There is a view that a tropical cyclone should weaken when it is approaching and close to landfall due to the disruptive effect of the land surface. However, recent observations have indicated that some cyclones may temporarily intensify when approaching the coast. An example is Hurricane Andrew in 1992 at Miami, which initially weakened, but then re-intensified as it approached the coast. After weakening whilst crossing Florida, Andrew re-intensified in the Gulf of Mexico, but then weakened continuously on approaching a second landfall in Louisiana.
To understand how a cyclone may weaken or intensify on approaching the coast, we have constructed several numerical experiments using a newly developed tropical cyclone model. We have found that the process is strongly dependent on the land-surface temperature. If the land is as warm as the sea surface, the simulated cyclone at first weakens then re-intensifies just before landfall. If the land surface is colder, the cyclone will weaken. The physical reasoning is as follows.
When the cyclone's circulation impinges on the coast, moisture convergence, and cumulus convection may be enhanced there. This asymmetric development introduces a tendency to weaken the cyclone. As time proceeds, the convective cells rotate cyclonically around the cyclone centre, and develop a new spiral band impinging upon the cyclone core. A cyclone core contraction then occurs with associated intensification of the cyclone. As the eye crosses the coast, the primary eye wall collapses, leading to weakening as the cyclone moves inland. Only when the landmass is warm is significant moisture convergence at the coast possible. Thus a knowledge of the coastal conditions is crucial to accurate forecasts of landfall intensity