Objective:
Use data archived at the Hurricane Research Division (HRD) and the National Climatic Data Center (NCDC) to derive an empirical model for predicting the decrease in tropical cyclone wind speeds after landfall for the New England region.
Rationale:
An empirical model for estimating the decrease in tropical cyclone (TC) wind speeds after landfall has been previously developed for the region south of 37° N (Kaplan and DeMaria 1995). Although this model is currently being used operationally by the National Hurricane Center (NHC) and by the Federal Emergency Management Agency (FEMA), it was derived exclusively for TCs that make landfall south of 37° N. The goal of this research is to derive an empirical inland wind decay model for the region north of 37° that is analogous to the model that Kaplan and DeMaria (1995) developed for the region south of that latitude and to make this model available to the NHC and FEMA.
Method:
Employ data archived at the Hurricane Research Division (HRD) and the National Climate Data Center (NCDC) to derive an empirical model for predicting the decrease in wind speeds of tropical cyclones that make landfall north of 37° latitude.
Accomplishment:
With partial financial support from FEMA, an empirical inland wind decay model has been developed for the New England region using data from 9 tropical cyclones (TCs) that made landfall north of 37° latitude between 1938 and the present. The model was derived using position and intensity estimates that were obtained primarily from data archived at the HRD and NCDC. These best track estimates were employed in place of those available from the NHC since they provided higher temporal resolution than was available in the NHC best track file. The increased temporal resolution was crucial to deriving an accurate decay model for this area since the TCs that make landfall in this region typically become extratropical and/or dissipate shortly after landfall. Consequently, obtaining position and intensity estimates at the highest possible temporal resolution was crucial to deriving an accurate decay model for the New England area.
The simple two-parameter exponential decay model derived from these data explained ~64% of the variance of the changes in maximum sustained wind speed of these 9 landfalling TCs with a mean absolute error of ~9 kt. Interestingly, the exponential decay rate obtained for this region was larger than that obtained for the region south of 37° N. It is hypothesized that the higher rate of decay observed in this region is due to the more rugged terrain and the more hostile synoptic environment encountered in this region. FEMA is planning to add maps generated with the New England Decay model to those previously generated for the region south of 37° N for use in the model it employs for evacuation planning. It is also anticipated that forecasts from this model will be made available for operational use at the NHC in future hurricane seasons. A journal article describing the derivation of this New England decay model is currently being prepared.
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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