Principal Investigator: James L. Franklin
Collaborating scientist(s):
Stephen J. Lord (NOAA/NCEP)
Robert W. Burpee (NOAA/NHC)
Robert E. Tuleya (NOAA/GFDL)
Sim D. Aberson
Objective: To evaluate the impact of special environmental observations on the objective hurricane track forecast guidance available to the National Hurricane Center.
Rationale: 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 prediction models.

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.

Method: 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).
Accomplishment: 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 (CLIPER).

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. Aberson. The impact of Omega dropwindsondes on operational hurricane track forecast models. Bull. Amer. Meteor. Soc., submitted.

Key reference:
Franklin, J. L., and M. DeMaria, 1992: The impact of Omega dropwindsonde observations on barotropic hurricane track forecasts. Mon. Wea. Rev., 120, 381-391.
Click here to return to the AOML project overview page.
Click here to return to the Advance Short-Term Warning & Forcast Services page.