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Tropical Storm Nora Discussion Number   5
NWS National Hurricane Center Miami FL       EP142021
400 PM CDT Thu Aug 26 2021
 
Scatterometer data from around midday showed that Nora has an
expansive circulation with tropical-storm-force winds nearly
reaching the coast of Mexico.  The data also showed a possible
center embedded within a larger area of light winds, but it is
possible that there's another similar feature farther west where
the instrument did not sample.  Nora's winds remain 35 kt based on
the ASCAT pass and the latest Dvorak fixes from TAFB and SAB, and
the center has been placed between the two dumb-belling vorticity 
maxima.
 
Even with the updated position, Nora is moving toward the 
west-northwest (285/8 kt), to the south of mid-level ridging over 
the southern United States.  A shortwave trough currently over the 
northern Rockies is expected to erode the ridge over the next 12-24 
hours, allowing Nora to turn toward the northwest and then 
north-northwest by the weekend.  Even with the GFS's solution of 
multiple swirls consolidating over the next day or so, the 12Z run 
shifted left and now shows Nora potentially moving inland over 
Mexico farther west than it had in previous runs.  A few of the 
other models--for example the HWRF and HMON--also bring the center 
inland as well, but the bulk of the interpolated model trackers 
continue to keep Nora just offshore but very near the coast of 
southwestern Mexico in about 48 hours.  Model spread remains larger 
than normal, but no significant changes were required from the 
previous NHC track forecast based on the latest guidance suite.  
After passing southwestern Mexico, Nora is expected to be over Baja 
California Sur or the Gulf of California on days 4 and 5.

Moderate northeasterly shear continues to affect Nora, but that 
shear is expected to decrease to a less-intrusive magnitude during 
the next 24 hours.  Along with warm sea surface temperatures of 
28-30 degrees Celsius, a moist mid-level environment, and 
upper-level divergence, Nora is expected to strengthen in the coming 
days.  The rate of intensification could, however, be tempered by 
Nora's large size and structure.  Assuming Nora does not move inland 
over southwestern Mexico, the storm is expected to become a 
hurricane on Saturday and then possibly continue strengthening up 
until the point it reaches the Baja California Peninsula.  Much of 
the intensity guidance is based on scenarios showing Nora moving 
inland, which is suppressing the intensity consensus aids.  
Therefore, the NHC intensity forecast is mostly based on the 
ECMWF-based SHIPS and LGEM models, since the parent ECMWF model does 
not show Nora moving inland.
 
Given Nora's larger wind field, tropical-storm-force winds are 
likely to reach the coast of Mexico earlier than expected.  
Therefore, the government of Mexico has issued a Tropical Storm 
Warning for a portion of the southwestern coast of Mexico.  The 
Hurricane Watch issued earlier today also remains in effect.

 
Key Messages:
 
1. Nora is forecast to strengthen to a hurricane by Saturday
while it is near the coast of southwestern Mexico, and a hurricane
watch and tropical storm warnings are in effect for portions of that
area.  Interests along the southwestern coast of Mexico should
closely monitor the progress of this system and updates to the
forecast.
 
2. Heavy rain associated with Nora is expected across coastal
sections of the Mexican states of Oaxaca, Guerrero, Michoacan,
Colima, and Jalisco.  As a result, life-threatening flash flooding
and mudslides could occur.
 
3. Nora is forecast to be near the southern portion of Baja
California Sur as a hurricane early next week, bringing a risk of
wind and rain impacts to that area.  Given the above average
uncertainty in the forecast, it is too soon to determine the
magnitude and location of these potential impacts.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  26/2100Z 13.4N 101.7W   35 KT  40 MPH
 12H  27/0600Z 14.1N 102.7W   40 KT  45 MPH
 24H  27/1800Z 15.3N 103.8W   50 KT  60 MPH
 36H  28/0600Z 16.8N 104.7W   55 KT  65 MPH
 48H  28/1800Z 18.6N 105.6W   65 KT  75 MPH
 60H  29/0600Z 20.3N 106.7W   70 KT  80 MPH
 72H  29/1800Z 21.6N 107.9W   75 KT  85 MPH
 96H  30/1800Z 23.6N 110.0W   75 KT  85 MPH...OVER BAJA CAL SUR
120H  31/1800Z 25.2N 111.7W   55 KT  65 MPH...OVER BAJA CAL SUR
 
$$
Forecaster Berg
 
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