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Hurricane Nora Discussion Number  12
NWS National Hurricane Center Miami FL       EP142021
1000 AM CDT Sat Aug 28 2021
 
Nora continues to show signs of strengthening with the center 
embedded beneath a Central Dense Overcast, where clouds tops are
now as cold as -85 degrees Celsius.  Dvorak fixes from TAFB and SAB 
are T4.0/65 kt and T4.5/77 kt, and the most recent objective 
numbers are near 75 kt.  Nora's initial intensity is conservatively 
estimated to be 70 kt, but an Air Force Reserve Hurricane Hunter 
aircraft should help us verify the maximum winds later this 
afternoon.

The latest fixes indicate that Nora is moving west of due north, or 
350/10 kt.  A shortwave trough over the northern Rockies has created 
a weakness in the subtropical ridge over the southwestern U.S., 
which should allow Nora to continue moving northward or 
north-northwestward through tonight.  This motion will take Nora's 
center and hurricane-force winds very close to or over portions of 
Jalisco, Mexico, later today and this evening.  On Sunday, the track 
guidance suggests that Nora will make a turn back toward the 
northwest, bringing the center over the Gulf of California by Monday 
at a much slower forward speed.  The track guidance is in good 
agreement on this scenario, but the narrow width of the Gulf of 
California means that hazards away from the center could affect both 
the coast of mainland Mexico and the east coast of Baja California 
Sur.  Due to this uncertainty, new watches and warnings have been 
extended northward along both coasts.  The track guidance--and the 
NHC official forecast--suggest that Nora's center could move inland 
over Sonora, Mexico, in 4 to 5 days.

Assuming Nora's center remains over water, low shear and warm waters 
should allow for additional strengthening during the next 24-36 
hours.  After that time, possible land interaction, influences of 
nearby topography, and potential ingestion of dry air from the 
Mexican plateau could all conspire to cause at least gradual 
weakening while Nora begins to move into the Gulf of California.  
That said, there is still a lot of uncertainty in the intensity 
prediction, and Nora is forecast to remain as a hurricane through 
early Tuesday, a scenario supported by the ECMWF model.  One thing 
the models do agree on is that Nora's wind field should contract 
after it passes Cabo Corrientes and heads into the Gulf of 
California, and this is reflected in the NHC forecast.

Key Messages:
 
1. Nora is forecast strengthen through tonight as it moves near the
coasts of the Mexican states of Colima, Jalisco, Nayarit, and 
southern Sinaloa, and hurricane warnings are in effect for portions 
of that coastline.  Interests in these areas and points farther 
north 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 Mexican states of Guerrero, northward to southern 
Sonora, including  Baja California Sur.  This rain will likely 
result in life-threatening flash flooding and mudslides across these 
regions.  Rainfall from Nora may spread into the southwestern U.S. 
and central Rockies during the middle to latter portion of next 
week.
 
3. Nora is forecast to move over the Gulf of California as a
hurricane by Monday, bringing a risk of wind impacts to portions of 
the Mexican states of Baja California Sur, Sinaloa, and Sonora.  
Given the above-average uncertainty in the forecast intensity, 
confidence is not high enough to determine the magnitude and 
location of these potential impacts.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  28/1500Z 18.4N 105.4W   70 KT  80 MPH
 12H  29/0000Z 20.1N 105.8W   75 KT  85 MPH
 24H  29/1200Z 22.0N 106.5W   80 KT  90 MPH
 36H  30/0000Z 23.1N 107.3W   80 KT  90 MPH
 48H  30/1200Z 23.8N 108.0W   75 KT  85 MPH
 60H  31/0000Z 24.5N 108.9W   70 KT  80 MPH
 72H  31/1200Z 25.2N 109.6W   65 KT  75 MPH
 96H  01/1200Z 26.9N 110.5W   60 KT  70 MPH
120H  02/1200Z 29.3N 111.0W   40 KT  45 MPH...INLAND
 
$$
Forecaster Berg
 
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