MESOSCALE PRECIPITATION DISCUSSION 0841
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
559 PM EDT FRI SEP 29 2017

AREAS AFFECTED...CENTRAL/SOUTH FL

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

VALID 292155Z - 300345Z

SUMMARY...SOME CONCENTRATED BANDS OF VERY HEAVY SHOWERS AND
THUNDERSTORMS ARE EXPECTED THROUGH THE EVENING HOURS. SOME RUNOFF
PROBLEMS AND/OR FLASH FLOODING ARE POSSIBLE.

DISCUSSION...AN UPPER LOW OVER THE EASTERN GULF OF MEXICO
CONTINUES TO INTERACT WITH A WELL-DEFINED SURFACE TROUGH OF LOW
PRESSURE LIFTING NORTHWEST ACROSS THE SOUTHERN FL PENINSULA. OVER
THE LAST COUPLE OF HOURS THERE HAS BEEN AN EXPANSION OF COLD
CONVECTIVE TOPS...WITH RADAR IMAGERY CONFIRMING MULTIPLE
CLUSTERS/BANDS OF CONVECTION WITH SOME CYCLONIC MOTION NOTED TO
THE MORE ORGANIZED CONVECTIVE STRUCTURES. THIS APPEARS TO BE
CONNECTED TO SOME STRENGTHENING OF LOW LEVEL SURFACE CONVERGENCE
ACROSS THE REGION BASED ON SURFACE OBSERVATIONS...AND THERE HAS
BEEN SOME GENERAL LOWERING OF SURFACE PRESSURES OFF THE SOUTHWEST
COAST OF FL THE LAST FEW HOURS.

THE ENVIRONMENT IS HIGHLY TROPICAL IN NATURE WITH PWATS OVER SOUTH
FL OF AS MUCH AS 2.25 TO 2.5 BASED OFF BLENDED-TPW AND GPS-DERIVED
DATA. THE DEEP COLUMN OF TROPICAL MOISTURE STRONGLY SUPPORTS
HIGHLY EFFICIENT RAINFALL PROCESSES FOR ENHANCED RAINFALL RATES
THAT MAY EXCEED 3 INCHES/HR...AND ESPECIALLY WITH RECENT COOLING
CLOUD TOP TRENDS.

GIVEN THE SURFACE FORCING ENVIRONMENT AND RATHER DIFFLUENT FLOW
ALOFT AROUND THE EASTERN FLANK OF THE UPPER LOW...EXPECT
ADDITIONAL BANDS AND CLUSTERS OF ORGANIZED CONVECTION THROUGH THE
EVENING WITH SOME CELL-MERGER ACTIVITY AS WELL. ADDITIONAL
RAINFALL AMOUNTS OF AS MUCH AS 4 TO 6+ INCHES WILL BE POSSIBLE
THROUGH LATE-EVENING. SOME RUNOFF PROBLEMS AND/OR FLASH FLOODING
WILL BE POSSIBLE.

ORRISON

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

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

LAT...LON   28938211 28828118 28078045 27238012 26188015
            25348094 25798170 26048199 26478217 26948255
            27458275 28438270