Near-Surface Satellite Wind Observations of Hurricanes and Their Impact on ECMWF Model Analyses and Forecasts

Abstract

During August?September 1995 new near-surface wind datasets over the tropical Atlantic from both the ERS-1 scatterometer and Meteosat satellites were available at the European Centre for Medium-Range Weather Forecasts. At this time there was an unusually high number of hurricanes present in the tropical Atlantic and so the impact of these data on analyzing and forecasting the main cyclones was investigated. Assimilation experiments using a new variational scheme, with the ERS-1 winds, showed clear improvements both in the analyses and short-range forecasts, 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 was included. For Hurricane Luis the improvement was for a higher percentage of cases when the model identified the cyclone in the 24- and 48-h forecasts. For the 72-h forecasts 80% of the reported cyclones were detected compared with only 33% for the analyses without ERS-1 data. The impact of the Meteosat lower-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 time. The impact of one profile from a ship in the vicinity of Hurricane Luis just before its approach to the Caribbean Islands was clearly demonstrated by large improvements to both analyses with and without the scatterometer winds.