328
WTPZ45 KNHC 102059
TCDEP5
HURRICANE SIMON DISCUSSION NUMBER 14
NWS NATIONAL HURRICANE CENTER MIAMI FL EP202026
300 PM CST SAT OCT 10 2026
AIR FORCE RESERVE HURRICANE HUNTERS HAVE BEEN INVESTIGATING SIMON
THIS AFTERNOON, FINDING THAT THE HURRICANE IS INDEED A CATEGORY 4
STORM. THE MINIMUM PRESSURE IS ESTIMATED TO BE DOWN TO 932 MB, AND
THE PEAK 700 MB FLIGHT LEVEL WINDS WERE 134 KT IN THE EASTERN
QUADRANT OF THE HURRICANE. WHILE A STANDARD 0.9 REDUCTION WOULD
TYPICALLY SUPPORT A 10 METER SUSTAINED WIND OF 120-125 KT, THE
ENTIRE WIND FIELD OF SIMON WAS NOT FULLY SAMPLED. IN ADDITION, THERE
WAS AN EARLIER PARTIAL SYNTHETIC APERTURE RADAR (SAR) RCM-1 PASS
WHICH HAD A PEAK WIND OF 138 KT. SATELLITE INTENSITY ESTIMATES,
WHICH HAVE BEEN LAGGING BEHIND THE ESTIMATED INTENSITY OF SIMON,
HAVE ALSO RISEN SOMEWHAT TODAY. TAKING ALL THESE DATA POINTS
TOGETHER, THE INITIAL INTENSITY IS HELD AT 130 KT THIS ADVISORY. THE
AIRCRAFT ALSO REPORTED CONCENTRIC EYEWALLS, WITH THE INNER EYEWALL
12 N MI AND OUTER WALL AT 36 N MI. SOME CONCENTRIC BANDS WERE ALSO
PICKED UP BY A RECENT AMSR-3 MICROWAVE PASS.
AFTER SLOWING DOWN TO A CRAWL EARLIER, AIRCRAFT FIXES INDICATE THAT
SIMON STARTING TO MOVE DUE NORTH AGAIN, WITH AN ESTIMATED MOTION AT
360/4 KT. AS PREVIOUSLY DISCUSSED, THE HURRICANE IS BEING PRIMARILY
STEERED BY A WEAK MID-LEVEL RIDGE TO THE EAST, PROVIDING DEEP-LAYER
SOUTHERLY FLOW. A SUBTLE NARROW MID-LEVEL RIDGE TO THE NORTHWEST IS
ALSO IMPARTING A SLIGHT AMOUNT OF NORTHERLY FLOW. ONCE AGAIN, THE
TRACK GUIDANCE THIS AFTERNOON HAS MADE A SLOWER ADJUSTMENT. IN
ADDITION, THERE IS A BIT OF AN EASTWARD SHIFT IN THE GUIDANCE
ENVELOPE. ONE NOTABLE CHANGE FROM THIS MORNING, NOW ALL THE
HURRICANE-REGIONAL MODEL RUNS (HWRF, HMON, HAFS-A, HAFS-B) ALL SHOW
SIMON MAKING LANDFALL IN JALISCO IN 24-36 H. IN ADDITION, BOTH THE
GOOGLE DEEPMIND ENSEMBLE MEAN (GDMI) AND ITS UPGRADED WEATHER NEXT
MODEL (WN3I) ALSO NUDGED THEIR TRACKS EASTWARD. THUS, THE NHC TRACK
FORECAST HAS SHIFTED A BIT TO THE EAST, BUT STILL LIES ON THE
EASTERN END OF THE GUIDANCE. PART OF THE REASON FOR FAVORING THE
EASTERN EDGE OF THE GUIDANCE IS THAT THERE IS A PRETTY WELL-KNOWN
BIAS THAT TROPICAL CYCLONES IN THIS AREA TEND TO TRACK EAST OF THE
FORECAST TRACK DUE TO INTERACTION WITH THE HIGH TOPOGRAPHY OF
COASTAL MEXICO.
AS MENTIONED THIS MORNING, THE FUTURE INTENSITY FORECAST OF SIMON IS
HEAVILY INFLUENCED BY SIMON'S ULTIMATE TRACK. BECAUSE LARGE-SCALE
ENVIRONMENTAL CONDITIONS REMAIN FAVORABLE, SIMON'S SHORT-TERM
INTENSITY FORECAST WILL LIKELY BE CONTROLLED BY INNER-CORE
FLUCTUATIONS, LIKE EYEWALL REPLACEMENT CYCLES. THIS IS PERTINENT
GIVEN THE CONCENTRIC EYEWALLS NOTED BY THE AIRCRAFT MISSION.
HOWEVER, AS SIMON NEARS THE MEXICAN COAST, THE HIGH TOPOGRAPHY WILL
INTERACT WITH THE HURRICANE'S OUTER CIRCULATION, AND SPOT SOUNDINGS
IN THE HAFS-A/B RUNS SHOW EVIDENCE OF DOWNSLOPE SUBSIDENCE OCCURRING
AS SIMON NEARS LANDFALL. THIS EFFECT WILL BOTH CAUSE THE HURRICANE'S
WIND FIELD TO SHRINK IN SIZE, AND WILL LIKELY RESULT IN WEAKENING
EVEN BEFORE THE HURRICANE MAKES LANDFALL IN MEXICO. WEAKENING IS
EXPECTED TO BEGIN BETWEEN 12-24 H, WITH MORE SUBSTANTIAL WEAKENING
OCCURRING WHEN SIMON MOVES FULLY ONSHORE. ONCE AGAIN, THIS INTENSITY
FORECAST IS QUITE UNCERTAIN. IF SIMON REMAINS OFFSHORE, LIKE THE
ECMWF AND A DECENT CHUNK OF GDM ENSEMBLE MEMBERS SHOW, IT MAY REMAIN
MUCH STRONGER THAN THE LATEST NHC INTENSITY FORECAST. THE LATEST
FORECAST IS A BIT LOWER THAN THE PRIOR ONE, WITH A BIT MORE
CONFIDENCE THAT SIMON WILL MOVE INLAND, THOUGH THE LATEST FORECAST
STILL SHOWS SIMON DISSIPATING OVER MEXICO AFTER 60 H.
KEY MESSAGES:
1. CATASTROPHIC WIND AND LIFE-THREATENING STORM SURGE IMPACTS ARE
LIKELY ALONG A PORTION OF THE WEST-CENTRAL COAST OF MEXICO, AND A
HURRICANE WARNING IS IN EFFECT FROM PUNTA SAN TELMO TO EL ROBLITO.
PREPARATIONS TO PROTECT LIFE AND PROPERTY SHOULD BE COMPLETED THIS
AFTERNOON.
2. HEAVY RAINFALL ASSOCIATED WITH SIMON WILL IMPACT PORTIONS OF
SOUTHWESTERN MEXICO THROUGH THIS WEEKEND. THIS RAINFALL WILL PRODUCE
LIFE-THREATENING FLOODING AND MUDSLIDES, ESPECIALLY IN AREAS OF
STEEP TERRAIN.
3. SWELLS WILL AFFECT PORTIONS OF THE SOUTHWESTERN AND WEST-CENTRAL
COAST OF MEXICO THROUGH THE WEEKEND. THESE SWELLS ARE LIKELY TO
CAUSE LIFE-THREATENING SURF AND RIP CURRENT CONDITIONS. PLEASE
CONSULT PRODUCTS FROM YOUR LOCAL WEATHER OFFICE.
FORECAST POSITIONS AND MAX WINDS
INIT 10/2100Z 17.6N 104.8W 130 KT 150 MPH
12H 11/0600Z 18.3N 104.9W 130 KT 150 MPH
24H 11/1800Z 19.4N 105.1W 110 KT 125 MPH
36H 12/0600Z 20.8N 105.2W 70 KT 80 MPH...INLAND
48H 12/1800Z 21.9N 105.2W 45 KT 50 MPH...INLAND
60H 13/0600Z 22.8N 105.1W 15 KT 15 MPH...POST-TROP/INLAND
72H 13/1800Z...DISSIPATED
FORECASTER PAPIN
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page