AN EMPIRICAL MODEL FOR PREDICTING THE DECAY OF TROPICAL CYCLONE WINDS AFTER LANDFALL

Principal Investigator: John Kaplan
Collaborating scientist(s):

Mark DeMaria (NHC)

Objective: To derive an empirical model for predicting the decrease in tropical cyclone (TC) wind speeds after landfall.

Rationale: 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 landfall.

Method: 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.

Accomplishment: 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 Center (NHC).

Key reference:
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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