High Surface Winds in Tropical Cyclones: Boundary-Layer Models vs. Dropsonde Observations

A two-layer similarity planetary boundary layer model developed at the University of Washington (UWPBL) is modified to calculate the surface winds in tropical cyclones. A unique characteristics of this model is that it accounts for the effects of organized large eddies, which transport momentum and heat fluxes more efficiently than the smaller scale local turbulence included in most boundary models. The GPS dropwindsonde observations archived by the NOAA/Hurricane Research Division are compared to the surface winds calculated by the UWPBL model and the analyses from a numerical weather prediction (NWP) model. It is shown that the dropwindsonde, NWP and UWPBL model winds are comparable at moderate wind speeds. However, at high wind speeds, the UWPBL model wind speeds (1) are significantly and consistently greater than the NWP winds but (2) compare well with the dropwindsonde observations.