000
WTNT45 KNHC 210843
TCDAT5

Hurricane Maria Discussion Number  21
NWS National Hurricane Center Miami FL       AL152017
500 AM AST Thu Sep 21 2017

Although the large, 40 n mi diameter, eye of the hurricane is still
a little ragged-looking, it is gradually becoming better defined,
and a ring of cold cloud tops is intensifying around the eye.  The
current intensity estimate is 100 kt based on earlier Air Force
Hurricane Hunter data and recent Dvorak classifications from TAFB
and SAB.  Maria is likely to move over warm waters with moderate
southwesterly vertical shear for the next couple of days.  Maria's
well-developed upper-level outflow suggests that shear is probably
not having much influence over the hurricane at this time.  Although
the numerical guidance is not very aggressive about intensification,
based on the current trends of the cloud pattern, some strengthening
seems likely over the next day or so.  Later in the forecast period,
shear will probably cause gradual weakening.  The official intensity
forecast is a little above the latest model consensus.

Maria continues its northwestward motion, at about 315/8 kt.  The
hurricane is expected to turn north-northwestward and northward
around a subtropical ridge over the Atlantic for the next 2 to 3
days.  Late in the forecast period, a mid-level high over the
northeastern U.S. could slow the forward motion somewhat.  This
high is forecast by the global models to subsequently weaken
however, which should allow Maria to turn north-northeastward in
the flow on the northwestern edge of a subtropical ridge over the
west-central Atlantic.  The official track forecast lies between
the corrected consensus guidance and the latest ECMWF prediction.
This is quite similar to the previous NHC track.

KEY MESSAGES:

1. Heavy rainfall is expected to continue, and catastrophic flash
flooding is occurring in Puerto Rico, especially in areas of
mountainous terrain.  Everyone in Puerto Rico should continue to
follow advice from local officials to avoid these life-threatening
flooding conditions.

2. A Hurricane Warning is 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  21/0900Z 19.6N  68.4W  100 KT 115 MPH
 12H  21/1800Z 20.5N  69.3W  105 KT 120 MPH
 24H  22/0600Z 21.6N  70.4W  110 KT 125 MPH
 36H  22/1800Z 22.9N  71.1W  105 KT 120 MPH
 48H  23/0600Z 24.3N  71.7W  100 KT 115 MPH
 72H  24/0600Z 27.4N  72.3W  100 KT 115 MPH
 96H  25/0600Z 30.0N  72.0W   90 KT 105 MPH
120H  26/0600Z 32.5N  70.5W   80 KT  90 MPH

$$
Forecaster Pasch