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Hurricane Maria Discussion Number 30
NWS National Hurricane Center Miami FL AL152017
1100 AM EDT Sat Sep 23 2017

Data from this morning's Air Force Hurricane Hunter flight suggests that Maria's maximum winds may be decreasing a bit--a trend which was noted in the previous advisory package. The plane measured a maximum 700-mb flight level wind of 102 kt and SFMR winds as high as 85 kt, neither of which supports an intensity of 105 kt. The initial intensity is therefore conservatively lowered to 100 kt.

Maria is now located between a mid-level high centered near Bermuda and a cut-off low over the northeastern Gulf of Mexico, both of which are steering the hurricane north-northwestward, or 340/7 kt. Maria should turn northward between these two features beginning in about 12 hours, but its forward motion is likely to be impeded in a couple of days by ridging developing over the northeastern United States. As a result, the hurricane's forward speed will decrease to 5 kt or less from day 2 and beyond. The track guidance has continued to trend toward slower and farther westward solutions, and as we had foreshadowed in previous discussions, an additional westward adjustment to the new NHC track forecast was required on this cycle. The updated forecast is between the GFS and ECMWF solutions and close to the consensus aids and HCCA through day 3. After that time, the new forecast is slower and southwest of the consensus aids, but still not quite as far west as the GFS, ECMWF, and UKMET solutions.

Based on various analyses, the southwesterly shear over Maria has decreased since yesterday, and it appears to remain relatively low for the next 2 days or so. Maria will be moving over very warm waters during that time, although the depth of the warm pool does decrease, and Maria's slower motion could increase the effects of colder upwelled water. After 48 hours, vertical shear is forecast to increase again, and a critical part of the intensity forecast will be whether or not Maria moves over the cold wake left behind by Jose. The recent westward shifts in the forecast track make it more likely that Maria would avoid the cold wake and move over the warmer Gulf Stream waters. Since the environment may not be as hostile as the dynamical models are assuming, the NHC intensity forecast is a little above the intensity consensus for much of the forecast period.

To increase the sampling of the environment upstream and north of Maria, supplemental 0600/1800 UTC upper-air soundings are scheduled to begin from the eastern and southeastern United States this afternoon. In addition, NOAA G-IV missions are scheduled to begin sampling the environment around Maria on Sunday.



KEY MESSAGES:

1. Maria's forecast track has shifted closer to the U.S. east coast, and it is becoming increasingly likely that some direct impacts will occur along portions of the coast next week. Interests along the coast of the Carolinas and the Mid-Atlantic should monitor the progress of Maria, as tropical storm or hurricane watches may be needed for part of this area on Sunday.

2. Swells from Maria are increasing along the coast of the southeastern United States and are expected to reach the Mid-Atlantic coast tonight and on Sunday. These swells will likely cause dangerous surf and rip currents at the beach through much of next week. For more information, please monitor information from your local National Weather Service office at www.weather.gov.

FORECAST POSITIONS AND MAX WINDS

INIT 23/1500Z 25.4N 72.3W 100 KT 115 MPH 12H 24/0000Z 26.7N 72.6W 105 KT 120 MPH 24H 24/1200Z 28.3N 73.0W 105 KT 120 MPH 36H 25/0000Z 29.5N 73.3W 100 KT 115 MPH 48H 25/1200Z 30.5N 73.4W 95 KT 110 MPH 72H 26/1200Z 32.1N 73.4W 85 KT 100 MPH 96H 27/1200Z 33.5N 73.5W 75 KT 85 MPH 120H 28/1200Z 34.5N 72.5W 65 KT 75 MPH

$$ Forecaster Berg

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