Impact of Storm structure and the Environmental Conditions in the the Rapid Intensification of Hurricanes Katrina and Patricia

The GFDL coupled regional hurricane model provided operational guidance for Hurricane Katrina in 2005 and Hurricane Patricia in 2015.Although the track guidance in Hurricane Katrina was outstanding from the August 27th, 00 UTC synoptic time up to the period of landfall, the version of the model run operationally at the time was unable to predict the rapid intensification of Katrina once it moved into the Eastern Gulf of Mexico. One of the contributing factors to the under prediction of the intensity of this hurricane was inadequate representation of the Loop Current in the ocean initialization, despite otherwise very favorable conditions for Rapid Intensification that existed at the time(e.g. high SSTs, weak wind shear, upper level anticyclone aloft). Subsequent upgrades to the GFDL model since 2005 have included the capabilities of assimilating real-time sea surface height satellite measurements for more realistic ocean model initialization. Recent analyses have suggested that the storm size of Hurricane Katrina that was based on the observed storm radii available in real time, was also underestimated in the GFDL initial condition. In this study, we conducted sensitivity experiments with the 2015 version of the GFDL operational hurricane to evaluate the impact of atmospheric and ocean initial conditions on the intensity prediction for Hurricane Katrina. It will be shown that with more accurate representation of both the Loop Current in the Gulf of Mexico and storm size, the rapid intensification of Katrina could be accurately predicted in the new version of the GFDL model. These results demonstrate the critical role these two parameters played in Katrina's intensity and suggest that accurate representation of both is critical in predicting hurricane intensity with high resolution regional models.

Hurricane Patricia, a late season Eastern Pacific storm in 2015, underwent record rapid deepening, from Tropical Storm to Category 5 intensity status in only 24h. Unlike Hurricane Katrina, numerical experiments with the GFDL hurricane model have shown that the ocean interaction had little impact on the overall storm intensification, due to the storms' fast translational speed. However, sensitivity experiments with the CHIPS statistical-dynamical intensity model, suggest that the wind shear in the global analysis may have been too large, significantly inhibiting the storm rapid intensification by the dynamical models. This important impact of the environmental conditions will be investigated further as well as the specification of the storm size for this very compact hurricane. The properties that governed the Rapid Intensification of these 2 storms will be compared and contrasted.

Disclaimer: The views, opinions, and findings contained in this article are those of the authors and should not be construed as an official National Oceanic and Atmospheric Administration (NOAA) or U.S. Government position, policy, or decision.