MESOSCALE PRECIPITATION DISCUSSION 0141
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
929 AM EDT MON MAY 14 2018

AREAS AFFECTED...CENTRAL AND SOUTH FLORIDA

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

VALID 141328Z - 141915Z

SUMMARY...HEAVY RAINFALL IS LIKELY ACROSS PORTIONS OF SOUTH AND
CENTRAL FLORIDA TODAY ESPECIALLY TO THE NORTH OF THE ALLIGATOR
ALLEY 1-75 CORRIDOR. HOURLY RAIN RATES COULD EXCEED 2 IN/HR IN THE
HEAVIEST RAIN BANDS...WITH LOCALIZED FLASH FLOODING POSSIBLE.

DISCUSSION...REGIONAL RADAR MOSAICS SHOWED NUMEROUS SHOWERS AND
THUNDERSTORMS ACROSS FLORIDA THIS MORNING...IN THE BROAD CYCLONIC
FLOW AROUND AN AREA OF WEAK LOW PRESSURE IN THE EASTERN GULF OF
MEXICO. IN THE FLORIDA PENINSULA AS OF 13Z...THE AREAL COVERAGE
AND INTENSITY OF RAIN WAS GENERALLY HIGHEST IN CENTRAL FLORIDA
BETWEEN TAMPA AND THE TREASURE COAST. TO THE SOUTH OF THAT...SKIES
WERE CLEARING PER GOES-16 VISIBLE SATELLITE IMAGERY...AND THAT MAY
BE PARTIALLY DUE TO A MID-LEVEL DRY AIR INTRUSION NOSING INTO
SOUTH FLORIDA PER GOES-16 AIR MASS RGB IMAGERY. THIS WAS NOTED IN
THE CIRA BLENDED PRECIPITABLE WATER PRODUCT...AS WELL AS IN THE
12Z MIAMI SOUNDING (1.75 INCH PW VS 1.96 AT TAMPA). AS INSOLATION
INCREASES THIS MORNING...THIS MAY SET UP A DIFFERENTIAL HEATING
BOUNDARY OR PSEUDO-WARM FRONT STRETCHING IN A WEST-EAST FASHION
ACROSS THE FLORIDA PENINSULA. THIS MAY HELP FOCUS LOW-LEVEL
CONVERGENCE IN A WAY OTHER THAN ALONG THE EAST COAST OF FLORIDA
(FRICTIONAL...GIVEN BROAD E-SE FLOW). THERE WAS ALREADY SOME
EVIDENCE OF THIS HAPPENING IN MESONET WIND FIELDS.
ADDITIONALLY...THERE IS A PROMINENT MCV JUST NORTH OF KEY WEST AND
IT WAS DRIFTING TO THE NORTHEAST. THIS MAY ALSO PROVIDE SOME MORE
FOCUSED AND ENHANCED VERTICAL MOTION TO THE EAST AND
NORTHEAST...ACROSS PORTIONS OF THE FLORIDA PENINSULA...DURING THE
LATE MORNING AND EARLY AFTERNOON.

GIVEN THE COMBINATION OF AN APPROACHING MCV...INCREASING
INSTABILITY WITH AT LEAST PARTIAL CLEARING...AND CONTINUED
CYCLONIC FLOW IN A VERY MOIST ENVIRONMENT...THE EXPECTATION IS
THAT CONVECTION WILL LIKELY BE MAINTAINED ACROSS PORTIONS OF
FLORIDA INTO THE EARLY AFTERNOON. THE BEST CHANCES OF HEAVY RAIN
RATES (NEAR OR ABOVE 2 IN/HR) WOULD LIKELY BE NEAR THE PSEUDO-WARM
FRONT AND JUST ON THE NOSE OF THE DRY AIR INTRUSION AT MID
LEVELS...MAXIMIZING BOTH PRECIPITATION EFFICIENCY IN THE HIGHER
PWAT AIR AND BACKBUILDING POTENTIAL INTO THE UNSTABLE AIR TO THE
SOUTH. THIS ZONE MAY DRIFT GRADUALLY NORTH FROM ITS CURRENT
POSITION...LIKELY PLACING THE GREATER FLASH FLOOD POTENTIAL FROM
LAKE OKEECHOBEE NORTH TO NEAR ORLANDO...AND OVER TO THE SPACE AND
TREASURE COASTS WHERE LOW-LEVEL CONVERGENCE WOULD NATURALLY BE
MAXIMIZED IN AN EASTERLY FLOW REGIME. HOWEVER...FLASH FLOODING
COULD NOT BE RULED OUT ANYWHERE IN SOUTH AND CENTRAL
FLORIDA...GIVEN SOME MESOSCALE UNCERTAINTIES WITH THE PRECISE
MOTION AND EVOLUTION OF THE MCV AND THE INFLUENCE OF ONGOING
CONVECTION. HOWEVER...FLASH FLOOD GUIDANCE REMAINS RELATIVELY HIGH
AND THIS SHOULD KEEP THE THREAT OF FLASH FLOODING ISOLATED OVER
THE NEXT SEVERAL HOURS.

LAMERS

ATTN...WFO...MFL...MLB...TBW...

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

LAT...LON   29038072 28658044 27478001 26457991 25848024
            25998086 25778143 26168192 26658237 27268272
            27918284 28438241 28918139