MESOSCALE PRECIPITATION DISCUSSION 0795
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
414 AM EDT SUN SEP 10 2017

AREAS AFFECTED...NORTHEAST AND EAST CENTRAL FLORIDA

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

VALID 100814Z - 101414Z

SUMMARY...ONGOING FLASH FLOODING IN THE FORT PIERCE AREA MAY BE
EXACERBATED BY CONTINUED TRAINING OF TROPICAL CONVECTION...WITH AN
INCREASING FLASH FLOOD THREAT IN THE REST OF COASTAL NORTHEAST AND
EAST CENTRAL FLORIDA.

DISCUSSION...A LOW-LEVEL CONVERGENCE ZONE BECAME FOCUSED FROM NEAR
THE NORTH END OF LAKE OKEECHOBEE...TO FORT PIERCE...AND EXTENDING
ENE INTO THE ATLANTIC OCEAN BETWEEN 04Z AND 08Z. TROPICAL RAIN
BANDS HAVE BECOME BETTER ORGANIZED ALONG THIS MESOSCALE FOCUSING
MECHANISM AND HAVE PRODUCED SIGNIFICANT RAINFALL TOTALS IN JUST A
FEW HOURS. AN ADDITIONAL CONVERGENT RAIN BAND ALSO EXTENDED FROM
NEAR FORT PIERCE TO THE SOUTHEAST...AND LIKELY CONTRIBUTED TO
EXTREMELY HIGH RAIN RATES. A WEATHER STATION ON THE SOUTH SIDE OF
FORT PIERCE HAD A 4-HOUR TOTAL OF 10.53 INCHES OF RAIN SINCE
MIDNIGHT EDT. KMLB RADAR KDP VALUES HAVE BEEN ELEVATED IN THESE
BANDS...SUGGESTING EXTREMELY HIGH INSTANTANEOUS RAIN RATES.

IT IS ENTIRELY POSSIBLE THAT THIS TRAINING CONVECTION WILL BE
MAINTAINED FOR ANOTHER SEVERAL HOURS...ALTHOUGH KMLB RADAR DID
SHOW A SLIGHT NORTHWARD DRIFT BEGINNING AROUND 08Z. THIS COULD
SPREAD THE HEAVY RAINFALL AND THREAT OF FLASH FLOODING A BIT
FURTHER UP THE EAST CENTRAL FLORIDA COAST.

HI-RES MODEL GUIDANCE DOES SUGGEST AN ADDITIONAL AREA OF FOCUSED
HEAVY RAINFALL DEVELOPING IN NORTHEAST FLORIDA NEAR JACKSONVILLE
METRO BETWEEN 09Z AND 15Z NEAR A STATIONARY FRONT AND LOW-LEVEL
THETAE GRADIENT. THE FUNDAMENTAL SETUP IS SIMILAR TO THAT FURTHER
DOWN THE COAST - FOCUSED LOW-LEVEL CONVERGENCE MAINTAINED FOR AT
LEAST A FEW HOURS...AND INCREASING UPPER LEVEL DIVERGENCE IN THE
RIGHT ENTRANCE REGION OF A DEVELOPING JET STREAK OVER GEORGIA AND
SOUTH CAROLINA. THIS DEVELOPING JET STREAK AND ATTENDANT REGION OF
ASCENT ARE EVIDENT IN SATELLITE IMAGERY WITH LARGE CURVED BAND OF
CIRRUS WITH EMBEDDED TRANSVERSE BANDS...ARCING FROM THE NORTHEAST
GULF TO THE COASTAL CAROLINAS.

THEREFORE...THERE MAY BE ANOTHER FOCUSED AREA WITH POTENTIAL FOR
HIGHER RAIN TOTALS NEAR JACKSONVILLE IN NORTHEAST
FLORIDA...ALTHOUGH HEAVY RAIN RATES WILL BE POSSIBLE ANYWHERE
ALONG THE EASTERN FLORIDA COASTLINE IN THE TROPICAL ENVIRONMENT
AHEAD OF HURRICANE IRMA. IF RAIN BANDS ARE PERSISTENT
ENOUGH...HOURLY TOTALS IN EXCESS OF 3 IN/HR ARE CERTAINLY
ACHIEVABLE ANYWHERE WITHIN THE MPD AREA WHICH WOULD LIKELY LEAD TO
FLASH FLOODING.

LAMERS

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

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

LAT...LON   30778148 30588131 29648107 29068071 28608034
            28248038 27768020 27187991 26968011 26978074
            27288108 27728128 28118143 28298147 28718186
            29288207 29858253 30438244 30748193