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Tropical Storm Odette Forecast Discussion Number 4
2021-09-18 16:49:32| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Sat Sep 18 2021 000 WTNT45 KNHC 181449 TCDAT5 Tropical Storm Odette Discussion Number 4 NWS National Hurricane Center Miami FL AL152021 1100 AM AST Sat Sep 18 2021 Strong shear of about 30 kt from the west-southwest continues to push all of Odette's deep convection well to the east of the surface center. The center itself lacks some definition, with multiple low-level swirls rotating around a common point. Odette is well on its way through the extratropical transition process, with cold air advection noted on the west side of the circulation, and a band of overcast clouds on the north side of the developing warm front. We're awaiting some new ASCAT data, which should arrive soon, and for now the initial intensity remains 40 kt based on continuity. Odette is being picked up by the mid-latitude westerlies, and it is moving a little faster toward the northeast, or 055/15 kt. The cyclone should turn to the east-northeast and accelerate further later today, but then a significant slow down is expected on days 3 through 5 when Odette detaches from the mid-latitude flow and meanders to the southeast of Newfoundland. In contrast to yesterday, the global models are in much better agreement on this scenario, and the updated NHC track forecast has been hedged in the direction of the GFEX consensus aids, since the GFS and ECMWF global models should have a good handle on the behavior of an extratropical cyclone. The global models vary slightly on when extratropical transition will be complete, but the GFS- and ECMWF-based SHIPS diagnostics indicate that it should happen by this evening or tonight. Baroclinic forcing will likely be the main contributor to Odette's expected strengthening over the next few days, and the intensity models, including the GFS and ECMWF global models, have been consistent in showing the peak winds reaching about 55 kt in 36-48 hours. The post-tropical cyclone is expected to occlude and lose its upper-air support in about 48 hours, which should lead to gradual weakening through the end of the 5-day forecast period. Odette's wind field is expected to expand significantly during the next few days while the system becomes a strong post-tropical cyclone. The post-tropical cyclone is forecast to affect portions of Newfoundland with strong winds and heavy rainfall Sunday and Monday. Please refer to products from the Canadian Hurricane Centre for additional information on potential impacts in Newfoundland. FORECAST POSITIONS AND MAX WINDS INIT 18/1500Z 38.5N 67.3W 40 KT 45 MPH 12H 19/0000Z 40.0N 64.2W 45 KT 50 MPH 24H 19/1200Z 41.8N 59.9W 50 KT 60 MPH...POST-TROP/EXTRATROP 36H 20/0000Z 42.7N 56.4W 55 KT 65 MPH...POST-TROP/EXTRATROP 48H 20/1200Z 42.8N 53.1W 55 KT 65 MPH...POST-TROP/EXTRATROP 60H 21/0000Z 42.2N 50.5W 50 KT 60 MPH...POST-TROP/EXTRATROP 72H 21/1200Z 41.5N 49.1W 45 KT 50 MPH...POST-TROP/EXTRATROP 96H 22/1200Z 41.3N 48.7W 40 KT 45 MPH...POST-TROP/EXTRATROP 120H 23/1200Z 42.7N 48.8W 35 KT 40 MPH...POST-TROP/EXTRATROP $$ Forecaster Berg
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