155
WTPZ45 KNHC 231447
TCDEP5
TROPICAL STORM JOHN DISCUSSION NUMBER 4
NWS NATIONAL HURRICANE CENTER MIAMI FL EP102024
900 AM CST MON SEP 23 2024
SATELLITE IMAGES SHOW THAT JOHN HAS BEEN STRENGTHENING QUICKLY. A
LARGE AREA OF COLD CLOUD TOPS BETWEEN -70C AND -85C IS PRESENT OVER
THE TROPICAL CYCLONE, WITH TIGHT CURVED BANDS WRAPPING AROUND THE
CENTER. THE LATEST SUBJECTIVE DVORAK INTENSITY ESTIMATES ARE
T-3.5/55 KT FROM TAFB AND T-3.0/45 KT FROM SAB. RECENT OBJECTIVE
DVORAK INTENSITY ESTIMATES FROM UW-CIMSS HAVE BEEN RANGING BETWEEN
57 AND 76 KT. A 23/0836 UTC AMSR-2 MICROWAVE PASS SHOWS THAT THE
INNER CORE HAS BECOME MUCH BETTER DEFINED, SHOWING A SMALL EYE-LIKE
FEATURE ON MICROWAVE IMAGERY, ALTHOUGH THERE ARE NO SIGNS OF AN EYE
SHOWING UP YET IN INFRARED OR VISIBLE IMAGES. A 23/1011 UTC SSMIS
PASS SHOWED A SIMILAR STRUCTURE TO THE AMSR-2 PASS. BASED ON THE
ABOVE DATA AND IMAGERY, THE INITIAL INTENSITY IS RAISED TO 60 KT.
JOHN WILL CONTINUE TO BE LOCATED WITHIN AN ENVIRONMENT OF EXTREMELY
WARM OCEAN TEMPERATURES, LIGHT WIND SHEAR AND A MOIST LOW- TO
MID-LEVEL TROPOSPHERE AS IT APPROACHES THE COAST OF MEXICO. WHILE
THE HURRICANE REGIONAL AND DYNAMICAL MODELS SHOW A MORE LIMITED
AMOUNT OF ADDITIONAL STRENGTHENING, THE STATISTICAL MODELS LIKE
SHIPS AND LGEM ARE AT THE HIGH END OF THE GUIDANCE SUITE. GIVEN
THAT THE SYSTEM HAS ALREADY INTENSIFIED BY 30 KT IN THE PAST 18 H,
AND GIVEN THAT THE SHIPS RAPID INTENSITY INDEX IS SHOWING GREATER
THAN AN 85 PERCENT CHANCE OF A 30-KT INCREASE IN THE NEXT 24 H, THE
NHC INTENSITY FORECAST WILL NOW EXPLICITLY SHOW RAPID STRENGTHENING
OVER THE NEXT 24 H. THIS INTENSITY FORECAST IS AT THE HIGH END OF
THE GUIDANCE SUITE. IT IS POSSIBLE THAT JOHN COULD PEAK EVEN
HIGHER THAN SHOWN BELOW BETWEEN THE 24 H FORECAST POINT AND WHEN IT
IS FORECAST TO MOVE INLAND AROUND 36 HOURS. INTERESTS ALONG THE
COAST OF SOUTHERN MEXICO SHOULD CLOSELY MONITOR FUTURE FORECAST
UPDATES ON JOHN.
BASED ON CENTER FIXES OVER THE PAST 6 TO 12 HOURS, JOHN'S MOTION IS
ESTIMATED TO BE NORTHWARD, OR 0 DEGREES AT 3 KT. JOHN IS EMBEDDED
IN VERY WEAK STEERING CURRENTS, AND THE PRIMARY STEERING MECHANISM
IS LIKELY THE SOUTHWESTERLY MONSOONAL FLOW THAT THE CYCLONE IS
EMBEDDED IN. THE NEW NHC TRACK FORECAST HAS BEEN SHIFTED TO THE
WEST OF THE PREVIOUS OFFICIAL FORECAST AND NOW LIES VERY NEAR THE
LATEST MODEL CONSENSUS. IT SHOULD BE NOTED THAT THE TRACK FORECAST
AND TIMING OF WHEN THE CENTER REACHES THE COAST IS MORE UNCERTAIN
THAN NORMAL.
KEY MESSAGES:
1. JOHN IS EXPECTED TO BECOME A HURRICANE LATER TODAY AND
ADDITIONAL STRENGTHENING IS LIKELY BEFORE THE CENTER REACHES THE
COAST OF SOUTHERN MEXICO WITHIN THE HURRICANE WARNING AREA ON
TUESDAY. DAMAGING HURRICANE-FORCE WINDS AND A DANGEROUS STORM SURGE
ARE EXPECTED WITHIN PORTIONS OF THE WARNING AREA.
2. JOHN WILL BRING VERY HEAVY RAINFALL TO COASTAL PORTIONS OF
SOUTHERN MEXICO THROUGH THIS 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.
FORECAST POSITIONS AND MAX WINDS
INIT 23/1500Z 14.8N 98.5W 60 KT 70 MPH
12H 24/0000Z 15.2N 98.3W 75 KT 85 MPH
24H 24/1200Z 15.7N 97.9W 90 KT 105 MPH
36H 25/0000Z 16.0N 97.6W 90 KT 105 MPH...INLAND
48H 25/1200Z 16.2N 97.4W 35 KT 40 MPH...INLAND
60H 26/0000Z...DISSIPATED
FORECASTER HAGEN
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