MESOSCALE PRECIPITATION DISCUSSION 0751
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1107 AM EDT MON AUG 28 2017

AREAS AFFECTED...SOUTHERN LA...EXT EASTERN TX...EXT
SOUTHWEST/COASTAL MS

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

VALID 281505Z - 282015Z

SUMMARY...WARM SECTOR/TROWAL HEAVY RAINFALL ASSOCIATED WITH
TROPICAL STORM HARVEY

DISCUSSION...EXPERIMENTAL GOES-16 7.3UM WV CHANNEL SHOWS STRONGER
THAN EXPECTED DRY CONVEYOR BELT PRESSING ACROSS THE THE
NORTHWESTERN GULF.  THIS HAS PRESSED THE MATURE WARM CONVEYOR
FURTHER EAST TOWARD THE CENTRAL LA COAST ATTM AND IN DOING SO
MAINTAINS SOLID MOISTURE CONVERGENCE ALONG IT SUFFICIENTLY TO
MAINTAIN SOME CONVECTION WITH RECENT OVERSHOOTING TOPS BREAKING
THROUGH THE CIRRUS CANOPY JUST OFF THE COAST OF MARSH ISLAND. 
HOWEVER...BROADENING OF THE LOW LEVEL PRESSURE FIELDS WILL SUPPORT
SLIGHTLY DECREASING SOUTHERLY FLOW ASHORE WITH TIME BUT ALSO SLOW
EASTWARD PROGRESS OF THE EFFECTIVE TROF/BOUNDARY.  STRONG
FRICTIONAL CONVERGENCE AT THE COAST SHOULD ALSO SUPPORT
REDEVELOPMENT BEFORE MOISTURE TRANSPORT ISENTROPICALLY ASCENDS
INTO THE TROWAL ACROSS CENTRAL LA INTO E TX.  RATES NEAR/ALONG THE
COAST WHERE REMAINING INSTABILITY OF 2000-2500 J/KG AND SATURATED
PROFILES SUPPORTING 2.75" TPWS...SHOULD ALLOW FOR 3"/HR RATES TO
OCCUR AND 6-8" TOTALS THROUGH 21Z MAINLY IN THE COASTAL VICINITY
OF THE VERMILLION/BLANCHE BAY.

COASTAL SE LA/MS...GOES-16 .6 & 1.6UM VISIBLE CHANNEL ALONG WITH
SURFACE OBSERVATIONS DEPICT A WARM FRONT THAT IS HUGGING THE SE LA
COAST EXTENDING ESE TO THE WEAKNESS SOUTH OF TAMPA BAY.  SOUTHERLY
ISENTROPIC ASCENT COMBINED WITH CONFLUENT LOW LEVEL FLOW ON BOTH
SIDES OF THE BOUNDARY (EFFECTIVE COOL CONVEYOR BELT) SUPPORT
SUFFICIENT ASCENT/INSTABILITY TRANSPORT TO LEAD TO ISOLATED
CONVECTION ALONG IT.
12Z LIX SOUNDING SUGGEST WARM CLOUD PROCESSES ALONG WITH AMPLE
MOISTURE WILL ALLOW FOR EFFICIENT RAINFALL FROM THESE CELLS.

CURRENT CELL MOTIONS ARE GENERALLY WESTWARD ALSO ASCENDING INTO
THE BROAD DEFORMATION ZONE/TROWAL OVER CENTRAL LA.  ALSO GIVEN
RELATIVE STATIONARY NATURE OF THE BOUNDARY...COULD SUPPORT
CORRIDOR OR TWO OF TRAINING AND POSE A POSSIBLE FLASH FLOOD RISK. 
WHILE CURRENTLY THIS APPEARS TO BE NORTH OF THE NOLA METRO
AREA...THERE ARE SOME RADAR TRENDS THAT SUGGEST SOME WSW
PROPAGATION ON ISENTROPIC ASCENT...AS CLOUD BASES LOWER TOWARD SFC
BASED.  IF THIS OCCURS...THE THREAT OF TRAINING WILL EXIST ACROSS
THE METRO WITH RATES OF 2"/HR LIKELY POSING FF RISK GIVEN
COMPROMISED PUMP SITUATION. 

CENTRAL LA/SW MS...CONFLUENCE OF WARM/COOL CONVEYOR BELTS ACROSS
CENTRAL LA WILL SUPPORT EFFICIENT RAINFALL PROCESSES EVEN WITHOUT
INSTABILITY/CONVECTIVE DEVELOPMENT. STRONG FLUX/ASCENT SHOULD
SUPPORT RATES OF UP TO 1.0" OVER A BROAD AREA POSING MORE OF A
LONGER DURATION/INUNDATION FLOODING CONCERN THAN FLASHY CONDITIONS
BUT GIVEN DURATION ARE LIKELY TO EXCEED LONGER TERM FFG VALUES.

GALLINA

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

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

LAT...LON   31899334 31899213 31329043 30598912 29918854
            29268885 28898894 28978966 29039012 28869085
            29069131 29249176 29679236 30139283 30529347
            30999411 31559396