077
WTNT44 KNHC 280323 CCA
TCDAT4
TROPICAL DEPRESSION NINE DISCUSSION NUMBER 6...CORRECTED
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092025
1100 PM EDT SAT SEP 27 2025
CORRECTED FIRST SENTENCE OF THIRD PARAGRAPH
THE DEPRESSION THIS EVENING REMAINS FAIRLY DISORGANIZED, WITH
CONVECTION MAINLY ORIENTED IN A NORTH-SOUTH FASHION WITH ONLY A
HINT OF BANDING ON THE NORTHERN SIDE. A NOAA-P3 AIRCRAFT THAT
HAS BEEN FLYING THROUGH THE SYSTEM ONLY FOUND A PEAK 700 MB FLIGHT
LEVEL WIND OF 34 KT ABOUT 60 N MI AWAY FROM THE CENTER. TAIL DOPPLER
RADAR (TDR) ANALYSIS FROM THE AIRCRAFT ALSO SHOWS THE CENTER IS
QUITE BROAD AT THE 1 KM LEVEL WITH THE MID-LEVEL CENTER TILTED TO
THE SOUTH WITH HEIGHT. BASED ON THE PLANE DATA, THE INITIAL
INTENSITY REMAINS 30 KT THIS ADVISORY, WHICH IS A LITTLE UNDER THE
VARIOUS SATELLITE-BASED ESTIMATES, BUT CLOSE TO A RECENTLY
RECEIVED SCATTEROMETER PASS WHICH HAD A PEAK WIND OF 31 KT.
AIRCRAFT FIXES BOTH AT 700 MB AND FROM THE TDR ANALYSIS SHOWS THE
CYCLONE IS MEANDERING RIGHT NOW, WITH A BEST GUESS AT A MOTION OF
310/2 KT. OVER THE NEXT COUPLE OF DAYS, THE SYSTEM SHOULD TURN
NORTH-NORTHWESTWARD WITH A SOMEWHAT FASTER FORWARD MOTION, MOVING
WITHIN THE FLOW BETWEEN AN UPPER TROUGH OVER THE SOUTHEAST U.S. AND
A SUBTROPICAL RIDGE OVER THE ATLANTIC. THIS FORECAST BRINGS THE
DEPRESSION OVER THE CENTRAL AND NORTHWESTERN BAHAMAS THROUGH EARLY
MONDAY, THEN TOWARD THE SOUTHEAST U.S. COAST BY TUESDAY. IT IS
NOTABLE TO POINT OUT THE SYSTEM HAS BEEN MOVING SLOWER THAN
ANTICIPATED OVER THE LAST 12-24 HOURS, AND THIS COULD HAVE
SIGNIFICANT IMPLICATIONS ON ITS ULTIMATE TRACK. EVEN IN THE FIRST
48 HOURS OF THE TRACK, THERE IS QUITE A BIT OF SPREAD IN THE
NORTH-SOUTH DIRECTION IN BOTH THE DETERMINISTIC AND ENSEMBLE MODEL
GUIDANCE. FASTER TRACKS APPEAR TO INTERACT MORE WITH THE UPPER-LEVEL
TROUGH TO THE WEST, RESULTING IN A TRACK CLOSER TO THE CAROLINA
COASTLINE, WHILE SLOWER TRACKS LARGELY MISS A DIRECT INTERACTION
WITH THIS FEATURE, AND TURN SHARPLY EAST FASTER AS HURRICANE
HUMBERTO APPROACHES FROM THE EAST, ERODING THE MID-LEVEL RIDGING
STEERING TD9 NORTHWARD. BECAUSE IT HAS BEEN MOVING SLOWER THAN
EXPECTED, ITS BECOMING MORE LIKELY ITS ULTIMATE TRACK WILL FALL IN
THE SLOWER AND SHARPER EAST CAMP. IN RESPONSE, THE OVERALL TRACK
GUIDANCE THIS CYCLE SHIFTED SLOWER AND FURTHER EAST, AND THE NHC
TRACK FORECAST WAS SHIFTED IN THAT DIRECTION. THE LATEST TRACK
ROUGHLY SPLITS THE DIFFERENCE BETWEEN THE ECMWF AND GFS TRACKS, AND
LIES QUITE CLOSE TO THE HCCA CONSENSUS AID, BUT STILL NOT AS FAR
SOUTH AND EAST AS THE GOOGLE DEEPMIND ENSEMBLE MEAN (GDMI).
THE DEPRESSION IS NOT SHOWING SIGNS OF INTENSIFICATION YET, WITH A
BROAD DIFFUSE STRUCTURE ON AIRCRAFT OBSERVATIONS PERSISTING.
HOWEVER, THE INTENSITY GUIDANCE IS INSISTENT THAT DEEP CENTRAL
CONVECTION WILL SOON FORM NEAR THE CENTER, HELPING TO TIGHTEN UP THE
SURFACE WIND FIELD. WHILE THE CYCLONE WILL HAVE SOME SOUTHERLY SHEAR
TO DEAL WITH, IT DOES NOT APPEAR TO BE PROHIBITIVELY STRONG, ONLY
15-20 KT FOR THE NEXT 48 HOURS IN BOTH THE GFS AND ECMWF-BASED SHIPS
GUIDANCE. THAT, COMBINED WITH WARM 29-30 C SEA-SURFACE TEMPERATURES
SHOULD PROMOTE STEADY INTENSIFICATION ONCE A CENTRAL CORE DEVELOPS,
AND THE NHC INTENSITY FORECAST WAS NUDGED UP A LITTLE HIGHER SHOWING
A 70 KT PEAK IN 48 HOURS. AFTER THIS PERIOD IS WHERE THE INTENSITY
FORECAST GETS TRICKY. THE LARGE SPREAD IN NORTH-SOUTH TRACKS ALSO
HAS A SIGNIFICANT IMPACT ON THE AMOUNT OF SHEAR THE SYSTEM WILL FACE
IN THE 48-96 HOUR TIME-FRAME. SOLUTIONS THAT ARE FURTHER SOUTH HAVE
LESS SHEAR TO CONTEND WITH AND ARE GENERALLY STRONGER. FOR NOW, THE
LATEST INTENSITY FORECAST WILL CAP THE PEAK INTENSITY AT 70 KT
THROUGH THE END OF THE FORECAST, CLOSE TO THE HCCA INTENSITY
GUIDANCE, BUT THIS COULD BE CONSERVATIVE IF THE TRACK SHIFTS FURTHER
SOUTH AND EAST. THE SYSTEM COULD ALSO INTERACT WITH A BAROCLINIC
ZONE TOWARDS THE END OF THE FORECAST, BUT BECAUSE THE FORECAST TRACK
REMAINS OVER WARM WATERS AT DAY 5, EXTRATROPICAL TRANSITION WON'T BE
SHOWN QUITE YET.
EVEN IF THIS FURTHER OFFSHORE TRACK PANS OUT, THE WIND FIELD IS
EXPECTED TO EXPAND QUITE A BIT, AND GIVEN THE EXPECTED STORM
STRUCTURE, A RISK OF SIGNIFICANT HEAVY RAINFALL, STORM SURGE, AND
WIND IMPACTS IS STILL POSSIBLE FOR THE SOUTHEAST U.S. COAST EVEN IF
THE STORM CENTER REMAINS OFFSHORE.
KEY MESSAGES:
1. THE DEPRESSION IS EXPECTED TO STRENGTHEN AND BRING TROPICAL STORM
CONDITIONS TO PORTIONS OF THE CENTRAL AND NORTHWESTERN BAHAMAS
THROUGH SUNDAY NIGHT. TROPICAL STORM CONDITIONS ARE ALSO POSSIBLE
ALONG PORTIONS OF THE EAST COAST OF CENTRAL FLORIDA BEGINNING
MONDAY, WHERE A TROPICAL STORM WATCH IS IN EFFECT.
2. RAINFALL WILL CONTINUE TO IMPACT EASTERN CUBA AND THE BAHAMAS
THROUGH THE WEEKEND, WHICH WILL LIKELY PRODUCE FLASH AND URBAN
FLOODING. MUDSLIDES ARE POSSIBLE IN THE HIGHER TERRAIN.
3. THERE IS A SIGNIFICANT THREAT OF HEAVY RAINFALL EARLY NEXT WEEK
FROM PORTIONS OF THE EAST COAST OF FLORIDA NORTHWARD INTO THE
CAROLINAS, WHICH COULD CAUSE FLASH, URBAN, AND RIVER FLOODING.
4. THE DEPRESSION IS EXPECTED TO BE AT OR NEAR HURRICANE INTENSITY
WHEN IT IS CLOSEST TO THE SOUTHEAST U.S. COAST EARLY NEXT WEEK,
WHERE THERE IS A RISK OF STORM SURGE AND WIND IMPACTS. ALTHOUGH IT
IS TOO SOON TO SPECIFY THE EXACT LOCATION AND MAGNITUDE OF IMPACTS,
RESIDENTS SHOULD CLOSELY MONITOR THE LATEST FORECAST UPDATES AND
ENSURE THAT THEY HAVE THEIR HURRICANE PLAN IN PLACE.
FORECAST POSITIONS AND MAX WINDS
INIT 28/0300Z 22.4N 76.7W 30 KT 35 MPH
12H 28/1200Z 23.6N 77.0W 35 KT 40 MPH
24H 29/0000Z 25.5N 77.5W 50 KT 60 MPH
36H 29/1200Z 27.3N 77.9W 60 KT 70 MPH
48H 30/0000Z 28.7N 78.2W 70 KT 80 MPH
60H 30/1200Z 29.9N 78.1W 70 KT 80 MPH
72H 01/0000Z 30.4N 77.3W 70 KT 80 MPH
96H 02/0000Z 31.0N 75.0W 70 KT 80 MPH
120H 03/0000Z 31.5N 71.4W 70 KT 80 MPH
FORECASTER PAPIN
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