A study of Doppler radar winds in Hurricane Wilma (2005)

This study documents the maximum Doppler velocities observed by the Miami National Weather Service Doppler radar (WSR-88D)during Hurricane Wilma's passage across South Florida on 24 October 2005 These observations serve as a proxy for observations of surface wind in regions where surface observing systems either failed or were not deployed. This has been used by engineers at Florida Power and Light Corporation to relate Hurricane Wilma's structure to damage to elements of the power grid. In Miami Dade, Broward and Palm Beach counties, power outages were widespread and, because of the loss of main transmission lines, long-lasting.

The Doppler wind speeds at altitude must be adjusted to provide the equivalent of a sustained 1 m surface wind at 10 m elevation. To estimate this reduction factor we compared the Doppler velocities with quality controlled surface data from the H*Wind data base. For the region of high winds along the East coast, a reduction factor of 68 – 70% gave the best comparison.

Because the Doppler radar only measures the total wind speed when the wind is parallel to the radar beam, we can expect a fair estimate of the maximum wind speed when the radar beam is tangent to the eyewall. Consequently there are regions where the geometry precludes representative wind estimates. We get good estimates of wind speed in regions NW to N of the radar, which comprises the more highly populated areas of South Florida. We will extend these results to Hurricanes Frances, Jeanne and Katrina and discuss implications for estimating landfall winds in real time from the operational WSR-88D data.