Clark
(Meteorologist)
Sun Jul 10 2005 08:52 PM
Re: Dennis Aftermath

Lysis, there is a means by which you can see higher inland gusts, but it's not really friction. Where friction saps wind speed compared to being over water, the loss of the mechanism to maintain the hurricane (the warm waters & moisture off of the ocean) also leads to a greater susceptibility for downdrafts to form.

Primarily, these things can form with the introduction of dry air into the midlevels of the column, where evaporative cooling from precipitation leads to an increased susceptibility for downdrafts as the convection dies out within the storm. In the tropics, the moisture and heating that is carried upward by convective updrafts helps to maintain the atmosphere in a state not to allow this to happen, maintaining the convection and updrafts and leading to a feedback cycle upon which the storm may grow. (As an aside, note that it is not the convection that drives the storm, but it is the updrafts from the convection which provide a conduit for the moisture and energy to be transported aloft and drive the storm.)

In summary, higher winds are felt at the low-levels off-shore as a result of a strong, well-defined circulation...upon landfall, this begins to be impacted at the lower levels first, resulting in lower overall winds speeds, but the landfall also results in the decay of the convection, by which high winds still present above the boundary layer (about 5000ft up) not impacted by friction may be transported down to the surface. After this point, the winds aloft begin to die off with the overall circulation as it spins down over land.

Hope this helps clarify things somewhat!



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