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Hurricane Norma Discussion Number   9
NWS National Hurricane Center Miami FL       EP172017
900 AM MDT Sat Sep 16 2017

Norma displayed a large convective band that wrapped most of the way
around the center overnight.  This band appears to be fragmenting
this morning, though a new rainband has developed closer to the
center.  The Dvorak Current Intensity numbers from both SAB and TAFB
remain 4.0 and thus the maximum winds are kept at 65 kt.  However,
the ADT and AMSU estimates are below hurricane force, so my initial
intensity may be somewhat high.  An Air Force reconnaissance mission
will be investigating Norma around 20Z, so we should have a more
accurate assessment of the intensity this afternoon.

While the vertical shear is currently low and should remain that way
for the next few days, the hurricane no longer has a well-defined
outflow channel to its south and the upper-level divergence appears
to be less conducive.  Additionally, a prominent tongue of dry air
seen in the total precipitable water imagery has wrapped around the
southern semicircle about 200 nm from the center.  Model guidance
suggests that the mid-level humidities should dry substantially
while Norma encounters increasingly cooler SSTs during the next few
days.  The official intensity forecast shows some slight
intensification followed by a faster decay compared with the
previous advisory.  This forecast is based a blend of the LGEM
statistical and HWRF/COAMPS dynamical guidance.

Norma continues to be nearly stationary, though a developing
deep-layer ridge over central Mexico/Gulf of Mexico should begin
moving the hurricane toward the north later today.  A motion toward
the north-northwest or northwest should then continue for about
three days.  By days 4 and 5, a substantially weaker Norma is
anticipated to meander while located just west of southern Baja
California.  The official track forecast is based upon the HFIP
Corrected Consensus Approach and is slightly east of the previous
advisory for the next two days and then about the same thereafter.

FORECAST POSITIONS AND MAX WINDS

INIT  16/1500Z 19.3N 110.1W   65 KT  75 MPH
 12H  17/0000Z 19.7N 110.0W   70 KT  80 MPH
 24H  17/1200Z 20.8N 110.4W   70 KT  80 MPH
 36H  18/0000Z 21.8N 110.8W   65 KT  75 MPH
 48H  18/1200Z 22.6N 111.3W   60 KT  70 MPH
 72H  19/1200Z 23.5N 112.5W   50 KT  60 MPH
 96H  20/1200Z 24.0N 113.0W   35 KT  40 MPH
120H  21/1200Z 24.5N 112.7W   25 KT  30 MPH...POST-TROP/REMNT LOW

$$
Forecaster Landsea

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