Assimilation of T-TREC-Retrieved Wind Data with WRF 3DVAR for the Short-term Forecasting of Typhoon Meranti (2010) near Landfall

An extended Tracking Radar Echo by Correlation (TREC) technique, called T-TREC technique, has been developed recently to retrieve horizontal circulations within tropical cyclones (TCs) from single Doppler radar reflectivity (Z) and radial velocity (Vr, when available) data. This study explores, for the first time, the assimilation of T-TREC-retrieved winds for a landfalling typhoon, Meranti (2010), into a convection-resolving model, the WRF. Assimilating T-TREC wind data once with WRF-3DVAR results in much better structure and intensity analysis of Meranti than that from the operational GFS analysis or when directly assimilating Vr data. With the improved initial conditions, the subsequent 18-h forecasts for the track, intensity, structure and precipitation are also improved. The ability of the T-TREC retrieval in capturing more accurate and complete vortex circulations in the inner-core region of TC is the primary reason for its superior performance over direct assimilation of Vr data; for the latter, the data coverage is much smaller when the TC is far away and the cross-beam wind component is difficult to analyze accurately with a 3DVAR method.