MESOSCALE PRECIPITATION DISCUSSION 0739
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
932 PM EDT SAT AUG 26 2017

AREAS AFFECTED...SOUTHEAST TX AND NEARBY SOUTHWEST LA

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

VALID 270130Z - 270600Z

SUMMARY...BANDING ASSOCIATED WITH TROPICAL STORM HARVEY WILL
CONTINUE TO AFFECT PORTIONS OF SOUTHEAST TX INTO SOUTHWEST LA
THROUGH THE EARLY MORNING HOURS. SIGNIFICANT FLASH FLOODING IS
EXPECTED WHERE THE BANDING PERSISTS.

DISCUSSION...THE GOES-16 CLEAN IR LOOP SHOWED DEEPENING CONVECTION
ASSOCIATED WITH BANDING FEATURES ACROSS SOUTHEAST TX...JUST WEST
OF HOUSTON EARLY THIS EVENING. ANOTHER BAND WITH VERY HEAVY
RAINFALL WAS COMING ONSHORE FROM THE GULF OF MEXICO ALONG THE
TX/LA BORDER.

EACH OF THESE BANDS WERE PRODUCING HOURLY RAINFALL RATES BETWEEN
1.50 AND 2.00 INCHES OVER THE MID AND UPPER TX COAST INTO FAR
SOUTHWEST LA. THE BANDS WERE BEING FOCUSED BY THE LOW LEVEL
CONVERGENT FLOW (PER THE MORE RECENT REGIONAL VWP)...WHICH HAS
RESULTED IN AN ASYMMETRIC RAINFALL DISTRIBUTION ASSOCIATED WITH
HARVEY.

THE GOES-16 SHORT WAVE IR LOOP SHOWED CURVED BANDS TRYING TO FORM
TO THE SOUTH AND EAST OF THE LOW LEVEL CIRCULATION OF HARVEY...AND
THE BANDING THAT DEVELOPS EAST OF THE CENTER WILL POSE THE
GREATEST THREAT FOR TORRENTIAL RAINFALL AND SIGNIFICANT FLASH
FLOODING. THE AIRMASS AROUND THE LOW LEVEL CIRCULATION HAS CHANGED
LITTLE DURING THE LATE AFTERNOON AND EARLY EVENING HOURS... WITH
2.50/2.75 INCH PRECIPITABLE WATER (THE 00Z CRP SOUNDING SHOWED A
2.48 INCH PRECIPITABLE WATER VALUE) SWIRLING WITH THE VERY SLOWLY
MOVING SYSTEM.

THERE IS STILL A FAIRLY SOLID HIGH RESOLUTION MODEL SIGNAL THAT
BANDED CONVECTION WILL PRODUCE LOCAL 3.00 TO 6.00 INCH RAINFALL
AMOUNTS WHERE THE BANDS FORM AND COME ASHORE. HOWEVER...THERE IS
SOME SPREAD AS TO WHERE THE BEST BANDING SETS UP...SO THERE IS
SOME SPREAD IN THERE AS TO WHERE THE HIGHEST RAINFALL ARE
EXPECTED. THE MOST RECENT HRRR REMAINS THE MOST BULLISH WITH
RAINFALL AMOUNTS IN THE BANDING...SHOWING THE POTENTIAL FOR LOCAL
6.00+ INCH RAINFALL AMOUNTS NEAR AND JUST TO THE WEST OF THE
HOUSTON METRO AREA.

LESSER AMOUNTS ARE POSSIBLE ACROSS PORTIONS OF NEARBY SOUTHWEST
LA...WHERE THE HIGH RESOLUTION MODEL SIGNAL IS NOT QUITE AS STRONG
FOR SIGNIFICANT FLASH FLOODING. HOWEVER...PORTIONS OF SOUTHWEST LA
HAVE ALREADY RECEIVED THEIR AVERAGE YEARLY RAINFALL...AND REMAINS
SENSITIVE TO ADDITIONAL HEAVY RAINFALL.

FINALLY...RAIN BANDS ROTATING NORTH OF THE LOW LEVEL CIRCULATION
CONTINUE TO PRODUCE MODERATE TO HEAVY RAINFALL ACROSS PORTIONS OF
CENTRAL TX...WHERE ADDITIONAL HEAVY RAINFALL COULD RESULT IN FLASH
FLOODING.

HAYES

ATTN...WFO...CRP...EWX...HGX...LCH...

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

LAT...LON   30799388 30449313 29919257 29739305 29709410
            29469453 28609577 28579664 28739724 29109759
            29639780 30129755 30139752 30519664 30689598
            30779492