Hurricane Intensity Response to Changes in Inflow Thermodynamics

University Of Hawaii, Honolulu

Investigators

Abstract

Tropical cyclone intensity, defined as the minimum sea level pressure or the maximum sustained winds found in the eyewall, remains a major forecasting challenge. Current theories identify the energy content of the low-level inflow to the eyewall as one of the key factors affecting intensity, but there is a dearth of observations in the low levels available to test or refine the theoretical arguments. The Principal Investigator will examine the response of tropical cyclone (TC) intensity to changes in the energy content of the low-level inflow to the eyewall for TCs Guillermo (1997), Gabrielle (2001), and Humberto (2001). Each TC was sampled on two or more consecutive days with the new Global Positioning System (GPS) sondes deployed from the NOAA WP-3D aircraft. Consecutive day sampling enables the correlation of changes in the inflow energy with changes in TC intensity. The combination of the vertical profiles of thermodynamic and kinematic variables derived from these sondes, airborne expendable bathythermographs that provide sea surface temperature, and reflectivity fields from the aircraft radars, are the basis for the production of storm scale maps of kinematic and thermodynamic variables and trajectory analyses. Trajectory analyses are used to determine where, when, and how much energy is acquired or lost as the inflow column moves toward the eyewall. These fluxes at the top and bottom of the column, and the disposition of the energy through the column, are critical for the intensification and maintenance of the hurricane. Variations in the larger scale environment will be assessed with GPS sondes deployed from the NOAA Gulfstream, and from numerical model analyses. Determining what changes occur in the large-scale environment will allow the role that changes in the inflow layer have on TC intensity to be isolated. The broader impacts of the research include the development of effective and economic sampling strategies to ascertain factors that affect TC intensity change, leading to improved forecasts of intensity that result in substantial safety and economic benefits to the United States. Educational benefits of the work include the training of graduate students, and in particular, the placement of women into the field. The work also enhances the partnership between the University of Hawaii and NOAA's Hurricane Research Division. This research is of high priority within the U.S. Weather Research Program.