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Hurricane Maria Discussion Number  25
NWS National Hurricane Center Miami FL       AL152017
500 AM EDT Fri Sep 22 2017

Reports from an Air Force Reserve Hurricane Hunter aircraft near
0500 UTC indicated that the central pressure of Maria had risen to
959 mb, accompanied by flight-level winds and SFMR surface wind
estimates that supported an intensity near 110 kt.  Since that time,
the cloud tops in the eyewall have cooled, but the eye has become
less distinct in conventional satellite imagery.  The initial
intensity is held at 110 kt pending the arrival of the next plane
near 1200 UTC, but it is possible this is a little generous.  Maria
is starting to be affected by 15-20 kt of southwesterly vertical
wind shear, with the first sign of this being a decrease in
convective banding in the western semicircle.

The large-scale models forecast some shear to persist through the
forecast period, and as a result the intensity guidance predicts a
gradual weakening.  In addition, after 48 h the forecast track takes
the center of Maria over waters that were cooled significantly by
the passage of former Hurricane Jose.  Based on these factors, the
new intensity forecast calls for a slow weakening during the first
48 h similar to the previous forecast, then calls for more weakening
than previously forecast as the cyclone reaches the colder waters.

The initial motion is 315/6.  Maria will be moving between the
subtropical ridge to the east and a broad trough over the
southeastern United States and the adjacent Atlantic waters during
the next several days.  This pattern should cause the hurricane to
turn north-northwestward and then northward during the next 72 h.
The track guidance is tightly clustered during this part of the
forecast, and the new forecast track is an update of the previous
track.  After 72 h, the guidance becomes a little more divergent.
The Canadian and ECMWF models are on the left side of the envelope
showing a generally northward motion, while the GFS is on the right
side showing a north-northeastward motion.  This part of the
forecast track is nudged just a little to the left of the old
forecast and the consensus models to account for the ECMWF/Canadian
forecasts.


KEY MESSAGES:

1. Flash flood warnings continue in portions of Puerto Rico due
to persistent heavy rainfall from Maria's trailing rainbands.
Everyone in Puerto Rico should continue to follow advice from local
officials to avoid these life-threatening flooding conditions.

2. Swells from Maria are expected to begin reaching the coast of
the southeastern United States today.  These swells are likely to
cause dangerous surf and life-threatening rip currents along the
coast for the next several days, even with Maria forecast to remain
well offshore over the western Atlantic Ocean.


FORECAST POSITIONS AND MAX WINDS

INIT  22/0900Z 21.6N  70.6W  110 KT 125 MPH
 12H  22/1800Z 22.6N  71.1W  105 KT 120 MPH
 24H  23/0600Z 24.2N  71.7W  105 KT 120 MPH
 36H  23/1800Z 25.9N  72.2W  100 KT 115 MPH
 48H  24/0600Z 27.4N  72.3W   95 KT 110 MPH
 72H  25/0600Z 29.5N  72.0W   85 KT 100 MPH
 96H  26/0600Z 31.5N  71.0W   75 KT  85 MPH
120H  27/0600Z 33.5N  70.5W   65 KT  75 MPH

$$
Forecaster Beven

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