370
FXUS62 KCAE 081719
AFDCAE
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE COLUMBIA SC
119 PM EDT THU OCT 8 2026
WHAT HAS CHANGED
HURRICANE ISAIAS CONTINUES TO STRENGTHEN IN THE GULF. 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.
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.
OVERVIEW: MODERATE TO HEAVY RAINFALL IS LIKELY AS HURRICANE
ISAIAS PASSES TO OUR WEST ON SATURDAY AND INTO SATURDAY NIGHT.
DISCUSSION: HURRICANE ISAIAS REMAINS IN A HURRICANE IN THE
CENTRAL GULF THIS AFTERNOON, IN LINE WITH FORECAST EXPECTATION
SO FAR. GUIDANCE CONTINUES TO BE IN FAIRLY GOOD AGREEMENT ON IT
INTENSIFYING QUICKLY OVER THE NEXT 24-36 HOURS AS IT TREKS
NORTHEASTWARD AND BEGINS INTERACTING WITH AN UPPER LEVEL TROUGH
PUSHING EASTWARD OUT OF TEXAS. WHILE CONTINUING TO DECREASE IN
THE 00Z AND 12Z MODEL SUITES, THERE IS STILL SOME SPREAD BETWEEN
THE AI & PHYSICS- BASED MODELS ON HOW FAR EAST ISAIAS
EVENTUALLY MAKES LANDFALL. REGARDLESS, THE IMPACTS TO THE
MIDLANDS AND CSRA ARE EXPECTED TO BE RELATIVELY UNCHANGED
REGARDLESS OF TRACK WITH OUR MAIN FEATURE BEING A SECONDARY AXIS
OF MOISTURE AND FORCING.
ISAIAS WILL OVERSPREAD THE AREA WITH WIDESPREAD HIGH CLOUD COVER
OVER THE NEXT COUPLE OF DAYS AS THE SYSTEM INTERACTS WITH A REMNANT
TROUGH OVER TEXAS. THIS TROUGH WILL CONTINUE TO SHIFT THE ISAIAS
NORTHEASTWARD AND EVENTUALLY NORTHWARD AS THE NORTHERN/SOUTHERN
STREAM OF THE JET STREAK MERGE OVER THE MID-ATLANTIC AND EVERYTHING
GRADUALLY AMPLIFIES. THE RIGHT ENTRANCE REGION OF THIS UPPER LEVEL
JET STREAK IS FORECAST TO OVERSPREAD MUCH OF THE SOUTHEASTERN CONUS
BY FRIDAY AFTERNOON, HELPING MOISTURE ADVECTION TO BEGIN GOING TO
OUR SOUTH. AS ISAIAS MOVE NORTHWARD, IT WILL BEGIN INTERACTING WITH
THE OVERALL SYNOPTIC PATTERN & IS EXPECTED TO EXPAND IN SIZE,
PUSHING UP AGAINST A LOW-LEVEL HIGH PRESSURE SYSTEM & DEVELOP A
STRONG EASTERLY BRANCH OF THE LOW-LEVEL JET THAT EXTENDS ACROSS
OUR AREA. THIS FEATURE, IN SOME FORM OR FASHION, IS EXPECTED TO
OVERSPREAD THE AREA DURING THE DAY ON SATURDAY. AS IT DOES SO,
SIGNIFICANT PWS ON THE ORDER OF 2-2.5 STANDARD DEVIATIONS ABOVE
NORMAL (2.25"+) WILL OVERSPREAD THE REGION.
THE SYNOPTIC PATTERN ASSOCIATED WITH THIS, FEATURING HIGH PWS, A
BROAD ENTRANCE REGION OF AN UPPER LEVEL JET, ONSHORE 850 HPA FLOW
ATOP A STRONG SURFACE HIGH PRESSURE, THE ASSOCIATED WARM FRONTAL
AND ISENTROPIC LIFT ZONE, SHOULD FAVOR WIDESPREAD AND HEAVY
RAINFALL ON SATURDAY. GUIDANCE HAS FINALLY ACQUIESCED AND IN
GENERAL HAS STEADILY RAMPED UP PRECIP TOTALS ACROSS SC AND
EASTERN GA, FALLING IN LINE WITH THE AFOREMENTIONED
METEOROLOGICAL AND CLIMATOLOGICAL EXPECTATIONS. WHILE SOME
"DRY" SLOT DOES DEVELOP ACROSS PARTS OF THE INTERIOR SOUTHEAST
AS A SORT OF COASTAL LOW, OR MORE FOCUSED TROUGH ALONG THE WARM
FRONT AND SURFACE BOUNDARY FORMS, THIS DOES NOT APPRECIABLY
REDUCE RAINFALL TOTALS LIKE PREVIOUS GUIDANCE HAS SUGGESTED.
EXTREMELY IMPRESSIVE PWATS AND AN EASTERLY 925-700MB JET OVER 50
KNOTS COMBINE TO PRODUCE A BROAD SHIELD OF IVT AND ASSOCIATED
STRONG ISENTROPIC LIFT ACROSS THE NORTHWARD LIFTING SURFACE
BOUNDARY AND WARM FRONT. THIS STRONG IVT AND WAA DEVELOPS BY
SATURDAY MORNING, CONTINUING THROUGH EARLY SUNDAY, ALL WITHIN A
PLUME OF 2.25" PWATS AND A LOOSELY UNSTABLE WARM SECTOR SOUTH OF
THE BOUNDARY AND RECIPE FOR AT LEAST PERIODS OF HEAVY RAIN FOR
THE AREA.
WHILE TICKING UP, RAINFALL TOTALS STILL VARY A BIT ACROSS
GUIDANCE, BUT THE DISTRIBUTION AND POTENTIAL HAS COME INTO
BETTER FOCUS AND AGREE MUCH BETTER WITH THE METEOROLOGICAL
SETUP. IN GENERAL A WIDESPREAD 2-4" LOOKS LIKELY FOR MUCH OF
THE AREA, WITH LREF AND AI ENSEMBLES NOW IN MUCH BETTER
AGREEMENT. THE 10-90TH PERCENTILE RANGES ARE EXPECTEDLY LARGE
HOWEVER AND THIS WILL LIKELY REMAIN THE CASE UNTIL THE EVENT IS
UNFOLDING. BUT A REASONABLE WORST CASE FOR RAINFALL (90TH
PERCENTILE) IS GENERALLY 3-5" FOR OUR AREA. IN REALITY, THE
FOOTPRINT OF THE RAINFALL WILL LIKELY LOOK LIKE A MIX OF THE
10TH AND 90TH TOGETHER, SOME AREAS UNDERACHIEVING WHILE OTHERS
OVER. THESE TROPICAL HIGH PWAT, WEAKLY UNSTABLE EVENTS TEND TO
PRODUCE BANDING AND SPORADIC RAINFALL FOOTPRINTS THAT DEVELOPS
ALONG MESOSCALE FEATURES WITHIN THE STRONG LOW LEVEL FLOW. WHILE
WIDESPREAD FLOODING IS NOT EXPECTED GIVEN HOW DRY THE AREA HAS
BEEN, ANY LOCATIONS THAT PUSH TOWARDS THE HIGHER END SCENARIO
WILL EXCEED FLASH FLOOD GUIDANCE.
WHILE A SECONDARY HAZARD, THE TORNADO POTENTIAL IS ALSO WORTH
NOTING. IMPRESSIVE HODOGRAPHS SOUTH OF THE WARM FRONT WITH A 50
KNOT 850MB JET SURGE NORTH WITHIN THE BULK OF THE DEEPEST
PWATS. INSTABILITY WILL NOT BE IMPRESSIVE DESPITE LCLS SCRAPPING
THE GROUND HOWEVER, BUT IT WILL NOT TAKE MUCH FROM A CONVECTIVE
UPDRAFT AND STRETCHING POTENTIAL TO PRODUCE A FEW TORNADOES
WITHIN THIS ENVIRONMENT. SO A FEW WEAK SHORT LIVED TORNADOES
ACROSS THE AREA REMAINS POSSIBLE, PRIMARILY LATE SATURDAY
AFTERNOON INTO EARLY SUNDAY.
OVERALL, WHILE WE WILL SEE SOME HEAVY RAIN AND BREEZY WINDS, ISAIAS
LOOKS TO REMAIN WELL WEST OF THE REGION, AND ITS GREATEST
IMPACTS ARE FORECAST TO REMAIN THERE AS WELL. HOWEVER, THAT
DOESN'T MEAN THAT WE WON'T SEE IMPACTS HERE LOCALLY. KEEP AN EYE
ON THE FORECAST OVER THE NEXT COUPLE OF DAYS!
AVIATION /18Z THURSDAY THROUGH TUESDAY/
VFR CONDITIONS EXPECTED THROUGHOUT THE FORECAST PERIOD.
WIDESPREAD MID-UPPER LEVEL CLOUD WILL CONTINUE TO OVERSPREAD THE
AREA TODAY AND TONIGHT AND THIS WILL PREVENT ANY SORT OF FOG-
STRATUS CONCERNS FOR FRIDAY MORNING. WINDS WILL REMAIN FAIRLY
LIGHT AND VARIABLE THE REMAINDER OF THURSDAY INTO THURSDAY NIGHT
BEFORE STRENGTHENING OUT OF THE NORTHEAST FRIDAY MORNING. RAIN
CHANCES WILL HOLD OFF UNTIL AFTER THE TAF PERIOD WITH CIGS
REMAINING HIGH VFR UNTIL LATE FRIDAY NIGHT.
EXTENDED AVIATION OUTLOOK...THE THREAT OF RESTRICTIONS AND
RAINFALL INCREASES SATURDAY MORNING AS TROPICAL MOISTURE SURGES
INTO THE SOUTHEAST WITH ISAIAS. STRONG GUSTY NORTHEASTERLY
WINDS LIKELY THROUGHOUT SATURDAY AND SUNDAY ALONG WITH PERIODS
OF HEAVY RAIN AND LIFR CONDITIONS.
CAE WATCHES/WARNINGS/ADVISORIES
SC...NONE.
GA...NONE.
DISCUSSION...42
AVIATION...42
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