An Empirical Inland Wind Decay Model for the New England Region
Principal Investigator:
John Kaplan
Collaborating
scientist(s):
Mark DeMaria (NHC/TPC)
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 deg. 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 deg. N. The goal of this
research is to derive an inland wind decay model analogous to the model
developed by Kaplan and DeMaria for the region south of 37 deg. N 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 deg.
lat..
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 that made landfall north of 37 deg.
lat. 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 region since this model was
designed to reproduce the decay rate of tropical systems and storms in
this region are
rapidly becoming extratropical. 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 ~62% of the variance of the changes in maximum
sustained wind speed of these 9 landfalling TCs with a mean
absolute error of ~8 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 (Fig.1) to those previously
generated for the region south of 37 deg. 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 for the
1998 hurricane season.
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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