Assimilation of Coastal Ground-based and Airborne Doppler Radar Data with the ARPS 3DVAR and Cloud Analysis for the Prediction of Hurricane Ike (2008)

The impact of high-resolution radar data on the analysis and prediction of the structure, intensity and track of landfalling hurricane Ike (2008), at a cloud-resolving resolution, is examined. Radial velocity and reflectivity data from two coastal operational WSR-88D radars are assimilated over a 6-hour period before Ike landfall, using the ARPS 3DVAR and cloud analysis package through 30-min intermittent assimilation cycles. Eighteen-hour predictions were made. Three experiments that assimilate both radial velocity and reflectivity data, radial velocity data only, and reflectivity data only all produce better structure, intensity and precipitation forecasts than that from operational GFS analysis without radar data. The improvement to the track forecast lasts for the entire 18 hours while that to intensity prediction lasts about 12 hours. The velocity data help improve the track forecast more while reflectivity data help improve intensity forecast most. Best results are obtained when both Z and Vr data are assimilated. Moisture adjustment is found through sensitivity experiments to be more important than temperature adjustment when analyzing reflectivity data using the cloud analysis procedure. These conclusions are supported by subjective evaluation and quantitative precipitation verification. Additional experiments to examine the impact of airborne Doppler radar observations from NOAA P-3 reconnaissance aircraft on the prediction of hurricane Ike are underway, and will be examined at the conference.