A NUMERICAL INVESTIGATION OF TROPICAL ISLAND THUNDERSTORMS

A version of the United Kingdom Meteorological Office mesoscale weathe r prediction model is used to simulate cases of deep tropical convecti on from the Island Thunderstorm Experiment off the north coast of Aust ralia. Selected cases contrast rather isolated storm development in a dry basic state, with widespread precipitation from a moist basic stat e. Excellent agreement is found between the simulations and the observ ed early shower development on both occasions. Initiation of convectio n occurs along the sea-breeze front, which is then reinforced by downd raft outflows. Merging of simulated cells occurs where the outflows me et, producing cells with cloud tops above 18 km and updraft speeds of 60 m s-1. The later movement of the storms is less well represented, p robably due to weakness in the storm-mean flow interaction. Comparison of the cases shows that differences in the timing of initiation and i ntensity of subsequent convection are well captured, and relate to dif ferences in the initial sounding. Mean budgets of heat, moisture, and momentum are presented, and sensitivity of the simulations to resoluti on, island shape, and model microphysics is explored.