MESOSCALE PRECIPITATION DISCUSSION 0737
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
238 PM EDT SAT AUG 26 2017
AREAS AFFECTED...SOUTHEAST TX INTO SOUTHWEST LA
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY
VALID 261840Z - 262245Z
SUMMARY...BANDING ASSOCIATED WITH TROPICAL STORM HARVEY WILL
CONTINUE TO AFFECT PORTIONS OF SOUTHEAST TX INTO SOUTHWEST LA
THROUGH THE LATE AFTERNOON AND EARLY EVENING. SIGNIFICANT FLASH
FLOODING IS EXPECTED WHERE THE BANDING PERSISTS.
DISCUSSION...THE GOES-16 IR CLEAN LOOP SHOWED THE BEST BANDING
ASSOCIATED WITH HARVEY OVER THE UPPER TX COAST AND A PORTION OF
SOUTHWEST LA...AND THIS IS CONFIRMED BY REGIONAL RADARS. THE KHGX
RADAR SHOWED HOURLY RAINFALL RATES BETWEEN 1.50 AND 2.50 INCHES
ASSOCIATED WITH THE BEST BANDING BETWEEN HOUSTON TX AND LAKE
CHARLES LA.
THE BANDING FEATURES EXTEND OVER THE GULF OF MEXICO AS WELL...AND
THE TRAJECTORY FOR THE ELONGATED BAND APPEARS TO BE OVER PORTIONS
OF THE UPPER TX COAST DURING THE AFTERNOON HOURS. THE LOW LEVEL
CYCLONIC FLOW (PER REGIONAL VWP) IS EXPECTED TO FOCUS THESE BANDS
ON THE EASTERN SIDE OF THE CIRCULATION....WHICH WILL EXTEND INTO
PORTIONS OF SOUTHWEST LA. PORTIONS OF SOUTHWEST LA HAVE ALREADY
RECEIVED THEIR AVERAGE YEARLY RAINFALL...AND REMAINS SENSITIVE TO
ADDITIONAL HEAVY RAINFALL.
THERE IS A SOLID HIGH RESOLUTION MODEL SIGNATURE (LED BY THE MOST
RECENT HRRR) FOR ADDITIONAL RAINFALL AMOUNTS BETWEEN 4.00 AND 8.00
INCHES BETWEEN KLBX AND KBPT... AND THIS LOOKS REASONABLE BASED ON
THE CURRENT POSITIONING OF THE BANDING ON SATELLITE AND RADAR. THE
ADDITIONAL RAINFALL IS EXPECTED TO PRODUCE SIGNIFICANT FLASH
FLOODING WHERE BANDING PERSISTS... ESPECIALLY IF THE BANDING
AFFECTS THE HOUSTON METRO AREA.
AS THE BANDS DRIVE FURTHER INLAND...FLASH FLOODING COULD BECOME A
CONCERN AS FAR NORTH AS KUTS AND SOUTH OF KLFK.