MESOSCALE PRECIPITATION DISCUSSION 0551
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1026 AM EDT SUN OCT 04 2015
 
AREAS AFFECTED...SOUTH CAROLINA...EXTREME SOUTHEAST NORTH CAROLINA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 041415Z - 042015Z
 
SUMMARY...A HISTORIC RAINFALL EVENT CONTINUES ACROSS MUCH OF SOUTH
CAROLINA THIS MORNING WITH VERY HEAVY RAINFALL RATES CONTINUING.
WIDESPREAD SEVERE AND LOCALLY CATASTROPHIC FLASH FLOODING WILL
CONTINUE THROUGH THE AFTERNOON.

DISCUSSION...A WELL-DEFINED AND DEEP TROPICAL MOISTURE PLUME
FEEDING IN OFF THE ATLANTIC OCEAN INTO THE NORTH SIDE OF THE
CLOSED UPPER LEVEL LOW OVER THE SOUTHEAST U.S. HAS BEEN SLOWLY
PIVOTING IN A CYCLONIC FASHION TO MORE OF A WEST/EAST ORIENTATION.
THIS HAS ALLOWED THE PERSISTENT AND INTENSE BAND OF HEAVY RAINFALL
AND THUNDERSTORMS OVER CENTRAL AND EASTERN SOUTH CAROLINA TO PIVOT
VERY SLOWLY NORTHEASTWARD...WHICH HAS TAKEN THE WORST OF THE
RAINFALL OUT OF THE CHARLESTON METROPOLITAN AREA FOR THE TIME
BEING.

THE DEEP MOISTURE PLUME IS COINCIDING WITH TREMENDOUS MID AND
UPPER LEVEL DIVERGENCE AROUND THE NORTHEASTERN FLANK OF THE UPPER
LOW...WHICH IS FOSTERING VIGOROUS ASCENT IN AN ENVIRONMENT WITH
1.8 TO 2.3 INCH PW VALUES AS PER GOES-SOUNDER AND GPS DATA.  SOME
OF THIS MOISTURE AGAIN IS ORIGINATING FROM HURRICANE JOAQUIN WELL
OFF THE EAST COAST WHICH IS CONFIRMED BY THE CIRA LAYERED PW
PRODUCT. A RATHER STRONG INSTABILITY GRADIENT IS NOTED TOO NEAR
THE COASTAL FRONT AND OFFSHORE...WITH MUCAPE VALUES OF 1000-2000
J/KG NEAR THE UPPER SOUTH CAROLINA COAST. THE ENHANCED DEEP LAYER
MOISTURE AND INSTABILITY TRANSPORT INTO THE BOUNDARY ARE
CONTRIBUTING TO ENHANCED RAINFALL RATES...WHICH ARE NEAR 3
INCHES/HR WITHIN THE STRONGER CONVECTIVE BANDS NEAR THE COAST. 

HI RES GUIDANCE INDICATES THAT ADDITIONAL RAINFALL AMOUNTS OVER
THE NEXT SIX HOURS WILL BE ON THE ORDER OF 3 TO 6 INCHES WITH
ISOLATED HEAVIER AMOUNTS TO NEAR 8 INCHES. THESE AMOUNTS WILL BE
ON TOP OF AREAS THAT HAVE ALREADY SEEN WELL IN EXCESS 12 INCHES OF
RAIN...AND ISOLATED AREAS OF OVER 20 INCHES. THE HEAVIER AMOUNTS
OVER THE NEXT FEW HOURS ARE EXPECTED TO BE CONFINED TO CENTRAL AND
EASTERN SOUTH CAROLINA AND WITH A STRONGER FOCUS CLOSER TO THE
NORTH CAROLINA BORDER WHERE ENHANCED LOW LEVEL CONVERGENCE IS
NOTED. 

THESE RAINFALL TOTALS WILL EXACERBATE WHAT IS ALREADY A SERIOUS
LIFE-THREATENING EVENT WITH SEVERE AND LOCALLY CATASTROPHIC FLASH
FLOODING.

ORRISON

ATTN...WFO...CAE...CHS...GSP...ILM...MHX...RAH...

ATTN...RFC...SERFC...

LAT...LON   35088198 34657999 34727832 34867730 34537689 
            34207735 33557834 32947916 32958048 33418182 
            34158273 34708284