Seasonal Prediction of Tropical Cyclone by GFDL's 25-km High-Resolution Global Model

Seasonal predictions of tropical cyclones (TCs) in the three major ocean basins of the Northern Hemisphere are implemented by using the Geophysical Fluid Dynamics Laboratory (GFDL) High-Resolution Atmospheric Model (HiRAM) which is designed for both weather and climate-change predictions at 25-km resolution. The persistent sea surface temperature (SST) anomaly and initialized atmospheric states are adopted in the 5 ensemble members for the forecast period from July to November during 1990-2010. It shows that the storm counts are highly predictable in the North Atlantic basin during the past 21 years for both tropical storms (TS) and hurricane categories. The correlation between the observed and model predicted hurricane (TS) counts is 0.88 (0.89) for the 21-year period, while it can be 0.94 (0.92) for the period of 2000-2010. The prediction skill in the eastern Pacific is not as prominent as that in the North Atlantic, while it is even more challenging in the western Pacific basin. The examinations of the SST anomaly used in the model illustrate that the persistent assumption is adequate to the end of the hurricane season in the Atlantic Main Development Region, but the differences between the model and observation SST anomalies are larger in the main TC genesis areas in the eastern and western Pacific.

The HiRAM performed good climatology of the 21-year seasonal prediction by showing highly similar temporal variations of the large-scale systems (e.g. the Siberian High and the African easterly jet) to the ERA Interim analysis data. The differences of the sea-level pressure and the wind shear between the model and the ERA-Interim data during the peak hurricane season also exhibited the corresponding signals to the storm number biases in the three basins. The analyses of storm intensity showed that the intense hurricanes can be characterized well by using the minimum sea-lever pressure instead of the wind information. It demonstrated the potential capability of using the HiRAM on the long-term studies of how climate change impacts on the activities of intense hurricanes that is not easy carried out by most of current global models.