THE HRD SYNOPTIC FLOW FIELD EXPERIMENT: THE IMPACT OF OMEGA DROPWINDSONDES ON OPERATIONAL HURRICANE TRACK FORECAST MODELS
James L. Franklin
Stephen J. Lord (NOAA/NCEP)
Robert W. Burpee (NOAA/NHC)
Robert E. Tuleya (NOAA/GFDL)
Sim D. Aberson
To evaluate the impact of special environmental observations on the objective
hurricane track forecast guidance available to the National Hurricane Center.
Recent research with dynamical and statistical models has shown that improved
prediction of hurricane motion requires more information on the hurricane's
large-scale environmental wind and height patterns than is typically available.
While satellites can provide some wind data using cloud-tracking procedures in
the upper and lower troposphere, the middle levels are frequently almost void of
observations. Operational models used for hurricane track forecasting need
information from throughout the troposphere to be initialized. As a result,
operational models may fail to predict important changes of storm speed or
direction due to inadequate initial data, rather than inadequate physics of the
The Hurricane Synoptic Flow Experiment uses Omega dropwindsondes (ODWs)
to gather vertical profiles of wind, temperature, and humidity within 1,000 km
of hurricanes. The experiment is typically conducted over the data-sparse
oceanic regions of the western Atlantic or Gulf of Mexico roughly 48-72 hours
before the projected landfall of a mature hurricane on the coast of the United
States. The ODWs define the hurricane's surrounding large-scale flow,
particularly in the 400-700 mb middle tropospheric layer - the layer most
directly related to tropical cyclone motion.
Using the historical sample of Synoptic Flow experiments conducted by HRD from
1982-1993, an assessment was made of the impact of ODW data on three dynamical
hurricane track models providing operational guidance to the forecasters at NHC:
HRD's barotropic VICBAR model, NCEP's global spectral model, and the GFDL
hurricane model. The overall impact of the ODWs was obtained by averaging the
forecasts from the three models to form a "consensus" forecast (CON3).
In the historical sample of cases, the ODW observations accounted for
statistically significant reductions in 12-60 h track errors in the CON3
forecasts. The error reductions, which ranged from 16%-30%, are at least as
large as the accumulated improvement in operational forecasts attained over the
last 20-25 years. (FIGURE 1) shows the mean
forecast errors with and without the
ODW data, relative to forecast errors from a climatology and persistence model
On 15 August 1995, the Director of NHC requested an additional Synoptic Flow
experiment to gather data in the environment of Hurricane Felix, which was then
threatening the North Carolina coast. ODW data identifying key environmental
features influencing the track of Felix were successfully gathered and
transmitted to NHC and NMC.
The following manuscript has been submitted for publication:
Burpee, R. W., J. L. Franklin, S. J. Lord, R. E. Tuleya, and S. D.
impact of Omega dropwindsondes on operational hurricane track forecast models.
Bull. Amer. Meteor. Soc., submitted.
Franklin, J. L., and M. DeMaria, 1992: The impact of Omega
observations on barotropic hurricane track forecasts. Mon. Wea. Rev.,
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