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Hurricane Nora Discussion Number  16
NWS National Hurricane Center Miami FL       EP142021
900 AM MDT Sun Aug 29 2021
 
Nora has a healthy satellite appearance this morning. The deep
convection near and to the west of the estimated center is
maintaining a fairly large central dense overcast with very cold
infrared cloud tops. Recent ATMS and SSMIS microwave data indicate
Nora still has a pronounced mid-level eye structure, with the center
very near the coast of extreme southern Sinaloa. A blend of the
UW-CIMSS objective ADT estimate and 12 UTC subjective Dvorak
classifications from TAFB and SAB support holding the initial
intensity at 65 kt for this advisory.
 
The estimated initial motion of Nora is north-northwestward or 345/9
kt, although this is somewhat uncertain due to the lack of in-situ
observations. A mid-level ridge should continue to steer the
tropical cyclone generally north-northwestward to northwestward
during the next few days. This motion will bring the center over the
eastern Gulf of California and very near or over the coast of
west-central Mexico. The official NHC track forecast is adjusted
just slightly to the right of the previous one, in line with the
latest track guidance.
 
Nora's intensity forecast remains highly dependent on whether the
center moves inland over mainland Mexico or along the Gulf of
California, parallel to the west-central coast of Mexico. Given the
slight eastward track adjustment, the official NHC intensity 
forecast shows gradual weakening over the next few days due to at
least intermittent land interaction as Nora skirts the coast. This
is consistent with the general intensity guidance consensus, which
no longer supports strengthening given Nora's proximity to land. Due
to the complex geography of western Mexico, even a slight eastward
deviation from the forecast track would result in more rapid
weakening as Nora moves further inland. Conversely, a more
northwestward motion over the warm Gulf of California waters could
allow Nora to remain a stronger tropical storm early this week. As
previously mentioned, confidence in the intensity forecast is lower
than normal.

Key Messages:
 
1. Nora is forecast to be at or near hurricane strength while it
moves near the coasts of Nayarit and Sinaloa today and into Monday,
and hurricane warnings or watches are in effect for portions of that
coastline.  Interests in these areas should closely monitor the
progress of Nora and subsequent updates to the forecast.
 
2. Heavy rain associated with Nora is expected across the west coast
of Mexico from the states of Colima northward to southern Sonora.
This rain will likely result in life-threatening flash flooding and
mudslides across these regions.  Rainfall from Nora is likely to
spread into the southwestern U.S. and central Rockies during the
middle to latter portion of the week, bringing the potential for
flash flooding to the region.
 
3. Nora is forecast to move north-northwestward to northwestward
near or over the Gulf of California Tuesday and Wednesday, bringing
a risk of wind impacts to portions of the Mexican states of Baja
California Sur, northern Sinaloa, and Sonora.  Given the
above-average uncertainty in the intensity forecast, confidence is
not high enough to determine the magnitude and location of these
potential impacts.

FORECAST POSITIONS AND MAX WINDS
 
INIT  29/1500Z 23.3N 106.4W   65 KT  75 MPH
 12H  30/0000Z 23.8N 106.9W   60 KT  70 MPH...NEAR THE COAST
 24H  30/1200Z 24.3N 107.5W   55 KT  65 MPH...NEAR THE COAST
 36H  31/0000Z 24.9N 108.2W   55 KT  65 MPH...NEAR THE COAST
 48H  31/1200Z 25.6N 109.0W   50 KT  60 MPH...NEAR THE COAST
 60H  01/0000Z 26.5N 109.6W   50 KT  60 MPH...NEAR THE COAST
 72H  01/1200Z 27.5N 110.0W   40 KT  45 MPH...INLAND
 96H  02/1200Z 29.5N 111.2W   30 KT  35 MPH...INLAND
120H  03/1200Z...DISSIPATED
 
$$
Forecaster Reinhart
 
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