776
WTNT44 KNHC 290856
TCDAT4
TROPICAL STORM IMELDA DISCUSSION NUMBER 11
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092025
500 AM EDT MON SEP 29 2025
IMELDA CONTINUES TO SLOWLY BECOME BETTER ORGANIZED. EARLIER
AIRCRAFT DATA INDICATED THAT THE PRESSURE HAS FALLEN TO 996 MB, AND
SATELLITE IMAGERY SHOWS PERSISTENT CONVECTION NEAR AND NORTH OF THE
CENTER. THE INITIAL INTENSITY IS SET TO 40 KT WITH NUMEROUS 35 KT
WIND VECTORS ON THE EVENING SCATTEROMETER PASS AND HIGHER DVORAK
ESTIMATES.
THE STORM IS PROGRESSING NORTHWARD AT ABOUT 7 KT. THIS MOTION IS
FORECAST TO CONTINUE TODAY DUE TO STEERING ALONG THE WESTERN SIDE
OF THE SUBTROPICAL RIDGE. HUMBERTO IS FORECAST TO ERODE THE RIDGE
BY TUESDAY, CAUSING AN ABRUPT TURN OF IMELDA TO THE EAST-NORTHEAST
WITH SOME ACCELERATION AS THE CYCLONE ENCOUNTERS FASTER MID-
LATITUDE FLOW. THERE IS INCREASING CONFIDENCE IN THE STORM STAYING
WELL OFFSHORE OF THE SOUTHEASTERN UNITED STATES COAST. THE
LATEST TRACK GUIDANCE IS SIMILAR TO THE PREVIOUS CYCLE, ALTHOUGH
FASTER AT THE END, AND REMAINS CLOSE TO BERMUDA. THE MEDIUM RANGE
FORECAST BEYOND BERMUDA IS QUITE UNCERTAIN WITH A COMPLICATED FLOW
PATTERN DUE TO A DIGGING NORTH ATLANTIC TROUGH AND
THEN-EXTRATROPICAL HUMBERTO INTERACTIONS.
IMELDA IS FORECAST TO GRADUALLY STRENGTHEN WITHIN AN ENVIRONMENT OF
MODERATE SOUTH-SOUTHWESTERLY VERTICAL WIND SHEAR, WARM OCEAN WATERS
AND WITHIN A FAIRLY MOIST MID-LEVEL AIR MASS FOR THE NEXT COUPLE OF
DAYS. THEREAFTER, AN UPPER-LEVEL TROUGH WILL HELP TO INITIATE
EXTRATROPICAL TRANSITION, AND SOME OF THE MODELS ARE SHOWING THIS
AS A FAVORABLE TROUGH INTERACTION, CAUSING A LARGER AND STRONGER
CYCLONE. THE GFS AND ECMWF MODELS ARE ALSO SHOWING A STING JET
DEVELOPING AS WELL ABOUT THE TIME THAT IMELDA IS NEAR BERMUDA, SO
THAT SITUATION WILL HAVE TO BE WATCHED CLOSELY. THE OFFICIAL
FORECAST REMAINS AT THE HIGHER END OF THE MODEL GUIDANCE. MOST OF
THE GLOBAL MODELS ARE SHOWING A FASTER EXTRATROPICAL TRANSITION
AFTER IMELDA MOVES PAST BERMUDA, AND THAT IS INDICATED IN THE NEW
NHC FORECAST.
KEY MESSAGES:
1. IMELDA IS EXPECTED TO CONTINUE TO BRING TROPICAL STORM CONDITIONS
TO PORTIONS OF THE NORTHWESTERN BAHAMAS TODAY.
2. RAINFALL ASSOCIATED WITH IMELDA WILL CONTINUE TO IMPACT EASTERN
CUBA AND THE BAHAMAS THROUGH TUESDAY, WHICH WILL LIKELY PRODUCE
FLASH AND URBAN FLOODING. MUDSLIDES ARE POSSIBLE IN THE HIGHER
TERRAIN. HEAVY RAINFALL ACROSS THE COASTAL CAROLINAS COULD CAUSE
ISOLATED FLASH AND URBAN FLOODING THROUGH TUESDAY.
3. INTERESTS IN BERMUDA SHOULD MONITOR THE PROGRESS OF IMELDA AS A
HURRICANE WATCH COULD BE REQUIRED LATE TODAY.
4. SWELLS AND HIGH SURF FROM BOTH HUMBERTO AND IMELDA ARE EXPECTED
TO PRODUCE DANGEROUS MARINE CONDITIONS AND RIP CURRENTS ALONG THE
EAST COAST OF FLORIDA AND THE GEORGIA COAST TODAY. THESE CONDITIONS
ARE EXPECTED TO SPREAD NORTHWARD ALONG MUCH OF THE EAST COAST OF THE
UNITED STATES EARLY THIS WEEK.
FORECAST POSITIONS AND MAX WINDS
INIT 29/0900Z 25.5N 77.1W 40 KT 45 MPH
12H 29/1800Z 26.7N 77.1W 50 KT 60 MPH
24H 30/0600Z 28.1N 76.8W 60 KT 70 MPH
36H 30/1800Z 28.9N 75.1W 65 KT 75 MPH
48H 01/0600Z 29.9N 72.3W 70 KT 80 MPH
60H 01/1800Z 31.1N 68.8W 75 KT 85 MPH
72H 02/0600Z 32.4N 63.8W 80 KT 90 MPH
96H 03/0600Z 35.0N 56.0W 70 KT 80 MPH...POST-TROP/EXTRATROP
120H 04/0600Z 39.5N 52.5W 60 KT 70 MPH...POST-TROP/EXTRATROP
FORECASTER BLAKE
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