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Tropical Storm Nora Discussion Number   9
NWS National Hurricane Center Miami FL       EP142021
400 PM CDT Fri Aug 27 2021
 
A 1656 UTC ASCAT-B scatterometer pass showed that Nora still does 
not have a tight inner core and instead has a 30-35 n mi region of 
winds 20 kt or less.  However, the pass did show maximum wind 
vectors a little over 50 kt, so the storm has been strengthening, 
and maximum winds are estimated to be 55 kt.  This is supported by 
Dvorak estimates of T3.5/55 kt from TAFB and SAB.

A slight adjustment was made to Nora's initial position based on 
the scatterometer data, but the storm is still moving toward the 
northwest (310/10 kt).  Nora is expected to maintain a motion 
toward the northwest or north-northwest as it heads in the 
direction of a weakness in the subtropical ridge which has 
developed over the U.S. southern Rockies and northern Mexico.  The 
track guidance envelope appears to have tightened up compared to 
the past few days, with nearly all the model trackers showing 
Nora's center passing offshore just west of Cabo Corrientes, 
Mexico, in about 24 hours and then continuing northwestward either 
across the waters of the Gulf of California or inland over Baja 
California Sur.  The new NHC track forecast has been nudged 
westward from this morning's forecast, but this is mainly due to 
the adjustment of the storm's initial position.  This track is very 
close to the HCCA and other consensus aids.

Nora's convective structure appears to be responding to a decrease 
in northeasterly shear, which is analyzed to be out of the 
northeast at 10-15 kt.  This shear is forecast to decrease to 10 kt 
or less by tonight.  Although Nora's broad structure could limit 
the storm's rate of strengthening, warm waters and upper-level 
divergence should allow it to become a hurricane over the next day 
or so.  After that time, Nora's intensity will be strongly 
modulated on whether its center moves over mainland Mexico or the 
Baja California peninsula.  If the center remains over water, as is 
shown in the official forecast, then environmental conditions 
appear conducive for Nora to remain as a hurricane for several more 
days, and the NHC forecast still closely follows the ECMWF-based 
SHIPS and LGEM models.  That said, there is still greater-than- 
normal uncertainty in the intensity forecast after 48 hours. 

 
Key Messages:
 
1. Nora is forecast to strengthen to a hurricane on Saturday while
passing nearby the coasts of the Mexican states of Jalisco and 
Nayarit, and hurricane watches and tropical storm warnings 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 coastal 
sections of the Mexican states of Oaxaca, Guerrero, Michoacan, 
Colima, and Jalisco, as well as Baja California Sur. 
Life-threatening flash flooding and mudslides are expected.
 
3. Nora is forecast to move over the Gulf of California as a
hurricane early next week, bringing a risk of wind and rain impacts
to portions of the Mexican states of Baja California Sur, Sinaloa,
and Sonora.  Given the above-average uncertainty in the forecast,
it is still too soon to determine the magnitude and location of
these potential impacts.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  27/2100Z 15.5N 104.9W   55 KT  65 MPH
 12H  28/0600Z 16.5N 105.6W   60 KT  70 MPH
 24H  28/1800Z 18.3N 106.2W   65 KT  75 MPH
 36H  29/0600Z 20.3N 107.0W   70 KT  80 MPH
 48H  29/1800Z 21.9N 107.8W   75 KT  85 MPH
 60H  30/0600Z 22.9N 108.6W   80 KT  90 MPH
 72H  30/1800Z 23.9N 109.4W   80 KT  90 MPH
 96H  31/1800Z 25.9N 110.9W   70 KT  80 MPH
120H  01/1800Z 28.4N 111.8W   55 KT  65 MPH
 
$$
Forecaster Berg
 
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