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Hurricane NORA

Hurricane Nora Discussion Number  11
NWS National Hurricane Center Miami FL       EP142021
400 AM CDT Sat Aug 28 2021
The inner-core structure appears to be tightening up with Nora this 
morning. Deep convection with tops colder than -70 C has been 
blossoming and wrapping around the center, first around the eastern 
side, but more recently in all quadrants as a distinct warm spot 
denotes the center. Earlier, there was a helpful SSMIS microwave 
pass at 0143 UTC that showed a closed cyan ring on the 37 GHz 
channel, which is a signal often related to a formative low-level 
eyewall and is often a harbinger for significant intensification. 
An ASCAT-B pass at 0403 UTC also suggested the wind-radii were 
gradually contracting, and also that the center position is a little 
further east of the short-term track. The latest subjective Dvorak 
estimates at 0600 UTC from SAB and TAFB have both increased to 
T4.0/65 kt. These estimates, in addition to the recent structural 
improvements in IR satellite and microwave imagery, support raising 
the intensity to 65-kt for this advisory, making Nora a hurricane.
Nora continues to move a little more poleward this morning, with the 
latest motion estimate at 345 degrees at 9 kt. While the track 
forecast philosophy hasn't changed much over the last day, as a 
weakening mid-level ridge provides a weakness for Nora to escape 
north-northwestward, there has been a notable eastward shift in the 
track guidance. The deterministic ECMWF run, for instance, is now 
showing the hurricane brushing the shoreline of Mainland Mexico near 
Cabo Corrientes in 24 hours, and is now quite similar to the latest 
GFS forecast. The ECMWF ensembles have also shifted further east, 
with around half of the members explicitly showing landfall over 
mainland Mexico. The latest NHC track forecast has thus been shifted 
eastward, especially during the first 24-48 hours of the forecast, 
but I did not want to shift Nora's track as far east as the latest 
HCCA and TVCE consensus aids and further eastward adjustments may 
be necessary in subsequent forecasts. Afterwards, if Nora remains 
intact, the guidance shows the system bending back to the northwest 
and running up the gap of the Gulf of California between Baja 
California Sur and Mainland Mexico. 
Now that Nora appears to developing an inner core, at least steady 
intensification is expected in the short-term while the hurricane 
remains far enough offshore of mainland Mexico in a favorable 
dynamic and thermodynamic environment. After 12 hours, the intensity 
forecast becomes very tricky, due to just how much land interaction 
Nora will encounter as it brushes by Mexico. Once again, a lot of 
the reliable intensity guidance shows substantial land interaction 
and are sharply lower after 24 hours. Because the latest forecast 
track has been shifted further east, it increases the chance that
significant disruption of the storm may occur by the mountainous 
terrain located near the coast of Mexico in that location. The 
latest intensity forecast was lowered after 24 hours and held at 
70 kt through 96 hours due to this large uncertainty tied to 
possible land interaction. The latest forecast remains higher than 
the majority of the guidance, but is lower than the previous 
forecast. The wind radii have also been adjusted smaller after 24 
hours, as the global model guidance suggests that the TC wind field 
will shrink quite dramatically as the system tracks near mainland 
Tropical Storm and Hurricane Warnings have been extended further 
north along the mainland Mexico coastline given the eastward 
adjustments in the latest forecast track.
Key Messages:
1. Nora is forecast strengthen today as it approaches the coasts of 
the Mexican states of Jalisco and Nayarit, and hurricane warnings 
are in effect for portions of that coastline.  Interests in these 
areas and points further north 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 Guerrero, Michoacan, Colima, 
Jalisco and Nayarit, as well as Baja California Sur. 
Life-threatening flash flooding and mudslides are expected. As Nora 
lifts northwest, heavy rainfall will spread into the Mexican states 
of Sinaloa and Sonora as well as the southwestern U.S. during the 
middle to latter portion of next week.
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 
intensity, confidence is not high enough to determine the magnitude 
and location of these potential impacts.
INIT  28/0900Z 17.1N 105.2W   65 KT  75 MPH
 12H  28/1800Z 18.8N 105.5W   75 KT  85 MPH
 24H  29/0600Z 20.8N 106.1W   75 KT  85 MPH...NEAR MAINLAND MEXICO
 36H  29/1800Z 22.4N 107.0W   70 KT  80 MPH
 48H  30/0600Z 23.3N 107.8W   70 KT  80 MPH
 60H  30/1800Z 24.1N 108.6W   70 KT  80 MPH
 72H  31/0600Z 24.9N 109.4W   70 KT  80 MPH
 96H  01/0600Z 26.4N 110.6W   70 KT  80 MPH
120H  02/0600Z 28.7N 111.0W   45 KT  50 MPH...INLAND
Forecaster Papin/Beven