MESOSCALE PRECIPITATION DISCUSSION 0139
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
301 AM EDT MON MAY 14 2018

AREAS AFFECTED...COASTAL SOUTHERN FL & THE KEYS

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

VALID 140700Z - 141300Z

SUMMARY...CONVERGENT CYCLONIC FLOW AROUND A LOW IN THE GULF OF
MEXICO IS EXPECTED TO LEAD TO HOURLY RAIN TOTALS TO 2.5" AND LOCAL
AMOUNTS TO 5" ON A LOCAL BASIS.

DISCUSSION...A BROAD/WEAK LOW NEAR 25N 84W SITTING WEST OF THE FL
KEYS HAS LED TO THE DEVELOPMENT OF A MESOCYCLONE JUST OFFSHORE
SOUTHWEST FL WHICH IS WEAKENING WHILE MOVING TOWARDS THE COAST. 
AN ASSOCIATED OUTFLOW BOUNDARY HAS BEEN EDGING SOUTHWARD TOWARDS
KEY WEST PER RADAR IMAGERY.  PRECIPITABLE WATER VALUES ARE ~2",
WHICH IS ON THE HIGH END OF CLIMATOLOGY FOR MID-MAY FOR TAMPA, KEY
WEST, AND MIAMI.  INFLOW AT 850 HPA IS CONVERGENT AT 20 KTS PER
VAD WIND PROFILES AT MIAMI AND KEY WEST.  MU CAPE VALUES ARE
500-1500 J/KG PER THE SPC MESOANALYSIS PAGE, WHILE EFFECTIVE BULK
SHEAR IS AROUND 25 KTS.

THE MESOSCALE GUIDANCE SHOWS A GOOD SIGNAL FOR HEAVY RAINFALL
DURING THE NEXT SEVERAL HOURS, WITH 850 HPA INFLOW INCREASING
SLIGHTLY FURTHER AND THE CONVERGENT INFLOW SLOWLY SHIFTING UP THE
KEYS INTO SOUTHERN FL.  THE RANGE IN THE MESOSCALE GUIDANCE IS
3-8" THROUGH 13Z, WITH A MODE NEAR 5".  THIS WOULD BE ASSOCIATED
BOTH WITH THE MESOCYCLONE JUST OFFSHORE SOUTHWEST FL PRESENTLY AND
WITH INCREASING EARLY MORNING CONVECTION WHICH MOVES ASHORE WITHIN
THE CONVERGENT ONSHORE FLOW REGIME.  GIVEN THE PRECIPITABLE WATER
VALUES, HOURLY RAIN TOTALS UP TO 2.5" ARE POSSIBLE ON A LOCAL
BASIS, WITH THE BEST CHANCES INDICATED BY THE HREF PROBABILITIES
OF EXCEEDING 2" IN AN HOUR AROUND 10Z.

ROTH

ATTN...WFO...KEY...MFL...

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

LAT...LON   26907995 25947999 25258025 24798071 24598121
            24518163 24478201 24578221 24638215 24728171
            24838133 24808112 25018073 25048087 24998108
            25158120 25478126 25768152 25868171 25998184
            26188172 26258146 25868107 25518086 25528067
            26008062 26338047 26598030 26908025