MESOSCALE PRECIPITATION DISCUSSION 0849
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1217 PM EDT SUN OCT 01 2017

AREAS AFFECTED...PORTIONS OF EASTERN FL

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

VALID 011617Z - 012117Z

SUMMARY...BANDS OF SHOWERS AND THUNDERSTORMS ARE EXPECTED TO
INCREASE IN COVERAGE ACROSS EAST-CENTRAL FL.  HOURLY RAIN TOTALS
TO 2" WITH LOCAL AMOUNTS TO 4" ARE EXPECTED.

DISCUSSION...A PAIR OF SURFACE BOUNDARIES ARE EVIDENT IN GOES-16
NON-OPERATIONAL "VEGGIE BAND" IMAGERY -- THE MAIN FRONTAL ZONE
ACROSS THE NORTHERN PENINSULA AND A WEAKER SOUTHERN BAND WHICH
APPEARS TO BE A COMPOSITE BOUNDARY MADE OF OUTFLOW BOUNDARIES FROM
PREVIOUS CONVECTION, A CONVERGENT CLOUD LINE NORTH OF THE BAHAMAS,
WITH SOME CONTRIBUTION FROM A LOW CLOUD BAND APPEARING TO EMANATE
FROM ELEUTHRA ISLAND.  PRECIPITABLE WATER VALUES OF 2-2.3" WERE
NOTED IN RECENT GPS DATA.  INFLOW AT 850 HPA IS SOUTHEAST AT 15
KTS, 2-3 TIMES THE MAGNITUDE OF THE 850-400 HPA MEAN WIND.  ML
CAPE VALUES OF 500-1500 J/KG EXIST WITHIN THIS SATURATED AIR MASS.
 EFFECTIVE BULK SHEAR OF 20-25 KTS NEAR AND OFFSHORE IS LEADING TO
OCCASIONAL BANDS WHICH DEVELOP FOR AN HOUR OR TWO BEFORE FADING.

AS A WEAK LOW/INVERTED TROUGH PULLS WESTWARD ACROSS THE GULF OF
MEXICO, THE FLOW ACROSS THE FL PENINSULA SHOULD BECOME A LITTLE
MORE EASTERLY (PARTICULARLY AT 850 HPA) WHICH WOULD CAUSE THE
SURFACE BOUNDARIES TO SHIFT SLIGHTLY SOUTHWARD WITH TIME.  THE
MESOSCALE GUIDANCE HAS A GOOD SIGNAL FOR LOCAL AMOUNTS OF ABOUT 4"
IN THIS AREA OVER THE NEXT SEVERAL HOURS.  HOURLY RAIN TOTALS TO
2" ARE EXPECTED.  ML CAPE VALUES ACROSS THE REGION ARE FORECAST TO
REMAIN FAIRLY STATIC OVER THE NEXT SEVERAL HOURS.  THERE ARE SIGNS
IN RECENT RAP RUNS OF THE BOUNDARY LAYER MOISTURE CONVERGENCE
SLOWLY FALLING OFF AFTER 18Z -- USED A FIVE HOUR WINDOW TO SPLIT
THE DIFFERENCE IN THE TIMING OF ITS WEAKENING SEEN ON VARIOUS RUNS.

ROTH

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

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

LAT...LON   29618158 29408096 29108082 28458046 28268056
            27568028 27328030 27288053 27498113 28048144
            28878183 29468199