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Tropical Storm Eta Forecast Discussion Number 34
2020-11-08 21:57:52| National Hurricane Center (Atlantic)
Issued at 400 PM EST Sun Nov 08 2020 000 WTNT44 KNHC 082057 TCDAT4 Tropical Storm Eta Discussion Number 34 NWS National Hurricane Center Miami FL AL292020 400 PM EST Sun Nov 08 2020 Eta's appearance in radar and satellite imagery has changed little since the previous advisory and the last reconnaissance mission a few hours ago, with a ragged mid-level eye-like feature briefly wrapping up for less than an hour before quickly decaying. Average velocity values from the Miami, Florida, NOAA WSR-88D Doppler weather radar have occasionally been as high as 60 kt between 10,000-12,000 ft ASL to the north and northeast of the center. Therefore, the initial intensity is being maintained at 55 kt for this advisory. A NOAA reconnaissance aircraft is scheduled to investigate Eta around 0000Z this evening. The initial motion estimate is 325/12 kt. There is no significant change to the previous track forecast reasoning from the last 36 hours. Eta is now moving northwestward around the northeastern side of an upper-level low that has formed over the extreme northwestern Caribbean Sea near the Isle of Youth. The combined easterly flow between the upper-low and a deep-layer ridge located near the U.S. mid-Atlantic coast is expected to force Eta westward overnight and then turn the cyclone slowly southwestward in the 24-48 hour period, with the cyclone possibly stalling just west of the lower Florida Keys when steering currents collapse around 48 hours. By 72 hours and beyond, a broad mid-latitude trough is forecast to move from the U.S. west coast eastward over the central U.S. by 96 hours, and then over the eastern U.S. by 120 hours, which will erode the western portion of the ridge and act to gradually lift Eta northeastward toward northern Florida. The latest NHC model guidance has shifted slightly northward, possibly due to the NOAA G-IV jet aircraft synoptic track dropsonde observations from earlier this morning, and now shows the center of Eta making landfall in the middle or lower Florida Keys late tonight and early Monday. The new NHC official track forecast has been nudged northward close to the consensus models HCCA and TCVA. It should be noted that although the latest model guidance and track forecast shows landfall in the Florida Keys, the strongest winds are occurring, and are expected to occur, well to the north and east of the center. Satellite imagery indicates that a pronounced dry slot has wrapped into the eastern portion of Eta's circulation, with radar data suggesting that it has occasionally penetrated into the inner core region as well, eroding the thunderstorm activity in the southern portion of the aforementioned eye-like feature. However, with the vertical shear forecast to steadily decrease from the current 25 kt down to less than 10 kt by 24 hours while Eta is moving over 28.5 deg C SSTs, strengthening is expected late tonight during the convective maximum period and continuing into Monday, resulting in Eta intensifying into a hurricane during that time. Environmental conditions are expected to remain somewhat favorable for Eta to maintain hurricane status through 60 hours, followed by gradual weakening from 72-120 hours due to increasing southwesterly shear of 20-25 kt and entrainment of very dry mid-level air. The latest official intensity forecast is similar to the previous NHC advisory, and remains above the model guidance through 36 hours and is a little below the guidance thereafter. Based on ASCAT data and surface observations, the wind radii were expanded in the northwest and northeast quadrants. Key Messages: 1. Hurricane conditions are expected tonight and early Monday across portions of the Florida Keys, and are possible across portions of southern Florida. Tropical storm conditions will extend well away from Eta's center across the southern and central portions of the Florida peninsula. 2. There is a danger of life-threatening storm surge in portions of the Florida Keys. Life-threatening storm surge is possible along portions of the southern coast of the Florida peninsula. Residents in these areas should follow any advice given by local officials. 3. Heavy rainfall from Eta will continue across portions of Cuba, Jamaica, the Bahamas, and southern Florida and will spread north into central Florida. This rain may result in significant, life- threatening flash flooding and river flooding in Cuba. Significant flash and urban flooding are also possible for Jamaica, the Bahamas and southern Florida, along with potential minor river flooding in central Florida. FORECAST POSITIONS AND MAX WINDS INIT 08/2100Z 23.9N 79.5W 55 KT 65 MPH 12H 09/0600Z 24.7N 81.1W 60 KT 70 MPH 24H 09/1800Z 24.6N 83.4W 65 KT 75 MPH 36H 10/0600Z 23.6N 84.8W 65 KT 75 MPH 48H 10/1800Z 24.0N 85.1W 65 KT 75 MPH 60H 11/0600Z 25.1N 85.0W 65 KT 75 MPH 72H 11/1800Z 25.8N 84.8W 60 KT 70 MPH 96H 12/1800Z 27.1N 84.0W 55 KT 65 MPH 120H 13/1800Z 29.0N 82.8W 50 KT 60 MPH $$ Forecaster Stewart
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