A numerical simulation of Hurricane Bret on 22-23 August 1999 initialized with airborne Doppler radar and dropsonde data

This study concerns the simulation of Hurricane Bret on 22-23 August 1999 with the MesoNH non-hydrostatic, two-way interactive, quadruple-nested grid mesoscale model. A 30 h integration, from 0000 UTC 22 August to 0600 UTC 23 August, covers the period of maximum intensity over the Gulf of Mexico and landfall over Texas. Special attention is paid to the initial conditions from which the model is integrated. A balanced vortex, derived from airborne Doppler radar data, is used to replace the ill-defined cyclone in the large-scale analysis. In addition, the analysed humidity field over the Gulf of Mexico is modified in accordance with specific dropsonde observations. A comparison between the simulated storm track and intensity for three different numerical experiments shows that the inclusion of the radar-derived vortex and high spatial resolution are necessary to obtain a realistic simulation. After an initial period of adjustment, the simulation with the inserted radar-derived vortex and high resolution produces a storm only 10 hPa weaker than the observation after 24 h, compared to the control run that is nearly 50 hPa weaker at the same time. The characteristics of this simulated storm at its mature stage are then presented, with particular emphasis on the processes that modulate the intensity of the inner core region.