583
WTPZ45 KNHC 132059
TCDEP5
HURRICANE SIMON DISCUSSION NUMBER 26
NWS NATIONAL HURRICANE CENTER MIAMI FL EP202026
200 PM MST TUE OCT 13 2026
SIMON'S STRUCTURE THIS AFTERNOON HAS BEEN MORE OR LESS STEADY STATE
AS ITS SMALL EYE CONTINUES TO BE DISCERNIBLE ON BOTH VISIBLE AND
INFRARED IMAGES. HOWEVER, THE SURROUNDING EYEWALL CLOUD TOP
TEMPERATURES HAVE WARMED A BIT THIS AFTERNOON, THOUGH IT IS UNCLEAR
IF THIS IS A DIURNAL FLUCTUATION OR EVIDENCE OF SOME COOLER OCEAN
UPWELLING GIVEN ITS SLOW MOTION. THE MOST RECENT HIGH-RESOLUTION
MICROWAVE IMAGE WAS AN WSFM PASS AT 1338 UTC, WHICH SHOWED A NEARLY
CLOSED EYEWALL AND IMPROVEMENT FROM EARLIER IMAGERY. THE EYE
SIGNATURE CAN ALSO BE PICKED UP ON THE EDGE OF THE CABO SAN
LUCAS, MEXICO RADAR. THE D-MINT MEAN ESTIMATE ASSOCIATED WITH THE
WSFM PASS WAS 79 KT, AND THE INITIAL INTENSITY IS HELD AT 80 KT
THIS ADVISORY, ON THE HIGHER END OF THE INTENSITY ESTIMATES. A
PARTIAL METOP-B SCATTEROMETER PASS WAS USEFUL TO INDICATE HOW
COMPACT SIMON'S WIND FIELD HAS BECOME, WITH 34-KT WINDS NOW ONLY
EXTEND OUT AN ESTIMATED 30 N MI.
THE INITIAL MOTION NOW APPEARS TO BE A SOUTH OF DUE WEST DRIFT, OR
260 DEGREES AT 2 KT. COMPARED TO THIS MORNING, THE FORECAST TRACK
REASONING HAS NOT CHANGED A TON. THE SMALL HURRICANE IS CURRENTLY
JUST ON THE SOUTH SIDE OF A SADDLE POINT, OR COL, IN THE STEERING
FLOW. SIMON'S FUTURE TRACK IS VERY SENSITIVE TO WHICH SIDE OF THIS
POINT THE HURRICANE IS LOCATED, WITH LIGHT STEERING CURRENTS
PREVAILING LEADING TO SLOW MOTION. IN THE LATEST ROUND OF GUIDANCE,
ALL OF THE HURRICANE-REGIONAL MODELS SHOW A MORE SUBSTANTIAL
SOUTHWARD TRACK THIS AFTERNOON WHILE SIMON REMAINS IN VERY LIGHT
DEEP-LAYER SOUTHERLY STEERING. WHILE THE ECMWF FORECAST IS FURTHER
NORTH, IT WAS INITIALIZED ALMOST A FULL DEGREE FURTHER NORTH OF
WHERE SIMON WAS LOCATED AT 12 UTC, PLACING IT OVER OR JUST ON THE
NORTH SIDE OF THE SADDLE POINT. THE GOOGLE DEEPMIND ENSEMBLES, WHICH
OFTEN FAVORS THIS INITIALIZATION, JUMP NORTH IN THE SHORT TERM,
WHICH APPEARS UNREALISTIC. THUS, THE LATEST NHC TRACK FORECAST IS
GOING TO PLACE A LITTLE MORE WEIGHT ON THE HURRICANE-REGIONAL MODEL
TRACKS WHICH HAD A BETTER INITIALIZATION, SHOWING A LITTLE MORE
SOUTHWARD MOTION OVER THE NEXT 24-36 H, ALBEIT AS A SNAIL'S PACE.
THIS TRACK STILL SHOWS A SMALL CYCLONIC LOOP AND IS SOUTH OF THE
PREVIOUS TRACK FORECAST. AFTER 48 H, THE LARGE-SCALE SYNOPTIC
PATTERN FINALLY BEGINS TO CHANGE, WHERE A DEEP-LAYER CUTOFF LOW DIGS
INTO SOUTHERN CALIFORNIA. THIS PATTERN WILL INDUCE MORE SOUTHERLY
ENVIRONMENTAL FLOW OVER SIMON, AND SHOULD DISLODGE IT FROM THIS VERY
STAGNANT STEERING PATTERN ASSUMING IT DOESN'T MOVE AS FAR SOUTH AS
THE HAFS-A/B TRACK AIDS. THE NHC TRACK FORECAST STILL SHOWS SIMON
GAINING LATITUDE AND TURNING MORE NORTH-NORTHWEST IN 60-72 H AND
LIES CLOSEST TO THE HFIP CORRECTED CONSENSUS APPROACH (HCCA) TRACK.
THIS COULD BRING SIMON CLOSER TO THE COAST OF BAJA CALIFORNIA SUR AS
IT MOVES UP THE GULF OF CALIFORNIA. HOWEVER, THERE REMAINS A WIDE
VARIETY OF TRACK SOLUTIONS THAT COULD VERIFY, FROM WELL SOUTH OF
BAJA CALIFORNIA NORTHWARD TO MAINLAND MEXICO OVER THE NEXT 5 DAYS.
SIMON HAS MAINTAINED A RELATIVELY HEALTHY APPEARANCE TODAY WITH A
WELL-ORGANIZED INNER CORE. AS STRESSED EARLIER, VERY SMALL
HURRICANES LIKE SIMON ARE KNOWN TO BE SENSITIVE TO SMALL CHANGES IN
THEIR ENVIRONMENTAL CONDITIONS THAT COULD RESULT IN RAPID CHANGES IN
INTENSITY, EITHER UP OR DOWN. ENVIRONMENTAL CONDITIONS ARE
FAVORABLE, WITH SHEAR OVER SIMON EXPECTED TO REMAIN LOW FOR THE NEXT
48 H WITH SEA-SURFACE TEMPERATURES (SSTS) IN THE 28-30 C RANGE.
ASSUMING SIMON DOES NOT COMPLETELY STALL AND UPWELL COOLER OCEAN
WATERS, SOME INTENSIFICATION COULD OCCUR. WITH THAT SAID, THERE IS
AN EXTREME RANGE OF INTENSITY SOLUTIONS OVER THE NEXT 48 H, FROM
INTENSIFYING INTO A CATEGORY 4 HURRICANE (HAFS-A) TO WEAKENING TO A
TROPICAL STORM (HMON). GIVEN THE CURRENT STRUCTURE, THE LATEST NHC
INTENSITY FORECAST NOW SHOWS SOME INTENSIFICATION, BUT REMAINS WELL
UNDER THE LATEST HAFS-A FORECAST AND IS CLOSEST TO THE ECMWF LGEM
GUIDANCE. AFTER 48 H, SOUTHWESTERLY VERTICAL WIND SHEAR IS FORECAST
TO INCREASE RATHER QUICKLY, AND THE SMALL SENSITIVE SIMON IS
FORECAST TO WEAKEN EVEN AS IT MOVES OVER WARMER SSTS WHEN IT TRACKS
NORTHWARD. THIS LATEST FORECAST IS INITIALLY ON THE HIGH SIDE OF THE
GUIDANCE, BUT FALLS BACK TO THE MIDDLE OF THE GUIDANCE ENVELOPE
AFTER
72 H.
IT IS WORTH STRESSING THAT THIS REMAINS A VERY LOW CONFIDENCE
FORECAST FOR BOTH TRACK AND INTENSITY, AND INTERESTS IN WEST-CENTRAL
MEXICO AND BAJA CALIFORNIA SUR SHOULD CONTINUE TO CLOSELY MONITOR
THE LATEST UPDATES. WHILE MAINLAND TROPICAL STORM AND HURRICANE
WATCHES HAVE BEEN DISCONTINUED, NEW WATCHES AND WARNINGS COULD BE
REQUIRED OVER THE NEXT DAY OR TWO AS SIMON'S ULTIMATE FORECAST COMES
INTO BETTER FOCUS.
KEY MESSAGES:
1. SIMON COULD APPROACH LAS ISLAS MARIAS ON WEDNESDAY AND THE COAST
OF WESTERN MEXICO LATER THIS WEEK AT OR NEAR HURRICANE STRENGTH, AND
A HURRICANE WATCH IS IN EFFECT FOR A PORTION OF THESE AREAS.
INTERESTS IN WEST-CENTRAL MEXICO AND BAJA CALIFORNIA SUR SHOULD
CONTINUE TO CLOSELY MONITOR THE LATEST UPDATES TO SIMON'S FORECAST.
CHANGES TO WATCHES AND WARNINGS COULD BE REQUIRED OVER THE NEXT DAY
OR TWO BASED ON THE LATEST FORECAST TRENDS.
2. LARGE SWELLS WILL AFFECT PORTIONS OF THE SOUTHWESTERN AND
WEST-CENTRAL COASTS OF MEXICO OVER THE NEXT SEVERAL DAYS. THESE
SWELLS ARE LIKELY TO CAUSE LIFE-THREATENING SURF AND RIP CURRENT
CONDITIONS.
FORECAST POSITIONS AND MAX WINDS
INIT 13/2100Z 20.2N 107.5W 80 KT 90 MPH
12H 14/0600Z 20.0N 107.8W 85 KT 100 MPH
24H 14/1800Z 19.8N 108.1W 90 KT 105 MPH
36H 15/0600Z 19.5N 108.0W 90 KT 105 MPH
48H 15/1800Z 19.8N 107.6W 85 KT 100 MPH
60H 16/0600Z 21.0N 107.8W 70 KT 80 MPH
72H 16/1800Z 22.6N 108.8W 60 KT 70 MPH
96H 17/1800Z 24.4N 110.2W 45 KT 50 MPH...NEAR BAJA CALIFORNIA
120H 18/1800Z 28.8N 111.1W 30 KT 35 MPH...POST-TROP/INLAND
FORECASTER PAPIN
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