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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