MESOSCALE PRECIPITATION DISCUSSION 0412
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
123 AM EDT MON AUG 03 2015
 
AREAS AFFECTED...NORTHWEST COAST OF THE FL PENINSULA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 030522Z - 031122Z
 
SUMMARY...SHORT CONVECTIVE BANDS OF HEAVY RAINFALL SHOULD BEGIN
IMPACTING THE NORTHWEST COAST OF THE FL PENINSULA SHORTLY, WITH
HOURLY RAIN RATES UP TO 3".  FLASH FLOODING IS POSSIBLE.

DISCUSSION...THE CIRCULATION AROUND A SURFACE LOW NEAR CROSS CITY,
CURRENTLY 1009 HPA IN CENTRAL PRESSURE, IS FUNNELING MOISTURE AND
INSTABILITY IN FROM THE GULF OF MEXICO.  IT HAS ALSO RETURNED AN
OUTFLOW BOUNDARY WHICH PREVIOUSLY MOVED OUT INTO THE GULF OF
MEXICO, WHICH IS ALLOWING A SHORT BAND OF CONVECTION TO APPROACH
THE COAST.  CIN IS NOT A FACTOR HERE -- CONVECTION WILL BE SURFACE
BASED VERY NEAR THE COASTLINE WHERE THE NATURAL TEMPERATURE
GRADIENT SHOULD LIE DUE TO ONSHORE FLOW.  PRECIPITABLE WATER
VALUES OF 2.25-2.5" EXIST ACROSS THE REGION PER GPS INFORMATION. 
INFLOW AT 850 HPA IS 20-25 KTS PER RECENT RAP FORECASTS AND VAD
WIND PROFILES FROM TAMPA BAY/RUSKIN FL.  MUCAPES OF 1000-3000 J/KG
LIE NEAR AND OFFSHORE THE IMMEDIATE WEST COAST OF FL PER RECENT
SPC MESOANALYSES.

THE SURFACE LOW RESPONSIBLE FOR THIS HEAVY RAINFALL IS EXPECTED TO
DRIFT EAST-NORTHEAST TO NORTHEAST OVERNIGHT, BUT THE THERMAL
BOUNDARY SHOULDN'T MAKE MUCH PROGRESS INLAND OVERNIGHT AS THE
BOUNDARY LAYER ACROSS THE PENINSULA CONTINUES TO THIN, SETTING UP
A FRICTIONAL CONVERGENCE ZONE NEAR THE IMMEDIATE COAST.  THE
EXPECTATION IS FOR ONE OR MORE CONVECTIVE BANDS TO FORM WITHIN
THIS MOIST AIRMASS WITHIN THE REGION OF BEST CLOUD BASE INFLOW,
WHICH IS BETWEEN TAMPA BAY AND CEDAR KEY.  THIS IS BORNE OUT IN
THE 18Z SSEO NEIGHBORHOOD PROBABILITIES, WHICH SHOW A 50-80%
CHANCE OF EXCEEDING THE THREE HOUR FLASH FLOOD GUIDANCE IN THIS
REGION.  HOURLY RAIN RATES OF UP TO 3" ARE POSSIBLE PER THE
AVAILABLE MOISTURE.    ISSUES ARE EXPECTED TO SPREAD DOWN THE
COAST WITH TIME.  THE MESOSCALE QPF GUIDANCE IS NEARLY UNANIMOUS
IN SHOWING 3-7" RAINFALL WITHIN THIS REGION OVER THE NEXT SIX
HOURS.  RADAR ESTIMATES FROM THIS REGION INDICATE 15-30" HAS
FALLEN OVER THE PAST 30 DAYS WITH 2/3 OF THIS FALLING OVER THE
PAST TEN DAYS -- SOILS ARE SATURATED.  THE SPATIAL COVERAGE OF
HEAVY RAINFALL EXPECTED WITHIN THE SCALLOPED AREA COULD BE SPOTTY,
WHICH KEPT THE CATEGORY OF THIS MPD AS POSSIBLE RATHER THAN LIKELY.

ROTH

ATTN...WFO...JAX...TBW...

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

LAT...LON   29288302 29248277 29088244 28268220 27848228 
            27368273 27888290 28538273 28948284 29098300 
            29148306