Principal Investigator: H. E. Willoughby
Collaborating scientist(s):
P. G. Black
Objective: Understanding of the meteorology behind this unprecedented disaster.
Rationale: Major hurricanes, category four or five on the Saffir--Simpson scale, are rare. They cross the US coastline only a handful of times in a century. These extreme storms inflict astonishing economic and human costs upon the communities that they ravage, all controlled by the details of their structure and motion. Better understanding of the meteorology that drives events on the ground is essential to better forecasts and more adequate disaster preparedness.
Method: Analysis of ground based radar images, flight--level aircraft data, satellite images, and debris patterns to reconstruct Andrew on the mesoscale and vortex scale.
Accomplishment: Four meteorological factors aggravated the devastation when Hurricane Andrew struck South Florida:
-completed replacement of the original eyewall by an outer, concentric eyewall while Andrew was still at sea;
-storm translation so fast that the eye crossed the populated coastline before the influence of land could weaken it appreciably;
-extreme wind speed, 82 m/s winds measured by aircraft flying at 2.5 km;
-and formation of an intense, but nontornadic, convective vortex in the eyewall at the time of landfall.

Although Andrew weakened for 12 h during the eyewall replacement, it contained vigorous convection and was reintensifying rapidly as it passed onshore. The Gulf Stream just offshore was warm enough to support a sea--level pressure 20--30 hPa lower than the 922 hPa attained, but Andrew hit land before it could reach this potential (Figure ). It was difficult--to--predict mesoscale and vortex--scale phenomena that determined the course of events on that windy morning, not a long--term trend toward worse hurricanes.
Key reference: Willoughby, H. E., and P. G. Black, 1995: Hurricane Andrew in Florida. Bulletin Amer. Meteor. Soc., 76, (in press).

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