Typhoon Intensity Forecasts using TIFS with Pseudo Ocean Coupling

Abstract

Typhoon HAISHEN, Typhoon No. 10 in 2020, was weaker than forecasts as it moved north over the western coast of Kyushu. The typhoon intensity forecasting scheme called TIFS operated at the Japan Meteorological Agency (JMA) tended to predict HAISHEN's intensity more strongly than the observed one, resulting in large errors in JMA's operational forecasts. One possible reason for the large errors is that TIFS does not include the effect of ocean cooling associated with tropical cyclones. Here, we investigated whether the accuracy of the typhoon intensity predictions can be improved by replacing static sea surface temperature and ocean heat content used in the conventional TIFS by those predicted by an ocean model. The results of prediction experiments using the pseudo-ocean-coupled TIFS show that the over-intensification of HAISHEN was suppressed and that the prediction errors were significantly reduced. We also extended the evaluation to all typhoons in 2020 and found that the pseudo-ocean-coupled TIFS reduced the prediction errors by about 10% compared to the conventional TIFS for prediction times of 3 to 5 days. This indicates that pseudo-ocean coupling of the conventional TIFS can improve the accuracy of typhoon intensity forecasts.