Tropical cyclone dynamic and thermodynamic effects were investigated to determine key threshold values to indicate possible rapid intensification into a major tropical cyclone. The study included 33 major tropical cyclones from 1988-2001 that had a rapid intensification period (RIP). To be included in the study, major tropical cyclones must have reached category 3 status on the Saffir-Simpson scale and exhibited a rapid intensification period, which was defined as having at least a 22 mb decrease over a 24 hour period. Data from the NCEP/NCAR Reanalysis Project were extracted and analyzed in 6 hour intervals beginning at 60 hours prior to each storm’s RIP and ending at 24 hours after the onset of the RIP. The data were averaged across the sample at each time interval and carefully examined particularly at the onset of the RIP to indicate possible threshold values for major tropical cyclone rapid intensification.

Vertical wind shear was analyzed at three different intervals, (850 mb – 500 mb), (850 mb – 200 mb), and (850 – 100 mb). The average major tropical cyclone exhibited lower than typically observed shears with magnitudes of 2.5 m s^-1, 6.4 m s^-1, and 4.2 m s^-1 respectively at the onset of the RIP. The Holland maximum potential intensity (MPI) method, which is strongly influenced by sea surface temperature and the vertical temperature profile, was utilized. MPIs were shown to reach a minimum at the onset of rapid intensification. The attained MPI, which is a function of the actual storm pressure and the MPI expressed as a percentage, was calculated similarly. The average major tropical cyclone exhibited a 28.8% attained MPI at the onset of the RIP. The average central pressure at the onset of the RIP was approximately 979 mb which closely corresponds with a category 1 storm. Future studies will compare these thresholds for major tropical cyclones with minor tropical cyclones to better distinguish the two classes, thereby improving the prediction of rapid intensification which commonly produces a major tropical cyclone.