The Impact of Omega Dropwindsonde Observations on Barotropic Hurricane Track Forecasts

Abstract

A scarcity of observations in the hurricane environment is one factor believed to be limiting the improvement in hurricane track forecast accuracy. Since 1982, the Hurricane Research Division (HRD) of the NOAA Atlantic Oceanographic and Meteorological Laboratory has conducted 14 experiments to determine the wind and thermodynamic fields within about 1000 km of tropical cyclones in the Atlantic basin. During these synoptic-flow experiments, Omega dropwindsondes (ODWs) are released from the two NOAA WP-3D research aircraft over a 9?10-h period in the hurricane environment. The ODWs measure pressure, temperature, humidity, and wind as they descend from flight level (about 400 mb) to the surface. These data are then transmitted in real time to the National Hurricane Center (NHC) and the National Meteorological Center (NMC). Recently, a barotropic, nested, spectral hurricane track forecasting model, VICBAR, has been developed at HRD and tested quasi-operationally during the 1989 and 1990 hurricane seasons. Forecasts from this model have compared favorably with other models run at NHC and NMC. In this study, the VICBAR model is used to evaluate the impact of ODW data on track forecast error for the 14 HRD synoptic-flow experiments. The ODW data produced highly consistent reductions in track forecast errors in this sample of cases. Forecast improvements due to single-level midtropospheric (aircraft) data were significantly smaller than those due to the ODWs. At the important verification times of 24?36 h (prior to landfall), when the decision to issue a hurricane warning is being made, the ODWs reduced the model mean forecast error by 12%?16%. These improvements, statistically significant at the 99% level, are comparable to the total improvement in normalized NHC official 24-h forecast error occurring over the, past 20?25 years.