The origin and evolution of tropical storms in the Eastern Pacific are investigated in a regional climate model based on the Pennsylvania State University/ National Center for Atmospheric Research Mesoscale Model Version 5 (MM5). The model simulations are 92 days in length beginning on June 1 for the years 1990-1997. NCEP reanalyses are used to initialize the model and for lateral boundary conditions. Reynold's SST fields are specified at the lower boundary. The horizontal resolution is 50 km.
This model provides a means to study the climatology of tropical storms since it lies between the GCMs with inadequate resolution and high resolution models designed to study individual storms in detail. Over the eight years 1990-1997, the number of tropical storms varies greatly, as does their spatial distribution. This variability is due in large part to SST anomalies, but other factors, such as large scale circulation changes, also contribute. Most storms in the model are generated where SST is highest-off the west coast of Mexico between 10N and 20N. The storms move with time to the west or northwest, generally dying out over the ocean, although some make landfall in Baja California or northern Mexico. These characteristics are in good agreement with reality; however, the simulated storms tend to occur too frequently and with shorter duration than those observed.