NEAR-SURFACE SATELLITE WIND OBSERVATIONS OF HURRICANES AND THEIR IMPACT ON ECMWF MODEL ANALYSES AND FORECASTS

During August-September 1995 new near-surface wind datasets over the t ropical Atlantic from both the ERS-1 scatterometer and Meteosat satell ites were available at the European Centre for Medium-Range Weather Fo recasts. At this time there was an unusually high number of hurricanes present in the tropical Atlantic and so the impact of these data on a nalyzing and forecasting the main cyclones was investigated. Assimilat ion experiment using a new variational scheme, with the ERS-1 winds, s howed clear improvements both in the analyses and short range forecast s. compared with the optimal interpolation scheme without these data. For example, the forecast positions for Hurricane Iris were reduced by almost 50% when the scatterometer data iras included. For Hurricane L uis the improvement was for a higher percentage of cases when the mode l identified the cyclone in the 24- and 48-h forecasts. For the 72-h f orecasts 80% of the reported cyclones were detected compared with only 33% for the analyses without ERS-1 data. The impact of the Meteosat l ower-tropospheric cloud motion winds was found to be small due to lack of coverage in the vicinity of the center of the hurricanes at this t ime. The impact of one profile from a ship in the vicinity of Hurrican e Luis just before its approach to the Caribbean Islands was clearly d emonstrated by large improvements to both analysts with and without th e scatterometer winds.