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Tropical Storm Delta Forecast Discussion Number 5
2020-10-05 22:56:07| National Hurricane Center (Atlantic)
Issued at 500 PM EDT Mon Oct 05 2020 000 WTNT41 KNHC 052055 TCDAT1 Tropical Storm Delta Discussion Number 5 NWS National Hurricane Center Miami FL AL262020 500 PM EDT Mon Oct 05 2020 Visible satellite imagery shows that the convective banding of Delta has continued to quickly improve since this morning. The primary convective band now wraps entirely around the center, with what appears to be a banding-type eye feature occasionally noted. There are some dry slots between the convective bands but those appear to be gradually filling in. A NOAA Hurricane Hunter aircraft currently collecting data in the storm environment found peak SFMR winds of 55 kt during its first pass through the center from northwest to southeast. The plane also reported a minimum pressure of 983 mb, much lower than previously estimated. The aircraft also observed an 18 nmi-wide-eye that was open to the west-northwest. Assuming that there are stronger winds yet to be sampled in the northeastern quadrant, the initial intensity has been raised to 60 kt. Delta is situated within a very conducive environment for strengthening. The storm will be moving over SSTs of 29-30 degrees Celsius and the vertical wind shear is forecast to remain 5 kt or less while Delta traverses the northwestern Caribbean. These conditions are expected to allow for rapid strengthening over the next 24 to 36 hours. The SHIPS Rapid Intensification Index gives a better than 50 percent chance of a 35-40 kt increase in wind speed over the next 24 hours. The NHC intensity forecast follow suit by calling for rapid intensification over the next day or so, and Delta is forecast to be a major hurricane when is passes near or over the northeastern portion of the Yucatan peninsula. Once the storm reaches the central Gulf of Mexico in 60-72 hours, increasing southwestern vertical wind shear and cooler shelf waters over the northern Gulf are likely to result in some reduction in wind speed as the system nears the northern Gulf coast. Although there is still significant uncertainty regarding Delta's intensity when it nears the northern Gulf coast, it is becoming increasing likely that the system will pose a significant wind and storm surge threat to a portion of that area. The center has jogged southward again this afternoon, which appears to be primarily due to the system organizing rather than a true storm motion. The initial motion estimate remains an uncertain 275/7 kt. Delta should begin moving west-northwestward this evening, and a west-northwestward to northwestward motion around the southwestern portion of a deep-layer ridge to its northeast is expected over the next couple of days. The more southward initial position and more ridging over the eastern Gulf of Mexico has resulted in a significant westward shift in the track envelope through the first 60-72 hours. The NHC has been adjusted in that direction, and this has required the issuance of a Hurricane Warning for the northeastern portion of the Yucatan peninsula of Mexico. After 72 hours, a mid- to upper-level trough is forecast to develop over Texas which should cause Delta to turn northward and then north-northeastward toward the northern Gulf Coast. Although the track forecast has not changed much during the latter portion of the period, there is more cross-track spread in the model guidance than before, which has increased the uncertainty regarding potential landfall and the timing of Delta's approach to the northern Gulf Coast. Key Messages: 1. Dangerous storm surge and hurricane conditions are expected within portions of the northern Yucatan Peninsula of Mexico and are possible in extreme western Cuba beginning Tuesday night, and a Hurricane Warning is in effect. 2. Heavy rainfall will affect portions of Jamaica, the Cayman Islands, western Cuba and the northern Yucatan Peninsula during the next few days. This rainfall could lead to significant flash flooding and mudslides. 3. Tropical storm conditions are expected in portions of the Cayman Islands beginning tonight or early Tuesday, and a Tropical Storm Warning is in effect. 4. Delta is forecast to approach the northern Gulf Coast late this week as a hurricane. While there is large uncertainty in the track and intensity forecasts, there is an increasing risk of dangerous storm surge, wind, and rainfall hazards along the coast from Louisiana to the western Florida Panhandle beginning Thursday night or Friday. Residents in these areas should ensure they have their hurricane plan in place and monitor updates to the forecast of Delta. FORECAST POSITIONS AND MAX WINDS INIT 05/2100Z 16.2N 79.4W 60 KT 70 MPH 12H 06/0600Z 17.1N 80.9W 75 KT 85 MPH 24H 06/1800Z 19.0N 83.5W 95 KT 110 MPH 36H 07/0600Z 21.0N 86.2W 105 KT 120 MPH 48H 07/1800Z 22.6N 88.7W 105 KT 120 MPH 60H 08/0600Z 23.7N 90.6W 105 KT 120 MPH 72H 08/1800Z 24.8N 91.5W 95 KT 110 MPH 96H 09/1800Z 28.5N 91.5W 85 KT 100 MPH 120H 10/1800Z 33.0N 89.0W 40 KT 45 MPH...INLAND $$ Forecaster Brown
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