The Impact of Boundary Layer Processes on the Rapid Intensification of Hurricane Wilma (2005)

It remains a great challenge to understand and predict tropical cyclone rapid intensification (RI, defined as a deepening rate of greater than 42 hPa per day) using mesoscale models with appropriate grid resolution, model physics options, and high-resolution observational data for the vortex initialization. Convective-permitting numerical simulations of Hurricane Wilma (2005) have been conducted using the Coupled Ocean/Atmosphere Mesoscale Prediction System – Tropical Cyclone (COAMPS-TC). The goal is to simulate the RI process, the secondary eyewall formation (SEF) and eyewall replacement cycles (ERCs) of Hurricane Wilma. The simulations results are used to further understand the impacts of the planetary boundary layer (PBL) processes (e.g., representation of vertical mixing associated with turbulence kinetic energy) and interaction between the PBL and TC environment (such as the sea surface temperature, vertical wind shear and upper-level relative humidity).

The nested-domain simulation of Wilma (with grid spacing of 45/15/5/1.67 km for the outer, intermediate, and inner nest, respectively) has successfully captured the RI process as the simulated storm intensifies from Cat 2 to Cat 5 in 24 h (a drop of minimal sea level pressure from 974 hPa to 896 hPa during the 24 h period from 1200 UTC 18 October 2005), which compares well with the best track (pressure dropping from 979 hPa to 882 hPa). The model also simulated successfully the SEF and ERCs processes. A series of sensitivity experiments with different PBL and turbulence mixing schemes have been performed to assess the impact of boundary layer processes on Wilma's RI process. Our results demonstrate that the Wilma track, intensity, and inner-core structure are highly sensitive to the selection of the PBL schemes. The PBL processes play an important role in modulating the RI process. Detailed results will be presented at the conference.