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Saturday, September 23

"Threat from Hurricane Maria to U.S. coast is increasing"

"Maria’s wind field has been gradually expanding ... Maria has been successfully fending off moderately strong wind shear of around 15 knots with the help of its well-established structure as well as very warm sea surface temperatures ..."

Maria’s Forecast Path Edging Closer to Outer Banks
By Bob Henson
September 23, 2017 - 1:06 PM EDT
Weather Underground

[See website for NASA infrared satellite image of Hurricane Maria at 12:27 pm EDT today and various charts showing Maria's projected path.]

Still a Category 3 storm on Saturday, Hurricane Maria was rolling northward away from the Bahamas on a path that could affect parts of the U.S. East Coast next week. Maria pummeled the Turks and Caicos Islands early Friday, its western eyewall passing over the capital city of Cockburn Town.

For the first time in several days, Maria poses no immediate threat to land. At 11 am EDT Saturday, Maria was located about 320 miles east of Nassau, The Bahamas, moving north-northwest at 8 mph. Maria’s top sustained winds had dropped to 115 mph, putting it at the low end of the Category 3 range.

Maria was not a classically symmetric hurricane on Friday night, but its appearance on satellite had become dramatically stronger by midday Saturday. Very strong thunderstorms (convection) were wrapping around Maria’s ragged, 35-mile-wide eye. As is typically the case for hurricanes moving poleward, Maria’s wind field has been gradually expanding. Hurricane-force winds now extend up to 60 miles from Maria’s center, with tropical-storm-force winds extending out some 200 miles to the northeast of the center.

Maria has been successfully fending off moderately strong wind shear of around 15 knots, with the help of its well-established structure as well as very warm sea surface temperatures (SSTs) of 29-30°C (84-86°F).

[...]


Intensity forecast for Maria

Maria will continue to traverse very warm water over the weekend, with oceanic heat content high enough to reduce the chance of cooler water being upwelled. Wind shear will drop to around 10 knots, which together with the warm water will help give Maria a bump-up in strength, perhaps to the high-end Cat 3 or low-end Cat 4 range. As time goes by, greater parts of the circulation will be passing over the wake of cooler water left by Jose. This should produce a gradual weakening trend, although Maria is still expected to be a Category 1 hurricane on Thursday. Wind shear should be around 10 – 15 knots for most of next week, which is moderately strong but not enough to destroy a well-organized hurricane like Maria. 

If Maria’s path continues trending westward, it will keep more of the circulation over the warm Gulf Stream waters and away from Jose’s wake, which would help Maria to maintain more of its intensity.

Regardless of Maria’s exact track, the hurricane is sure to bring a long period of increasing swells, dangerous surf, and rip currents to the Southeast U.S. coast, extending to the mid-Atlantic later next week. Significant beach erosion can be expected in and near the Outer Banks, given Maria’s strength and slow movement. There will also be an increasing chance of tropical-storm-force winds across parts of the U.S. East Coast by midweek (see Figure 4).

[...]

Plenty more in the report, which Weather Underground's Dr Jeff Masters contributed to.

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