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Chill falls over the Atlantic as the official season heads towards close
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| #1024796 (Received by flhurricane at: 9:53 AM 11.Nov.2020) TCDAT4 Hurricane Eta Discussion Number 45 NWS National Hurricane Center Miami FL AL292020 1000 AM EST Wed Nov 11 2020 Eta became much better organized between 0900-1000 UTC this morning, including the formation of a well-defined, closed circular eye about 20-25 nmi wide. However, since then the satellite and radar signature have become more ragged as dry air has entrained into the western semicircle of the cyclone and has also penetrated into the inner-core region, resulting in a significant degradation of the convection in that portion of Eta's circulation. A couple of hours ago, a NOAA Hurricane Hunter aircraft penetrated the remnant eye feature and measured a central pressure of 984-983 mb, and also measured 850-mb maximum flight-level winds of 83-85 kt east of the center just outside of a deep convective band. WSR-88D Doppler radar data from Tampa Bay (KTBW) indicated a long fetch of Doppler velocities of 80-88 kt at 13,500 ft directly above and east of the aircraft report, and this was within a band of strong convection characterized by radar reflectivities of 45-49 dBZ. Based on the combination of the wind data and the relatively low central pressure, Eta was upgraded to hurricane status at 1200 UTC. The initial motion estimate is north-northeastward, or 015/09 kt. The latest NHC model guidance is excellent agreement on Eta moving north-northeastward for the next 24 hours around the the western periphery of a deep-layer subtropical ridge that extends westward across the western Atlantic to just off the Florida east coast. Thereafter, the cyclone will move north of the ridge axis and come under the influence of southwesterly to westerly mid- to upper-level flow associated with an approaching cold front, which should result in a faster northeastward motion. By 72 hours, if not sooner, Eta is forecast to merge with the aforementioned frontal system off of the southeastern United States. The new official track forecast is similar to the previous advisory track, and lies just a tad east or to the right of the consensus models TVCN, NOAA-HCCA, and FSSE. It is quite possible that Eta has peaked in intensity based on the rapid erosion of the convective pattern and an eye feature no longer evident in radar or passive microwave satellite imagery. However, there still remains a band of strong convection in the northeastern quadrant that contains Doppler radar velocity values of 80-88 kt between 6000-9000 ft, which corresponds to equivalent surface winds of at least 65 kt. As long as that feature persists, hurricane-force winds are possible along immediate coastal areas within the hurricane watch area. The latest GFS-and ECMWF-based SHIPS intensity guidance shows significantly drier air wrapping into the center by 24 hours, along with the vertical wind shear increasing to more than 20 kt from the west at that time. That combination of unfavorable environmental parameters is expected to lead to gradual weakening until landfall occurs in about 24 hours, followed by rapid weakening after landfall. Eta is forecast to degenerate into a remnant low by 60 hours due to even stronger wind shear, and dissipate by 96 hours due to frontal interaction. Key Messages: 1. There is a danger of life-threatening storm surge along portions of the Florida Gulf Coast from Bonita Beach to Suwannee River, including Tampa Bay and Charlotte Harbor. Residents in this area should follow any advice given by local officials. 2. Hurricane-force winds are possible along portions of the west coast of Florida from Anna Maria Island to Yankeetown this evening and early Thursday. Tropical-storm-force winds are expected later today along portions of the Florida Gulf Coast from Bonita Beach to Suwanee River, and are possible early Thursday from Suwannee River to Aucilla River. Interests elsewhere along the Florida Gulf Coast should monitor the progress of Eta. 3. Heavy rainfall from Eta will continue across western Cuba and south Florida and spread northward across portions of west and north Florida today through Friday. Additional flash and urban flooding will be possible in South Florida today, especially across previously inundated areas, and across portions of west and central Florida today through Friday. FORECAST POSITIONS AND MAX WINDS INIT 11/1500Z 26.2N 83.7W 65 KT 75 MPH 12H 12/0000Z 27.5N 83.4W 60 KT 70 MPH 24H 12/1200Z 28.9N 82.7W 55 KT 65 MPH...NEAR FLORIDA COAST 36H 13/0000Z 30.5N 81.3W 30 KT 35 MPH...OVER WATER 48H 13/1200Z 31.6N 79.1W 30 KT 35 MPH 60H 14/0000Z 32.5N 76.9W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 14/1200Z 34.1N 73.0W 25 KT 30 MPH...POST-TROP/EXTRATROP 96H 15/1200Z...DISSIPATED $$ Forecaster Stewart |
