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Tropical Depression Norma Discussion Number  20
NWS National Hurricane Center Miami FL       EP172017
300 AM MDT Tue Sep 19 2017

Conventional satellite imagery shows continued deterioration of
Norma's cloud pattern this evening.  All that remains of the
associated deep convection is fragments in the northeast quadrant.
A 0518 UTC ASCAT-B overpass indicated winds of only 30 kt in the
north and east portions of the cyclone.  Therefore, Norma is
downgraded to a depression for this advisory.  Norma is forecast to
further weaken while traversing decreasing oceanic temperatures.  An
intruding drier and more stable marine layer will also contribute to
Norma's demise.  The official forecast is just an update of the
previous one and shows Norma becoming a remnant low in 36 hours and
dissipating in 2 days.

The initial motion is estimated to be west-northwestward, or
280/5 kt.  Norma is expected to move west during the next 24 hours,
within the southwestern peripheral mid-tropospheric flow of a
subtropical ridge extending westward from northern Mexico over the
eastern Pacific.  Afterward, the cyclone is forecast to gradually
turn northwestward as a remnant low.  The NHC forecast is just a bit
south of the previous package due to the position adjustment based
on the scatterometer data, and is nudged toward the HFIP Corrected
Consensus model.

FORECAST POSITIONS AND MAX WINDS

INIT  19/0900Z 21.6N 113.9W   30 KT  35 MPH
 12H  19/1800Z 21.7N 114.7W   30 KT  35 MPH
 24H  20/0600Z 22.1N 115.6W   25 KT  30 MPH
 36H  20/1800Z 22.6N 116.1W   25 KT  30 MPH...POST-TROP/REMNT LOW
 48H  21/0600Z...DISSIPATED

$$
Forecaster Roberts

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