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Highlight: Delta could become a category-4 major hurricane in the west-central Gulf of Mexico Thursday.

Fig. 1: Delta steadily becoming an impressive category-2 hurricane.

Discussion: At 5AM EDT Category-2 Hurricane Delta was located at 17.5N/81.3W or about 125 miles south of Grand Cayman. Top wind is near 100 mph and central pressure is 968 MB. Delta is moving west-northwest at 15 mph.

Delta is strengthening steadily due to presence over 85-86F water, light shear and excellent upper ventilation. The improving environment allowing Delta to intensify is in-part due to the heat release of weakening Gamma. The heat release strengthened the Florida subtropical ridge which is now pushing Delta more quickly west-northwestward. The warmer mid-to-upper atmosphere has also caused the upper shear near Delta to ease. The position of the jet stream and upper shear axis across the western Gulf of Mexico coupled with the anti-cyclone over Florida has provided Delta with excellent upper ventilation to allow Delta to fully express itself as a category-2 hurricane.

The outlook from NOAA/NHC is generally agreeable. There is one caveat. First, NOAA/NHC increases the intensity of Delta to a category-3 major hurricane shortly. Second, the NOAA/NHC track is toward the northern Yucatan Peninsula and a landfall is expected Wednesday morning. Some weakening should occur crossing the northern Yucatan Peninsula Wednesday.

Next, Delta re-emerges in the Gulf of Mexico northwest of the Yucatan Peninsula as a major hurricane late Wednesday. Tropical cyclone models indicate risk of a category-4 hurricane as Delta begins a northwest to north turn along 92W Thursday night. The forecast trend has been a little farther west with this turn. Forecast confidence is below average on the north turn. Usually, tropical cyclones gain strength when they turn north and given Delta’s location over very warm Gulf of Mexico water when the north turn begins a category-4 major hurricane is certainly possible.

Finally, the northern Gulf waters are cooler than normal. Delta should weaken to a category-2 hurricane on approach to the Louisiana coast Friday night. Delta fades to a depression in northeast Mississippi Saturday night and then accelerates northeastward into the Northeast Corridor early next week.

Right now, tropical storm force wind is expected by early Friday along the northwest/north Gulf of Mexico coast. Hurricane force wind arrives along the Louisiana coast Friday evening. Although Delta weakens on approach to land an immense storm surge already formed due to category-4 intensity offshore is likely to occur at land fall and to the east of landfall. An immense heavy rain storm with widespread flash flooding!

The caveat forecast is a farther west track and north turn toward the TX/LA state line at landfall based on the ECMWF (model) solution.

Fig. 2: NOAA/NHC 5-day forecast track with CIC commentary.