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Characteristics of Hurricane Lili's Intensity Changes
Babin, A.
LSU Master's Thesis.
Rapid intensity changes of Hurricane Lili in the Gulf of Mexico (GOM) were
studied in three distinct ways: climatology, satellite remote sensing, and
surface meteorological and oceanographic measurements. Each research
methodology provided insight about Hurricane Lili's intensity behavior.
A climatology of rapid and explosive intensifications of hurricanes was
developed using minimum central pressure observations for the Atlantic
tropical cyclone record. Results showed these events were frequent,
especially in the GOM. The majority of intensification events occurred <=
24 h before landfall, with a third to one-half <= 12 h. Lili emerged
anomalous as the only hurricane to weaken at a greater rate (+17 hPa over
6 h or +2.83 hPa h-1) than its rapid intensification event rate (-13 hPa
over 6 h or -2.16 hPa h-1).
GOES-8 satellite water vapor brightness temperature data were investigated
using a -24°C vapor front to delineate a dry air mass west of Lili. Drier
air was shown to affect Lili during a rapid weakening phase after the two
features were less than 250 km mean or 215 km minimum distance apart.
These critical distances are offered as a criterion for a relationship
between tropical cyclone weakening and dry air advection. During the time
periods where Lili was intensifying or maintaining intensity, this vapor
front exhibited more complex signatures of definitive breaks, shape
changes, and protrusions. During the rapid weakening phase and when the
two features were the greatest distance apart, the vapor front resembled a
smooth, strong boundary line. The dry air mass was shown to have the
greatest effect upon Lili after the rapid intensification phases.
SST and heat flux calculations illustrated that oceanic contributions to
hurricane intensity were more significant during rapid intensification
periods. Ocean heat content directly under the center was more vital as
seen in Lili's second rapid intensification phase occurring directly over
the GOM Loop Current. Although Tropical Storm Isidore cooled surface water
temperatures by around 1°C, pre-Isidore water temperature levels were
shown to increase latent heat flux values by > 100 W m-2 (+ 40%) over
observed values during Lili's weakening phase.
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