MESOSCALE PRECIPITATION DISCUSSION 0874
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
138 AM EDT SUN OCT 08 2017

AREAS AFFECTED...FAR ERN MS...SRN AND CTRL AL...FL PANHANDLE...WRN
GA

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

VALID 080535Z - 081135Z

SUMMARY...FLASH FLOODING WILL CONTINUE TO DEVELOP ALONG AND TO THE
EAST OF HURRICANE NATE'S TRACK AS RAIN BANDS PRODUCING PROLIFIC
RAIN RATES WRAP AROUND THE EASTERN HALF OF THE CIRCULATION. RAIN
RATES AROUND 3 IN/HR WILL BE POSSIBLE IN THE HEAVIEST AND MORE
PERSISTENT RAIN BANDS.

DISCUSSION...HURRICANE NATE HAS HAD AN ADDITIONAL BURST OF
CONVECTION ON IR SATELLITE AS IT APPROACHED THE COAST OVER THE
PAST THREE HOURS. THE RAIN DISTRIBUTION IS ASYMMETRIC...WITH RADAR
AND SATELLITE SHOWING THE BULK OF THE PRECIPITATION IMMEDIATELY
NORTH AND LARGELY EAST OF THE CIRCULATION CENTER. THE MOST
PROLIFIC RAIN RATES OVER THE NEXT SIX HOURS (THROUGH 12Z) SHOULD
CONTINUE TO BE IN THE ARCING RAIN BANDS AROUND 50-125MI EAST AND
EAST-NORTHEAST OF THE CIRCULATION CENTER...SITUATED IN THE
STRONGER LOW-MID LEVEL FLOW AND MOISTURE FLUX TO THE EAST OF THE
CENTER. KMOB DUAL POL AND MRMS RAIN RATE ESTIMATES ARE AS HIGH AS
2 IN/HR...BUT THIS MAY BE UNDERESTIMATING IN THE TROPICAL
ENVIRONMENT DOMINATED BY HIGHLY EFFICIENT WARM RAIN PROCESSES
(PARTICULARLY IN THE BUBBLE OF EXTREMELY HIGH PWATS WITHIN 100MI
OR SO OF THE CENTER OF NATE). ADDITIONALLY...SURFACE OBSERVING
SITES MAY ALSO BE UNDERESTIMATING RAINFALL A BIT DUE TO STRONG
WINDS AND THE VERY HEAVY RAIN RATES. WITH THAT IN MIND...BELIEVE
THAT 3 IN/HR RAIN RATES WOULD CERTAINLY BE ACHIEVABLE IN THESE
RAIN BANDS.

THE RAIN BANDS IN THE EASTERN SEMI-CIRCLE SHOULD GRADUALLY SHIFT
EAST WITH TIME...FROM THE BALDWIN COUNTY AL AND PENSACOLA
AREAS...TO NEAR DESTIN FL AND ANDALUSIA AL BY DAYBREAK. AS LONG AS
CONVECTION IS TIED CLOSE TO NATE'S CIRCULATION CENTER AS
WELL...THERE SHOULD BE HEAVY RAIN RATES JUST NORTH AND NORTHEAST
OF THE CENTER THAT CONTINUE TO SPREAD INTO SOUTHERN ALABAMA.
ALTHOUGH NATE'S FORWARD MOTION IS RELATIVELY FAST...MODELS AND
RADAR TRENDS SUGGEST THAT 3-6 HOURS OF MODERATE TO HEAVY RAIN
WOULD BE POSSIBLE AT A GIVEN LOCATION IN SOUTHERN ALABAMA AND THE
WESTERN FLORIDA PANHANDLE AS THE CURVED RAIN BANDS SHIFT THROUGH.

FURTHER TO THE EAST AND NORTH...SOME OF THE PERIPHERAL RAIN BANDS
AWAY FROM NATE'S CENTER HAVE ALSO BEEN PRODUCING RAIN RATES IN
EXCESS OF 1 IN/HR AT TIMES (PER RADAR ESTIMATES). THESE RAIN BANDS
HAVE BEEN MORE DISORGANIZED WITH SPACING BETWEEN INDIVIDUAL CELLS
OR DISCRETE BANDS OF HEAVY RAIN...WHICH WOULD TEND TO LESSEN THE
FLASH FLOOD THREAT A BIT COMPARED TO POINTS FURTHER WEST. THE
ENVIRONMENT STILL FAVORS VERY HEAVY RAIN RATES...BUT THE FORCING
IS LESS FOCUSED AWAY FROM THE CENTER. HOWEVER...LOCALIZED FLASH
FLOODING WILL BE POSSIBLE IF A RAIN BAND CAN PERSIST AT A GIVEN
LOCATION FOR A COUPLE HOURS.

LAMERS

ATTN...WFO...BMX...FFC...JAN...LIX...MOB...TAE...

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

LAT...LON   33678701 33518613 33408530 32678464 32198428
            31548389 30798373 30128385 29818420 29448494
            29438514 29558549 30028597 30258677 30108785
            30168908 30588926 31058923 31628910 32308868
            32878785 33348761