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Hurricane Delta Forecast Discussion Number 7
2020-10-06 10:57:45| National Hurricane Center (Atlantic)
Issued at 500 AM EDT Tue Oct 06 2020 000 WTNT41 KNHC 060857 TCDAT1 Hurricane Delta Discussion Number 7 NWS National Hurricane Center Miami FL AL262020 500 AM EDT Tue Oct 06 2020 Delta has maintained a very deep central dense overcast during the past several hours, with overshooting cloud-top temperatures to -90C, and perhaps hints of an eye trying to emerge. On the last pass through the center, the Air Force plane reported a 4-mb pressure fall in one hour to 968 mb, with believable SFMR values of 80-85 kt. Thus, the initial wind speed is set to 85 kt. The hurricane is in the midst of a very impressive rapid intensification episode, having strengthened over 50 kt during the past 24 hours. I honestly don't see much that will stop it until it reaches Yucatan, due to low vertical wind shear, high deep-layer moisture, and the very warm and deep waters of the northwestern Caribbean. This is also supported by SHIPS rapid intensification probabilities that are well above 50 percent for most categories. Thus, the intensity forecast is raised to 115 kt near Yucatan landfall, closest to the HWRF forecast model, which has been a good performer this year, especially after ingesting NOAA radar data. Some weakening is expected due to land interaction, but conditions look ripe for re-intensification over the Gulf of Mexico. Almost all the guidance is higher, now showing Delta reaching category 4 status in the 2-to-3 day time frame, and the new NHC intensity forecast reflects this likelihood. However, an increase in southwesterly shear and cooler shelf waters near the northern Gulf coast should promote weakening, and little change has been made to the intensity forecast near landfall. Delta is moving much faster this morning to the west-northwest, with the latest estimates at about 13 kt. A strengthening mid-level ridge across Florida should steer the hurricane to the west-northwest or northwest during the next couple of days. Likely because of the deterioration of Gamma, model guidance is showing less poleward motion before Yucatan, and the official track is shifted to the west for the first day or so. Over the Gulf of Mexico, Delta should slow down and turn northward ahead of a trough moving eastward across Texas in a few days. Model guidance has again shifted westward, like the last cycle, and the official forecast is trended in that direction. However, it remains slightly east of the model consensus, due to a notable westward bias in some of the guidance during this hurricane season. Users are reminded to not focus on the details of the track or intensity forecasts, as the average 4-day track error is around 150 miles and the average 4-day intensity error is close to 15 mph. Key Messages: 1. Extremely dangerous storm surge and hurricane conditions are expected within portions of the northern Yucatan Peninsula of Mexico beginning tonight, and a Hurricane Warning is in effect. 2. Heavy rainfall will affect portions of the Cayman Islands, western Cuba and the northern Yucatan Peninsula through midweek. This rainfall could lead to significant flash flooding and mudslides. The potential for heavy rain and flash flooding will increase across portions of the central Gulf Coast, Tennessee Valley, and southeastern United States as Delta moves inland later this week. 3. 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 a significant 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 06/0900Z 17.5N 81.3W 85 KT 100 MPH 12H 06/1800Z 18.7N 83.1W 100 KT 115 MPH 24H 07/0600Z 20.4N 85.8W 115 KT 130 MPH 36H 07/1800Z 21.8N 88.5W 105 KT 120 MPH 48H 08/0600Z 23.0N 90.4W 110 KT 125 MPH 60H 08/1800Z 24.2N 91.5W 115 KT 130 MPH 72H 09/0600Z 25.8N 92.0W 110 KT 125 MPH 96H 10/0600Z 29.8N 91.1W 85 KT 100 MPH...INLAND 120H 11/0600Z 34.0N 88.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Blake
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