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Hurricane Maria Forecast Discussion (Text)


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Hurricane Maria Discussion Number  17
NWS National Hurricane Center Miami FL       AL152017
500 AM AST Wed Sep 20 2017

Radar observations from the San Juan WSR-88D and wind data from an
Air Force Reserve Unit Hurricane Hunter aircraft indicate that
Maria has just about completed an eyewall replacement.  Based on
the now-dominant outer eyewall, the eye diameter has increased from
10 n mi to 30 n mi.  This has likely contributed to some weakening,
and based on the latest observations from the Hurricane Hunters, the
intensity is set at 135 kt which is at the top of category 4 range.
Although there has been a slight reduction of intensity, Maria
remains an extremely dangerous hurricane.  Some weakening is
likely while the system crosses Puerto Rico.  Later in the forecast
period, less favorable upper-level winds should cause further
weakening, but Maria is likely to remain a large and powerful
hurricane for the next 5 days.  The official intensity forecast is
near or a little above the model consensus.

Maria continues to move between west-northwest and northwest at
about 9 kt.  The flow on the south side of a weak mid-level ridge
over the western Atlantic is expected to steer the hurricane on this
general heading over the next couple of days.  This track will bring
the center of Maria across Puerto Rico and just north of the eastern
Dominican Republic over the next day or so.  After that time a
break in the ridge, partially associated with Tropical Storm Jose,
should cause Maria to turn north-northwestward, then northward by
the end of the forecast period.  The track guidance remains tightly
clustered through 72 hours, giving fairly high confidence in the
track forecast through that time.  There is some increase in the
spread of the models at days 4 and 5, with the latest ECMWF
prediction near the western edge of the guidance envelope but with
all of the reliable models well offshore of the southeast U.S. at
the end of the period.  The official forecast is very close to the
latest FSU Superensemble track.

KEY MESSAGES:

1. Maria's core will make landfall over Puerto Rico within the
next couple of hours, bringing life-threatening wind, storm surge,
and rainfall impacts to the island.  Everyone in Puerto Rico should
follow advice from local officials to avoid life-threatening
flooding from storm surge and rainfall.

2. Wind speeds atop and on the windward sides of hills and mountains
and on high-rise buildings could be much stronger than the
near-surface winds indicated in this advisory.

3. A Hurricane Warning is also in effect for the Virgin Islands,
the northern coast of the Dominican Republic, the Turks and
Caicos Islands and the southeastern Bahamas, where Maria is expected
to bring dangerous wind, storm surge, and heavy rainfall.

FORECAST POSITIONS AND MAX WINDS

INIT  20/0900Z 17.9N  65.6W  135 KT 155 MPH
 12H  20/1800Z 18.6N  66.7W  125 KT 145 MPH...INLAND
 24H  21/0600Z 19.5N  68.2W  120 KT 140 MPH
 36H  21/1800Z 20.5N  69.4W  120 KT 140 MPH
 48H  22/0600Z 21.5N  70.5W  115 KT 130 MPH
 72H  23/0600Z 24.2N  72.0W  105 KT 120 MPH
 96H  24/0600Z 27.3N  73.0W  100 KT 115 MPH
120H  25/0600Z 30.5N  73.0W   85 KT 100 MPH

$$
Forecaster Pasch

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Page last modified: Wednesday, 20-Sep-2017 08:58:46 UTC