MESOSCALE PRECIPITATION DISCUSSION 0554
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
956 PM EDT SUN OCT 04 2015
 
AREAS AFFECTED...PORTIONS OF EASTERN SC & SOUTHEAST NC 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 050156Z - 050756Z
 
SUMMARY...RAINFALL ACROSS THE REGION HAS DECREASED IN INTENSITY
AND COVERAGE AS OF LATE.  THE FLASH FLOOD EVENT APPEARS TO BE
WANING ALONG THE SC/NC COAST.

DISCUSSION...A PAIR OF LOW PRESSURE AREAS NEAR CHARLESTON SC AND
WELL OFFSHORE MYRTLE BEACH ARE ALONG A TROUGH AND COASTAL FRONT
WHICH APPEAR TO BE RECEDING INTO THE WESTERN ATLANTIC.  THE PARENT
UPPER LEVEL LOW HAS MOVED OFFSHORE ST. AUGUSTINE FL, WHICH IS
SHIFTING THE MOISTURE BAND/COMMA HEAD ALONG A MORE WSW-ENE
ORIENTATION NEAR THE SC COAST.  A LOOSE BAND OF SHOWERS AND
THUNDERSTORMS LIES JUST OFFSHORE THE NC COAST AND IS TRYING TO
ADVANCE INTO THE CENTRAL SC COAST.  HOWEVER, THE HIGHEST RAIN
RATES HAVE BEEN CLOSE TO 50 MILES OFFSHORE THE ISLE OF PALMS SC
DURING THE PAST HOUR, DESPITE RECENT SATELLITE TRENDS TO THE
CONTRARY.

SPC MESOANALYSES INDICATE THAT INSTABILITY IS SHIFTING MORE
OFFSHORE WITH TIME, WHICH HELPS EXPLAIN THE DECREASE IN RAIN RATES
-- RIGHT ALONG THE COAST, MLCAPES AND MUCAPES ARE 100-250 J/KG
WITH 1000+ J/KG MUCAPES NOW 60 MILES OFFSHORE.  ANOTHER PROBLEM IS
THAT THE EARLIER RAIN BAND WHICH WAS ALIGNED WITH THE STRONGEST
LOW-LEVEL INFLOW ACROSS SOUTHEAST NC HAS FADED, WITH THE NEW BANDS
OFFSET TO THE SOUTH.  STILL, INFLOW AT 850 HPA NEAR THE CURRENT
BANDS IS BETWEEN 25-50 KTS PER VAD WIND PROFILES, NEAR THE
MAGNITUDE OF THE MEAN 850-400 HPA WINDS.

THE CAM GUIDANCE INDICATES LOCAL RAIN AMOUNTS OF 3-5" REMAIN IN
THE CARDS ALONG THE SC COAST, BUT CONSIDERING THE ABOVE FACTORS,
THE GUIDANCE COULD BE TOO HIGH.  CONSIDERING THE DISTANCE OFFSHORE
THE INSTABILITY HAS RETREATED, HOURLY RAIN RATES UP TO 1.5" ARE
POSSIBLE, SHOULD THE CONVECTION MAKE LANDFALL FROM THE ATLANTIC. 
CONSIDERING THE UNCERTAINTY AND THE SATURATED SOILS/CONTINUED
FLOODING ACROSS THE REGION, USED THE POSSIBLE CATEGORY.

ROTH

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

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

LAT...LON   33997833 33847798 33807841 33487895 32997931 
            32557996 32348036 32228084 32568081 32938051 
            33628032 33887983 33747915