601
WTPZ45 KNHC 230853
TCDEP5
TROPICAL STORM JOHN DISCUSSION NUMBER 3
NWS NATIONAL HURRICANE CENTER MIAMI FL EP102024
300 AM CST MON SEP 23 2024
SATELLITE IMAGES INDICATE THAT JOHN CONTINUES TO BECOME BETTER
ORGANIZED, WITH VERY DEEP CONVECTION NEAR THE CENTER AND SOME TIGHT
CURVED BAND FEATURES. EARLIER MICROWAVE IMAGERY ALSO SHOWED SOME
INNER CORE DEVELOPMENT, WITH PERHAPS A PARTIAL EYEWALL TRYING TO
FORM. SUBJECTIVE DVORAK ESTIMATES AT 06Z WERE 35 KT FROM BOTH
TAFB/SAB, THOUGH THE OBJECTIVE VALUES WERE BETWEEN 40-50 KT. THE
INTENSITY IS SET TO 40 KT AS A BLEND OF THESE DATA.
THE STORM IS MOVING SLOWLY TO THE NORTH-NORTHEAST, CAUGHT IN THE
LARGE-SCALE SOUTHWESTERLY FLOW ASSOCIATED WITH THE MONSOON TROUGH
NEAR CENTRAL AMERICA. THERE HAS BEEN A BIG CHANGE IN MOST OF THE
TRACK GUIDANCE SINCE YESTERDAY, WITH A FAIR NUMBER OF THE MODELS
NOW SHOWING A STEADIER NORTHEASTWARD MOTION WITH LESS EASTWARD
STEERING FROM THE INCIPIENT TROPICAL CYCLONE IN THE NORTHWESTERN
CARIBBEAN SEA. CONSEQUENTLY, THE MODELS HAVE SHIFTED LEFTWARD AND
FASTER. THE OFFICIAL FORECAST IS ALSO TRENDED IN THAT DIRECTION,
BUT COULD STILL BE TOO FAR TO THE EAST.
JOHN IS FORECAST TO BE OVER VERY WARM WATERS WITH LIGHT SHEAR WHILE
IT APPROACHES THE COAST OF MEXICO OVER THE NEXT DAY OR SO. WHILE
NONE OF THE REGIONAL HURRICANE MODELS MAKE JOHN A HURRICANE BEFORE
LANDFALL, THE RAPID INTENSIFICATION INDICES ARE INDICATING AT LEAST
A 50 PERCENT CHANCE THAT THIS SYSTEM STRENGTHENS 30 KT IN THE NEXT
24 HOURS, WHICH WOULD INDICATE HURRICANE-STRENGTH. GIVEN THE
UNCERTAINTIES INVOLVED, A HURRICANE WATCH AND A TROPICAL STORM
WARNING HAVE BEEN ISSUED BY THE GOVERNMENT OF MEXICO FOR PORTIONS OF
THE COAST OF SOUTHERN MEXICO ON THIS ADVISORY, AND INTERESTS THERE
SHOULD CLOSELY MONITOR FOR FUTURE FORECAST UPDATES.
KEY MESSAGES:
1. SLOW-MOVING TROPICAL STORM 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.
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 MEXICO, WHERE TROPICAL STORM
CONDITIONS COULD BEGIN LATE TODAY.
3. JOHN COULD STRENGTHEN MORE THAN FORECAST DEPENDING ON HOW
LONG IT REMAINS OVER WATER. INTERESTS ALONG THE COAST OF SOUTHERN
MEXICO SHOULD MONITOR THE LATEST FORECAST UPDATES, AS HURRICANE
WARNINGS COULD BE REQUIRED FOR A PORTION OF THE COASTLINE LATER
TODAY.
FORECAST POSITIONS AND MAX WINDS
INIT 23/0900Z 14.4N 98.5W 40 KT 45 MPH
12H 23/1800Z 14.8N 98.2W 50 KT 60 MPH
24H 24/0600Z 15.4N 97.6W 60 KT 70 MPH
36H 24/1800Z 15.8N 97.2W 60 KT 70 MPH
48H 25/0600Z 16.0N 97.0W 45 KT 50 MPH...INLAND
60H 25/1800Z...DISSIPATED
FORECASTER BLAKE
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