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Tropical Storm Lee Forecast Discussion Number 9
2017-09-17 04:50:25| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Sat Sep 16 2017 000 WTNT44 KNHC 170250 TCDAT4 Tropical Storm Lee Discussion Number 9 NWS National Hurricane Center Miami FL AL142017 1100 PM AST Sat Sep 16 2017 Lee has a classic shear pattern appearance in satellite imagery this evening, with the center on the northern edge of a large convective burst due to the effects of 15-20 kt of northwesterly vertical shear. Two recent ASCAT overpasses indicate that the maximum winds are about 35 kt in the southern semicircle, with no winds of tropical-storm-force in the northern semicircle. The initial intensity of 35 kt is based on the scatterometer data. The initial motion is 275/7. Lee is moving along the south side of a weak mid-level ridge. After about 24 h, the ridge is expected to weaken and allow Lee to turn west-northwestward, a motion that should continue through the forecast period. The new track forecast is similar to the previous forecast and lies mainly between the ECMWF and the HFIP corrected consensus models. Lee is expected to encounter strong upper-level winds through the forecast period, with vertical shear values likely to exceed 30 kt after 48 h. While some short-term spin up due to convective bursts cannot be ruled out, overall the environment is not favorable for significant strengthening. Indeed, the intensity guidance calls for gradual weakening, and the GFS and ECMWF models forecast the cyclone to completely dissipate by 120 h. The new intensity forecast is weaker than the previous forecast and now calls for Lee to degenerate to a remnant low by 96 h. FORECAST POSITIONS AND MAX WINDS INIT 17/0300Z 12.8N 34.9W 35 KT 40 MPH 12H 17/1200Z 12.9N 36.0W 35 KT 40 MPH 24H 18/0000Z 13.1N 37.5W 35 KT 40 MPH 36H 18/1200Z 13.7N 39.2W 35 KT 40 MPH 48H 19/0000Z 14.4N 41.0W 30 KT 35 MPH 72H 20/0000Z 16.0N 44.5W 30 KT 35 MPH 96H 21/0000Z 17.5N 48.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 22/0000Z 19.0N 52.0W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Beven
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