MESOSCALE PRECIPITATION DISCUSSION 0847
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
557 AM EDT SUN OCT 01 2017

AREAS AFFECTED...NERN FL PENINSULA

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

VALID 010955Z - 011350Z

SUMMARY...SLOW MOVING CORES OF HEAVY RAIN ARE LIKELY TO PERSIST
ALONG THE NERN FL PENINSULA FOR AT LEAST ANOTHER 2-3 HOURS.
RAINFALL RATES NEAR 3 IN/HR WILL BE POSSIBLE WHICH MAY LEAD TO
FLASH FLOODING.

DISCUSSION...EXPERIMENTAL GOES 16 10.3 MICRON CLEAN WINDOW IR
IMAGERY SHOWED THE RECENT DEVELOPMENT OF COLDER CLOUD TOPS OVER
ST. JOHNS COUNTY IN NERN FLORIDA AFTER THE WARMING OF CLOUD TOPS
TIED TO A WEAKENING MCV FARTHER EAST OVER OPEN WATER. KJAX RADAR
IMAGERY SHOWED SLOW MOVING CORES OF HEAVY RAIN IN ST. JOHNS
COUNTY...STRETCHING SOUTH ALONG I-95 INTO FLAGLER COUNTY WITH TWO
WUNDERGROUND.COM OBSERVATION STATIONS JUST NORTH OF PALM COAST
REPORTING RAINFALL RATES NEAR 2 IN/HR ENDING 0920Z...SLIGHTLY
HIGHER THAN RADAR ESTIMATED RAIN RATES OF 1.5 IN/HR.

KJAX VAD WINDS AND RAP ANALYSES SUPPORT ROUGHLY 30 KT OF
CONVERGENT EASTERLY 850 MB FLOW INTO THE COAST WHERE LFC-EL MEAN
WINDS WERE NEARLY STATIONARY. IT APPEARS A SMALL MCV IN SOUTHERN
ST. JOHNS COUNTY COULD BE LATCHED ONTO A TROUGH ORIENTED NORTHEAST
TO SOUTHWEST ACROSS THE AREA...KEEPING HEAVY RAINFALL NEARLY
STATIONARY OVER THE REGION. SPC MESOANALYSES INDICATED THE
RAINFALL WAS OCCURRING ON THE NORTHERN EDGE OF WEAK MLCAPE WITH
VALUES OF 100-250 J/KG. SHORT TERM FORECASTS FROM THE RAP/HRRR
SUGGEST LOW LEVEL WINDS AND CAPE WILL REMAIN ABOUT THE SAME OVER
THE NEXT FEW HOURS AMID PRECIPITABLE WATER VALUES OF 2.2 TO 2.3
INCHES.

WHILE MANY OF THE RECENT HRRR AND EXPERIMENTAL HRRR CYCLES HAVE
NOT BEEN HANDLING ONGOING RAINFALL WELL...THE 01Z RUN OF THE
EXPERIMENTAL HRRR IS CLOSE TO CURRENT OBSERVATIONS...ALBEIT
DISPLACED TO THE NORTH. THIS RUN AND SHORT TERM EXTRAPOLATION
SUGGEST 3-6 ADDITIONAL INCHES OF RAINFALL WILL BE POSSIBLE OVER
NORTHEASTERN FLORIDA...FOCUSING FROM CLAY/PUTNAM INTO ST. JOHNS
AND FLAGLER COUNTIES. THESE AMOUNTS COULD LEAD TO FLASH
FLOODING...ESPECIALLY IF IT FALLS OVER MORE URBAN LOCATIONS.

OTTO

ATTN...WFO...JAX...MLB...

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

LAT...LON   30258139 30218106 29868053 29088066 29098133
            29458215 29828224 30168194