Principal Investigators:
Collaborating scientists:Michelle Huber and Mike Hopkins (NHC/TPC)
Rationale: That significant damage and loss of life often occurs inland after landfall (as
happened in Hurricane Hugo of 1989 and in Andrew) underscores the need for accurate forecasts
of tropical cyclone winds inland. When Hugo and Andrew made landfall, no operational
hurricane prediction models provided intensity forecasts over land. Subsequently, HRD
developed an empirical model for prediction of the decay of hurricane winds after landfall for
the U.S. south of 37 N. With financial support from the Federal Emergency Management
Agency (FEMA) the Inland Wind Decay Model (IWDM) has been recently completed (Kaplan
and DeMaria 1995). It is a simple two-parameter model which assumes that tropical cyclone
wind speeds decrease exponentially after landfall and that the rate of decrease is a function only
of the intensity and speed of hurricane motion at landfall. The IWDM has three basic uses. It
can be used to estimate the maximum sustained wind near the TC center as a function of time, to
predict a swath of wind speeds as the hurricane moves inland, and to support preparedness
planning with maps of the maximum possible wind speeds for hurricanes of various landfall
intensities and speeds of motion.
Method: Starting with the 1995 Hurricane season, forecasts from the IWDM were made available to forecasters at the National Hurricane Center/ Tropical Prediction Center (NHC/TPC) for select landfalling tropical cyclones. FEMA used the model for hurricane evacuation planning, also starting with the 1995 Hurricane season. An evaluation of the IWDM overland wind swath forecasts was performed for the two landfalling U.S. hurricanes (Erin and Opal) of 1995. The intensity and structure of these hurricanes at landfall required to run the IWDM, were obtained from the last NHC/TPC advisory prior to landfall. Comparison between forecast and observed winds were made at all inland sites where surface wind observations could be obtained. In addition, a comparison of the IWDM forecast maximum sustained wind near the TC center was performed for all 5 TCs that made landfall in the U.S. during 1995. For this comparison, the NHC/TPC best track position and intensity estimates were employed both for model input and evaluation.
Accomplishment: Comparison of observed winds in Hurricanes Erin and Opal with the forecast wind swath for indicate that the IWDM wind estimates were in error by about 11 kt (6 m/s) and that the IWDM tended to overestimate the observed wind speeds (see Kaplan et al. 1996 and Huber et al. 1996).Evaluation of the model predicted maximum sustained wind near the TC center for the 5 landfalling U.S. TCs showed that the IWDM was in error by about 7 kt (4 m/s) and that the model again tended to overpredict the observed maximum sustained wind speeds.
The IWDM was made operational at the NHC/TPC in 1996. An example of the IWDM predicted wind swath for hurricane Fran's landfall in North Carolina is shown in Fig. 1. Work on an empirical inland wind decay model analogous to the model described above, but for the region north of 37 N, is currently underway. Preliminary results suggest that the TCs in this region decay more rapidly than those south of 37 N. This is probably caused by cooler air and rougher terrain in this region.
Key references:
Huber, M.M., M. DeMaria, and J. Kaplan, 1996: Evaluation of an Empirical Inland Wind Decay
Model for the Landfall of Hurricane Opal. Minutes of the 50th Interdepartmental Conference,
Miami, FL, Office of Fed. Coord. for Meteor. Services and Supporting Research, NOAA.
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.
Kaplan, J., M. DeMaria, and M.M. Huber, 1996: A Preliminary Evaluation of Forecast from an Empirical Inland Wind Decay Model for Hurricane Erin (1995).Minutes of the 50th Interdepartmental Conference, Miami, FL, Office of Fed. Coord. for Meteor. Services and Supporting Research, NOAA.