523
WTPZ45 KNHC 240852
TCDEP5
TROPICAL STORM JOHN DISCUSSION NUMBER 8
NWS NATIONAL HURRICANE CENTER MIAMI FL EP102024
300 AM CST TUE SEP 24 2024
JOHN MOVED INLAND AT AROUND 0315 UTC AS A 105 KT CATEGORY 3
HURRICANE. SINCE THAT TIME, THE THE STORM HAS APPARENTLY TURNED MORE
LEFTWARD AND REMAINS JUST INLAND, SKIRTING THE SOUTHERN COAST OF
MEXICO. WHILE SURFACE OBSERVATIONS HAVE BEEN SPARSE, MY BEST GUESS
IS THAT THE STORM RECENTLY PASSED JUST TO THE NORTH OF ACAPULCO,
WHERE THE AIRPORT EARLIER REPORTED TROPICAL-STORM-FORCE WIND GUSTS
AND WEST WINDS AS THE PRESSURE DROPPED TO 998 MB. ASSUMING THE
SMALL CORE HAS CONTINUED TO QUICKLY WEAKEN, JOHN IS BEING
DOWNGRADED TO A TROPICAL STORM, AND THE INITIAL INTENSITY IS 60 KT
THIS ADVISORY.
FOLLOWING FIXES FROM EARLIER MICROWAVE AND MORE RECENT GEOSTATIONARY
SATELLITE IMAGERY, JOHN NOW APPEARS TO BE MOVING NORTHWESTWARD AT
310/7 KT. THE TRACK FORECAST, WHICH HAS BEEN PROBLEMATIC WITH JOHN
FROM THE START, IS JUST AS DIFFICULT NOW. JOHN HAS CONTINUED TO
DEVIATE WESTWARD OF THE PREVIOUS FORECAST TRACK AND IS NOW MOVING
ROUGHLY PARALLEL TO THE COAST OF MEXICO. TO MAKE MATTERS WORSE, A
DECENT CHUNK OF THE OF THE GLOBAL MODELS GUIDANCE (ECMWF, UKMET) AND
HURRICANE REGIONAL MODELS (HWRF, HMON) SUGGEST THE CIRCULATION COULD
CONTINUE TURNING WESTWARD AND ATTEMPT TO RE-EMERGE OVER THE EASTERN
PACIFIC. EVEN THE GFS AND CMC SOLUTIONS, WHICH APPEAR TO DISSIPATE
THE SURFACE CIRCULATION INLAND OVER MEXICO, SHOW THE MID-LEVEL
CIRCULATION PERSISTING AND DRIFTING BACK OFFSHORE, LEADING TO THE
DEVELOPMENT OF A NEW LOW-LEVEL CIRCULATION. BECAUSE IT IS BECOMING
DISTINCTLY POSSIBLE THAT JOHN DOES NOT MOVE FAR ENOUGH INLAND TO
DISSIPATE ENTIRELY, AND THE AFOREMENTIONED CONTINUED LEFTWARD
TRENDS, THE LATEST NHC TRACK FORECAST IS ALTERED QUITE A BIT FORM
THE PRIOR FORECAST, AND NOW SHOWS THE POSSIBILITY THAT JOHN, ALBEIT
AS A TROPICAL DEPRESSION, MOVING BACK OFFSHORE AS IT BECOMES TANGLED
IN THE LARGER MONSOONAL FLOW. BY 72 H, MOST OF THE TRACK GUIDANCE
SHOWS THE SYSTEM MOVING BACK INLAND. THE UPDATED TRACK FORECAST IS
ROUGHLY IN BETWEEN THE HCCA AND ECMWF TRACKERS, AND IS OF VERY LOW
CONFIDENCE GIVEN JOHN'S TRACK HISTORY. IT ALSO REMAINS POSSIBLE THE
SYSTEM COULD DISSIPATE LATER TODAY IF IT MOVES FURTHER INLAND.
INTENSITY-WISE, JOHN SHOULD CONTINUE TO RAPIDLY WEAKEN AS LONG AS
IT REMAINS ONSHORE, AND THE NHC INTENSITY FORECAST SHOWS THE
TROPICAL CYCLONE WEAKENING TO A TROPICAL DEPRESSION LATER TODAY.
HOWEVER, THE NEW NHC FORECAST NOW MAINTAINS THE SYSTEM AS A
DEPRESSION AND DOES NOT SHOW DISSIPATION BEYOND 24 H GIVEN THE
LATEST TRACK FORECAST TAKING THE SYSTEM ALONG THE COAST OF MEXICO
AND NOT FAR ENOUGH INLAND TO COMPLETELY DISSIPATE. SOME OF THE
MODELS (NOTABLY THE ECMWF) ATTEMPT TO ALSO RE-INTENSIFY JOHN AS IT
GETS FAR ENOUGH BACK OFFSHORE, BUT GIVEN THE LARGE CHANGES MADE ON
THIS FORECAST CYCLE, THE NHC INTENSITY WILL NOT SHOW THAT SOLUTION
QUITE YET.
EVEN IF JOHN REMAINS INLAND, LARGER-SCALE MOIST MONSOONAL
SOUTHEASTERLY FLOW WILL PERSIST ALONG THE SOUTHERN COAST OF MEXICO,
LIKELY CONTRIBUTING TO CATASTROPHIC RAINFALL BOTH ALONG THE COAST
AND INLAND OVER THE UP-SLOPE PORTION OF THE MOUNTAINOUS TERRAIN.
THIS IS A VERY DANGEROUS LIFE-THREATENING FLOODING SCENARIO.
KEY MESSAGES:
1. TROPICAL STORM JOHN COULD STILL PRODUCING TROPICAL STORM
CONDITIONS FOR THE NEXT FEW HOURS IN THE TROPICAL STORM WARNING
AREA.
2. SLOW-MOVING JOHN WILL BRING VERY HEAVY RAINFALL TO COASTAL
PORTIONS OF SOUTHWEST MEXICO THROUGH THE UPCOMING WEEK. THIS HEAVY
RAINFALL WILL LIKELY CAUSE SIGNIFICANT AND POSSIBLY CATASTROPHIC,
LIFE-THREATENING FLASH FLOODING AND MUDSLIDES TO THE MEXICAN STATES
OF CHIAPAS, OAXACA, AND SOUTHEAST GUERRERO, PARTICULARLY IN AREAS
NEAR THE COAST AND ALONG THE UP-SLOPE PORTION OF AREAS OF HIGHER
TERRAIN.
FORECAST POSITIONS AND MAX WINDS
INIT 24/0900Z 17.3N 100.0W 60 KT 70 MPH...INLAND
12H 24/1800Z 17.4N 100.8W 30 KT 35 MPH...INLAND
24H 25/0600Z 17.0N 101.0W 30 KT 35 MPH...OVER WATER
36H 25/1800Z 16.7N 100.9W 30 KT 35 MPH
48H 26/0600Z 16.9N 100.6W 30 KT 35 MPH
60H 26/1800Z 17.4N 100.7W 25 KT 30 MPH...INLAND
72H 27/0600Z 18.1N 101.3W 20 KT 25 MPH...POST-TROP/REMNT LOW
96H 28/0600Z...DISSIPATED
FORECASTER PAPIN
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