MESOSCALE PRECIPITATION DISCUSSION 0853
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
158 PM EDT MON OCT 02 2017

AREAS AFFECTED...SOUTHEAST LOUISIANA...

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

VALID 021800Z - 030000Z

SUMMARY...CONTINUED STRONG CONFLUENT ONSHORE UNSTABLE FLOW MAY
MAINTAIN THREAT FOR ADDITIONAL TRAINING BANDS OF CONVECTION
THROUGH THE AFTERNOON...POSING CONTINUED FLASH FLOOD RISKS. 

DISCUSSION...KLIX RADAR AND GOES-16 VISIBLE IMAGERY CURRENTLY
SHOWS LINEAR BAND MOVING THROUGH EASTERN NOLA METRO AREA WHERE
2-3"/HR RATES HAVE BEEN REPORTED VIA MULTIPLE BACKYARD GAUGES
LEADING TO TOTALS NEARING 5".  WHILE THIS BAND HAS BEEN GENERALLY
SHIFTING NW WITH TIME...THE ENVIRONMENT FOR ADDITIONAL FLASH
FLOODING REMAINS HIGH AS UPSTREAM MOISTURE/INSTABILITY AND FORCING
WILL CONTINUE TO SUPPORT CONVECTIVE REDEVELOPMENT. 

CURRENT SURFACE/RADAR/SATELLITE IMAGERY SHOWS A STRONG CLOSED
TROPICAL WAVE HEADING DIRECTLY TOWARD GALVESTON BAY...ALLOWING FOR
A BROAD BUT STRONG SELY FETCH INTO SE LA.  THE FETCH IS
REPRESENTED BY 20-25KTS SFC FLOW WITH NEAR 80F TDS AND TOTAL
COLUMN PW AT OR ABOVE 2.5".  ADDITIONALLY HEATING OF THE NEAR
SURFACE ALLOWS FOR MID-80S TEMPS SUPPORTING HIGH INSTABILITY FOR
CONVECTIVE DEVELOPMENT IN EXCESS OF 2000-2500 J/KG. FORCING IS
MAINTAINED BY STRONG SFC MOISTURE CONVERGENCE AS SSELY FLOW
SOUTHEAST OF THE MS RIVER DELTA CONVERGENCES WITH ESELY FLOW ALONG
SURFACE FRONT FROM N CHANDELEUR ISLANDS BACK TOWARD TAMPA BAY. 
THIS STRONG LOW LEVEL INFLOW COUNTERED BY MODEST UPPER LEVEL/MEAN
CLOUD MOTIONS TO THE NW AT 5-10KTS ALLOWS FOR VERY FAVORABLE
BACKBUILDING PROPAGATION VECTORS THROUGHOUT THE AFTERNOON HOURS.
AS SUCH SIMILAR BANDS TO WHAT IS OCCURRING NOW ARE PROBABLE WITH
SIMILAR RATES OF 2-3"/HR AND ADDITIONAL TOTALS OF 3-5".  RAP
FORECASTS SUGGEST THIS FLOW SHOULD PERSIST PROVIDING CONTINUED
FRICTIONAL SURFACE MOISTURE CONVERGENCE (ADDED IN VICINITY OF SFC
FRONT) THROUGH AT LEAST 23-00Z AS NORTHEASTERLY MID TO UPPER LEVEL
FLOW MIXES DRIER AIR THROUGH NORTHEAST GULF AS WELL REDUCING
INSTABILITY/MOISTURE FLUX.

THE LARGEST QUESTION IS PRECISELY WHERE BANDS WILL
TRACK/TRAIN...AND GIVEN A FEW BANDS OVER THE LAST 2 DAYS HAVE
COMPROMISED SOME AREAS SOIL CONDITIONS (SOUTH AS WELL AS EAST OF
DOWNTOWN NEW ORLEANS) FLASH FLOODING IS CONSIDERED LIKELY.
 
GALLINA

ATTN...WFO...LCH...LIX...

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

LAT...LON   30749044 30468968 30218907 29768858 29498875
            29168895 28958921 28938982 28969047 29109080
            29649148 30029155 30599114