Rapid decay of slowly moving Typhoon Soulik (2018) due to interactions with the cold wake in the northern East China Sea

Abstract

For a better prediction of the typhoon intensity before landfall, it is essential to understand the ocean-typhoon interaction processes on the shelf region. Improvement of typhoon intensity forecasting over the northern East China Sea (NESC) is particularly necessary because the typhoon frequently causes disastrous damages landing the neighboring countries. In 2018, Typhoon Soulik decayed abruptly over the western side of Jeju Island in the NESC (decrease in maximum wind speed by 12 m s-1 for 30 hours), which is significantly over-predicted. Along with the slow translation speed (~2 m s-1) of Typhoon Soulik (i.e. long residence time over the region), severe sea surface cooling (SSC> 8 ºC in an area of horizontal scale of ~150 km) occurred in the vicinity of the Ieodo Ocean Research Station (I-ORS; 32º7.4’N, 125º10.9’E) where the subsurface cold water pre-existed. From the time series of temperature observed at the I-ORS, it is revealed that the vertical mixing of the surface warm water and the pre-existed subsurface cold water is the main agent of the SSC. Due to the severe SSC, the enthalpy flux at the sea surface between the typhoon and the ocean changed its sign from upward (~+480 W m-2) to downward (~-810 W m-2). Large enthalpy loss due to the downward enthalpy flux for the long period over the cold wake, resulted in rapid decay of Typhoon Soulik with decreasing intensity at a rate of -4.4 × 1.0 hPa (kJ cm-2)-1. This strong case of rapidly decaying Typhoon Soulik over the NECS provides a better understanding TC (including hurricane) intensity, which will improve intensity predictions by considering two-way interactions, particularly between slowly translating typhoons and the strongly stratified extratropical shelf ocean.