The Upgrade of GRAPES_TYM and its performance in the western North Pacific Ocean in 2013

The Meso-scale TC numerical prediction system aimed at the intensity forecast was developed based on GRAPES_MESO by improvement of the physical processes and application of a vortex initialization. The integration domain of GRAPES_TYM covers the whole North West Pacific Ocean and South China Sea with 15km horizontal resolution and 31 vertical levels. GRAPES_TYM was put into operational running in July 2012. The statistical analyses of 2009-2012 forecasts show that GRAPES_TYM tend to predicted TC intensity stronger compared with the best track data especially for the forecasts within 48h.

GRAPES_TYM was upgraded through integrating the improvements from GRAPES_MESO that will affect TC forecasts, modifying the SLP and specific humidity calculation methods during TC vortex initialization process and introducing MESO-SAS from WRF. The forecast length was extended to 120h from 72h. The results from 2013 show that the new system greatly reduces the TC track and intensity forecast errors compared with the operational system. The results from the upgraded GRAPES_TYM are also compared with HWRF in North West Pacific Ocean and show that HWRF has smaller average track errors especially for 72h (191.96km(TYM)/164.08km(HWRF)) and 96h (309.77km(TYM)/256.84km(HWRF))forecasts, but the average intensity errors from these two system almost have no obvious difference from 24h-120h forecasts.