MESOSCALE PRECIPITATION DISCUSSION 0917
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
620 PM EDT SAT OCT 28 2017

AREAS AFFECTED...S-CNTRL FL INTO THE KEYS

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

VALID 282219Z - 290415Z

SUMMARY...SLOW MOVING CORES HEAVY RAIN ARE EXPECTED TO PRODUCE
3-6+ INCHES OF RAIN ACROSS PORTIONS OF S-CNTRL TO SRN FLORIDA OVER
THE NEXT 6 HOURS. FLASH FLOODING WILL BE POSSIBLE OVER MORE
URBANIZED LOCATIONS.

DISCUSSION...A TROPICAL AIRMASS OVER THE SOUTHERN HALF OF FLORIDA
IN ADVANCE OF NEWLY NAMED TROPICAL STORM PHILIPPE CONTINUES TO
SUPPORT LOCALLY VERY HEAVY INSTANTANEOUS RAINFALL RATES...WITH
LOCAL WUNDERGROUND.COM OBSERVATION STATIONS REPORTING AS HIGH AS
0.5 INCHES IN 10 MINUTES FROM 21Z. KAMX AND KMLB DUAL POL ONE HOUR
RAINFALL RATES APPEAR TO BE ROUGHLY HALF OF OBSERVATIONS AT
SELECTED SITES ACROSS THE REGION THROUGH 21Z.

IN ADDITION TO PHILIPPE WHICH WAS PLACED OVER WRN CUBA AT 21Z BY
NHC...A SECONDARY LOW WAS NOTED VIA EXPERIMENTAL GOES 16 VISIBLE
IMAGERY AND KBYX RADAR NEAR 25.5N 83.3W AT 2130Z. A JET STREAK WAS
ALSO NOTED ON THE VISIBLE IMAGERY VIA CIRRUS MOVEMENT NORTH OF THE
SECONDARY LOW WITH AN INFERRED RIGHT ENTRANCE REGION NORTHWEST OF
CHARLOTTE HARBOR OVER THE ERN GULF OF MEXICO AIDING DIVERGENCE
ALOFT. A PERSISTENT LOW LEVEL CONVERGENCE AXIS WAS NOTED NORTHEAST
OF THE SECONDARY LOW COINCIDENT WITH AN AREA OF MODERATE TO
LOCALLY HEAVY RAIN EXTENDING ROUGHLY WEST TO EAST FROM NEAR
CHARLOTTE COUNTY TO ST. LUCIE COUNTY. THE HEAVIEST RAIN FROM 2130Z
WAS TIED TO A MCV SLOWLY ARCING NORTH FROM LAKE OKEECHOBEE WITH
ENHANCED CONVERGENCE TO ITS NORTHWEST OVER HIGHLANDS COUNTY WITH
ESTIMATED RAINFALL RATES OF 2-3 IN/HR CORRECTING FOR THE NOTED LOW
BIAS IN DUAL POL ESTIMATES.

SHORT TERM FORECASTS FROM THE RAP HAVE GENERALLY BEEN CONSISTENT
FROM RUN TO RUN SHOWING THE EASTERN END OF THE LOW LEVEL
CONVERGENCE AXIS...ROUGHLY NEAR 850 MB...STAYING NEAR ST. LUCIE
AND INDIAN RIVER COUNTIES WHILE THE AXIS PIVOTS SOUTH WHERE IT
CROSSES THE WRN PENINSULA THROUGH 03Z. THE SECONDARY LOW IS
FORECAST TO SLOWLY MOVE ESE OVER THE NEXT 3-6 HOURS WHILE T.S.
PHILIPPE NEARS THE FLORIDA KEYS THROUGH 03Z. SELY LOW LEVEL FLOW
AHEAD OF PHILIPPE IS EXPECTED TO HELP SUPPORT AN AREA OF FOCUSED
NEAR SURFACE CONVERGENCE ACROSS THE SRN PENINSULA WITH RAINFALL
RATES IN EXCESS OF 3 IN/HR POSSIBLE BY 04Z. WHILE SOME OF THIS
WILL OVERLAP WITH SWAMPLAND...ANY OVERLAP WITH URBANIZED AREAS
WILL POSE A FLASH FLOOD THREAT...BOTH OVER SOUTH FLORIDA AND
LOCATIONS FARTHER NORTH IN AND AROUND THE ROUTE 70 CORRIDOR.

OTTO

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

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

LAT...LON   28348063 28198012 26817991 25408006 24728069
            24508147 24648198 25428202 27078253 27798159