Hurricane Intensity Change and Inner-Core SST: Warmer is Not Always Better

The existence of a direct link between warm ocean conditions and subsequent tropical cyclone intensification has long been suggested dating back to the 1960's, and more recently, in several tropical cyclone ocean heat content studies. However, ongoing analyses using inner-core sea surface temperatures (SST) and near-surface atmospheric thermodynamic observations from Atlantic and Gulf of Mexico hurricanes dating back to 1975 suggest a more nuanced and less “ocean-centric” conclusion. Preliminary results from this study do not support a statistically significant relationship between inner-core SST/mixed layer temperature (MLT) and intensity change. Instead, findings illustrate a clear link between the magnitude of the vertical moisture gradient (“Δq”) between the near-surface atmosphere and the ocean surface with subsequent changes in storm intensity. Here, storms associated with high values of Δq (and low values of inner-core SST/MLT) exhibited significantly greater rates of intensification over the subsequent 6-24h period, relative to storms that experienced low values of Δq (and high values of inner-core SST/MLT). It is also worth noting that in this case, the magnitude of atmospheric vertical wind shear for each sample was found to be similar. These findings suggest that observations of the ocean environment alone are inadequate (and in some instances potentially misleading) when it comes to assessing the potential likelihood of future storm intensification. Instead, a more complete investigation of near-surface conditions that include observations of atmospheric moisture is required in order to get an accurate assessment of actual thermodynamic conditions that directly impact surface moisture fluxes within the high-wind, inner-core hurricane environment. Detailed analyses highlighting these findings will be presented.