Effects of Observed Conditions on Evaluation of Tropical Cyclone Potential Intensity

The effects of near-surface thermodynamic conditions around and inside a tropical cyclone (TC) on potential intensity (PI; Emanuel 1995, 1997) are examined for 30 North Atlantic TC events. To test the effect of environmental variations, PI for each TC is calculated using three environmental conditions: the Dunion (2011) mean moist tropical sounding, the Dunion sounding modified by observed sea-surface temperature, and an observationally-based environmental sounding. PI varies by an average of 7-9 m s-1 among these tests, demonstrating that near-surface conditions around a TC substantially affect PI.

To test the effect of deviations from PI Theory's idealized boundary layer profiles, observationally-based near-surface temperature and moisture profiles are used to calculate PI. These values are compared to PI values calculated using PI Theory's idealized boundary layer. Temperature and moisture variations are each found to affect PI by an average of 3-4 m s-1, showing that conditions inside a TC play a non-negligible role in determining that storm's PI.

Finally, for four TCs in which a distinct specific entropy minimum is observed far from the TC center, PI is calculated using this minimum as the environment and compared to PI calculated using the standard observed environment. It is found that setting the environment to the radius of minimum entropy increases PI by 2 to 20 m s-1. This demonstrates that the location of the environment chosen for real-time PI calculation can greatly affect the value calculated.