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Chill falls over the Atlantic as the official season heads towards close
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| #1107355 (Received by flhurricane at: 4:50 PM 15.Sep.2022) TCDAT2 Tropical Storm Fiona Discussion Number 6 NWS National Hurricane Center Miami FL AL072022 500 PM AST Thu Sep 15 2022 Deep convection has been sheared more than a degree to the east of the center for much of the day, and as a result, the low-level center and circulation have become slightly less defined and elongated, respectively. That said, an Air Force Reserve Hurricane Hunter aircraft measured a peak 925-mb flight-level wind of 65 kt and SFMR winds as high as 46 kt. Assuming some undersampling of the surface winds, the initial intensity is set at 50 kt. This is in agreement with ASCAT-C data from earlier today, which showed an area of 45-50 kt winds to the northeast of the center. Fiona appears to have lost a little bit of latitude since earlier this morning, but the motion remains westward, or 270 degrees at 12 kt. Track models are in good agreement during the next 2 to 3 days, showing a low- to mid-level ridge steering Fiona westward across the Leeward Islands and over the far northeastern Caribbean Sea through Sunday. The HWRF is the only outlier during this period and appears to have a track too far to the north due to an unrealistically high intensity. After day 3, there is more divergence among the track models, with the stronger solutions (i.e., the GFS) indicating a sharper northwestward turn toward a weakness in the subtropical ridge. The weaker solutions (i.e., the ECMWF and HMON) keep Fiona on a westward or west-northwestward track, moving near or over Hispaniola. As a result, the 4- and 5-day forecasts are of lower-than-normal confidence, and ensembles from the main global models suggest that the cyclone could end up anywhere from eastern Cuba to well to the northeast of the Bahamas by the end of the forecast period. For now, the official track forecast is nudged southward and westward from the previous forecast, accounting for the adjusted initial position and the overall trend in the track guidance. Moderate, and even possibly strong, westerly shear is likely to continue for much of the 5-day forecast period. Given these conditions, the NHC intensity forecast flatlines Fiona`s intensity at 50 kt for the next 60 hours, with the caveat that fluctuations are possible related to the convective structure of the cyclone at any time. Fiona is forecast to slow down by the 3-5 day time frame, and the slower motion could allow for the circulation to become more vertically stacked, even in the face of continued shear. As a result, some gradual strengthening is indicated at the latter part of the forecast period. Given uncertainties in how much Fiona might interact with the islands of the Greater Antilles, the NHC intensity forecast lies about 5-10 kt below the IVCN and HCCA consensus aids. Key Messages: 1. Tropical storm conditions are expected in the Leeward Islands within the warning area by Friday evening. Tropical storm conditions are possible within the watch area across the Virgin Islands beginning on Saturday, and then reaching Puerto Rico late Saturday and Saturday night. 2. Heavy rains from Fiona will reach the northern Leeward Islands Friday afternoon, spreading to the British and U.S. Virgin Islands and Puerto Rico Saturday into Sunday morning, and reaching eastern Hispaniola Sunday. This rainfall may produce flash and urban flooding, along with isolated mudslides in areas of higher terrain. Considerable flood impacts are possible across eastern portions of Puerto Rico. 3. Fiona is expected to move near Hispaniola early next week, and watches could be required for parts of the island on Friday. FORECAST POSITIONS AND MAX WINDS INIT 15/2100Z 16.3N 55.4W 50 KT 60 MPH 12H 16/0600Z 16.3N 57.3W 50 KT 60 MPH 24H 16/1800Z 16.5N 59.8W 50 KT 60 MPH 36H 17/0600Z 16.8N 62.1W 50 KT 60 MPH 48H 17/1800Z 17.1N 64.1W 50 KT 60 MPH 60H 18/0600Z 17.3N 65.8W 50 KT 60 MPH 72H 18/1800Z 17.7N 67.1W 55 KT 65 MPH 96H 19/1800Z 19.3N 69.2W 60 KT 70 MPH 120H 20/1800Z 21.4N 71.1W 60 KT 70 MPH $$ Forecaster Berg |
