Hurricane Intensification Forecast Tool

temperature gradient map: the intensification of Hurricane Katrina occurred when the cyclone crossed regions of high oceanic heat content, in regions of high dynamic topography detected by altimetry. The sea level measured by an altimeter is the combined effect of geoid undulations, dynamic ocean topography produced by currents in geostrophic balance, tides, and the ocean's response to meteorological forcing. Popular press suggest that warm ocean surface waters intensified Katrina, but sea surface temperatures were around 30°C almost everywhere along Katrina's path through the ocean (top figure). If intensification was driven predominantly by sea surface temperature, Katrina would have strengthened gradually over time. Instead, Katrina intensified most rapidly when she was over anomalously high areas of dynamic topography measured by altimeters (Figure 2b): first over a warm-core eddy east of Florida as she grew from a tropical depression to a Category-1 hurricane, and then over the Loop Current and warm-core ring R05-1 in the Gulf of Mexico as she intensified from Category 1 to Category 5. These dynamic topography highs are a proxy for the vertically integrated heat content within the water column. It is the depth of the warm water pool, and not merely the temperature at the surface, that provides the reservoir of energy to intensify a storm. Since the dynamic topography changes only slowly over weeks, altimeter data collected long in advance of a hurricane can be used to forecast the potential for intensification.

The intensification of Hurricane Katrina occurred when the cyclone crossed regions of high oceanic heat content, in regions of high dynamic topography detected by altimetry.

Coincident SST data alone does NOT reveal the threat of hurricane intensification due to the presence of the Loop Current and warm-core rings.

Satellite altimeter measurements of sea surface height are routinely used by NOAA to estimate tropical cyclone heat potential (TCHP), essentially a measure of the amount of heat stored in the upper ocean, and its impact on hurricane intensity. The plot on the bottom shows Katrina intensified to a Category 5 hurricane as it passed over a region of high TCHP in the Gulf of Mexico. In contrast, the plot on the top shows uniformly warm sea surface temperatures along Katrina's path.