MESOSCALE PRECIPITATION DISCUSSION 0800
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
612 PM EDT SUN SEP 10 2017

AREAS AFFECTED...CENTRAL AND SOUTHERN FL

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

VALID 102210Z - 110410Z

SUMMARY...HURRICANE IRMA BRINGING EXTREMELY HEAVY RAIN TO CENTRAL
FLORIDA AS IT LIFTS NORTH ALONG THE WEST SIDE OF THE PENINSULA.
SIGNIFICANT RUNOFF AND FLASH FLOODING CONCERNS ARE EXPECTED
THROUGH THE EVENING. MEANWHILE...CONDITIONS ARE GRADUALLY
IMPROVING OVER SOUTHERN FLORIDA.

DISCUSSION...THE EYE OF HURRICANE IRMA AS OF 21Z WAS POSITIONED
JUST 5 MILES NORTH OF NAPLES FL AND IS MOVING NORTH AT 14 MPH.
VERY HEAVY RAINFALL ASSOCIATED WITH THE CORE OF IRMA CONTINUES
AROUND THE NORTHWEST TO NORTHEAST FLANK OF THE CIRCULATION. THE
LATEST NON-OPERATIONAL GOES-16 7.3 MICRON/WV IMAGERY CONTINUES TO
SHOW A SIGNIFICANT AMOUNT OF DRY AIR POURING SOUTHEAST ACROSS THE
GULF OF MEXICO IN ASSOCIATION WITH DIGGING SHORTWAVE ENERGY AND
EVOLUTION OF A LARGER SCALE UPPER TROUGH NEAR THE CENTRAL GULF
COAST. THIS STABLE AND DRY LOW TO MID LEVEL AIR HAS BEEN GETTING
ENTRAINED INTO THE SOUTHERN FLANK OF IRMA'S CIRCULATION WHICH HAS
BEEN HELPING TO ERODE THE DEEPER CONVECTION AROUND THIS SIDE OF
THE STORM.

OVER THE NEXT SEVERAL HOURS...THE HEAVIEST RAINFALL WILL CONTINUE
AROUND THE NORTHERN SEMICIRCLE OF THE STORM WHERE VERY STRONG LOW
LEVEL FORCING/CONVERGENCE AND SUFFICIENT INSTABILITY WILL BE IN
PLACE FOR VERY HEAVY RAINFALL TOTALS. SOME RAINFALL RATES OF OVER
3 INCHES/HR ARE LIKELY...AND ESPECIALLY INVOLVING THE NORTHEAST
EYEWALL OF IRMA AS IT LIFTS NORTH. GENERALLY THE WEST-CENTRAL TO
EAST-CENTRAL PART OF THE STATE WILL SEE THE WORST
CONDITIONS...WITH ADDITIONAL RAINFALL AMOUNTS OF 4 TO 6+ INCHES
EXPECTED THROUGH MIDNIGHT. THIS WILL AGAIN ENHANCE THE CONCERN FOR
SIGNIFICANT RUNOFF AND FLASH FLOODING.

FARTHER SOUTH OVER SOUTH FLORIDA...THE DEGREE OF DRY/STABLE AIR
INFILTRATING THE SOUTHERN FLANK OF IRMA SHOULD ALLOW THE MORE
ORGANIZED CONVECTIVE RAINS TO SUBSIDE/WEAKEN...ESPECIALLY OVER
SOUTHWEST FL. HOWEVER...THERE IS SOME POTENTIAL FOR SOME FOCUSED
BANDS OF CONVECTION TO SET UP NEAR THE SOUTHEAST COAST OF THE
PENINSULA WHERE THERE IS MUCH GREATER PROXIMITY TO A STRONG
INSTABILITY GRADIENT...AND ADDITIONAL HEAVY RAINFALL TOTALS OF AS
MUCH AS 2 TO 4 INCHES WILL BE POSSIBLE HERE THROUGH MIDNIGHT.

ORRISON

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

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

LAT...LON   28998115 28618064 28008035 27498006 26577988
            25508019 25178064 25288123 25818158 26138196
            26738240 27078257 27438271 28068278 28608257
            28908218