The 23rd Conference on Hurricanes and Tropical Meteorology

15B.17
WSR-88D OBSERVATIONS OF HURRICANE ATMOSPHERIC BOUNDARY LAYER STRUCTURE AT LANDFALL

Frank Marks, NOAA/AOML/HRD, Miami, FL; and P. Dodge and C. Sandin


On 5-6 September 1996 WSR-88D radar data was collected as Hurricane Fran made landfall near Wilmington, NC. Fran was a weak category 3 hurricane with peak winds near 50 m s-1. The WSR-88D passed through the eyewall and into the eye of the storm. Vertical profiles of the horizontal wind, analyzed using the velocity-azimuth display (VAD) technique, reveal
strong vertical wind shear in the lowest 1000 m above the ground. While the magnitude of the peak horizontal winds changed with radius from the storm center the magnitude of the vertical shear changed only slightly. The vertical profiles revealed a log-profile of wind speed from near the surface to the height of the wind maximum, ~1000 m. However, the wind direction changed little over the first 200 m, and then backed almost 50° to the height of the wind maximum. The lowest 200 m, characterized by little change in wind direction, was dominated by small (<10 km), narrow (<300 m) regions aligned along the vertical shear vector with large horizontal wind gradients (10-1 s-1) that resemble boundary layer rolls. The presence of these features is likely the cause for the small change in wind direction within this layer, and has possible implications in understanding atmospheric boundary layer fluxes in high wind regimes.

The 23rd Conference on Hurricanes and Tropical Meteorology