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Tropical Storm Norma Discussion Number  19
NWS National Hurricane Center Miami FL       EP172023
300 AM MDT Sun Oct 22 2023
 
Convective bursts have redeveloped over the northeastern potion of
Norma's circulation, but the center remains exposed due to strong
southwesterly shear.  Overnight shortwave infrared satellite
imagery and a couple of fortuitous ASCAT overpass showed that
the center of Norma exited the east coast of the Baja California
peninsula a little farther north than previously estimated.
Therefore, the initial position for this advisory has been adjusted
northward accordingly.  Peak winds in the scatterometer passes were
around 45 kt, but owing to that instrument's typical low bias the
initial intensity has only been lowered to 50 kt.
 
Since most of the Norma's circulation is forecast to remain over
the Gulf of California waters today, little change in strength is
expected in the short term. Once Norma moves inland over mainland
Mexico, rapid weakening and dissipation over the high terrain is
expected.
 
The initial motion estimate is north-northeastward or 25 degrees at 
6 kt. Most of the dynamical model guidance indicates that Norma will 
turn northeast, and then east-northeast during the next 12 to 24 
hours, and the official forecast follows this scenario.  There is 
fairly significant short-term spread in the guidance with the GFS 
taking the system more eastward, while the HWRF and ECMWF models 
depicted a more northeastward motion through landfall.  The NHC 
track has been shifted significantly north of the previous advisory 
due to the more northward initial position, and the new track lies 
near the middle of the guidance envelope.  It should be noted that 
although there is still a fair amount of uncertainty on exactly 
where and when the center of Norma will cross the coast of mainland 
Mexico, gusty winds and heavy rainfall are expected to spread 
onshore along much of the coast of the Mexican state of Sinaloa 
through tonight.
 
Key Messages:
 
1. Heavy rains from Norma will continue to impact Sinaloa into
Monday. Rainfall will continue to diminish across the southern
portions of Baja California Sur early this morning.  This rainfall
will produce flash and urban flooding, along with mudslides in areas
of higher terrain.
 
2. Tropical storm conditions will continue through this afternoon
within portions of the Tropical Storm Warning area over the southern
Baja California peninsula.
 
3. Tropical storm conditions are expected to spread onshore along
portions of the west coast of mainland Mexico within the Tropical
Storm Warning area through tonight.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  22/0900Z 24.5N 109.8W   50 KT  60 MPH
 12H  22/1800Z 25.0N 109.2W   50 KT  60 MPH
 24H  23/0600Z 25.3N 108.5W   45 KT  50 MPH...INLAND
 36H  23/1800Z 25.7N 107.6W   25 KT  30 MPH...POST-TROP/REMNT LOW
 48H  24/0600Z...DISSIPATED
 
$$
Forecaster Brown
 
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