65th IHC Booklet/Program (pdf - 4.9MB) - Office of the Federal ...

Collocated ASOS and WSR-88D Depict Collapsing Core and Maximum Wind Gust at
Melbourne FL in the Eyewall of Hurricane Erin (1995)
Keith G. Blackwell
(kblackwell@usouthal.edu)
Coastal Weather Research Center and
Center for Hurricane Intensity and Landfalls Investigations (CHILI)
Department of Earth Sciences, University of South Alabama
Landfalling tropical cyclones often contain collapsing cores of heavy precipitation within their
eyewalls. Several studies indicate the likely linkage between downburst-like features and strong
wind gusts in hurricane eyewalls; however, very few surface-based measurements of winds
associated with these features actually exist. In these studies, National Weather Service WSR-
88D Archive Level II data were analyzed in search of elevated reflectivity regions exceeding 50
dBZ and then temporally examined for signs of vertical collapse, in some cases near or over
surface wind observation sites.
Holmes et al. (2006) presented an introductory glimpse into collapsing precipitation cores in
hurricanes Ivan and Katrina; however no surface wind measurements were available in those
areas to verify the actual strength of the wind within those features. Blackwell and Medlin
(2008) produced a radar climatology of collapsing core frequency within all U.S. landfalling
hurricane eyewalls between 1994 and 2007. This climatological study found that some storms
were almost completely void of heavy eyewall convection and collapsing cores, whereby others
contained extremely prolific activity. One of the most prolific collapsing core producers was
Hurricane Danny (1997) in Mobile Bay, AL. Blackwell (2009) presented an example of a
possible collapsing core within Danny’s eyewall which produced a wind gust of 45 m s -1 (101
mph) at the C-MAN station on Dauphin Island, AL. Blackwell et al. (2010) detailed another
collapsing core event in a spiral band of Hurricane Katrina which produced a reported wind gust
to 122 mph on a docked ship and significant damage along the Mobile AL waterfront.
In each of the above studies, surface wind measurements were sparse or nonexistent and none
were collocated with the radar location; thus, near-surface radar information was not available
near the surface observation. The current study depicts a collapsing core eyewall event in which
the radar and wind observation sites are collocated, providing low-level radar detail. Melbourne,
FL (KMLB) experienced the northeastern eyewall of landfalling category 1 Hurricane Erin
(1995) in the predawn hours of 2 August 1995. A large convective core of >50 dBZ reflectivity
experienced a collapse from above 3000 m (~10,000 ft) to the surface as it approached and swept
across the ASOS station. A hurricane-force wind gust of 34 m s -1 (76 mph) occurred with the
passage of this feature, representing the highest wind measured at that location during the storm.
The adjacent WSR-88D clearly shows the descending reflectivity core and acceleration of the
near-surface winds as the feature approaches. The collocation of Doppler radar and surface wind
measurements make this a unique and interesting event for study and clearly links a collapsing
core with a strong hurricane wind gust. Details will be shown at the conference.
Poster Session – Page 4