The impact of environmental dry air and shear on the intensity of Hurricanes Katrina and Rita (2005) before landfall

Before making landfall along the U.S. Gulf Coast in late August and September of 2005 as major hurricanes, Katrina and Rita both had weakened from their respective Category Five peak intensities. In this study we examine how dry air and wind shear in the storm environment contributed to their decay. While oceanic thermal structure and internal dynamics are important factors in regulating the intensity of mature tropical cyclones, we are limiting our focus here to large-scale atmospheric influences. Using analyses from the NOAA National Centers for Environmental Prediction's (NCEP) Global Data Assimilation System (GDAS) over successive days that include GPS-dropwindsonde data from NOAA Gulfstream-IV synoptic surveillance missions, rawinsonde data, and satellite observations, we take a cursory look at the temporal evolution of the wind and relative humidity fields at select mandatory-pressure levels above the surface. We also explore the variations in the environmental vertical structure depicted by both individual dropsondes and the GDAS fields. These items will be related to the observed intensity and inner-core structural changes.