MESOSCALE PRECIPITATION DISCUSSION 0725
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
901 AM EDT FRI AUG 25 2017

AREAS AFFECTED...UPPER TX/SOUTHWEST LA COASTAL PLAIN

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 251300Z - 251900Z

SUMMARY...AN OUTER BAND FROM HURRICANE HARVEY IS APPROACHING AREAS
THAT HAVE EXPERIENCED THEIR ANNUAL AVERAGE RAINFALL.  FLASH
FLOODING IS A CONCERN.

DISCUSSION...HURRICANE HARVEY IS PINNING NORTHWEST OFFSHORE THE
LOWER TX COAST.  TO ITS NORTHEAST, A RAIN BAND IS INTERSECTING AN
EFFECTIVE FRONTAL ZONE JUST OFFSHORE SOUTHEAST TX AND STRADDLING
THE LA COAST.  THE EFFECTIVE FRONT SEPARATES DEW POINTS IN THE 60S
AND LOW 70S FROM MID AND UPPER 70S DEW POINTS TO THE SOUTH. 
PRECIPITABLE WATER VALUES ARE 2.25-2.5".  INFLOW AT 850 HPA IS
CONVERGENT AT 25-40 KTS, ABOUT 50% ABOVE THE MEAN 850-400 HPA WIND.

THE MAIN METEOROLOGICAL CONCERN IS THAT THE BAND COULD HANG UP AND
TRAIN SOMEWHERE NEAR THE GOLDEN TRIANGLE OF SOUTHEAST TX AND/OR
IMPERIAL CALCASIEU OF THE NEXT SEVERAL HOURS.  CLOUDY SKIES SHOULD
KEEP THE INSTABILITY GRADIENT RELATIVELY COASTAL, PARTICULARLY
NEAR SOUTHWEST LA.  THE MESOSCALE GUIDANCE APPEARS TOO FAR SOUTH
WITH HARVEY'S OVERALL RAIN PATTERN PER RECENT RADAR TRENDS. 
SOUTHWEST LA IN PARTICULAR HAS ALREADY RECEIVED THEIR ANNUAL
AVERAGE RAINFALL.  PORT ARTHUR TX ITSELF IS SENSITIVE TO
ADDITIONAL RAINS DUE TO DAM-RELATED ISSUES.  WITH HOURLY RAIN
RATES UP TO 3" AND LOCAL AMOUNTS TO 5" POSSIBLE, FLASH FLOODING IS
A THREAT ACROSS SENSITIVE AND URBAN AREAS.

ROTH

ATTN...WFO...HGX...LCH...

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

LAT...LON   30429384 30409296 30079258 29619279 29609368
            29249478 29349567 30029578