MESOSCALE PRECIPITATION DISCUSSION 0759
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
910 AM EDT TUE AUG 29 2017

AREAS AFFECTED...SOUTHEAST TX...CENTRAL/SOUTHERN LA

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

VALID 291310Z - 291910Z

SUMMARY...VERY HEAVY RAINFALL WILL CONTINUE TO EXACERBATE HISTORIC
LEVELS OF FLOODING OVER SOUTHEAST TX. STRONG BANDS OF
THUNDERSTORMS WILL ALSO BE FOCUSING OVER AREAS OF CENTRAL/SOUTHERN
LA WITH SEPARATE FOCUSED AREAS OF FLASH FLOODING CONCERNS.

DISCUSSION...T.S. HARVEY AS OF 12Z IS CENTERED 90 MILES
EAST-SOUTHEAST OF PORT OCONNOR TX AND IS MOVING VERY SLOWLY OFF TO
THE EAST-NORTHEAST. THE LATEST NON-OPERATIONAL GOES-16 WV/IR DATA
SHOWS A RATHER NON-TROPICAL LOOKING CLOUD PATTERN AS A SIGNIFICANT
DRY SLOT CONTINUES TO ADVANCE OVER THE CENTER OF HARVEY WHILE
WRAPPING NORTHEAST INTO PARTS OF SOUTH-CENTRAL LA.
SIMILARILY...THE NON-OPERATIONAL GOES-16 RGB AIRMASS IMAGERY HAS
BEEN CONFIRMING THIS DRY SLOT AS WELL.

COLD CONVECTIVE TOPS THOUGH NORTH OF THE CENTER WHICH ARE EMBEDDED
WITHIN A WELL-DEFINED MID LEVEL DEFORMATION ZONE ARE STILL
IMPACTING AREAS OF SOUTHEAST TX...AND ESPECIALLY
CHAMBERS...LIBERTY AND HARDIN COUNTIES...AND RADAR IMAGERY SHOWS
PERSISTENT AREAS OF VERY HEAVY RAINFALL IMPACTING THESE AREAS.

RAINFALL TOTALS OVER THE LAST 12 HOURS ACROSS SOME OF THESE AREAS
HAVE BEEN ON THE ORDER OF 6 TO 10+ INCHES...ESPECIALLY OVER
CHAMBERS COUNTY...AND THIS HAS BEEN RESULTING IN EXTREME FLOODING
CONDITIONS.

HARVEY WILL CONTINUE TO MOVE VERY SLOWLY THROUGH MIDDAY WITH A
GRADUAL TURN TO THE NORTHEAST EXPECTED. THIS WILL LIKELY MAINTAIN
HEAVY RAINFALL OVER SOUTHEAST TX...WITH SOME GRADUAL EASTWARD
SHIFTING OF THE HEAVIER RAINS. MEANWHILE...FARTHER EAST ACROSS
CENTRAL/SOUTHERN LA...THERE WILL LIKELY BE MULTIPLE BANDS OF
CONVECTION DEVELOPING AND ADVANCING NORTH FROM THE GULF OF MEXICO
AS VERY MOIST AND UNSTABLE AIR AROUND THE EAST SIDE OF HARVEY
LIFTS NORTH AND OVER A RATHER WELL-DEFINED STATIONARY FRONT FROM
THE UPPER TX COAST EAST ACROSS THE CENTRAL GULF COAST. THIS IS
RESULTING IN STRONG ISENTROPIC ASCENT AND HEAVIER RAINS NEAR THE
FRONT...AND ESPECIALLY OVER SOUTHEAST LA.

BASED ON THE LATEST HRRR AND HRRRX GUIDANCE...EXPECT AN ADDITIONAL
3 TO 6 INCHES OF RAIN OVER SOUTHEAST TX....GENERALLY EAST AND
NORTHEAST OF THE HOUSTON METROPOLITAN AREA. IN ANY EVENT...THESE
ADDITIONAL RAINS WILL EXACERBATE THE EXTREME FLOODING CONCERNS
HERE.

MEANWHILE...VERY HEAVY RAINS OVER PARTS OF SOUTHERN AND SOUTHEAST
LA WILL BE EXPECTED TOO...INCLUDING THE NEW ORLEANS METROPOLITAN
AREA...WITH LOCALIZED AMOUNTS THROUGH EARLY AFTERNOON OF UP TO AS
MUCH AS 4 TO 6 INCHES. SOME VERY COLD CONVECTIVE TOPS ARE
CURRENTLY APPROACHING THE NEW ORLEANS AREA AND THESE RAINS WILL
LIKELY RESULT IN FLASH FLOODING.

ORRISON

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

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

LAT...LON   31189443 30959261 31019121 30959037 30678977
            30058952 29598964 29318985 29109039 29099076
            29289168 29569286 29609374 29519425 29399458
            29169495 29349533 29709559 30179566 30729544