Graphic for MPD #0797

MESOSCALE PRECIPITATION DISCUSSION 0797
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1011 AM EDT SUN SEP 10 2017

AREAS AFFECTED...NORTHEASTERN AND EAST CENTRAL FL...SOUTHEASTERN
GA

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

VALID 101410Z - 102030Z

SUMMARY...FLASH FLOODING IS POSSIBLE INTO THE AFTERNOON HOURS AS A
SURFACE FRONT AND STRENGTHENING LOW-LEVEL FLOW ENHANCE ASCENT WELL
NORTH OF HURRICANE IRMA.

DISCUSSION...HURRICANE IRMA WAS POSITIONED NEAR THE LOWER FLORIDA
KEYS AS OF 14Z AND THE NATIONAL HURRICANE CENTER FORECASTS IT TO
CONTINUE MOVING NORTH-NORTHWEST ALONG THE WESTERN COAST OF FLORIDA
THROUGH TONIGHT. NORTH OF IRMA, A STATIONARY SURFACE FRONT, THE
LEADING EDGE OF A SIGNIFICANTLY DRIER AIR MASS ACROSS THE INTERIOR
SOUTHEASTERN U.S., WAS SITUATED ACROSS THE NORTHERN FLORIDA
PENINSULA. A HIGHLY MOIST (PWATS OF 2.3-2.4 IN.) AND MODERATELY
UNSTABLE (MLCAPE 1000-2000 J/KG) AIR MASS WAS IN PLACE FROM EAST
CENTRAL PORTIONS OF THE FL PENINSULA INTO THE ATLANTIC OCEAN, PER
LATEST SPC MESOANALYSIS. EASTERLY FLOW OF 40-45 KT AT 850 HPA WAS
TRANSPORTING THIS AIR MASS ACROSS THE FRONTAL BOUNDARY, ENHANCING
RAINFALL PRODUCTION. RAINFALL RATES HAVE WANED A BIT AT THE
MOMENT, WITH CURRENT OBSERVATIONS AND RADAR ESTIMATES GENERALLY
INDICATING MAXIMUM RATES UP TO 1 IN/HR.

LOW-LEVEL EASTERLY FLOW IS EXPECTED TO INCREASE FURTHER THROUGH
THE DAY, WITH THE LATEST RAP INDICATING 850 HPA EASTERLY FLOW
INCREASING TO 50 KT BY EARLY AFTERNOON. THIS COMBINED WITH A
DIURNAL INCREASE IN INSTABILITY IS EXPECTED TO GRADUALLY INCREASE
RAINFALL RATES. ADDITIONALLY, 250 HPA SPEED DIVERGENCE IS EXPECTED
TO INCREASE BY AFTERNOON, AS A JET STREAK IS FORECAST BY THE RAP
TO STRENGTHEN ACROSS GEORGIA, AIDING IN THE SUPPORT OF DEEPER
ASCENT. HI-RES GUIDANCE ARE IN GENERAL AGREEMENT ON THE POTENTIAL
FOR 1-2 IN/HR RAINFALL RATES BY EARLY AFTERNOON, WITH ISOLATED
AREAS EXCEEDING 2 IN/HR. ADDITIONAL RAINFALL AMOUNTS OF 2 TO 4
INCHES ARE EXPECTED THROUGH 2030Z, WITH LOCALLY HIGHER AMOUNTS
POSSIBLE. FLASH FLOODING IS POSSIBLE.

RYAN

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

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

LAT...LON   31278191 31268151 31148113 30948089 30598078
            30288068 29978065 29308051 28818048 28458051
            28168088 28268145 28888203 29428238 30528242
            31018219


Last Updated: 1011 AM EDT SUN SEP 10 2017