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Tropical Storm Eta Forecast Discussion Number 42
2020-11-10 21:52:49| National Hurricane Center (Atlantic)
Issued at 300 PM CST Tue Nov 10 2020 000 WTNT44 KNHC 102052 TCDAT4 Tropical Storm Eta Discussion Number 42 NWS National Hurricane Center Miami FL AL292020 300 PM CST Tue Nov 10 2020 Eta's convective structure has changed little since the previous advisory. A CDO-like feature with cloud tops colder than -70C has persisted, with some overshooting tops of -80C to -85C located east and southeast of the center. Recent passive microwave satellite data indicates that Eta is still sheared from the northwest, with an intermittent mid-level eye feature showing up. Satellite classifications have essentially remained unchanged, with SAB reporting 45-55 kt and TAFB reporting 55 kt. The initial intensity remains at 50 kt based on a blend of these satellite classifications and a UW-CIMSS SATCON estimates of 45-48 kt. The initial motion estimate is now northward, or 360/06 kt. The biggest surprise is the large eastward shift in all of the NHC model guidance, which was possibly due at least in part to all of the dropsondes that the NOAA G-IV jet aircraft dropped around Eta earlier this morning, All of the guidance is now in good agreement on a broad, deep-layer trough moving eastward across the south-central and southeastern United States, which will erode the subtropical ridge to the north of Eta that has been impeding Eta's poleward progress he past couple of days. This generally northward to northeastward steering pattern is expected to persist through the entire 120-h forecast period, with only slight shifts east or west of he current forecast track due to how vertically deep Eta remains when it reaches the northeastern Gulf of Mexico and Apalachee Bay in a few days. The current forecast track maintains Eta as at least a moderate tropical cyclone through the period, with only a slight bend back toward the northwest when the system is expected to interact with an approaching frontal system. The new NHC track forecast has been shifted about 150 n mi east of the previous advisory track at 96 and 120 hours, and further eastward shifts in the track may be required, closer to the consensus models TCVA/TVCN and NOAA-HCCA. Eta is forecast to remain in a low-to-moderate vertical wind shear environment and over SSTs of at least 27 deg C for the next 36 hours or so. Intermittent entrainment of dry mid-level air should prevent any rapid strengthening from occurring, but Eta could still become a hurricane between in 24 to 36 h before more significant shear begins to affect the cyclone. By day 3 and beyond, increasing northwesterly vertical wind shear combined with cooler SSTs should cause Eta to weaken. The new intensity forecast is essentially the same as the previous advisory, and is a little below the consensus models IVCN, HCCA, and FSSE, all of which make Eta a hurricane again by 36 hours. Due to the expected northwesterly shear after 36 hours, the 34-kt wind radii were expanded in the eastern semicircle, which is the side of the cyclone where most of the deep convection and associated stronger winds will be located. Given this and the eastward adjustment to the track forecast, a Tropical Storm Watch has been issued for portions of the Florida west coast, and a Tropical Storm Warning is in effect for the Dry Tortugas. Key Messages: 1. Tropical-storm-force winds are possible along portions of the Florida Gulf Coast by Thursday afternoon, and a Tropical Storm Watch has been issued. Interests elsewhere along the Florida Gulf Coast should monitor the progress of Eta, as additional watches may be needed tonight. 2. Heavy rainfall from Eta will continue across western Cuba and South Florida today and tonight, then potentially spread up the west coast of the Florida Peninsula Wednesday through Thursday. Additional flash and urban flooding will be possible in South Florida, especially across previously inundated areas, and eventually along portions of West Florida and the Sun Coast. Flash and urban flooding will also be possible for western Cuba. FORECAST POSITIONS AND MAX WINDS INIT 10/2100Z 23.2N 85.1W 50 KT 60 MPH 12H 11/0600Z 24.1N 84.9W 55 KT 65 MPH 24H 11/1800Z 25.6N 84.8W 60 KT 70 MPH 36H 12/0600Z 26.9N 84.5W 60 KT 70 MPH 48H 12/1800Z 27.9N 84.2W 55 KT 65 MPH 60H 13/0600Z 28.7N 84.0W 45 KT 50 MPH 72H 13/1800Z 29.1N 84.0W 40 KT 45 MPH 96H 14/1800Z 29.7N 84.6W 35 KT 40 MPH 120H 15/1800Z 30.7N 84.9W 30 KT 35 MPH...INLAND $$ Forecaster Stewart
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