056
FOUS30 KWBC 030740
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
340 AM EDT SAT OCT 3 2026
DAY 1
VALID 12Z SAT OCT 03 2026 - 12Z SUN OCT 04 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE CENTRAL
GULF COAST AND THE LOWER TEXAS COAST...
..CENTRAL GULF COAST
A TROPICAL WAVE MOVING ACROSS THE GULF WILL FUNNEL RECORD TO NEAR
RECORD AMOUNTS OF ATMOSPHERIC MOISTURE INTO MUCH OF THE GULF COAST
ON SATURDAY. A 15-25 KT SOUTHERLY FLOW INTO THE COAST AT 850 MB
WILL SUPPORT NUMEROUS SHOWERS AND THUNDERSTORMS ASSOCIATED WITH THE
WAVE MOVING INTO THE CENTRAL GULF COAST BOTH TODAY AND TONIGHT.
PWATS WILL BE AT OR ABOVE 2.5 INCHES FOR MANY AREAS. EXTENSIVE
CLOUD COVER AND THE OCTOBER SUN SHOULD LIMIT INSTABILITY
CONSIDERABLY WITH ANY REASONABLE DISTANCE FROM THE COAST. THUS, ANY
CONVECTION THAT IMPACTS THE COAST IS UNLIKELY TO BE ABLE TO TRAVEL
TOO FAR INLAND WITHOUT SIGNIFICANT WEAKENING. THUS, THE SLIGHT
HIGHLIGHTING MUCH OF THE COAST REMAINS UNCHANGED. A HIGHER-END
SLIGHT RISK WAS ADDED WITH THIS UPDATE FROM NEW ORLEANS THROUGH
MUCH OF THE WESTERN FLORIDA PANHANDLE. THEY WERE PRIMARILY
INCLUDED DUE TO URBAN IMPACTS AND THE SHEER VOLUME OF WATER
EXPECTED, AS THE COAST CAN EXPECT 3-6 INCHES OF RAIN TODAY, WITH
LOCALLY HIGHER AMOUNTS. DESPITE VERY HIGH FFGS AND DRY SOILS IN
THIS AREA, THIS AMOUNT OF RAINFALL MAY OVERCOME THAT, ESPECIALLY IN
URBAN AREAS TO RESULT IN WIDELY SCATTERED INSTANCES OF FLASH
FLOODING.
..LOWER TEXAS COAST
THE SLIGHT RISK REMAINS IN PLACE ALONG THE COAST OF DEEP SOUTH
TEXAS AS WELL. ONSHORE NORTHEASTERLY FLOW OF THE SAME DEEP TROPICAL
MOISTURE IMPACTING AREAS FURTHER NORTH AND EAST MAY IMPACT SOME
URBAN AREAS SUCH AS BROWNSVILLE. AS THIS PORTION OF THE LOWER TEXAS
COAST IS ROUGHLY PERPENDICULAR TO THE MEAN FLOW, EXPECT THE ONSHORE
PUSH TO ALLOW CONVECTION TO TRY TO MOVE A FEW MILES INLAND BEFORE
DISSIPATING. NO CHANGES WERE MADE TO THE AREA INCLUDED IN THE
SLIGHT RISK WITH THIS UPDATE.
WEGMAN
DAY 2
VALID 12Z SUN OCT 04 2026 - 12Z MON OCT 05 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
SOUTHEAST AND LOWER TEXAS COAST...
..SOUTHEAST
THE COMBINATION OF THE CONTINUED FUNNELING OF RECORD TO NEAR-
RECORD ATMOSPHERIC MOISTURE ACROSS THE SOUTHEAST FROM A TROPICAL
WAVE OVER THE GULF, AND AN APPROACHING COLD FRONT WILL ALLOW FOR A
SWATH OF HEAVY RAINFALL TO EXPAND FROM THE CENTRAL GULF COAST
NORTHEAST TO PORTIONS OF THE CAROLINA COAST. PWATS WILL RANGE FROM
2.25 TO 2.5 INCHES, WHICH WITH GOOD INSTABILITY WOULD BE AMPLE
MOISTURE TO PRODUCE AREAS OF SIGNIFICANT FLASH FLOODING. HOWEVER,
THE OCTOBER SUN AND EXTENSIVE CLOUD COVER WILL INSTEAD LIMIT
INSTABILITY SIGNIFICANTLY, WITH MOST AREAS STRUGGLING TO REACH EVEN
1,000 J/KG OF MUCAPE. THUS, THIS IS LIKELY TO END UP BEING A LONG-
DURATION HIGHLY-EFFICIENT RAINFALL ACROSS THE SLIGHT RISK AREA.
ONLY MINOR CHANGES WERE NEEDED, WHICH INCLUDED ADDING A BIT MORE OF
THE SOUTHERN OUTER BANKS TO THE SLIGHT, IN COORDINATION WITH
MHX/MOREHEAD CITY, NC FORECAST OFFICE. THE SLIGHT WAS ALSO EXPANDED
NORTH A BIT TO INCLUDE THE BIRMINGHAM, AL AND ATLANTA METROS. BOTH
OF THOSE CITIES WILL BE ON THE NORTHERN EDGE OF THE RAINFALL PLUME,
SO THERE'S CONSIDERABLE UNCERTAINTY GIVEN RECENT SOUTHWARD TRENDS
IN THE GUIDANCE AS TO THE EXTENT OF ANY FLASH FLOODING. THE URBAN
NATURE OF THE AREA WILL BE COUNTERED BY WEAK INSTABILITY.
ONCE AGAIN THE HEAVIEST RAINS ON SUNDAY WILL BE IN MANY OF THE SAME
AREAS HIT HARD ON SATURDAY, WITH PERHAPS A SLIGHT EASTWARD SHIFT
FROM SATURDAY. AREAS FROM MOBILE, AL EAST ACROSS MOST OF THE
FLORIDA PANHANDLE ARE LIKELY TO SEE THE MOST RAIN. SINCE THERE IS
SIGNIFICANT OVERLAP FROM SATURDAY, ANOTHER HIGHER-END SLIGHT WAS
INTRODUCED FOR THIS REGION. THERE IS A NON-ZERO CHANCE, DEPENDING
ON HOW EXTENSIVE ANY FLASH FLOODING FROM THE RAINS TODAY ARE, THAT
A MODERATE RISK UPGRADE MAY BE NEEDED FOR SUNDAY.
MEANWHILE ACROSS THE CAROLINAS, THE SECOND CONSECUTIVE DAY OF RAIN,
AND FOR MOST AREAS, FAR MORE THAN ON SATURDAY, SHOULD ALLOW FOR
MORE WIDELY SCATTERED INSTANCES OF FLASH FLOODING, SO THE SLIGHT
RISK IS LARGELY UNCHANGED AND STILL LOOKS ON TRACK. PORTIONS OF THE
SOUTH CAROLINA LOW COUNTRY AND GEORGIA COAST WERE TRIMMED SINCE
SANDY SOILS AND SWAMPY TERRAIN SHOULD PRECLUDE ANY FLASH FLOODING,
SINCE THE HEAVIEST RAINS ARE LIKELY TO BE NORTH AND WEST OF THIS
AREA.
..LOWER TEXAS COAST
NO CHANGES WERE NEEDED ALONG THE LOWER TEXAS COAST, AS CONTINUED
ONSHORE FLOW WILL CONTINUE THE SAME PATTERN FROM SATURDAY. SOME
CONVECTION THAT DEVELOPS OVER THE GULF WILL ATTEMPT TO MOVE
ASHORE, THEN QUICKLY DIE OFF DUE TO A LACK OF INSTABILITY FURTHER
INLAND.
WEGMAN
DAY 3
VALID 12Z MON OCT 05 2026 - 12Z TUE OCT 06 2026
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHEAST AND LOWER TEXAS COAST...
..SOUTHEAST
VERY FEW CHANGES WERE NEEDED WITH THIS UPDATE ACROSS THE SOUTHEAST.
WHILE THE TRENDS IN THE GUIDANCE CONTINUE TO SUGGEST A SOUTHWARD
TREND, GIVEN THE HEAVIER RAINS FROM SUNDAY, THE ERO REMAINS
GENEROUS ON THE NORTHERN SIDE OF THE RAINFALL FOOTPRINT, TO ACCOUNT
FOR POTENTIAL ONGOING FLOODING CONTINUING INTO MONDAY. THE HEAVIEST
RAINS ON MONDAY WILL FOCUS IN FAR SOUTHEASTERN GEORGIA AND FROM
JACKSONVILLE NORTH AND WEST IN FLORIDA. AS ON PREVIOUS DAYS,
INSTABILITY WILL BE AT A PREMIUM DUE TO EXTENSIVE CLOUD COVER FROM
THE EXTREMELY HIGH MOISTURE AMOUNTS IN THE ATMOSPHERE. MUCH OF THE
FLORIDA PENINSULA WILL HAVE PWATS AT OR ABOVE 2.25 INCHES,
SUPPORTING HIGHLY EFFICIENT WARM RAIN PROCESSES. THIS WILL BE
COUNTERED BY THE LACK OF INSTABILITY, WHICH WILL LIMIT THE LIFT ANY
STORMS WILL HAVE TO WORK WITH. BY MONDAY, A SOMEWHAT FASTER
SOUTHWARD MOVEMENT OF THE COLD FRONT LIFTING ALL THIS MOISTURE
SHOULD SIGNIFICANTLY LIMIT OVERLAP IN THE FORECAST RAINFALL
FOOTPRINTS FROM SUNDAY TO MONDAY. GIVEN HOW DIFFICULT MOST OF
SOUTHEAST GEORGIA CAN BE TO FLOOD DUE TO FLAT, SANDY TERRAIN AND
NUMEROUS SWAMPS, A HIGH-END MARGINAL REMAINS IN PLACE.
A CONTINUED SOUTHWARD TREND IN THE FRONT COULD ALLOW FOR TRIMMING
ON THE NORTHERN END OF THE MARGINAL WITH FUTURE UPDATES.
..LOWER TEXAS COAST
AN OVERALL WEAKENING OF BOTH THE TROPICAL WAVE OVER THE GULF AND
THE SUBSEQUENT EASTERLY/ONSHORE FLOW SHOULD LIMIT ADDITIONAL
RAINFALL ALONG THE IMMEDIATE COAST ON MONDAY. THUS, DESPITE SEVERAL
DAYS OF PRIOR RAINS, THE INHERITED MARGINAL WAS LEFT IN PLACE WITH
FEW CHANGES.
WEGMAN
DAY 4 AND DAY 5
VALID 12Z TUE OCT 06 2026 - 12Z THU OCT 08 2026
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL TUESDAY-TUESDAY
NIGHT OVER FAR SOUTHEAST GEORGIA INTO NORTHERN AND CENTRAL PORTIONS
OF THE FLORIDA PENINSULA...
DAY 4 (12Z TUE-12Z WED) -- LITTLE CHANGE MADE TO YESTERDAY'S DAY 5
MARGINAL RISK AREA. THE MARGINAL AREA SLIPS A LITTLE FARTHER SOUTH
INTO NORTH-CENTRAL FL AND FAR SOUTHEAST GA TUE-TUE NIGHT, WHERE
THE SURFACE FRONT MORE THAN LIKELY WILL BEGIN TO STALL AND BECOME
QUASI-STATIONARY. THE AXIS OF HIGHEST PWS (2-2.5") AND MID-LEVEL
SHORTWAVE ENERGY WILL BE DRAPED ALONG AND SOUTH OF THE FRONT, AS
WILL SOME (ALBEIT WEAK) DEEP-LAYER INSTABILITY. DEEP WEST/WEST-
SOUTHWESTERLY FLOW WILL ENHANCED THE RISK FOR TRAINING CELLS COMING
OFF THE EASTERN GULF, AS ALL THE GLOBAL ENSEMBLES (GEFS/ECENS/CMC)
HAVE AT LEAST A FEW MEMBERS NOTING RAINFALL TOTALS OF 3-5+" WITHIN
THE 24HR PERIOD. HOWEVER IT SHOULD BE NOTED THE QPF (DETERMINISTIC
AND PROBABILISTIC) TRENDS IN THE GUIDANCE HAS DECREASED OVER THE
PAST COUPLE OF MODEL CYCLES, WITH NOW THE HIGHEST 3-5+ INCH QPF
PROBABILITIES OVER THE WATERS OF EASTERN GULF AND OFF THE ATLANTIC
COAST PER THE GEFS/ECENS/CMC (WHERE DEEP-LAYER INSTABILITY IS MORE
CONDUCIVE).
FOR NOW, WE DID NOT INCLUDE ANOTHER MARGINAL RISK IN THE DAY 5 ERO
(12Z WED-12Z THU) ACROSS CENTRAL FL. YES THE FRONT WILL REMAIN HUNG
UP IN THE VICINITY, HOWEVER THE HEAVY RAINFALL SIGNAL IS MORE
DIFFUSE WITH THE 0-6KM BULK SHEAR VALUES OVER 20KTS ALONG AND NORTH
OF THE FRONT, IMPLYING MORE ANAFRONTAL RAINFALL WHERE THE DEEP-
LAYER INSTABILITY (ELEVATED) IS MARGINAL AT BEST. AREAL SPREAD IN
THE QPF AMONG THE GLOBAL MODELS IS ALSO RATHER HIGH, AGAIN WITH THE
HEAVIER AMOUNTS OVER THE WATER (GULF AND ATLANTIC) WHERE THE
INSTABILITY IS DECIDEDLY MORE FAVORABLE. MEANWHILE, OF LATE THE AI
GUIDANCE (BOTH ECMWF AIFS AND AIGFS QPF) HAVE VERIFIED BETTER OF
LATE, LARGELY DUE TO THE AI MODELS HAVING A BETTER HANDLE ON THE
FRONTAL PROGRESSION. BY DAY 5, BOTH THE AIGFS AND EC AIFS SHOW THE
QPF AXIS A BIT FARTHER SOUTH (CENTRAL-SOUTH FL) COMPARED TO THE
REST OF THE GUIDANCE, AND NOT NEARLY AS HEAVY WITH THE AMOUNTS COMPARED
TO THE LATEST NBM. GIVEN THE HIGH FFG OVER THIS AREA, AND THE
CONCERN THAT THE RATES WILL NOT BE SUFFICIENTLY HIGH GIVEN THE LACK
OF DEEP-LAYER INSTABILITY, WE OPTED TO REFRAIN FROM HOISTING A
MARGINAL RISK AREA.
HURLEY
DAY 1 THREAT AREA: HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/94EPOINTS.TXT
DAY 2 THREAT AREA: HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/98EPOINTS.TXT
DAY 3 THREAT AREA: HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/99EPOINTS.TXT
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