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Tropical Storm Norma Discussion Number  14
NWS National Hurricane Center Miami FL       EP172017
300 PM MDT Sun Sep 17 2017

Deep convection has been holding steady in Norma this afternoon with
a large curved band in its northwestern semicircle. Two ASCAT
scatterometer passes at 1647Z and 1733Z showed peak winds of about
45 kt, which is consistent with the Dvorak classifications from SAB
and TAFB. Either Norma was a bit stronger than earlier estimated or
it has made a slight comeback.  But, regardless, the initial
intensity is 45 kt, up from 40 kt previously.

Norma should experience a slow decay due to the combination of dry
air, cooler SSTs, and a convergent upper-troposphere.  Transition to
a remnant low is expected in about three days and dissipation around
day 5.  The official intensity forecast is based upon the tightly
clustered members of the IVCN consensus technique and is slightly
higher than previous advisory due to the stronger initial intensity.

Norma is moving northwestward at about 5 kt, steered by a deep-layer
ridge over the Gulf of Mexico.  The tropical storm should turn
toward the west-northwest at about the same rate of forward speed
during the next couple of days.  By days 3 to 4, Norma's remnant low
should meander west of the southern tip of Baja California.  The
official track forecast is again shifted westward based upon a blend
of the TVCN consensus and the ECMWF model.

The ASCAT passes showed that the tropical-storm-force winds were
smaller in extent than previously indicated, though the cyclone has
a large - 40 nm - radius of maximum wind.  The official size
forecast is based upon the RVCN consensus approach.

FORECAST POSITIONS AND MAX WINDS

INIT  17/2100Z 21.1N 111.1W   45 KT  50 MPH
 12H  18/0600Z 21.5N 111.6W   45 KT  50 MPH
 24H  18/1800Z 21.8N 112.5W   40 KT  45 MPH
 36H  19/0600Z 22.1N 113.4W   35 KT  40 MPH
 48H  19/1800Z 22.3N 114.2W   30 KT  35 MPH
 72H  20/1800Z 22.8N 115.2W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  21/1800Z 23.6N 114.6W   20 KT  25 MPH...POST-TROP/REMNT LOW
120H  22/1800Z...DISSIPATED

$$
Forecaster Landsea

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