MESOSCALE PRECIPITATION DISCUSSION 0807
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1032 PM EDT MON SEP 11 2017

AREAS AFFECTED...PORTIONS OF THE CAROLINAS

CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY

VALID 120231Z - 120831Z

SUMMARY...IRMA CONTINUES TO EVOLVE WHILE DROPPING HEAVY RAINS ON
PORTIONS OF THE CAROLINAS.  HOURLY RAIN TOTALS TO 1.5" WITH LOCAL
AMOUNTS TO 3" CONTINUES FLASH FLOOD CONCERNS.

DISCUSSION...IRMA'S EXTRATROPICAL TRANSITION CONTINUES THIS
EVENING.  A TEXTBOOK EXAMPLE OF A DRY SLOT HAS PUNCHED THROUGH GA,
SC, AND INTO SOUTHERN NC, NOTED ON INFRARED AND WATER VAPOR
IMAGERY.   THE LEADING EDGE OF WARMER TEMPERATURES AND LOWERING
DEW POINTS AT THE SURFACE LIES OFFSHORE EASTERN FL AND EXTENDS
INTO SOUTHERN SC.  PRECIPITABLE WATER VALUES RANGE FROM 1.6" IN
THE SOUTHERN APPALACHIANS TO 2.5" NEAR GEORGETOWN SC PER GPS
VALUES.  INFLOW AT 850 HPA IS CONVERGENT AT 25-45 KTS PER 00Z
SOUNDINGS, NEAR THE MAGNITUDE OF THE 850-400 HPA WIND.  EFFECTIVE
BULK SHEAR OF 35-40 KTS IS SEEN IN RECENT SPC MESOANALYSES ACROSS
SC.  AN AREA OF 500-1000 J/KG OF MU CAPE LIES NEAR AND OFFSHORE
THE SC COAST.

AS IRMA PULLS AWAY TO THE NORTHWEST, A NEW CIRCULATION COULD FORM
ACROSS SC TOWARD THE END OF THE PERIOD NEAR THE COASTAL
FRONT/EASTERN SIDE OF THE COLD AIR DAM WHICH COULD ENHANCE
BOUNDARY LAYER MOISTURE CONVERGENCE BOTH WITHIN THE COASTAL FRONT
AND NEAR THE LEADING EDGE OF THE DEW POINT/TEMPERATURE DROP OFF. 
WHILE INFLOW AT 850 HPA AND EFFECTIVE BULK SHEAR ARE EXPECTED TO
SLOWLY DROP OFF, THEY SHOULD REMAIN SUFFICIENT FOR THE DEVELOPMENT
OF SHORT TRAINING BANDS.  WITHIN UPSLOPE AREAS, HOURLY RAIN TOTALS
TO 0.5" ARE EXPECTED, WHILE 2" AN HOUR TOTALS ARE EXPECTED IN THE
COASTAL PLAIN.  FLASH FLOOD ISSUES ARE MOST LIKELY FROM THE FALL
LINE SOUTHEASTWARD IN SC.

ROTH

ATTN...WFO...CAE...CHS...GSP...ILM...MRX...RAH...RNK...

ATTN...RFC...LMRFC...OHRFC...SERFC...

LAT...LON   36558140 36358021 35858054 35448010 34977903
            34287782 33807791 33727869 33007929 32618020
            33178113 35228340