Outer Rainband Formation on Land Ahead of Typhoon Hato (2017)

Abstract

An outer rainband develops rapidly on land of South China from afternoon to evening of 22 August 2017 when Typhoon Hato is approaching, leading to an early arrival of convective storms prior to typhoon's landfall. The convective cells initiate on the eastern coasts and move to the western inland region where they grow upscale into a fully fledged outer rainband. Convective‐permitting simulations suggest that the new‐born convective cells on the eastern coasts are associated with the increasing convective instability and low‐level lifting by the land‐sea differences of non‐gradient winds. Such differences are established by the horizontal and vertical components of thermal contrasts. In the following stage of convection organization, the convectively induced cold pools in turn strengthen the updrafts at their leading edges, which help to organize the convective cells on rainband as a fast‐moving squall line in the western region. Such storm‐feedback processes of rainband convection and cold pools strongly respond to the changing convective instability and mid‐level dry conditions on land. These regional environmental conditions are closely associated with the large‐scale subsidence in the outer region of typhoon. The results highlight that the new outer rainband can form rapidly on land due to surface heating, and the storm‐feedback processes in response to the changing environmental conditions when a tropical cyclone is approaching land.