Minimum Potential Pressures of Tropical Cyclones over the Eastern North Pacific Ocean from the NCEP/NCAR Reanalyses.

The maximum potential intensity (MPI) of a tropical cyclone represents a theoretical upper limit to the strength of the storm imposed by the laws of physics and the energy available to the system in the atmosphere and upper ocean. Simulated tropical cyclones intensify to their MPIs in the absence of any inhibiting factors, such as vertical wind shear. Tropical cyclones have been observed to approach their MPIs in regions of little wind shear. Thus, the MPI provides a useful measure of the upper bound for potential intensification of a tropical cyclone. In this study the MPI is defined in terms of the minimum possible pressure computed thermodynamically using the method described by Holland (1997). In this method the cyclone is assumed to consist of an environment, an eyewall and an eye. The calculation of the minimum possible pressure requires a vertical sounding of temperature, the surface pressure and the surface air temperature. The data for the soundings used in this study were taken from the daily analyses of the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalyses for the period 1992-98. The minimum potential pressures were also calculated for soundings in which the surface air temperature was replaced with the sea surface temperature minus one degree Celsius. The minimum potential pressures computed from the NCEP/NCAR reanalyses were compared with those computed previously from soundings taken at Isla Socorro, Mexico (latitude 18.72°N, longitude 110.95°W, WMO 76723). Case studies were performed for major tropical cyclones that occurred over the eastern North Pacific Ocean during the period of this study.