Impact of High-Resolution Atmospheric Motion Vectors Data Assimilation on Typhoon Forecasts in HWRF

Accurate estimations of tropical cyclone intensity and structure are essential to improving tropical cyclone forecasts and for detailed diagnosis of numerical model characteristics. HWRF is one of the more sophisticated tropical cyclone forecast systems, which covers all global basins. However the initialization method differs among basins; self-cycled EnKF hybrid data assimilation (DA) is applied in North Atlantic and Eastern Pacific basins but not in other basins. A new geostationary meteorological satellite, Himawari-8 provides high spatiotemporal resolution atmospheric motion vectors and has potential to resolve both the TC inner structure as well as initial conditions of the surrounding environment, leading to more skillful forecasts.

To investigate impacts of initialization through DA with GSI in HWRF, three sets of cycle forecast experiments were conducted. Each set contains 73 five-day forecast experiments. The HWRF configuration is almost the same as the recent operational HWRF (H217). One set includes a HWRF cycle run which includes vortex initialization without GSI, second run is HWRF with GSI , and third is HWRF with GSI and high-resolution AMV derived from Himawari-8 (H8AMV).

H8AMV produced the smallest track errors for forecast hours of 84-126 among these experiments. One of the factor for the improvement can be explained by reduction of northward track bias. However, the intensity forecast error was the largest for almost all forecast lead times in H8AMV. This could be caused by larger negative (weak) bias of intensity in H8AMV as compared to the other two experiments. The track forecast error of GSI is a little larger than HWRF and the intensity error is comparable with HWRF.

Our preliminary results indicate that the assimilation of high resolution AMV leads to improved track forecasts but a remedy for weak bias is needed. Detailed differences in TC development and structure among the three experiments will be presented.