Hurricane Norma Forecast Discussion Number 12

NOAA - Tropical Weather Updates

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Issued at 900 AM MDT Fri Oct 20 2023

WTPZ42 KNHC 201500
Hurricane Norma Discussion Number  12
NWS National Hurricane Center Miami FL       EP172023
900 AM MDT Fri Oct 20 2023
The center of Norma is embedded underneath a cold central dense 
overcast this morning. The GOES-West derived motion winds and 
satellite images show healthy upper-level outflow to the north, but 
moderate shear continues to impinge on the south side of the 
hurricane. Recent SSMIS passive microwave images show a ragged 
mid-level eyewall structure, with a thinner ring of convection noted 
on the south and west sides of the inner core. The objective and 
subjective satellite intensity estimates from UW-CIMSS, TAFB, and 
SAB have decreased this morning, and the initial intensity is 
lowered to 95 kt based on a blend of these data. An Air Force 
Reserve Hurricane Hunter aircraft is scheduled to investigate Norma 
later today.
Norma is moving north-northwestward (335 degrees) at 7 kt. A gradual 
turn toward the north is expected through Saturday while Norma moves 
within the flow between a mid-level ridge to its east and a mid- to 
upper-level trough to its northwest. This will bring the center of 
Norma near or over the southern tip of Baja California Sur between 
24-36 h. From there, a turn toward the northeast with a slower 
forward speed is forecast as Norma approaches the west-central coast 
of Mexico. The overall track guidance envelope has shifted slightly 
westward this cycle. The updated NHC forecast from 24-72 h has been 
nudged in that direction, generally between the simple (TVCE) and 
corrected (HCCA) consensus aids. This track shows Norma reaching the 
west coast of Mexico on Sunday night and dissipating early next 
week. There are still pronounced speed differences between the 
global and regional models regarding when Norma reaches the coast of 
mainland Mexico, so further adjustments could be required. 
Although Norma remains over very warm SSTs, it is moving into a more 
hostile environment. Drier mid-level air and increasing 
southwesterly shear will likely cause continued weakening during the 
next few days. Still, Norma is expected to be a hurricane when it 
moves near or over the southern portion of Baja California Sur on 
Saturday within the Hurricane Warning area. The continued shear and 
potential land interaction with the Baja peninsula will likely cause 
Norma to weaken to a tropical storm on Sunday while it approaches 
the west coast of Mexico. Based on the threat of tropical storm 
conditions there, the government of Mexico has issued a Tropical 
Storm Watch for a portion of the west coast.
Key Messages:
1. Norma is expected to bring hurricane conditions to the far
southern portion of the Baja California peninsula within the
hurricane warning area on Saturday.
2. Heavy rains from Norma will begin to impact the far southern
portions of Baja California Sur later today and continue through
Sunday, with heavy rains reaching Sinaloa on Saturday. This rainfall
may produce flash and urban flooding, along with possible mudslides
in areas of higher terrain.
3. Norma is forecast to approach the west coast of Mexico as a
tropical storm on Sunday and Sunday night, and a Tropical Storm
Watch has been issued for a portion of that area.
INIT  20/1500Z 19.4N 109.2W   95 KT 110 MPH
 12H  21/0000Z 20.6N 109.6W   85 KT 100 MPH
 24H  21/1200Z 22.1N 109.8W   75 KT  85 MPH
 36H  22/0000Z 23.3N 109.6W   65 KT  75 MPH
 48H  22/1200Z 23.9N 109.1W   60 KT  70 MPH
 60H  23/0000Z 24.3N 108.3W   50 KT  60 MPH
 72H  23/1200Z 24.7N 107.4W   40 KT  45 MPH...INLAND
 96H  24/1200Z 26.0N 106.0W   20 KT  25 MPH...POST-TROP/INLAND
120H  25/1200Z...DISSIPATED
Forecaster Reinhart

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