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Hurricane Maria Discussion Number  13
NWS National Hurricane Center Miami FL       AL152017
500 AM AST Tue Sep 19 2017

Interaction of the small core of Maria with the mountainous terrain
of Dominica caused only a slight diminution of the intensity of
the hurricane.  Data from the Air Force Hurricane Hunter aircraft
after the center passed the island indicate an intensity of about
135 kt, at the high end of category 4 strength.  Another Air Force
aircraft has begun investigating Maria, and preliminary data
from the plane suggest that the hurricane may have regained
category 5 intensity.  Maria will be moving through a low-shear
atmospheric environment and mainly over warm waters for the next
couple of days.  Some fluctuations in intensity are possible in the
early part of the forecast period due to eyewall replacement events.
Land influences could cause some weakening within the next 36
hours.  Later in the forecast period, a modest increase in vertical
shear could cause some weakening.  The official intensity forecast
is near or above the latest model consensus.

After smoothing out the trochoidal wobbles of Maria's eye, the
initial motion estimate remains west-northwestward, or 300/8 kt.
There is little change to the track forecast reasoning from the
previous advisory package.  A weak ridge situated over the western
Atlantic is expected to steer Maria west-northwestward through 48
hours, and on this track the center of the hurricane is forecast to
pass near or over the Virgin Islands and Puerto Rico on Wednesday.
After that time, the western portion of the ridge is forecast to
weaken, partially due to the influence of the large circulation of
Hurricane Jose.  This should cause Maria to turn northwestward, then
north-northwestward by day 4-5.  There is fairly good agreement
amongst the reliable guidance, and the new official track forecast
is very similar to the previous one.  This is generally near the
left side of the envelope of model tracks, and favors the ECMWF and
the corrected consensus predictions.


KEY MESSAGES:

1. Maria will affect portions of the northern Leeward Islands as an
extremely dangerous major hurricane during the next day or so.

2. Maria is likely to affect Puerto Rico and the U.S. and British
Virgin Islands as an extremely dangerous major hurricane tonight
and Wednesday.  Preparations to protect life and property should be
rushed to completion.

3. A life-threatening storm surge, accompanied by large and
destructive waves, is expected for the Leeward Islands, the U.S. and
British  Virgin Islands, and Puerto Rico.

4. Life-threatening flash floods and mudslides from heavy rainfall
are expected across the Leeward Islands, including Puerto Rico and
the U.S. and British Virgin Islands.


FORECAST POSITIONS AND MAX WINDS

INIT  19/0900Z 16.0N  62.3W  135 KT 155 MPH
 12H  19/1800Z 16.7N  63.4W  140 KT 160 MPH
 24H  20/0600Z 17.6N  64.8W  135 KT 155 MPH
 36H  20/1800Z 18.5N  66.3W  125 KT 145 MPH...NEAR PUERTO RICO
 48H  21/0600Z 19.3N  67.8W  125 KT 145 MPH
 72H  22/0600Z 21.2N  70.4W  120 KT 140 MPH
 96H  23/0600Z 23.7N  71.7W  110 KT 125 MPH
120H  24/0600Z 26.5N  72.5W  100 KT 115 MPH

$$
Forecaster Pasch

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