872
FXUS02 KWBC 271957
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
357 PM EDT SAT SEP 27 2025
VALID 12Z TUE SEP 30 2025 - 12Z SAT OCT 04 2025
...TROPICAL DEPRESSION NINE WILL BRING TROPICAL IMPACTS TO THE
SOUTHEAST/CAROLINAS NEXT WEEK...
..OVERVIEW
THE PATH AND IMPACTS OF TROPICAL DEPRESSION NINE WILL BE A PRIMARY
FORECAST CONCERN INTO NEXT WEEK. THE CURRENT FORECAST TRACK SHOWS
NINE STALLING JUST OFFSHORE IN THE WESTERN ATLANTIC BUT PROVIDING
RAIN AND POSSIBLE FLOODING TO AT LEAST THE COASTAL CAROLINAS FOR
THE START OF THE MEDIUM RANGE PERIOD TUESDAY. THERE REMAINS AMPLE
UNCERTAINTY IN RAIN AMOUNTS ESPECIALLY FARTHER INLAND, WHICH DEPEND
ON THE UNCERTAIN TRACK OF THE SYSTEM INFLUENCED BY HURRICANE
HUMBERTO TO ITS EAST, COOL SURFACE HIGH PRESSURE IN THE NORTHEAST,
AND A NORTHERN STREAM TROUGH. FARTHER WEST, MEAN UPPER RIDGING IS
FORECAST TO SET UP FROM THE SOUTHWEST NORTHEASTWARD INTO THE
MIDWEST PROMOTING WARM TEMPERATURES AND MAINLY DRY CONDITIONS.
MEANWHILE THE WEST CAN EXPECT MEAN TROUGHING WITH COOLER
TEMPERATURES AND ROUNDS OF PRECIPITATION.
..GUIDANCE/PREDICTABILITY ASSESSMENT
WPC FOLLOWS THE NATIONAL HURRICANE CENTER (NHC) TRACK FOR T.D.
NINE, WHICH SHOWS THE STRENGTHENING TROPICAL CYCLONE REMAINING
OFFSHORE IN THE WESTERN ATLANTIC BUT CLOSE ENOUGH TO LAND TO BRING
HEAVY RAINFALL TO THE CAROLINAS TUESDAY. RECENT DETERMINISTIC MODEL
GUIDANCE FROM THE 00/06Z CYCLE AND THE NEW 12Z CYCLE IS AGREEABLE
WITH THIS TYPE OF TRACK SHOWING NO LANDFALL THROUGH MIDWEEK.
HOWEVER, THERE ARE STILL ENSEMBLE MEMBERS FROM THE GEFS/EC/CMC
ENSEMBLES AND THE AI/ML GOOGLE DEEPMIND AND AIFS ENSEMBLES THAT
SHOW A LANDFALLING SYSTEM, SO COASTAL AREAS MAY NOT BE OUT OF THE
WOODS FOR LANDFALL YET. FOR THE WPC FORECAST, USED THE
ECMWF/CMC/AIFS THROUGH AROUND MIDWEEK FOR QPF AND BACKGROUND MODEL
DATA WITH THE NHC POINTS FOR THE SYSTEM. THE INCOMING 12Z GUIDANCE
CONTINUES TO INDICATE SPLITTING MODEL GUIDANCE, WITH THE NEW 12Z
CMC MUCH FASTER IN TURNING THE CYCLONE EAST THAN ITS 00Z RUN, THE
12Z GFS SLOWING DOWN SOMEWHAT (MORE FAVORABLY WITH THE NHC TRACK),
AND THE 12Z ECMWF SLOWING IT DOWN CONSIDERABLY WHERE IT STALLS/DOES
NOT GET TAKEN EAST EVEN INTO LATER WEEK. CONTINUE TO MONITOR NHC
FORECASTS FOR FURTHER DETAILS AND UPDATES TO THE TRACK AND TIMING
OF NINE.
ELSEWHERE, MODELS ARE GENERALLY AGREEABLE ON THE LARGE SCALE WITH
THE MEAN TROUGH IN THE WEST SLOWLY MOVING EASTWARD WITH LESS
CERTAIN SHORTWAVES MOVING THROUGH AND PUSHING FRONTS THROUGH THE
REGION, BUT THE SPREAD IS TYPICAL FOR THE MEDIUM RANGE TIME FRAME.
ADDITIONALLY, THE ELONGATED UPPER RIDGE SHOWS REASONABLE CONSENSUS
AS IT STRETCHES FROM THE SOUTHWEST ACROSS PARTS OF THE CENTRAL U.S.
INTO THE OHIO VALLEY AND EVENTUALLY THE NORTHEAST. WEAK ENERGY MAY
CUT OFF FROM THIS RIDGE IN THE SOUTHERN STREAM OVER THE SOUTHEAST
OR SO, WITH MORE UNCERTAINTY. OVERALL ACROSS THE LOWER 48, A MULTI-
MODEL BLEND OF MAINLY DETERMINISTIC GUIDANCE WAS USED FOR THE
EARLY TO MID MEDIUM RANGE PERIOD, WITH INCREASING PROPORTIONS OF
THE GEFS AND EC ENSEMBLE MEANS DURING THE LATTER PERIOD.
..WEATHER/HAZARDS HIGHLIGHTS
THE CAROLINAS CAN EXPECT WET AND UNSETTLED CONDITIONS INTO TUESDAY
AS T.D. NINE APPROACHES WITH ITS ANOMALOUSLY HIGH TROPICAL
MOISTURE AND ITS INTERACTION WITH A LINGERING STATIONARY FRONT.
HEAVY RAIN AND FLASH FLOODING ARE THREATS WITH THIS SYSTEM, WITH
HIGHEST RAINFALL TOTALS PARTICULARLY ALONG COASTAL AREAS. IT IS
MORE UNCERTAIN HOW MUCH RAIN WILL REACH FARTHER INLAND. MARGINAL
AND SLIGHT RISKS WERE MAINTAINED IN THE DAY 4/TUESDAY ERO, WITH
SOME MINOR SHIFTS BASED ON NEWEST GUIDANCE LIKE TRIMMING OUT THE
NORTHERN SIDE OF THE PREVIOUS ISSUANCE OF THE SLIGHT (TAKING IT OUT
OF SOUTHERN VIRGINIA). MOST OF THE RECENT GUIDANCE AND THE NHC
TRACK TAKES THE SYSTEM FARTHER EAST BY DAY 5/WEDNESDAY FOR LESS OF
A RAINFALL THREAT BY THEN, SO REMOVED THE MARGINAL RISK AT THIS
TIME AND WILL SEE HOW FUTURE FORECASTS EVOLVE. IN ADDITION TO
RAIN/FLOODING THREATS, THE SOUTHEAST COAST WILL LIKELY EXPERIENCE
DANGEROUS SURF AND RIP CURRENT CONDITIONS INTO TUESDAY, AND SOME
COASTAL AREAS MAY EXPERIENCE STRONG WINDS. THEN SCATTERED SHOWERS
AND STORMS ARE POSSIBLE IN FLORIDA AND INTO THE GULF COAST THROUGH
MUCH OF THE WEEK.
A WEAK ATMOSPHERIC RIVER IS FORECAST TO PUSH ACROSS THE PACIFIC
NORTHWEST INTO CALIFORNIA ON TUESDAY AND WEDNESDAY WITH A COLD
FRONT AHEAD OF THE UPPER TROUGH. RAIN TOTALS GENERALLY UNDER AN
INCH OR TWO DO NOT APPEAR TO CAUSE HAZARDOUS CONDITIONS IN THE
COASTAL MOUNTAIN AREAS THAT ARE ACCUSTOMED TO SEEING MULTIPLE
INCHES OF RAIN. RAIN COULD CONTINUE IN THE WEST COAST STATES
THROUGH THURSDAY WITH ANOTHER FRONT. ROUNDS OF PRECIPITATION WILL
BE LIKELY ACROSS PARTS OF THE INTERMOUNTAIN WEST/ROCKIES THROUGH
MULTIPLE DAYS NEXT WEEK, AND THE HIGHER ELEVATIONS CAN EXPECT SNOW.
PRECIPITATION CHANCES MAY ALSO INCREASE LATER NEXT WEEK ACROSS THE
NORTH-CENTRAL U.S. ONCE THE FRONTAL SYSTEM PUSHES ACROSS THE
MOUNTAIN AND EMERGES IN THE PLAINS.
WITH UPPER RIDGING BUILDING OVERHEAD, WARMER THAN SEASONAL AVERAGE
TEMPERATURES ARE EXPECTED ACROSS THE CENTRAL U.S., ESPECIALLY FOR
THE NORTHERN PLAINS TO UPPER MIDWEST. HIGHS OF 10 TO 20 DEGREES
ABOVE NORMAL WILL BE COMMON IN THOSE AREAS, WITH HIGHS OF 80F
REACHING TO THE CANADIAN BORDER TUESDAY-WEDNESDAY. 90S ARE LIKELY
TO CONTINUE FOR EARLY OCTOBER INTO THE DESERT SOUTHWEST AND TEXAS.
MEANWHILE, BELOW NORMAL TEMPERATURES ESPECIALLY FOR HIGHS ARE
LIKELY ACROSS THE WEST DUE TO UPPER TROUGHING AND RAINY/CLOUDY
CONDITIONS.
TATE
ADDITIONAL 3-7 DAY HAZARD INFORMATION CAN BE FOUND ON THE WPC
MEDIUM RANGE HAZARDS OUTLOOK CHART AT:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,
QUANTITATIVE PRECIPITATION FORECAST (QPF), EXCESSIVE RAINFALL
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=ERO
HTTPS://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW
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