A case-study of a tropical low over northern Australia

We examine in some detail a low that intensified over land near the northern coast of Western Australia in January 2015. The study is based on European Centre for Medium Range Weather Forecasts (ECMWF) analyses as well as two cloud-permitting, six-day, limited-area forecasts using the UK Met Office Unified Model (UM) with 4 km horizontalgrid spacing. In one of the UM forecasts, the latent heat fluxes were suppressed over the land so as to assess the importance of soil moisture on the intensification of the low. We show that the UM forecasts perform well using the ECMWF analyses as "truth", suggesting that the forecasts can be used to learn about the details of storm behaviour. Analyses of the forecasts support the results of previous studies showing that the intensification of the low over land can be interpreted in terms of the rotating-convection paradigm for intensification articulated in recent studies. The forecasts indicate also that high soil moisture or special soil types are not essential to vortex intensification over land, at least in a monsoonal environment.