547
WTNT44 KNHC 281451
TCDAT4
TROPICAL DEPRESSION NINE DISCUSSION NUMBER 8
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092025
1100 AM EDT SUN SEP 28 2025
STRUCTURALLY, THE DEPRESSION CONTINUES TO GRADUALLY BECOME BETTER
ORGANIZED, WITH AN ATTEMPT AT MORE BURSTING CONVECTION CLOSER TO THE
ESTIMATED CENTER. HOWEVER, RECENT OBSERVATIONS FROM THE ONGOING AIR
FORCE RESERVE RECONNAISSANCE AIRCRAFT MISSION HAVE BEEN RATHER
UNDERWHELMING, WHICH STILL SHOWS A BROAD WIND FIELD AND A PEAK
850-MB WIND OF ONLY 37 KT. BASED ON THIS INFORMATION, THE SYSTEM
WILL REMAIN A DEPRESSION FOR THIS ADVISORY WITH MAXIMUM SUSTAINED
WIND OF 30 KT, WHICH IS A LITTLE UNDER THE SATELLITE-BASED
INTENSITY ESTIMATES.
THE DEPRESSION HAS NOT REALLY ACCELERATED MUCH YET THIS MORNING, AND
IT APPEARS TO BE MOVING SLOWLY NORTHWARD AT 350/6 KT. A GENERAL
NORTH-NORTHWEST TO NORTHWARD MOTION IS EXPECTED TO CONTINUE FOR THE
NEXT 24-36 HOURS AS SOUTHERLY STEERING PERSISTS FROM BOTH AN UPPER
TROUGH OVER THE SOUTHEASTERN UNITED STATES AND THE SUBTROPICAL RIDGE
CENTERED JUST EAST OF BERMUDA. AFTER THAT PERIOD OF TIME, THE
SUBTROPICAL RIDGE'S STEERING INFLUENCE DECREASES AS HURRICANE
HUMBERTO'S LARGER OUTER CIRCULATION CREATES A LARGE WEAKNESS. GIVEN
THE SLOW MOTION OF THE DEPRESSION SO FAR, IT HAS ALSO REMAINED
SOUTH OF A TRACK BIFURCATION POINT THAT WAS SEEN YESTERDAY IN THE
ENSEMBLE GUIDANCE. THE TROPICAL CYCLONE NOW APPEARS MORE LIKELY TO
TURN SHARPLY EAST-NORTHEASTWARD STARTING ON TUESDAY AND CONTINUING
THROUGH THE REMAINDER OF THE FORECAST. THE TRACK GUIDANCE THIS CYCLE
HAS MADE ANOTHER SOUTH AND EASTWARD SHIFT, AND THE NHC TRACK
FORECAST HAS BEEN MOVED IN THAT DIRECTION. IN PARTICULAR, THE
TRACK GUIDANCE CONTINUES TO SHOW MUCH MORE EAST-NORTHEASTWARD
ACCELERATION AT THE END OF THE FORECAST, REQUIRING LARGE SPEED
CHANGES IN DAYS 4 AND 5, AND THIS STILL MIGHT NOT BE FAST ENOUGH.
THE LATEST TRACK FORECAST IS VERY CLOSE TO THE HCCA CONSENSUS AID,
BUT BLENDS IT WITH A LITTLE MORE OF THE GOOGLE DEEPMIND ENSEMBLE
MEAN (GDMI) BY THE DAY 5 FORECAST.
WHILE THE DEPRESSION HAS NOT YET DEVELOPED AN INNER CORE, ONE IS
EXPECTED TO FORM IN THE NEXT 12-24 HOURS. SOME SOUTHERLY VERTICAL
WIND SHEAR IS EXPECTED TO PERSIST, THOUGH IT NEVER GETS
PROHIBITIVELY STRONG, REMAINING UNDER 20 KT FOR THE NEXT 48-72 H IN
THE GFS-BASED SHIPS. THEREFORE, INTENSIFICATION IS EXPECTED AND THE
LATEST NHC INTENSITY FORECAST IS ROUGHLY IN LINE WITH THE INTENSITY
GUIDANCE CONSENSUS AIDS. IN 3-4 DAYS, THE CYCLONE IS EXPECTED TO
FIND ITSELF IN THE RIGHT ENTRANCE REGION OF AN INTENSIFYING
UPPER-LEVEL JET, AND THE ENHANCED UPPER-LEVEL DIVERGENCE IN THAT
TIME MAY HELP SUPPORT ADDITIONAL INTENSIFICATION EVEN AS THE SHEAR
BEGINS TO INCREASE TOWARDS THE END OF THE FORECAST. AFTER THE SYSTEM
PASSES BERMUDA, A STRONG BAROCLINIC ZONE IS EXPECTED TO INTERACT
WITH THE SYSTEM, RESULTING IN EXTRATROPICAL TRANSITION BY DAY 5 AS
IT GETS TANGLED UP WITH A FRONTAL BOUNDARY. HOWEVER, AS STRESSED
PREVIOUSLY, THIS IS A LOW CONFIDENCE FORECAST AT LONG RANGE GIVEN
THE RECENT LARGE TRACK CHANGES, ESPECIALLY SINCE THE SOUTHWARD SHIFT
IN TRACK KEEPS THE CYCLONE OVER WARMER SEA-SURFACE TEMPERATURES.
KEY MESSAGES:
1. THE DEPRESSION IS EXPECTED TO STRENGTHEN AND BRING TROPICAL STORM
CONDITIONS TO PORTIONS OF THE CENTRAL AND NORTHWESTERN BAHAMAS
THROUGH MONDAY. TROPICAL STORM CONDITIONS ARE ALSO POSSIBLE
ALONG PORTIONS OF THE EAST COAST OF CENTRAL FLORIDA BEGINNING
MONDAY.
2. RAINFALL ASSOCIATED WITH THE SYSTEM 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 FLASH, URBAN, AND RIVER FLOODING INTO WEDNESDAY MORNING.
3. THE RISK OF SIGNIFICANT WIND IMPACTS ALONG THE SOUTHEASTERN
UNITED STATES COAST IS DECREASING, BUT INTERESTS IN THAT AREA SHOULD
CONTINUE TO MONITOR THE LATEST FORECAST UPDATES.
4. SWELLS AND HIGH SURF FROM BOTH HUMBERTO AND TROPICAL DEPRESSION
NINE ARE EXPECTED TO PRODUCE DANGEROUS MARINE CONDITIONS AND RIP
CURRENTS ALONG THE EAST COAST OF FLORIDA AND THE GEORGIA COAST
THROUGH MONDAY. 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 28/1500Z 23.5N 77.3W 30 KT 35 MPH
12H 29/0000Z 24.5N 77.4W 40 KT 45 MPH
24H 29/1200Z 26.2N 77.6W 50 KT 60 MPH
36H 30/0000Z 27.7N 77.6W 60 KT 70 MPH
48H 30/1200Z 28.8N 77.1W 65 KT 75 MPH
60H 01/0000Z 29.3N 75.7W 70 KT 80 MPH
72H 01/1200Z 29.9N 73.5W 75 KT 85 MPH
96H 02/1200Z 31.0N 68.0W 80 KT 90 MPH
120H 03/1200Z 32.5N 61.5W 70 KT 80 MPH...POST-TROP/EXTRATROP
FORECASTER PAPIN
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