Towards Improved High-Resolution Forecasts of Tropical Storm Development and Intensity Changes

There has been increased emphasis on high resolution (convection and/or cloud allowing) forecasting of tropical storms. Yet, it has been difficult to develop a consensus on the efficacy of these forecasts. Through multiple WRF re-forecasts of tropical storms Debbie, Helene, and Irene, we show that the (arbitrary) choice of microphysical scheme is one of the main reasons these forecasts do not necessarily show improvement over non cloud-allowing (traditional) forecasts. In fact, the choice of microphysical scheme can change the forecast minimum surface pressure by as much as 30 mb. We also found that changes in aerosol concentrations can have a secondary impact on intensity changes. To put the results in context, we compare re-forecast results obtained after changing other physical parameterization types in the forecast model. We conclude that high-resolution tropical storm forecasts require high accuracy in the simulation of microphysical processes to correctly simulate thermodynamic feedbacks in storm development.