897
WTPZ45 KNHC 130842
TCDEP5
HURRICANE SIMON DISCUSSION NUMBER 24
NWS NATIONAL HURRICANE CENTER MIAMI FL EP202026
200 AM MST TUE OCT 13 2026
SIMON REMAINS A VERY SMALL HURRICANE. SYNTHETIC APERTURE RADAR (SAR)
DATA FROM AROUND 01 UTC SHOWED ITS COMPACT WIND FIELD, WITH A 5-N-MI
RADIUS OF MAXIMUM WIND AND TROPICAL-STORM-FORCE WINDS THAT EXTENDED
ONLY 30-40 N MI FROM THE CENTER. SATELLITE IMAGES REVEAL SIMON HAS
MAINTAINED A SMALL CENTRAL DENSE OVERCAST TONIGHT, WITH A SHARPER
EDGE TO THE CLOUD TOPS ON THE NORTHEASTERN SIDE, PERHAPS THE RESULT
OF SOME VERTICAL WIND SHEAR. GIVEN THE SMALL SIZE OF SIMON, IT IS
POSSIBLE THAT CONVENTIONAL SATELLITE ESTIMATES ARE STRUGGLING TO
REPRESENT ITS TRUE INTENSITY. THE INITIAL INTENSITY IS SET AT 80 KT,
WHICH LIES IN BETWEEN THE LATEST DVORAK CI NUMBER FROM TAFB (4.5/77
KT) AND THE EARLIER SAR DATA.
THE HURRICANE IS MOVING SLOWLY NORTHWESTWARD (310/3 KT) AROUND A
SUBTROPICAL RIDGE OVER THE SOUTHERN UNITED STATES. DURING THE NEXT
COUPLE OF DAYS, SIMON IS FORECAST TO BECOME CAUGHT IN WEAK STEERING
CURRENTS BETWEEN THIS RIDGE AND ANOTHER RIDGE THAT SHOULD BUILD TO
THE NORTHWEST OVER THE EASTERN PACIFIC. AS A RESULT, MOST OF THE
TRACK GUIDANCE NOW SHOWS LITTLE NET MOTION OF THE STORM THROUGH 60
H, ALTHOUGH SIMON MEANDERS IN SEVERAL DIFFERENT DIRECTIONS IN THE
VARIOUS GLOBAL MODELS AND ENSEMBLES. GIVEN THE LACK OF A CLEAR MODEL
SIGNAL, THE NEW NHC FORECAST ATTEMPTS TO MAINTAIN SOME CONTINUITY BY
USING A BLEND OF THE LATEST GOOGLE DEEPMIND, AI-GFS, AND ECMWF TRACK
AIDS THROUGH 72 H. ONCE AGAIN, THE TREND IS SLOWER AND FARTHER WEST
THAN THE PREVIOUS PREDICTION. A GENERAL NORTHWARD MOTION IS SHOWN AT
96-120 H AS THE SYSTEM (IF IT SURVIVES THAT LONG) SHOULD BECOME
STEERED BY A CUTOFF UPPER LOW TO ITS NORTHWEST. NEEDLESS TO SAY, THE
LACK OF MODEL AGREEMENT MAKES THIS A VERY LOW CONFIDENCE FORECAST.
SIMON'S INTENSITY FORECAST IS ALSO VERY CHALLENGING AND HIGHLY
SENSITIVE TO ITS UNCERTAIN TRACK. THE SMALL SYSTEM IS FORECAST TO BE
WITHIN A GENERALLY LOW SHEAR ENVIRONMENT OVER VERY WARM SSTS FOR THE
NEXT COUPLE OF DAYS. HOWEVER, THE SLOW FORWARD SPEED OF SIMON COULD
LEAD TO UPWELLING OF COOLER WATERS, AND ITS PROXIMITY TO LAND COULD
MAKE IT SUSCEPTIBLE TO INTRUSIONS OF DRIER AIR FROM MAINLAND MEXICO.
MUCH OF THE GUIDANCE SHOWS LITTLE INTENSITY CHANGE OR EVEN SOME
WEAKENING THROUGH MIDWEEK, AND THE NHC FORECAST REMAINS ON THE
HIGHER END OF THE INTENSITY GUIDANCE. BY THURSDAY, THE MODEL
CONSENSUS FAVORS MORE STEADY WEAKENING THROUGH THE REST OF THE
PERIOD DUE TO INCREASED VERTICAL WIND SHEAR, AND THE LATTER HALF OF
THE NHC FORECAST HAS BEEN LOWERED NOTABLY FROM THE PREVIOUS ONE.
IT IS WORTH EMPHASIZING THAT THIS IS A VERY LOW CONFIDENCE FORECAST,
AND INTERESTS IN WEST-CENTRAL MEXICO SHOULD CONTINUE TO CLOSELY
MONITOR THE LATEST UPDATES. CHANGES TO WATCHES AND WARNINGS MAY
BE REQUIRED LATER TODAY BASED ON THE LATEST FORECAST TRENDS.
KEY MESSAGES:
1. HURRICANE CONDITIONS ARE LIKELY ON LAS ISLAS MARIAS OVER THE
NEXT DAY OR SO, WHERE A HURRICANE WARNING REMAINS IN EFFECT.
2. SIMON COULD APPROACH THE COAST OF WESTERN MEXICO LATER THIS
WEEK AT OR NEAR HURRICANE STRENGTH, AND A HURRICANE WATCH REMAINS
IN EFFECT FOR A PORTION OF THE AREA.
3. HEAVY RAINFALL ASSOCIATED WITH SIMON WILL IMPACT PORTIONS OF
WEST-CENTRAL MEXICO OVER THE NEXT FEW DAYS. THIS RAINFALL WILL
PRODUCE LIFE-THREATENING FLOODING AND MUDSLIDES, ESPECIALLY IN AREAS
OF STEEP TERRAIN.
4. 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 13/0900Z 20.6N 107.2W 80 KT 90 MPH
12H 13/1800Z 20.7N 107.4W 75 KT 85 MPH
24H 14/0600Z 20.9N 107.7W 75 KT 85 MPH
36H 14/1800Z 21.0N 107.8W 75 KT 85 MPH
48H 15/0600Z 21.2N 107.9W 75 KT 85 MPH
60H 15/1800Z 21.8N 108.0W 70 KT 80 MPH
72H 16/0600Z 23.0N 108.1W 65 KT 75 MPH
96H 17/0600Z 24.2N 108.1W 55 KT 65 MPH
120H 18/0600Z 25.4N 108.2W 30 KT 35 MPH...POST-TROP/INLAND
FORECASTER REINHART
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