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Tropical Storm Delta Forecast Discussion Number 4
2020-10-05 16:53:31| National Hurricane Center (Atlantic)
Issued at 1100 AM EDT Mon Oct 05 2020 000 WTNT41 KNHC 051453 TCDAT1 Tropical Storm Delta Discussion Number 4 NWS National Hurricane Center Miami FL AL262020 1100 AM EDT Mon Oct 05 2020 The convective structure of Delta has continued to improve this morning. Earlier microwave data and early-light visible satellite imagery showed that the center of the tropical cyclone re-formed farther south within the area of deep convection. Since that time, banding has continued to increase around the southern and eastern portion of the circulation, and a small CDO-like feature has formed. The intensity has been set at 40 kt, which is a blend of the subjective Dvorak estimate from TAFB and objective satellite intensity estimates from UW/CIMSS. A NOAA Hurricane Hunter aircraft is scheduled to investigate the tropical storm this afternoon, which should provide a better assessment of the cyclone's intensity, structure, and wind field. With the earlier center re-formation, the initial motion estimate is a somewhat uncertain 280/6 kt. Delta is expected to resume a west-northwestward motion later today. A northwestward heading around the southwestern portion of a deep-layer ridge should begin tonight or Tuesday, and that general motion with some increase in forward speed is expected to continue through 60-72 hours. After that time, a broad mid- to upper-level trough is forecast to develop over the south-central United States, which should weaken the western portion of the ridge and cause Delta to turn northward toward the northern Gulf Coast. After day 4, Delta should begin to accelerate north-northeastward or northeastward ahead of the aforementioned trough. The new NHC track forecast has been adjusted to the south and west of the previous advisory during the first couple of days, primarily due to the recent center re-formation and more southward initial position. After that time, the NHC track is not much different than the previous forecast and lies near the center of the tightly clustered dynamical model envelope. Delta is forecast to traverse very warm waters over the northwestern Caribbean Sea and be in a very low vertical wind shear environment during the next couple of days. These conditions should allow for significant strengthening during that time, and the NHC intensity forecast is at or above the various intensity aids. It is somewhat surprising that the intensity aids were generally a little lower this cycle, but the expected low shear and SHIPS rapid intensification index support the higher than climatological rate of intensification. After 72 hours, increasing southwesterly shear and the cooler shelf waters over the northern Gulf are likely to induce some weakening later in the period. The updated NHC intensity forecast calls for a faster rate of intensification over the next 48-60 hours, but is similar to the previous advisory thereafter. Key Messages: 1. Tropical storm conditions are expected in the Cayman Islands beginning late today or tonight, and a Tropical Storm Warning is in effect. 2. Dangerous storm surge and hurricane conditions are expected in portions of western Cuba by Tuesday afternoon, and a Hurricane Warning is in effect. 3. Heavy rainfall will affect portions of Jamaica, the Cayman Islands, and western Cuba during the next few days. This rainfall could lead to significant flash flooding and mudslides. 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 at these time ranges, there is an increasing risk of dangerous storm surge, wind, and rainfall hazards along the coast from Louisiana to the western Florida Panhandle. Residents in these areas should monitor the progress of Delta and check for updates to the forecast during the week. FORECAST POSITIONS AND MAX WINDS INIT 05/1500Z 16.4N 78.6W 40 KT 45 MPH 12H 06/0000Z 17.1N 79.6W 50 KT 60 MPH 24H 06/1200Z 18.7N 81.7W 60 KT 70 MPH 36H 07/0000Z 20.8N 84.3W 75 KT 85 MPH 48H 07/1200Z 22.8N 86.8W 85 KT 100 MPH 60H 08/0000Z 24.6N 89.1W 90 KT 105 MPH 72H 08/1200Z 26.0N 90.7W 90 KT 105 MPH 96H 09/1200Z 28.8N 91.1W 85 KT 100 MPH 120H 10/1200Z 33.1N 88.2W 40 KT 45 MPH...INLAND $$ Forecaster Brown
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