000
WTPZ42 KNHC 181448
TCDEP2

Tropical Storm Norma Discussion Number  17
NWS National Hurricane Center Miami FL       EP172017
900 AM MDT Mon Sep 18 2017

Norma has made a bit of a convective comeback this morning.  A large
convective band extends from the northwest to the southeast
quadrant, and another small burst has recently developed near the
center.  The estimated intensity remains 45 kt, based on the latest
TAFB Dvorak fix.  Despite this recent resurgence, there is still
unanimous support from the intensity guidance that Norma will
gradually weaken during the next couple of days.  This seems
reasonable since the cyclone is slowly passing over a sharp SST
gradient, and should cross the 26 C isotherm in about 24 hours.  No
change has been made to the intensity forecast, which is close to
just about all of the models.

Based on first-light visible imagery from GOES-16, Norma is now
moving generally toward the west.  As long as it maintains a medium
to deep circulation, Norma should continue to be steered westward
to west-northwestward by a mid-level ridge to the north.  An
approaching low to mid-level trough should cause the cyclone to
slowly turn northward after it becomes a remnant low.  The GFS and
GFS-based models have shifted a little toward the southwest, closer
to the ECMWF, especially for the first 36 hours of the forecast.
The NHC track forecast has therefore also been moved in that
direction, and splits the tracks of the ECMWF and HCCA.

FORECAST POSITIONS AND MAX WINDS

INIT  18/1500Z 21.4N 112.1W   45 KT  50 MPH
 12H  19/0000Z 21.5N 113.1W   40 KT  45 MPH
 24H  19/1200Z 21.7N 114.1W   35 KT  40 MPH
 36H  20/0000Z 22.1N 115.0W   30 KT  35 MPH
 48H  20/1200Z 22.8N 115.8W   30 KT  35 MPH...POST-TROP/REMNT LOW
 72H  21/1200Z 24.5N 116.0W   20 KT  25 MPH...POST-TROP/REMNT LOW
 96H  22/1200Z...DISSIPATED

$$
Forecaster Zelinsky