-3 intense typhoon (increased 10 kt within 3 h) just before making landfall in Macau along the South China coast on 23 August 2017. Emanuel [16] proposed that SST cooling induced by a typhoon could be negated over warm shallow waters due to the lack of deeper cold water, and may affect subsequent intensity. Emanuel [16] proposed that SST cooling induced by a typhoon could be negated over warm shallow waters due to the lack of deeper cold water, and may affect subsequent intensity changes of typhoons. Based on satellite remote sensing, reductions in SST cooling were observed over the coastal waters along the Florida and east coast of the US after storm passages [30,31].
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