Feasibility Study of Seasonal Forecasts of Tropical Cyclones in the Western North Pacific Area using RegCM3

The potential use of a regional climate model for forecasting seasonal tropical cyclone (TC) activity is studied here. Seasonal tropical cyclone activity over the western North Pacific area are simulated by a modified version of Regional Climate Model Version 3 (RegCM3) to study the ability of the model to simulate the genesis and landfalling TC tracks. In the model, a TC is identified as a vortex with several conditions, including local maximum vorticity at 850 hPa with vorticity larger than 350 × 10-6 s-1 and the temperature at 300 hPa being 1 oC higher than the average temperature within 15o latitude radius from the TC center. Tracks are traced by these found vortices. Six-month ensemble (8 member each) simulations are performed for each year from 1982 to 2001 so that the climatology of the model can be compared to the Joint Typhoon Warning Center (JTWC) observed best track dataset.

The 20-year ensemble experiments show that RegCM3 is able to simulate vortices with wind structure and temperature profile resembling the TCs in a real world. The model reproduces tracks which are very similar to the observed tracks with features like genesis in the tropics, recurvature and landfall/decay. The similarity of the 500hPa geopotential height between RegCM3 and the ECMWF reanalysis shows that the model is able to simulate subtropical high to a large extend. The simulated distributions of TC occurrence along latitude and longitude are also similar to the JTWC data. This implies the possibility of seasonal forecast of tropical cyclones using real-time climate model predictions as boundary conditions for RegCM3.