MESOSCALE PRECIPITATION DISCUSSION 0870
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
214 PM EDT SAT OCT 07 2017

AREAS AFFECTED...SOUTH-CENTRAL TO SOUTHEAST LA...SOUTHERN
MS...SOUTHERN AL...EXTREME WESTERN FL PANHANDLE

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

VALID 071810Z - 080010Z

SUMMARY...HEAVY RAINFALL ASSOCIATED WITH HURRICANE NATE WILL BEGIN
TO OVERSPREAD THE REGION THROUGH THE AFTERNOON AND EVENING HOURS.
SOME RUNOFF PROBLEMS AND/OR FLASH FLOODING WILL BE POSSIBLE...AND
ESPECIALLY IN THE MORE URBANIZED CORRIDORS NEAR THE GULF COAST.

DISCUSSION...NON-OPERATIONAL GOES-16 10.3 MICRON/IR IMAGERY SHOWS
HURRICANE NATE RAPIDLY APPROACHING FAR SOUTHEAST LA...WITH A
WELL-DEFINED OUTER RAINBAND NOW ADVANCING NORTHWEST ACROSS FAR
SOUTHEAST LA. CENTRAL CONVECTION ASSOCIATED WITH NATE IS NOW
WITHIN 100 MILES OF SOUTHEAST LA AND THE EYE OF NATE IS BEGINNING
TO APPEAR ON THE  SLIDELL LA RADAR.

VERY HIGH PWATS ARE FIRMLY ENTRENCHED ACROSS THE CENTRAL GULF
COAST REGION RIGHT NOW...WITH VALUES NEAR 2.5 INCHES ALREADY IN
PLACE AHEAD OF NATE. MEANWHILE...THE AIRMASS CONTINUES TO
DESTABILIZE WITH THE AID OF DIURNAL HEATING...AND MLCAPE VALUES
ARE CURRENTLY ON THE ORDER OF 1500 J/KG. THIS LEVEL OF INSTABILITY
WILL LIKELY SUSTAIN THE INITIAL CONVECTIVE BAND AROUND THE
NORTHERN SEMICIRCLE OF NATE AND MAY ALLOW IT TO STRENGTHEN A BIT.
ENHANCED SURFACE CONVERGENCE/FORCING IS NOTED JUST OFFSHORE AND
ALREADY OVER THE LAST 15 TO 30 MINUTES VIA THE GOES-16 1-MINUTE
0.64 MICRON/VIS IMAGERY...THERE HAS BEEN A NOTABLE INCREASE IN
OVERSHOOTING TOPS IN THE NORTHEAST PORTION OF THE BAND SOUTHEAST
OF LA THAT WILL BE SETTING UP POTENTIALLY IN A TRAINING FASHION
FOR VERY HEAVY RAINFALL OVER SOUTHEAST LA AND INCLUDING THE NEW
ORLEANS METROPOLITAN AREA WITHIN THE NEXT COUPLE OF HOURS.
ADJACENT AREAS OF SOUTHERN MS MAY ALSO SEE THIS TRAINING POTENTIAL
OVER THE NEXT COUPLE OF HOURS.

NATE WILL BE MOVING RAPIDLY TOWARD FAR SOUTHEAST LA THROUGH THE
AFTERNOON AND THIS WILL BRING NUMEROUS CONVECTIVE BANDS AND
GRADUALLY MORE ORGANIZED CENTRAL CONVECTION INTO AREAS OF
SOUTH-CENTRAL TO SOUTHEAST LA AND FARTHER EAST ACROSS SOUTHERN
MS/SOUTHERN AL AND POSSIBLY ADJACENT AREAS OF THE WESTERN FL
PANHANDLE TOWARD EVENING. EXPECT RAINFALL RATES OF AS MUCH AS 2.5
INCHES/HR...WITH STORM TOTALS THROUGH 00Z OF AS MUCH AS 4 TO 6
INCHES POSSIBLE...AND ESPECIALLY WHERE ANY TRAINING BANDS SET UP.
THE URBANIZED AREAS NEAR THE GULF COAST AND ESPECIALLY THE NEW
ORLEANS METROPOLITAN AREA WILL BE PARTICULARLY SENSITIVE TO THESE
HIGH RAINFALL RATES...AND SO LOCALLY SIGNIFICANT RUNOFF AND/OR
FLASH FLOODING WILL BE POSSIBLE. ADDITIONAL VERY HEAVY RAIN WILL
BE EXPECTED ESPECIALLY OVER SOUTHERN MS AND INTO SOUTHERN AL AFTER
00Z AS NATE ADVANCES NORTH AND MAKES A FINAL LANDFALL LATER THIS
EVENING.

ORRISON

ATTN...WFO...JAN...LCH...LIX...MOB...

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

LAT...LON   31599019 31578840 31238728 30798691 30298714
            30158836 29878870 29468877 29248889 29018922
            29158983 29069067 29349154 29689185 30339192
            31039150