A simple parameterization of sea surface cooling beneath a hurricane inner core

Changes in SST beneath the inner core of a hurricane have been shown to have a significant impact on its intensity. Although it has been found that reductions in SST directly beneath the inner core are significantly smaller than those observed in the wake region, it has also been shown that even small SST reductions (~ 1 C) below the eyewall may significantly reduce the enthalpy flux from the ocean surface to the storm. This finding would suggest that inner core SST changes and their subsequent impact on hurricane development must be understood and properly quantified in order to accurately forecast hurricane intensity change.

The Statistical Hurricane Intensity Prediction Scheme (SHIPS) model uses a parameterization for inner core SST cooling that depends on latitude and storm translational speed only. However, there exist other storm characteristics, such as intensity, that may also play an important role in this localized SST change. Adding further complexity to this problem, there are also properties of the upper ocean, such as the thermocline depth, that have a relationship with inner core SST change as well.

This study seeks to investigate the role of these various tropical cyclone and upper ocean variables and to develop a simple parameterization for inner core SST change and its resultant impact on hurricane development. Since SST observations under the eyewall are very scarce, output from the GFDL ocean-atmosphere coupled model is used as data for the statistical development. From the results of this analysis, a parameterization function will be developed that uses the physical variables found to have the strongest relationship to inner core SST change. Only those variables that can be estimated in real-time, such as storm maximum wind, translation speed and thermocline depth (from satellite altimetry) will be considered. The views, opinions, and findings in this report are those of the authors and should not be construed as an official NOAA and/or U.S. Government position, policy, or decision.