92nd American Meteorological Society Annual Meeting (January 22-26, 2012)

Thursday, 26 January 2012
Observations of Tropical Atlantic Weather Systems From PREDICT
Hall E (New Orleans Convention Center )
Christopher A. Davis, NCAR, Boulder, CO; and D. A. Ahijevych

Three Atlantic tropical weather systems whose mesoscale structure was well observed by research aircraft during the 2010 hurricane season are analyzed. One case was the failed former tropical storm Gaston (ex-Gaston) that failed to redevelop into a tropical cyclone; the other two cases were developing storms Karl and Matthew. Geostationary satellite, multi-sensor derived precipitation and dropsondes from the NSF/NCAR Gulfstream V (GV), National Aeronautics and Space Administration (NASA) DC-8 and the National Oceanic and Atmospheric Administration (NOAA) Gulfstream IV (G-IV) aircraft are analyzed in a system-following frame to quantify the mesoscale dynamics of these systems.

Ex-Gaston featured extensive dry air surrounding an initially moist core. Vertical shear resulted in a misalignment of mid-tropospheric and lower-tropospheric circulation centers, and allowed dry air to intrude above the lower-tropospheric center. This severely limited the area influenced by deep moist convection, thus providing little chance of maintaining or rebuilding the vortex in sheared flow. By contrast, Karl and Matthew developed in moist, but not entirely saturated, regions. Deep, moist convection was highly intermittent and quasi-diurnal. For Karl, deep convection was initially organized away from the lower-tropospheric circulation center, creating a misalignment of the vortex. The vortex gradually re-aligned over several days and genesis followed this realignment within roughly one day. Matthew experienced weaker shear, was vertically aligned through most of its early evolution and developed more rapidly than Karl, although ultimately Matthew did not become a hurricane presumably because of the influence of vertical shear after genesis.

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