Impact of Assimilations of Dropwindsonde Data and SSM/I Rain Rates on Numerical Predictions of Hurricane Florence (1988)

Abstract

Numerical experiments were conducted to assess the impact of Omega dropwindsonde (ODW) data and Special Sensor Microwave/Imager (SSM/I) rain rates in the analysis and prediction of Hurricane Florence (1988). The ODW data were used to enhance the initial analysis that was based on the National Meteorological Center/Regional Analysis and Forecast System (NMC/RAFS) 2.5° analysis at 0000 UTC 9 September 1988. The SSM/I rain rates at 0000 and 1200 UTC 9 September 1988 were assimilated into the Naval Research Laboratory's limited-area model during model integration. Results show that the numerical prediction with the ODW-enhanced initial analysis was superior to the control without ODW data. The 24-h intensity forecast error is reduced by about 75%, landfall location by about 95% (reduced from 294 to 15 km), and landfall time by about 5 h (from 9 to 4 h) when the ODW data were included. Results also reveal that the assimilation of SSM/I-retrieved rain rates reduce the critical landfall location forecast error by about 43% (from 294 to 169 km) and the landfall time forecast error by about 7 h (from 9 to 2 h) when the NMC/RAFS 2.5° initial analysis was not enhanced by the ODW data. The assimilation of SSM/I rain rates further improved the forecast error of the landfall time by 4 h (from 4 to 0 h) when the ODW data were used. This study concludes that numerical predictions of tropical cyclone can benefit from assimilations of ODW data and SSM/I-retrieved rain rates.