Graphic for MPD #0794

MESOSCALE PRECIPITATION DISCUSSION 0794
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1157 PM EDT SAT SEP 09 2017

AREAS AFFECTED...CTRL AND SRN FL PENINSULA...FLORIDA KEYS

CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY

VALID 100355Z - 100955Z

SUMMARY...FLASH FLOODING IS LIKELY OVER PORTIONS OF CENTRAL AND
SOUTHERN FLORIDA THROUGH THE REST OF THE NIGHT AS HURRICANE IRMA
APPROACHES FROM THE SOUTH.

DISCUSSION...HURRICANE IRMA WAS SITUATED OVER THE FLORIDA STRAIT
AS OF 03Z AND THE NATIONAL HURRICANE CENTER FORECASTS IT TO
CONTINUE MOVING TOWARD SOUTH FLORIDA TONIGHT. GOES-16 IR CHANNEL
IMAGERY SHOWS THAT IRMA'S CDO HAS EXPANDED IN SIZE (120MI AT 00Z
TO 150MI AT 03Z) AND CLOUD TOPS HAVE COOLED. THIS REGION CLOSER TO
THE CENTER OF IRMA WILL CONTAIN THE HIGHEST PRECIPITABLE
WATER...AND CONSISTENT WITH INCREASINGLY ORGANIZED RAIN
BANDS...SHOULD CONTAIN VERY HIGH RAIN RATES CAPABLE OF PRODUCING
FLASH FLOODING. USING A COMBINATION OF HI-RES GUIDANCE AND
EXTRAPOLATION...THE CDO SHOULD EXPAND ROUGHLY TO ALLIGATOR ALLEY
BY 09Z. THE GREATEST FLASH FLOOD THREAT WOULD EXIST SOUTH OF THAT
AND IN URBAN AREAS. HI-RES MODELS ARE IN AGREEMENT THAT SOME
LOCATIONS IN THE FLORIDA KEYS OR FAR SOUTHEAST FLORIDA COULD
RECEIVE OVER 6 INCHES OF RAIN IN 6 HOURS...AND THIS SEEMS
REASONABLE.

FURTHER TO THE NORTH...THE GREATEST THREAT OF FLASH FLOODING
OUTSIDE THE ADVANCING CDO OF IRMA WILL BE ALONG THE EAST COAST OF
FLORIDA. BROAD EASTERLY FLOW TO THE NORTH OF IRMA WILL FAVOR
ENHANCED LOW-LEVEL CONVERGENCE IN THE I-95 CORRIDOR ALONG THE
COAST. ADDITIONALLY...SEVERAL PROMINENT CONVERGENT BANDS OF HEAVY
RAIN AND THUNDERSTORMS HAVE DEVELOPED IN A PLUME OF GREATER
INSTABILITY FROM COASTAL EAST-CENTRAL FLORIDA EASTWARD INTO THE
ATLANTIC OCEAN...WITH MLCAPE AS HIGH AS 1500-2000 J/KG. THESE
BANDS HAVE BEEN BECOMING MORE ORGANIZED AND PRODUCED RAIN RATES AS
HIGH AS 2 IN/HR EARLIER THIS EVENING.

SPATIAL COVERAGE AND INTENSITY OF RAIN BANDS IN CENTRAL FLORIDA
COULD BE ENHANCED BY INCREASING UPPER LEVEL DIVERGENCE OVER THE
NEXT SEVERAL HOURS...DUE TO AN AGEOSTROPHIC RESPONSE TO A +PV
ANOMALY NEAR ALABAMA AND STRENGTHENING JET STREAK OVER GA/SC. THE
FAVORED AREA WITH A JUXTAPOSITION OF UPPER LEVEL DIVERGENCE AND
FOCUSED LOW-LEVEL CONVERGENCE APPEARS TO BE FROM NEAR MELBOURNE
SOUTH TO NEAR JUPITER...AND WITHIN 20 MILES OF THE COAST. SOME
HI-RES MODELS DO SHOW A SIGNAL FOR ENHANCED RAINFALL IN THIS SAME
AREA OVER THE NEXT 6 HOURS...WITH RAIN TOTALS IN THAT TIME FRAME
POSSIBLY REACHING 3-5 INCHES WHERE RAIN BANDS BECOME MORE FOCUSED.

LAMERS

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

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

LAT...LON   29078077 28868047 28558034 28138044 27748027
            27268005 26647989 25808005 25278017 24698072
            24448176 24478236 24668246 24888176 25288131
            25738170 25968201 26388214 26458235 26908233
            27308201 27488151 27858126 28338137 28618141
            28968112


Last Updated: 1157 PM EDT SAT SEP 09 2017