MESOSCALE PRECIPITATION DISCUSSION 0736...CORRECTED
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
843 AM EDT SAT AUG 26 2017

CORRECTED FOR TYPO IN FIRST DISCUSSION PARAGRAPH

AREAS AFFECTED...SOUTHEAST TX & SOUTHWEST LA

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

VALID 261240Z - 261840Z

SUMMARY...HURRICANE HARVEY CONTINUES TO MOVING NORTHWARD THROUGH
SOUTHEAST TX.  HOURLY RAIN TOTALS UP TO 3" WITH LOCAL AMOUNTS TO
7" ARE EXPECTED.  SIGNIFICANT FLASH FLOODING IS ANTICIPATED.

DISCUSSION...THE EYE OF HURRICANE HARVEY CONTINUES TO FILL IN ON
RADAR AND SATELLITE IMAGERY THIS MORNING WHILE MOVING FARTHER INTO
SOUTHEAST TX.  PRECIPITABLE WATER VALUES ARE UP TO ~2.75" PER GPS
DATA.  INFLOW AT 850 HPA IS 25-50 KTS PER VAD WIND PROFILES, BUT
ARE LIKELY AS HIGH AS 80 KTS GIVEN HARVEY'S INTENSITY.  THE INFLOW
IS NEARLY DOUBLE THE 850 HPA WIND, WHICH IS LEADING TO
PRECIPITATION EFFICIENCY.  UNIDIRECTIONAL FLOW WITHIN THE LOW- TO
MID-LEVELS COMBINED WITH BULK SHEAR OF AT LEAST 30 KTS IS LEADING
TO ORGANIZED CYCLONIC BANDING.  ON WATER VAPOR IMAGERY, SHORTWAVES
ALOFT ARE EVIDENT ACROSS OK/THE TX PANHANDLE AND CENTRAL MEXICO TO
THE SYSTEM'S WEST, WHICH COMBINED WITH STABLE CONDITIONS INLAND
ARE LEADING TO ITS LOPSIDED CONVECTIVE APPEARANCE FAVORING THE
EASTERN SIDE OF ITS CIRCULATION.

THERE IS A STRONG SIGNAL IN THE MESOSCALE GUIDANCE FOR 7" OF
RAINFALL WITHIN THE NEXT SIX HOURS.  COMBINED WITH THE 3-12" OF
RAINFALL THIS REGION HAS ALREADY RECEIVED, SENSITIVE URBAN AREAS
IN THE HOUSTON METROPOLITAN AREA, DAM ISSUES IN PORT ARTHUR TX,
AND ABOVE AVERAGE RAINFALL IN SOUTHWEST LA IN 2017, SIGNIFICANT
FLASH FLOODING IS EXPECTED ACROSS SOUTHWEST TX, WITH FLASH FLOOD
RISK IN SOUTHWEST LA INCREASING WITH TIME AS A INFLOW BAND MOVING
IN FROM THE SOUTHWEST INTERSECTS OR MERGES WITH EXISTING ACTIVITY
NEAR THE EFFECTIVE STATIONARY FRONT.

ROTH

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

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

LAT...LON   31109553 30709401 30389336 29479233 29719323
            29629371 29339456 28819531 28239645 27849702
            28969801 30689738