435
FXUS62 KCAE 091837
AFDCAE
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE COLUMBIA SC
237 PM EDT FRI OCT 9 2026
WHAT HAS CHANGED
HURRICANE ISAIAS STRENGTHENS AND TURNS NORTHWARD TOWARD THE GULF
COAST. WIND ADVISORY OUT FOR THE CSRA SATURDAY. AVIATION
DISCUSSION UPDATED FOR 18Z TAFS.
KEY MESSAGES
- 1. AN ACTIVE WEEKEND AHEAD AS HURRICANE ISAIAS MOVES INLAND TO
OUR WEST. CONFIDENCE IN THE EXTENT OF IMPACTS INCREASING WITH
PERIODS OF HEAVY RAIN BRINGING AN ISOLATED FLOODING THREAT.
ISOLATED TORNADOES ARE POSSIBLE ON SATURDAY NIGHT AS WELL.
DISCUSSION
KEY MESSAGE 1: AN ACTIVE WEEKEND AHEAD AS HURRICANE ISAIAS
MOVES INLAND TO OUR WEST. CONFIDENCE IN THE EXTENT OF IMPACTS
INCREASING WITH PERIODS OF HEAVY RAIN BRINGING AN ISOLATED
FLOODING THREAT. ISOLATED TORNADOES ARE POSSIBLE ON SATURDAY
NIGHT AS WELL.
OVERVIEW: MODERATE TO HEAVY RAINFALL IS LIKELY AS HURRICANE
ISAIAS PASSES TO OUR WEST ON SATURDAY AND INTO SATURDAY NIGHT.
OVERALL, THE FORECAST HAS NOT CHANGED SIGNIFICANTLY SINCE
YESTERDAY AFTERNOON WITH THE 00Z AND 12Z SUITE OF GUIDANCE IS
FAIRLY SIMILAR AND IN LINE WITH FORECAST THINKING. HIGH CIRRUS
AND NOW SOME VIRGA IS PUSHING IN AND WILL CONTINUE TO GROW IN
THICKNESS AS THE HURRICANE APPROACHES THE FLORIDA/ALABAMA
COASTLINE THIS EVENING. THESE CLOUDS WILL CONTINUE TO KEEP
TEMPERATURES COOLER THAN THEY WOULD BE OTHERWISE. MOISTURE
ADVECTION WILL BE RELATIVELY QUICK THIS EVENING WITH PWS RISING
FROM WHERE THEY ARE CURRENTLY WHICH IS AROUND 0.8" TO WELL OVER
2" BY SATURDAY MORNING.
RAINFALL IS EXPECTED TO ACCOMPANY THIS & SHOULD BEGIN SOMETIME
AFTER MIDNIGHT TONIGHT. FORCING THIS RAINFALL WILL BE A
COMBINATION OF STRONG MOISTURE TRANSPORT & ISENTROPIC ASCENT
ATOP AN IN-SITU WEDGE ACROSS THE AREA. IT DOESN'T HURT THAT
SYNOPTIC SCALE LIFT SHOULD BE PRETTY GOOD AS WELL AS THE RIGHT-
ENTRANCE REGION OF AN UPPER LEVEL JET STREAK PUSHES NORTHWARD
INTO THE MID-ATLANTIC. GUIDANCE IS EFFECTIVELY IN TWO CAMPS:
NARROW BANDS OF HEAVY CONVECTIVE PRECIP VS WIDESPREAD
ISENTROPICALLY FORCED PRECIP. AS EXPECTED, AND WHAT IS LIKELY
MORE PHYSICALLY LIKELY, THE HI- RES GUIDANCE FOCUSES TWO BANDS
OF TRAINING CONVECTION. ONE ACROSS CENTRAL GA AND ANOTHER ALONG
A SECONDARY TROUGH AND HEAVY RAINFALL AXIS ALONG THE COAST WITH
RAINFALL TOTALS 3-5", BUT OUTSIDE OF OUR FORECAST AREA FOR NOW.
THE HRRR, HREF, AND REFS ALL PAINT A SIMILAR PICTURE WITH THIS
BANDING SETUP, LEAVING THE MIDLANDS AS A RELATIVE MINIMUM IN THE
REGION. THE GLOBAL AND AI GUIDANCE DO NOT CAPTURE THIS BANDING,
WITH A BROAD BRUSH 2-4" ACROSS THE REGION BUT IS LIKELY NOT A
PHYSICALLY REALISTIC SOLUTION. TRUSTING THE ENTIRE HI-RES
ENSEMBLE A BIT MORE, THE CONCERN IS THAT ANY OF THESE HEAVY
BANDS PUSH INTO OUR AREA, ESPECIALLY IN THE CSRA WHICH WOULD
PRESENT A INCREASED FLOOD RISK. SO THE I-20 CORRIDOR IN WESTERN
SC AND EASTERN GA SHOULD REMAIN ON GUARD IF THIS PRECIP BANDING
DECIDES TO SHIFT EAST; LREF-HREF-REFS PROBS OF OVER 4" ARE
ABOUT 30% IN THESE AREAS, DECREASING QUICKLY TO THE EAST. THE
HI- RES LPMM GENERALLY DOES A NICE JOB PORTRAYING THE FOOTPRINT
WELL FOR HEAVY RAIN EVENTS AS THIS TIME RANGE, BUT USUALLY
STRUGGLES SPATIALLY. SO SHIFTS OF 25-50 MILES WITH THIS BANDING
IS HIGHLY PLAUSIBLE, BRINGING A BOOM OR BUST POTENTIAL TO MUCH
OF THE AREA. CONFIDENCE IS INCREASING THAT THE NORTHERN MIDLANDS
WILL LIKELY BE THE DRIEST SPOT, SANDWICHED BETWEEN AREAS OF
STRONG CONVECTION AND LIFTING DYNAMICS BY THE TIME THE DEEPEST
MOISTURE ARRIVES.
THERE ARE OTHER POTENTIAL HAZARDS AT PLAY WITH THIS EVENT.
TORNADOES ARE CERTAINLY POSSIBLE IN THIS EVENT, ESPECIALLY
SATURDAY AFTERNOON AND NIGHT. AS ISAIAS' CIRCULATION LIFTS
NORTHWARD, THE AFORMENTIONED THERMAL GRADIENT IS EXPECTED TO
LIFT NORTHWARD AS WELL. THE TIMING OF THIS SHOULD BE SUCH THAT
IT OCCURS AS THE BEST MOISTURE TRANSPORT APPROACHES BEHIND THE
INITIAL WARM FRONT, WHICH COULD CREATE A SCENARIO ON SATURDAY
NIGHT THAT WE SEE LOW- TOPPED SUPERCELLS DEVELOP IN A HIGHLY
SHEARED ENVIRONMENT. LCLS WILL BE QUITE LOW, AND WE TYPICALLY
DON'T NEED MUCH MORE THAN A SURFACE DEWPOINT OF 70F TO HAVE SOME
TROPICAL TORS DEVELOP. THE RRFS AND HRRR HAVE BOTH SHOWN SIGNS
OF DEVELOPING THE NECESSARY CONVECTION AS WELL AS PUSHING
SUFFICIENT LOW-LEVEL CAPE INTO THE AREA ON SATURDAY NIGHT. SPC
HAS PLACED THE AREA IN A SLIGHT RISK, DRIVEN BY A TORNADO
THREAT. HAVE MULTIPLE WAYS TO RECEIVE WARNINGS ON SATURDAY
NIGHT!
WINDS ARE THE OTHER THREAT BUT LIKELY THE LEAST IMPACTFUL. SOME
GUSTS OVER 40 MPH ARE EXPECTED IN THE WESTERN MIDLANDS AND AS A
RESULT, A WIND ADVISORY HAS BEEN ISSUED TO COVER THIS POTENTIAL
THROUGHOUT SATURDAY. OTHERWISE, IT SHOULD JUST BE BREEZY ACROSS
MUCH OF THE AREA, WITH GUSTS OF 25-35 MPH POSSIBLE ESPECIALLY
SATURDAY MORNING AND EARLY AFTERNOON.
AVIATION /18Z FRIDAY THROUGH WEDNESDAY/
VFR CONDITIONS EXPECTED INTO FRIDAY EVENING FOLLOWED BY
DETERIORATING CONDITIONS FRIDAY NIGHT AND SATURDAY.
MID-LEVEL CLOUD COVER WILL REMAIN IN PLACE AS MOISTURE STEADILY
PUSHES IN THE FROM THE SOUTH THIS AFTERNOON AND EVENING. RAIN
CHANCES WILL HOLD OFF UNTIL LATER THIS EVENING AND OVERNIGHT,
WITH CIGS STEADILY FALLING AFTER 00Z EVENTUALLY DOWN TO IFR
SATURDAY MORNING. RAIN WILL OVERSPREAD THE AREA THROUGHOUT MUCH
OF SATURDAY BUT WILL BE PERIODIC IN NATURE WITH WAVES OF HEAVIER
RAIN BRINGING IFR-LIFR CONDITIONS THROUGHOUT THE DAY. WINDS WILL
BE STRENGTHENING OUT OF THE EAST OVERNIGHT AND ESPECIALLY
SATURDAY WITH GUSTS OVER 15 KNOTS TONIGHT AND OVER 25 KNOTS
SATURDAY MORNING AND AFTERNOON. CONDITIONS WILL CONTINUE TO
REMAIN IFR-LIFR THROUGH THE END OF THE TAF PERIOD WITH GUSTY
WINDS, RAIN, AND LOW CIGS LASTING INTO SUNDAY MORNING.
EXTENDED AVIATION OUTLOOK...STRONG GUSTY NORTHEASTERLY WINDS
LIKELY THROUGHOUT SATURDAY EVENING AND SUNDAY ALONG WITH
PERIODS OF HEAVY RAIN AND IFR CONDITIONS.
THE THREAT OF
RESTRICTIONS AND RAINFALL INCREASES SATURDAY MORNING/AFTERNOON
AS TROPICAL MOISTURE SURGES INTO THE SOUTHEAST WITH ISAIAS.
CAE WATCHES/WARNINGS/ADVISORIES
SC...WIND ADVISORY FROM 5 AM TO 11 PM EDT SATURDAY FOR SCZ018-025.
LAKE WIND ADVISORY FROM 5 AM TO 11 PM EDT SATURDAY FOR SCZ016-
020>022-026>031-035-037-038-041-115-116-135>137.
GA...WIND ADVISORY FROM 5 AM TO 11 PM EDT SATURDAY FOR GAZ040-
063>065-077.
DISCUSSION...42/PL
AVIATION...42/PL
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