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| #904247 (Received by flhurricane at: 4:58 AM 23.Sep.2017) TCDAT4 Tropical Storm Lee Discussion Number 20 NWS National Hurricane Center Miami FL AL142017 500 AM AST Sat Sep 23 2017 Not much has changed with Lee over the past six hours. The convection previously observed in the SE quadrant appears to have rotated around the tropical storm and faded, but a 0609 UTC SSMI overpass indicates that a new burst has since taken its place. Dvorak intensity estimates range from 30 to 35 kt, so the intensity has been held at 35 kt for this advisory. Every aspect of the forecast is highly uncertain. With regards to intensity, the model forecasts range from dissipation (GFS) to a category 2 or 3 hurricane (HWRF, HMON). Since the environment still appears to be generally favorable for intensification, my forecast remains close to the HWRF, and a little above the intensity consensus through 72 h. The forecast shows gradual weakening after that time as the shear increases. Because Lee is so small, it is very possible that the tropical storm could strengthen far more quickly than indicated here, at just about any time during the forecast period. Likewise, rapid weakening could occur later in the period if the shear increases like the SHIPS diagnostics indicate it will. As uncertain as the intensity forecast is, the track forecast may be even more so. The ECMWF now shows a relatively deep Lee drifting south for the next 72 hours, followed by a gradual turn toward the northwest. On the other hand, the GFS continues to depict a shallow Lee (or its remnants) moving steadily eastward through the forecast period. As a result, these two typically reliable models differ by more than 900 miles at day 5. The new official track forecast is generally close to the corrected consensus models, FSSE and HCCA, but hedges somewhat toward the ECMWF since it's version of Lee is more in line with the NHC intensity forecast. As a result, the NHC track forecast has been shifted significantly to the west, especially at 72 h and beyond, but still lies nearly 400 miles to the east of the ECMWF. Needless to say, confidence in the forecast is low, and significant changes to the track or intensity forecast may be required during the next day or two. FORECAST POSITIONS AND MAX WINDS INIT 23/0900Z 31.9N 49.2W 35 KT 40 MPH 12H 23/1800Z 32.3N 49.1W 40 KT 45 MPH 24H 24/0600Z 32.5N 48.4W 45 KT 50 MPH 36H 24/1800Z 32.2N 47.4W 50 KT 60 MPH 48H 25/0600Z 31.7N 46.2W 60 KT 70 MPH 72H 26/0600Z 30.5N 44.5W 75 KT 85 MPH 96H 27/0600Z 29.8N 45.0W 70 KT 80 MPH 120H 28/0600Z 30.5N 46.5W 60 KT 70 MPH $$ Forecaster Zelinsky |
