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Tropical Storm Lee Forecast Discussion Number 23
2017-09-24 04:55:52| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Sat Sep 23 2017 000 WTNT44 KNHC 240255 TCDAT4 Tropical Storm Lee Discussion Number 23 NWS National Hurricane Center Miami FL AL142017 1100 PM AST Sat Sep 23 2017 An ASCAT overpass around 0014 UTC caught the western half of Lee, and showed a maximum wind of about 40 kt. On that basis, the initial intensity has been increased to 45 kt, on the assumption that the ASCAT instrument is undersampling the tiny circulation of the tropical storm. A WindSat overpass from 2102 UTC indicated that Lee has developed a coherent inner-core. In fact, the 37 GHz RGB composite from the WindSat overpass indicated that a ring of shallow to moderate convection surrounds the center of Lee, often a signature of a rapidly intensifying cyclone. The NHC intensity forecast has therefore been significantly increased for the first 48 hours of the forecast, but falls short of explicitly forecasting rapid intensification. Beyond that time, most of the intensity guidance is higher than before, and shows Lee maintaining hurricane throughout the forecast period. The NHC forecast is just a little above the previous forecast at days 3-5, and close to the intensity consensus. It is still worth noting that small tropical cyclones can go up or down quickly in intensity with little warning, and confidence in the forecast is low, even with reasonable agreement among the intensity models. After turning almost due west earlier this evening, Lee appears to have come to a near halt and is beginning to turn slowly toward the southeast. Lee continues to follow the trend of the ECMWF, so the NHC forecast has been moved farther west, closer to that model. Although the GFS continues to insist on a east to northeast track, I am treating it as an outlier at this time. The remaining global models (and the HWRF) show that Lee will gradually rotate clockwise around a building mid-level ridge to the northwest for the next few days before turning more toward the north at day 4. The NHC forecast lies between HCCA and the ECMWF, but confidence in the track forecast is still low given the high model spread at this time. FORECAST POSITIONS AND MAX WINDS INIT 24/0300Z 31.9N 50.1W 45 KT 50 MPH 12H 24/1200Z 31.8N 50.0W 55 KT 65 MPH 24H 25/0000Z 31.5N 49.4W 65 KT 75 MPH 36H 25/1200Z 30.9N 48.9W 75 KT 85 MPH 48H 26/0000Z 30.2N 48.9W 75 KT 85 MPH 72H 27/0000Z 30.0N 50.5W 75 KT 85 MPH 96H 28/0000Z 31.5N 52.0W 75 KT 85 MPH 120H 29/0000Z 34.5N 52.5W 70 KT 80 MPH $$ Forecaster Zelinsky
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