MESOSCALE PRECIPITATION DISCUSSION 0758
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
309 AM EDT TUE AUG 29 2017

AREAS AFFECTED...SERN TX INTO CNTRL/SRN LA

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

VALID 290708Z - 291300Z

SUMMARY...THE HEAVIEST RAIN OVER THE NEXT 4-6 HOURS WILL LIKELY
IMPACT LOCATIONS IN SERN TX WHERE ANOTHER 5-10 INCHES IS EXPECTED
THROUGH 13Z WHILE PORTIONS OF S-CNTRL LA LIKELY SEE AN ADDED 4-8
INCHES. THESE AMOUNTS WILL ONLY WORSEN ONGOING FLOODING.

DISCUSSION...TROPICAL STORM HARVEY WAS LOCATED ABOUT 80 MILES SSW
OF GALVESTON ISLAND AT 06Z ACCORDING TO NHC WITH A SLOW ESE
MOVEMENT NEAR 4 KT. A STEADY HEAVY RAIN WITH EMBEDDED CONVECTION
WAS OBSERVED WITHIN A DEFORMATION AXIS LOCATED NNE OF THE CENTER
OVER SERN TX WITH GENERALLY 1-2 IN/HR RAINFALL RATES
OBSERVED...AND THERE HAS BEEN LITTLE MOVEMENT TO THIS AREA OVER
THE PAST 6 HOURS. FARTHER EAST OVER LA...RAINFALL WAS MORE
CELLULAR AND SCATTERED IN NATURE.

A STATIONARY FRONT HOVERING JUST OFFSHORE OF SERN TX/SWRN LA WAS
CONNECTED TO MLCAPE OF 500-1000 J/KG ALONG THE COAST WITH LIMITED
MLCAPE TO THE NORTH AS OBSERVED ON THE LATEST SPC MESOANALYSIS.
SIMILARLY TO THE EAST...THE STATIONARY FRONT HAS LIMITED THE
NORTHWARD EXTENT OF BETTER INSTABILITY OVER LA WITH HEAVY RAIN
CORES STRUGGLING TO REACH I-10.

GIVEN ONLY A SLOW NEWD FORECAST MOVEMENT TO HARVEY THROUGH
12Z...THE ONGOING AXIS OF STEADY/HEAVY RAINFALL OVER SERN TX IS
NOT EXPECTED TO MOVE MUCH FROM ITS CURRENT POSITION...PERHAPS A
SMALL NORTHWARD DRIFT. GIVEN RAINFALL RATES OF 1-2 IN/HR...WITH
LOCALLY EMBEDDED HIGHER RATES...AN ADDITIONAL 5-10+ INCHES OF RAIN
IS EXPECTED FROM NEAR GALVESTON BAY EASTWARD INTO CHAMBERS AND
JEFFERSON COUNTIES THROUGH 13Z.

FARTHER TO THE EAST...SHORT TERM GUIDANCE HINTS AT THE FRONTAL
BOUNDARY LIFTING NORTH OVER ERN LA WHICH WOULD TEND TO ALLOW
ISENTROPIC ASCENT AND HEAVIER RAINFALL TO MOVE NORTH FROM THE
CURRENT LOCATION ALONG THE SRN LA COAST INTO PORTIONS OF S-CNTRL
LA INCLUDING PARTS OF I-10. GIVEN THE MORE SCATTERED NATURE TO
CONVECTION OVER LA...4-8 INCH AMOUNTS APPEAR LIKELY HOWEVER THESE
TOTALS WILL BE LOCALIZED MAXIMA AND NOT WIDESPREAD ACROSS THE
REGION.

OTTO

ATTN...WFO...HGX...LCH...LIX...SHV...

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

LAT...LON   31399375 30999234 30249122 29919090 29569067
            29079061 28889085 28899130 29199261 29199416
            28829504 28769549 28789572 29029594 29439608
            30149581 30529551 31199494