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| #1020235 (Received by flhurricane at: 5:03 AM 07.Oct.2020) TCDAT1 Hurricane Delta Discussion Number 11 NWS National Hurricane Center Miami FL AL262020 400 AM CDT Wed Oct 07 2020 Satellite images show very deep convection associated with Delta, with extremely cold cloud-top temperatures to -97C noted southwest of the center overnight. However, this structure has not resulted in a stronger cyclone, and the full NOAA Hurricane Hunter aircraft mission actually indicated that Delta has significantly weakened since earlier today. The maximum flight-level winds were 98 kt, with SFMR values near 90 kt. Early in the mission, the flight director indicated that the eyewall had dissipated, but on the last fix, she noted that the eyewall had re-formed. Recent Cuban radar data also indicate that at least a partial eyewall is present, so the initial wind speed is generously kept at 100 kt. Delta should begin to re-intensify late today as it moves into an area of fairly warm and deep waters, with fairly light shear. The regional hurricane models all show Delta attaining category 4 status in 36-48 hours, and so does the NHC forecast. As Delta approaches the Louisiana coast, lower oceanic heat content and an increase in shear is likely to cause some weakening before landfall. The NHC intensity forecast is very similar to the previous one, and leans on the stronger regional hurricane models. I should also note that all of the guidance show Delta becoming considerably larger than it is now by the time it reaches the northern Gulf coast, so even if weakening occurs there, the hurricane will likely bring a sizable area of hazardous conditions to the coast. Fixes from the aircraft and Cuban radar data indicate the storm is moving faster to the northwest or 305/15 kt. Delta should make landfall during the next few hours between Cozumel and Cancun, and move quickly across northeastern Yucatan before emerging in the southern Gulf of Mexico early this afternoon. The hurricane is then expected to move to the northwest or west-northwest around the southwestern and western portion of the subtropical ridge for about the next 36 hours. Thereafter, Delta will likely turn northward by early Friday between the ridge and a mid-level trough over Texas. While there is broad agreement on the synoptic pattern, subtle differences in the subtropical ridge and the depth of the cyclone are causing some challenges. The ECMWF and its ensembles, for instance, are showing a stronger ridge and a weaker storm, which results in a slower track toward southwestern Louisiana. The GFS and UKMET, on the other hand, are showing a deeper cyclone, which would feel stronger upper-level winds, and move Delta faster to the coast. Given the expectation of a powerful cyclone at landfall, the NHC forecast is shaded toward the latter two models, which results in a slightly faster and westward-shifted forecast from before, not too different from the model consensus. Key Messages: 1. Life-threatening storm surge and dangerous winds are expected within portions of the northern Yucatan Peninsula of Mexico during the next few hours. Now is the time to be in your storm shelter. 2. Heavy rainfall will affect portions of western Cuba and the northern Yucatan Peninsula through early Thursday. This rainfall could lead to significant flash flooding and mudslides. Flash, urban, and small stream flooding, along with minor river flooding is likely Friday through Saturday across portions of the central Gulf Coast north into portions of the Lower Mississippi Valley. The heavy rainfall will spread northeastward into the Tennessee Valley and interior southeastern United States this weekend into early next week. 3. There is an increasing likelihood of life-threatening storm surge and dangerous hurricane-force winds, especially along the coasts of Louisiana and Mississippi, beginning on Friday. Residents in these areas should ensure they have their hurricane plan in place and follow advice given by local officials. Storm surge and hurricane watches will likely be issued for portions of the northern Gulf Coast later today. FORECAST POSITIONS AND MAX WINDS INIT 07/0900Z 20.6N 86.4W 100 KT 115 MPH 12H 07/1800Z 21.9N 88.4W 90 KT 105 MPH 24H 08/0600Z 23.3N 90.8W 95 KT 110 MPH 36H 08/1800Z 24.9N 92.4W 105 KT 120 MPH 48H 09/0600Z 26.7N 92.9W 115 KT 130 MPH 60H 09/1800Z 29.2N 92.3W 100 KT 115 MPH 72H 10/0600Z 32.0N 91.0W 50 KT 60 MPH...INLAND 96H 11/0600Z 35.5N 87.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 12/0600Z 38.5N 82.0W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Blake |