MESOSCALE PRECIPITATION DISCUSSION 0805
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1044 AM EDT MON SEP 11 2017

AREAS AFFECTED...SE AND CENTRAL GEORGIA AND SOUTHERN SC

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

VALID 111443Z - 112043Z

SUMMARY...FLASH FLOODING LIKELY TO THE NORTH AND NORTHEAST OF
IRMA'S TRACK WITH THE GREATEST RISK FROM CENTRAL GEORGIA TO
SOUTHERN SOUTH CAROLINA.

DISCUSSION...DRY AIR CONTINUES TO WRAP AROUND THE SOUTHEAST AND
SOUTH SIDE OF IRMA ...AS EVIDENT IN LATEST GOES 16 RGB AIRMASS
PRODUCTS...BRINGING A QUICK END TO PRECIPITATION SOUTH OF THE
CENTER. THESE PRODUCTS ALSO SHOW A COOLING OF CLOUD TOPS TO THE
NORTHEAST OF THE LOW CENTER WHERE CONVECTION WILL REINVIGORATE
INTO THIS AFTERNOON. THE THREAT AREA WILL SHIFT TO THE NORTH WITH
PERSISTENT RAIN BANDS BRINGING HIGH RAINFALL RATES TO COASTAL
AREAS OF SOUTHEAST GEORGIA AND SOUTHERN SOUTH CAROLINA AND INTO
CENTRAL GEORGIA WHERE THE RAIN BANDS WILL LIFT OVER THE COASTAL
FRONT.

THESE RAIN BANDS CONTINUE TO REFIRE IN STRONG CONVERGENT FLOW
TAPPING INTO OFFSHORE INSTABILITY OF 1000-2000 J/KG CAPE. LOW
LEVEL INFLOW IS EXPECTED TO INCREASE THIS AFTERNOON AS THE MAIN
CIRCULATION OF IRMA MOVES CLOSER TO THE AREA BEFORE TURNING TO THE
NORTHWEST. AS IRMA BEGINS TO TAKE A MORE WESTERLY COMPONENT THESE
RAIN BANDS WILL SLOW THEIR NORTHWARD PROGRESSION AND POSSIBLY EVEN
STALL. A STRONG COASTAL FRONT ACROSS SOUTHEAST GEORGIA AND
SOUTHERN SOUTH CAROLINA WILL FOCUS INTENSE RAINFALL RATES ALONG
THE COAST UNTIL STRENGTHENING LOW LEVEL FLOW CAN PUSH THE COASTAL
FRONT INLAND. MEANWHILE...STRONG LOW LEVEL FLOW LIFTING OVER THE
COASTAL FRONT WILL SUSTAIN AN AREA OF MODERATE RAINFALL RATES
NORTH OF IRMA'S TRACK INTO CENTRAL GEORGIA.

WHILE HI-RES MODELS ARE IN CONSIDERABLY GOOD AGREEMENT WITH
MAGNITUDE AND PLACEMENT OF PRECIP OVER THE NEXT 6 HOURS THERE IS
CONCERN THAT THE MAXIMUM MAY BE MISPLACED TOO FAR INLAND. WITH THE
INSTABILITY REMAINING OFFSHORE...WOULD TEND TO THINK THAT
PRECIPITATION RATES WILL BE MAXIMIZED WITH THE RAIN BANDS COMING
ONSHORE. THIS HAS BEEN THE CASE FOR MUCH OF IRMA'S PATH ACROSS
FLORIDA.  MORE MODEST RATES ARE EXPECTED INLAND WHERE INSTABILITY
WILL BE LACKING....BUT COULD SEE INCREASING THREAT AS LOW AND MID
LEVEL FORCING INCREASES WITH THE APPROACH OF IRMA'S CIRCULATION.

KREKELER

ATTN...WFO...CAE...CHS...FFC...JAX...TAE...

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

LAT...LON   33568225 33488078 32797963 32028008 31098137
            31238328 31558428 32478431 33118373