Ensemble Forecast of Typhoon Fanapi (2010) Using a High-Resolution Coupled Model: Effects of TC-Ocean Interaction

Ensemble forecast of typhoon Fanapi (2010) is conducted with a high-resolution coupled model to investigate the impact of TC-ocean interaction on TC simulation, in particular that Fanapi encountered a cold ocean eddy during its development. The coupled effects are examined by comparing the forecast results from the atmosphere-ocean (AO) coupled model and from the uncoupled atmospheric (UA) model.

Forecast results show that the TC-ocean interaction have significant impact on TC intensity and structure. With the TC-ocean coupled effect, the TC minimum sea level pressure (maximum wind speed) is weakened by 15 hPa (10 m/s) on average after 3-day forecast. The simulated TC become smaller and more asymmetric. Results show that the weakening of TC is mainly due to the reduction of surface heat and moisture flux. In addition, ocean coupling has induced unfavorable conditions for TC intensification, such as increasing the vertically tilted structure of TC and suppressing the convective burst. These factors also contribute to the weakening of TC. Besides the impact on intensity, notable northward deflection in TC track prediction of AO is observed. It is because the weakening of TC in coupled forecast leads to lower TC vertical development, and thus the steering flow acting on TC movement is different than that in the uncoupled forecast.