595
WTPZ45 KNHC 251456
TCDEP5
TROPICAL STORM JOHN DISCUSSION NUMBER 11
NWS NATIONAL HURRICANE CENTER MIAMI FL EP102024
900 AM CST WED SEP 25 2024
JOHN HAS REFORMED NEAR THE SOUTHWESTERN COAST OF MEXICO. THE
CIMSS-UW SATELLITE VORTICITY ANALYSES SHOW REMNANTS OF VORTICITY,
LIKELY ASSOCIATED WITH THE MID-LEVEL CIRCULATION OF JOHN, HAVE
MERGED WITH A LARGER SOURCE OF VORTICITY FROM THE MONSOON TROUGH.
CONVECTION HAS GRADUALLY BECOME BETTER ORGANIZED BASED ON
GEOSTATIONARY INFRARED AND VISIBLY IMAGERY. AN AMSR2 MICROWAVE PASS
AT 0807 UTC SHOWED CURVED BANDING NEAR THE SURFACE, INDICATING A
WELL-DEFINED SURFACE CENTER. A DVORAK CLASSIFICATION FROM TAFB HAS
GIVEN JOHN A 2.0/35 KT AND THAT IS THE INITIAL INTENSITY FOR THIS
ADVISORY.
THE ENVIRONMENTAL CONDITIONS APPEAR CONDUCIVE FOR JOHN TO STRENGTHEN
IN THE NEXT DAY OR SO, AS LONG AS THE CIRCULATION STAYS OVER WATER.
GLOBAL MODELS SHOW THE VERTICAL WIND SHEAR REMAINING
WEAK-TO-MODERATE, AMPLE MID-LEVEL MOISTURE, AND VERY WARM SEA
SURFACE TEMPERATURES. STATISTICAL GUIDANCE EVEN SUGGESTS THERE IS
AN ABOVE AVERAGE POSSIBILITY FOR STRONG-TO-RAPID INTENSIFICATION.
THE LATEST NHC INTENSITY FORECAST SHOWS JOHN REACHING A PEAK
INTENSITY OF 55 KT IN 24 H, WHICH IS NEAR THE HCCA INTENSITY AID AND
AT THE TOP OF THE GUIDANCE ENVELOPE. HOWEVER, THERE IS A CHANCE
JOHN MAY BECOME A HURRICANE PRIOR TO LANDFALL.
THE TROPICAL STORM IS MEANDERING EASTWARD IN THE MONSOONAL FLOW WITH
AN ESTIMATE MOTION OF 80/2 KT. MODELS INDICATE THAT JOHN WILL
GRADUALLY TURN TOWARDS THE NORTH LATER TODAY AND ACCELERATE SLIGHTLY
TOWARDS THE COAST ON THURSDAY. REGIONAL AND GLOBAL MODELS VARY THE
TIMING OF LANDFALL, WITH THE GFS AND GFS-BASED HURRICANE MODELS
SHOWING JOHN AT THE COAST BY TOMORROW EVENING AND THE ECMWF
LINGERING OFFSHORE UNTIL FRIDAY. THE OFFICIAL TRACK FORECAST CALLS
FOR LANDFALL ALONG THE SOUTHERN AND SOUTHWESTERN COAST OF MEXICO ON
THURSDAY EVENING, HOWEVER, THERE IS UNCERTAINTY ASSOCIATED WITH THIS
TIMING. A HURRICANE WATCH AND TROPICAL STORM WARNING HAVE BEEN
ISSUED BY THE GOVERNMENT OF MEXICO FOR PORTIONS OF THE COAST OF
SOUTHERN MEXICO AND INTERESTS THERE SHOULD CLOSELY MONITOR FUTURE
FORECASTS FOR UPDATES.
KEY MESSAGES:
1. TROPICAL STORM JOHN WILL BRING ADDITIONAL VERY HEAVY RAINFALL TO
COASTAL PORTIONS OF SOUTHWEST MEXICO THROUGH FRIDAY. THE ADDITIONAL
RAINFALL TOTALS WILL BE FALLING ACROSS AREAS THAT HAVE RECEIVED VERY
HEAVY RAINFALL AMOUNTS OVER THE PAST FEW DAYS. THIS HEAVY RAINFALL
WILL LIKELY CAUSE SIGNIFICANT AND CATASTROPHIC, LIFE-THREATENING
FLASH FLOODING AND MUDSLIDES TO THE MEXICAN STATES OF GUERRERO,
OAXACA, COASTAL CHIAPAS, AND COASTAL MICHOACA.
2. JOHN IS FORECAST TO STRENGTHEN BEFORE LANDFALL, AND A HURRICANE
WATCH AND A TROPICAL STORM WARNING HAVE BEEN ISSUED FOR A PORTION OF
THE COASTLINE OF SOUTHERN AND SOUTHWESTERN MEXICO, WHERE TROPICAL
STORM CONDITIONS COULD BEGIN LATER TODAY.
FORECAST POSITIONS AND MAX WINDS
INIT 25/1500Z 16.2N 101.4W 35 KT 40 MPH
12H 26/0000Z 16.3N 101.2W 45 KT 50 MPH
24H 26/1200Z 16.7N 101.1W 55 KT 65 MPH
36H 27/0000Z 17.3N 101.1W 55 KT 65 MPH
48H 27/1200Z 17.8N 101.2W 30 KT 35 MPH
60H 28/0000Z...DISSIPATED
FORECASTER BUCCI/R. ZELINSKY
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