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Tropical Storm Eta Forecast Discussion Number 33
2020-11-08 16:00:41| National Hurricane Center (Atlantic)
Issued at 1000 AM EST Sun Nov 08 2020 000 WTNT44 KNHC 081500 TCDAT4 Tropical Storm Eta Discussion Number 33 NWS National Hurricane Center Miami FL AL292020 1000 AM EST Sun Nov 08 2020 Eta remains a sheared tropical storm, although the low-level center has become embedded a little farther into the convective cloud mass. Cuban radar data from Camaguey indicate that Eta's center has moved back over water and is now located just offshore the east-central coast of Cuba. Radar imagery also indicates that a fairly impressive band of deep convection wraps more than half way around the center, especially in the western semicircle. Cirrus outflow has expanded in the southern semicircle, and indication that the shear may be decreasing somewhat. However, water vapor satellite imagery still shows a fair amount of dry mid-/upper-level air impinging on the cyclone from the southwest. The initial intensity of 55 kt is based on a report of 850-mb flight-level winds of 70 kt and reliable SFMR winds of 55-57 kt. The initial motion estimate is now 355/10 kt. Eta is interacting with a sharp mid-/upper-level, negatively tilted trough that extends east-southeastward across the Gulf of Mexico and into the northwestern Caribbean Sea. The eastern end of the trough is forecast to develop into a cutoff low alter today, which will act to turn Eta northwestward by this afternoon, and westward later tonight. The complex interaction between these two features is forecast to continue through 72 hours, resulting in the development of weak steering currents and Eta slowing down and possibly stalling near or just west of the Florida Keys by day 3. Thereafter, the global and regional models show widely varying solutions ranging from a motion toward the south or southwest (UKMET) toward Yucatan, to slow northward (ECMWF) or northeastward motion (GFS/HWRF) over the eastern Gulf of Mexico. The new NHC track forecast lies to the north, or to the right, of the 12Z interpolated models and consensus models (due to the interpolater possibly having some problems handling the sharp westward turn that Eta is forecast to make), and lies close to the previous advisory track and a blend of the operational 00Z ECMWF, and 06Z GFS and UKMET model tracks. Now that Eta's center is back over water, gradual re-strengthening is expected to begin later this afternoon. The global models are forecasting to vertical wind shear to steadily decrease across the center for the next next 48 hours as Eta moves north of the cutoff low and into a col small region region between the low and an upper-level trough moving eastward across northern Florida. The GFS- and ECMWF-based SHIPS intensity guidance indicate that the shear will decrease to less than 10 kt by 36 hours, but the shear will likely decrease sooner since SHIPS model uses winds that extend out 500 km (270 nmi) from the center, which are not always representative of the wind flow near the center. With favorable low-shear conditions and sea-surface temperatures warmer than 28 deg C, the only hindering factor appears to be proximity to dry mid-level air, which could get entrained into the inner core and inhibit development of deep convection in that part of the cyclone. For now, the new NHC intensity forecast remains similar to the previous advisory, which is above the model guidance up to 36 hours and a little below the guidance thereafter, and shows Eta at 65 kt or Category 1 hurricane intensity in the 24-72 hour period. However, it is certainly possibly that if dry air does not penetrate into Eta's inner core later today, then the cyclone could become a hurricane before it reaches the Florida Keys tonight. For this reason, a Hurricane Warning has been issued for portions of the Florida Keys. Key Messages: 1. Heavy rainfall from Eta will continue across portions of Cuba, Jamaica, the Bahamas, and southern Florida and spread north into central Florida. This rain may result in significant, life-threatening flash flooding and river flooding in Cuba. Flash and urban flooding will also be possible for Jamaica, the Bahamas and southern Florida, along with potential minor river flooding in central Florida. 2. Tropical storm conditions are expected to continue today in portions of Cuba and the northwestern Bahamas, where Tropical Storm Warnings are in effect. 3. Hurricane conditions are expected in portions of the Florida Keys by early Monday where a Hurricane Warning is now in effect. Damaging tropical-storm-force winds are expected to begin in the Florida Keys by this afternoon. Tropical Storm conditions are also expected and hurricane conditions are possible for portions of the southern Florida peninsula where a Tropical Storm Warning and Hurricane Watch are in effect. Elsewhere across portions of the east and west coasts of the Florida peninsula, the risk of tropical-storm-force winds will extend well away from Eta's center, and Tropical Storm Watches and Warnings are in effect. 4. A dangerous storm surge is expected in portions of the Florida Keys where a Storm Surge Warning is in effect. A Storm Surge Watch is also in effect for portions of the southern coast of the Florida peninsula. Residents in the Storm Surge Warning and Watch areas should follow any advice given by local officials. FORECAST POSITIONS AND MAX WINDS INIT 08/1500Z 22.5N 79.2W 55 KT 65 MPH 12H 09/0000Z 24.1N 79.8W 60 KT 70 MPH 24H 09/1200Z 24.5N 82.4W 65 KT 75 MPH 36H 10/0000Z 23.9N 84.1W 65 KT 75 MPH 48H 10/1200Z 23.8N 85.0W 65 KT 75 MPH 60H 11/0000Z 24.0N 85.5W 65 KT 75 MPH 72H 11/1200Z 24.9N 85.2W 65 KT 75 MPH 96H 12/1200Z 26.2N 84.5W 55 KT 65 MPH 120H 13/1200Z 26.9N 83.9W 50 KT 60 MPH $$ Forecaster Stewart
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