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Tropical Storm Norma Discussion Number  15
NWS National Hurricane Center Miami FL       EP172017
900 PM MDT Sun Sep 17 2017

The satellite appearance of Norma hasn't changed much since the
last advisory, with a large curved band in the northwestern
quadrant of the storm.  Dvorak estimates support keeping the wind
speed 45 kt for this advisory.  Norma is forecast to gradually
weaken starting Monday since it will be moving over cooler SSTs and
into a drier, more stable airmass.  No change was made to the
previous forecast as the guidance is in very good agreement on this
scenario.

Norma is now moving west-northwestward, turning slightly to the
left since the last advisory while it moves around a deep-layer
ridge over northwestern Mexico.  In about 3 days, the ridge weakens
somewhat, which should allow the cyclone, or its remnants, to turn
northwestward then northward.  Guidance has continued to shift
westward, and the official forecast is again moved in that
direction.  Because of the more offshore track, the chances of
seeing tropical-storm-force winds over land are quite low, and the
government of Mexico has discontinued the Tropical Storm Watch.

FORECAST POSITIONS AND MAX WINDS

INIT  18/0300Z 21.4N 111.4W   45 KT  50 MPH
 12H  18/1200Z 21.6N 112.1W   45 KT  50 MPH
 24H  19/0000Z 21.8N 113.0W   40 KT  45 MPH
 36H  19/1200Z 22.1N 113.8W   35 KT  40 MPH
 48H  20/0000Z 22.5N 114.5W   30 KT  35 MPH
 72H  21/0000Z 23.7N 115.5W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  22/0000Z 24.5N 115.0W   20 KT  25 MPH...POST-TROP/REMNT LOW
120H  23/0000Z...DISSIPATED

$$
Forecaster Blake

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