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Hurricane Maria Forecast Discussion (Text)


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Hurricane Maria Discussion Number  18
NWS National Hurricane Center Miami FL       AL152017
1100 AM AST Wed Sep 20 2017

The last radar image from the San Juan WSR-88D was received at 0950
UTC when Maria's eye was located only about 5 n mi off the
southeastern coast of Puerto Rico.  Subsequent 1-minute imagery from
the GOES-16 satellite, as well as surface observations, indicate
that the eye made landfall a little south of Yabucoa Harbor, Puerto
Rico, around 1015 UTC.  Now that the center is moving over the
mountainous terrain of the island, the eye has become cloud filled,
and the infrared satellite presentation has degraded. Without radar
velocity data, the initial intensity is incredibly uncertain, but my
best guess is 120 kt based on a typical inland decay rate.  Maria's
center is expected to move off the northern coast of Puerto Rico
soon, and an Air Force Reserve reconnaissance aircraft is scheduled
to intercept the center early this afternoon and provide a better
estimate of how much Maria has weakened.

The initial motion is northwestward, or 305/10 kt.  This
northwestward motion is forecast to continue for the next 48 hours,
followed by a turn toward the north by days 4 and 5, while Maria
moves between a mid-level high centered southeast of Bermuda and a
broad trough extending from Tropical Storm Jose southwestward into
the Gulf of Mexico.  The track guidance is tightly clustered this
cycle, and there were no significant changes made to the NHC
forecast track.

Once Maria moves off the coast of Puerto Rico, it will take some
time for the structure to reorganize over the warm waters of the
Atlantic Ocean.  However, the shear is expected to be less than 10
kt for the next 24-36 hours, and Maria has an opportunity to
restrengthen a bit over that time period.  After 36 hours, a gradual
increase in shear is likely to lead to a commensurate gradual
decrease in the hurricane's intensity through the end of the
forecast period.  Since the SHIPS model, in particular, responds to
the favorable conditions for intensification, the NHC intensity
forecast lies just above the intensity consensus through much of the
forecast period.

Since we don't have radar imagery from San Juan, and the eye has
become cloud filled in satellite imagery, the hourly position
updates are being discontinued.


KEY MESSAGES:

1. Maria's core is moving over Puerto Rico, with life-threatening
wind, storm surge, and rainfall impacts continuing over the
island. Everyone in Puerto Rico should follow advice from local
officials to avoid life-threatening flooding from storm surge and
rainfall. A Hurricane Warning remains in effect for the Virgin
Islands, but conditions should gradually improve there later today.

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 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  20/1500Z 18.4N  66.5W  120 KT 140 MPH...OVER PUERTO RICO
 12H  21/0000Z 19.2N  67.6W  120 KT 140 MPH
 24H  21/1200Z 20.2N  69.0W  125 KT 145 MPH
 36H  22/0000Z 21.2N  70.1W  125 KT 145 MPH
 48H  22/1200Z 22.4N  71.0W  120 KT 140 MPH
 72H  23/1200Z 25.3N  72.4W  110 KT 125 MPH
 96H  24/1200Z 28.5N  73.0W  100 KT 115 MPH
120H  25/1200Z 31.5N  73.0W   90 KT 105 MPH

$$
Forecaster Berg

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Page last modified: Wednesday, 20-Sep-2017 14:40:59 UTC