434
WTPZ42 KNHC 201500
TCDEP2
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.
FORECAST POSITIONS AND MAX WINDS
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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