MESOSCALE PRECIPITATION DISCUSSION 0210
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
212 AM EDT MON MAY 28 2018

AREAS AFFECTED...COASTAL SOUTH CAROLINA...

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 280615Z - 281200Z

SUMMARY...TRAINING, HIGHLY EFFICIENT TROPICAL THUNDERSTORMS POSE
FLASH FLOOD RISK ACROSS COASTAL SC THROUGH EARLY MORNING HOURS.

DISCUSSION...GOES-16 WV SUITE DEPICT A WELL DEFINED DRY SLOT
ACROSS THE FL PENINSULA PUNCHING INTO S GA.  SATELLITE DERIVED AMV
SUGGEST A LOCAL SPEED MAX ALONG THE INTERFACE OF THE DRY SLOT AND
WARM CONVEYOR WITH A SHORTWAVE TROF AT THE LEADING EDGE NEARING
THE GA/SC COAST.  IN RESPONSE...LOW LEVEL FLOW AS BACKED IN THE
WARM CONVEYOR BELT AND INCREASED CONVERGENCE TO SPARK DEEP
CONVECTION ALONG THE INTERFACE.  ORIENTATION OF THE BOUNDARY IS
FAIRLY PERPENDICULAR TO THE SC COASTLINE BETWEEN HILTON HEAD
ISLAND AND CHS AND PROVIDES AN EXCELLENT CHANNEL FOR N-S TRAINING.

CIRA LPW SHOW STRONG ALIGNMENT OF DEEP TROPICAL MOISTURE ALLOWING
FOR NEARLY SATURATED DEEP PROFILES WITH TPWS IN THE 2.25" RANGE. 
UNDERLAYED IS A VERY WARM GULF STREAM SUPPORTING STRONG
INSTABILITY UP TO 2000 J/KG EVEN THOUGH PROFILES WOULD BE 'SKINNY'
WITH NEAR ZERO DEWPOINT DEPRESSIONS THROUGH THE CLOUD GROWTH
LAYERS.  AS SUCH RAINFALL EFFICIENCY WILL BE QUITE HIGH EVEN WITH
SHALLOW CONVECTION...YET DEEPER CONVECTION MAY HAVE THE POTENTIAL
FOR 2.5"/HR.  HOWEVER...GOES-16 CLEAR IR DOES NOT SUGGEST EXTREME
CONVECTIVE DEPTH WITH CYCLING WEAK SMALL/NARROW CONVECTIVE TOWERS
TO -65C.  EXPECT THIS COVERAGE AND COOLING TO CONTINUE ESPECIALLY
TOWARD DIURNAL CONVECTIVE MAXIMA JUST BEFORE DAY BREAK. 
ADDITIONALLY...20 KT ONSHORE FLOW BECOMES CONVERGENT INTO ENELY
FLOW ONSHORE DELINEATING AN EFFECTIVE COASTAL FRONT WHICH COULD
AID SOME UPGLIDE/ISENTROPIC ASCENT.  IN THE UPPER LEVELS, WV SUITE
DOES DEPICT SOME DIFFLUENCE ALONG/JUST AHEAD OF THE JET STREAK
OVER SC ATTM...THIS MAY HELP ASCENT BUT OVERALL FLOW ALOFT IS
WEAK...SO IT MAY NOT BE HIGHLY EFFECTIVE FOR BROADER GROWTH BUT
LIKELY WILL AID ANY CELLS ONGOING.

HI-RES CAMS SUPPORT THIS GENERAL IDEA BUT ARE LESS FOCUSED WITH
EXCEPTION OF THE NAM CONEST (THOUGH CURRENTLY NOT DIRECTED
PROPERLY TO SC COAST).  THIS BROADENS OVERALL TOTALS BUT STILL A
SUGGESTION OF 3-4" IS PROBABLE.  IF TRAINING IS MORE FOCUSED
TOTALS COULD BE SIGNIFICANT OVER 6" WHICH WOULD BE LIKELY TO
PRODUCE FLASH FLOODING EVEN ALONG THE COAST WHERE FFG VALUES OF
2.5-3.5" WOULD BE EXCEEDED.  CONFIDENCE (MAINLY DUE TO SMALL
CONVECTIVE GROWTH CURRENTLY OBSERVED) IS A BIT LOW AND FF IS
CURRENTLY CONSIDERED POSSIBLE LIKELY TO PEAK CLOSER FROM 9-12Z
THAN EARLIER.

GALLINA

ATTN...WFO...CAE...CHS...ILM...

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

LAT...LON   34367973 34367936 34147899 33917872 33687867
            33287899 33007931 32717979 32268043 32028086
            32398112 32888110 33568085 33878059 34108026