AN EMPIRICAL MODEL FOR PREDICTING THE DECAY OF TROPICAL CYCLONE
WINDS AFTER LANDFALL
Mark DeMaria (NHC)
To derive an empirical model for predicting the decrease
in tropical cyclone (TC) wind speeds after landfall.
Unlike most previous U.S. landfalling tropical cyclones, the
majority of damage and fatalities that resulted from the
landfalls of Hurricanes Hugo (1989) and Andrew (1992) were
due to wind not storm surge. At the time these storms made
landfall, no operational TC prediction models provided
intensity forecasts over land. Consequently, work commenced on
developing an empirical model for predicting the decay of TCs after
Employ data from TCs that made landfall in the U.S.
from 1967-1993 south of 37 deg N to derive an empirical model
for predicting the decrease in TC wind speeds after landfall.
With financial support from the Federal Emergency
Management Agency (FEMA), an empirical inland wind
decay model (IWDM) has been developed for TCs that make landfall in the
U.S. south of 37 deg N. The IWDM is a simple two-parameter model that was
derived based upon the assumption that TC wind speeds decrease
exponentially with time after landfall. It was shown that the IWDM
explains 93% of the variance of the decrease in the maximum sustained
wind speeds of the 67 landfalling TCs that comprised the developmental
dataset. FEMA is currently employing maps generated using the IWDM for
hurricane evacuation planning (Figure). The IWDM is
also available for operational use by forecasters at the National Hurricane
Kaplan, J., and M. DeMaria, 1995: A simple empirical
model for predicting the decay of tropical cyclone winds
after landfall. J. Appl. Meteor., 34, 2499-2512.
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