MESOSCALE PRECIPITATION DISCUSSION 0031
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
640 AM EDT FRI MAY 03 2013
 
AREAS AFFECTED...NORTHEAST FL 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 031040Z - 031640Z
 
SUMMARY...PERSISTENT HEAVY RAINFALL WITH LOCAL RATES OF 2-3 INCHES
PER THREE HOURS COULD CAUSE FLASH FLOODING IN NORTHEAST FL.

DISCUSSION...A LONG-DURATION BAND OF RAIN AND THUNDERSTORMS IS
LOCATED WITHIN THE WARM CONVEYOR BELT OF AN UPPER LEVEL CYCLONE,
TO THE NORTH OF A SURFACE LOW PRESSURE AREA POSITIONED OFFSHORE
THE GOLD COAST OF FL.  THE RAINFALL WAS FOCUSED INTO THE NORTHEAST
FLORIDA COAST BETWEEN JACKSONVILLE AND MARINELAND FL EARLY THIS
MORNING, AND JUST OFFSHORE CAPE CANAVERAL.  THE PRECIPITATION BAND
COULD SLOWLY SHIFT SOUTHWARD DURING THE DAY TODAY.  THE 850 HPA
INFLOW FROM THE ATLANTIC IS EXPECTED TO REMAIN IN THE 35-50 KNOT
RANGE BETWEEN DAYTONA BEACH AND JACKSONVILLE, WHICH SHOULD
MAINTAIN PRECIPITABLE WATER (PW) VALUES OF 1.50-1.75 INCHES ACROSS
THE REGION.  OVERNIGHT FLASH FLOOD GUIDANCE VALUES (FFGS) ARE
LOCALLY IN THE 2-2.50 INCH RANGE WITHIN THREE HOURS, WHICH LATEST
RADAR ESTIMATES SHOW IS BEING LOCALLY EXCEEDED.  IT SHOULD BE
NOTED THAT FFGS SHOULD BE LOWER AT 12Z/8 AM EDT BECAUSE OF THE
HEAVY OVERNIGHT RAINFALL.  DIVERGENCE ALOFT IS EXPECTED TO
CONTINUE THROUGH THE MORNING HOURS AS A 250 HPA TROUGH/SHEAR LINE
MOVES SLOWLY THROUGH THE FLORIDA PENINSULA.  THE 00Z ARW, 06Z
HRRR, AND 09Z RAP MESOSCALE MODEL RUNS HAVE BEEN TOO FAR SOUTH
WITH THIS ACTIVITY, WITH THE ARW AND HRR RAINFALL AMOUNTS SOMEWHAT
HIGH.  THE GUIDANCE SHOWS THE INFLOW BAND AND HIGHER PWS SLOWLY
SHIFTING SOUTHWARD WITH TIME, WHICH HAS YET TO OCCUR.  SINCE ANY
SOUTHWARD SHIFT IN THE BAND WOULD CLIP CAPE CANAVERAL, USED
MERRITT ISLAND AS THE SOUTHERN BOUNDARY OF THE SCALLOPED REGION. 
LOCAL AMOUNTS OF 2-3 INCHES WITHIN THREE HOURS TIME ARE EXPECTED
TO CONTINUE WITHIN THE PRECIPITATION BAND FOR THE REMAINDER OF THE
MORNING, WHICH COULD LEAD TO FLASH FLOODING.


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

LAT...LON   28388046 28818109 29418160 30178186 30648174 30648142
            29918116 28388046 


Á