A Spectrum of Mesoscale Circulations Observed within
Tropical Cyclone Rain Bands
Scott M. Spratt and Stephen J. Hodanish
National Weather Service, Melbourne, Florida
As the coastal suite of Weather Surveillance Doppler Radars
(WSR-88D) have come on-line during the past five years, numerous
tropical cyclone rain bands have been interrogated. Real-time and
post analyses of base and derived radar products have lead to the
detection of a spectrum of mesoscale circulations. Many of these
rotational cells have correlated temporally and spatially with
confirmed damage patterns.
This poster will illustrate the life cycles of three
particular circulation scales within the spectrum. The most
apparent type, similar in horizontal diameter, vertical depth, and
persistence to the traditional midwest mesocyclone, was observed
within Hurricane Opal (1995), prior to landfall in the Florida
panhandle. This type of feature was easily recognized through
manual examination of reflectivity and velocity products, and was
also frequently identified by the automated mesocyclone algorithm.
A smaller scale of rotation was observed within the far outer bands
of Tropical Storm Gordon (1994). These features occurred offshore
and along the east-central Florida coast, and possessed a diameter
and depth near that of low-topped mesocyclones observed within non-tropical, low buoyancy environments. Although this type of feature
was also manually identified for long time periods, algorithm
detection was limited by the reduced scale. The smallest
circulations observed occurred within a rain band on the western
periphery of Hurricane Erin (1995). The rotation associated with
this type of cell was very subtle, weak, and generally lasted less
than 15 minutes.
Improved weather warnings associated with tropical mesoscale
circulations can likely be achieved. The first step toward this
goal is an increased familiarity and anticipation of the wide range
of potential circulation scales. Since both large, intense
mesocyclones and small, weak circulations can produce localized
severe wind damage, warning meteorologists must react quickly to
potential threats.
Corresponding author address:
Scott M. Spratt, National Weather Service
421 Croton Road, Melbourne, FL 32935 scott.spratt@noaa.gov