MESOSCALE PRECIPITATION DISCUSSION 0764
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
252 AM EDT WED AUG 30 2017

AREAS AFFECTED...SOUTHEAST TX/WESTERN AND SOUTHWESTERN LA

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

VALID 300652Z - 301252Z

SUMMARY...CATASTROPHIC AND LIFE THREATENING FLASH FLOODING
RESULTING FROM HEAVY RAINFALL WILL CONTINUE OVER EXTREME
SOUTHEASTERN TEXAS THROUGH 12Z. AN ADDITIONAL 5-10 INCHES OF RAIN
IS EXPECTED WITH SOME OVERLAP EXPECTED ON TOP OF LOCATIONS WHERE
6-12 INCHES FELL IN JEFFERSON/ORANGE COUNTIES THROUGH 06Z.

DISCUSSION...NHC PLACED TROPICAL STORM HARVEY ABOUT 45 MILES SSW
OF CAMERON LOUISIANA AT 06Z...MOVING TO THE NORTHEAST AT AROUND 6
KT. EXTREMELY DANGEROUS RAINFALL CONTINUES WITH THIS SYSTEM WITH
JACK BROOKS REGIONAL AIRPORT...LOCATED HALFWAY BETWEEN BEAUMONT
AND PORT ARTHUR TEXAS...MEASURING A 3 HOUR RAINFALL OF 8.05 INCHES
ENDING AT 06Z. AN INTENSE...SLOW MOVING AXIS OF HEAVY RAIN REMAINS
WITHIN A DEFORMATION ZONE LOCATED NORTHWEST OF THE CENTER OF
HARVEY OVER SOUTHEASTERN TEXAS WHERE SOUTHEASTERLY LOW LEVEL FLOW
HAS BEEN SHARPLY CONVERGING JUST WEST OF THE SABINE RIVER. THE
HEAVIEST RAINFALL HAS BEEN LOCALIZED OVER JEFFERSON COUNTY
ASSOCIATED WITH A MESO-VORTEX AND ENHANCED LOW LEVEL CONVERGENCE
WHICH HAS BEEN MEANDERING SLOWLY OVER THE PAST FEW HOURS WITH
RAINFALL RATES APPROACHING 4 IN/HR. FOR LOCATIONS JUST NORTH OF
JEFFERSON/ORANGE COUNTIES...WHERE ACCESS TO INSTABILITY IS
REDUCED...RAINFALL RATES HAVE BEEN STEADY IN THE 1-2 IN/HR RANGE
AND LOWER YET ACROSS THE CENTRAL TEXAS/LOUISIANA BORDER.

AN UPPER TROUGH LOCATED OVER CENTRAL TEXAS AT 06Z IS EXPECTED TO
CONTINUE AMPLIFYING TOWARD THE SOUTHEAST OVER THE NEXT FEW HOURS
WHICH WILL HAVE THE EFFECT OF INCREASING DIFFLUENCE ALOFT OVER THE
SOUTHERN TEXAS/LOUISIANA BORDER BY 12Z. LANDFALL IS EXPECTED ALONG
CAMERON PARISH  EARLY THIS MORNING AS HARVEY CONTINUES TOWARD THE
NORTHEAST AND THIS TRACK SHOULD ALLOW THE HEAVIEST RAINFALL RATES
TO SLOWLY EDGE NORTH...BUT LOCALIZED ENHANCED CONVERGENCE LOCATED
JUST EAST OF THE AFOREMENTIONED MESO-VORTEX IN JEFFERSON COUNTY
MAY PIVOT ABOUT ITSELF FOR ANOTHER COUPLE OF HOURS ALLOWING FOR
CONTINUED RAINFALL RATES NEAR 3 IN/HR IN THE VICINITY OF THE LOWER
SABINE RIVER VALLEY. WHILE THE HEAVIEST OF THE RAINFALL RATES ARE
FORECAST TO DIMINISH TOWARD 13Z...AN ADDITIONAL 5-10 INCHES OF
RAIN IS EXPECTED WHERE THE SLOW PIVOTING OCCURS...ALONG WITH
CONTINUED DANGEROUS/LIFE-THREATENING FLASH FLOODING.

FARTHER NORTH INTO CENTRAL LOUISIANA...AN ADDITIONAL 1-3 INCHES OF
RAIN IS EXPECTED THROUGH 13Z WITH RAINFALL RATES BRIEFLY
APPROACHING 1 IN/HR. GIVEN SOME OVERLAP WITH HEAVY RAINFALL OVER
THE PAST 24 HOURS...FLASH FLOODING WILL BE POSSIBLE FARTHER NORTH
INTO PORTIONS OF CENTRAL LOUISIANA.

OTTO

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

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

LAT...LON   32569257 32229213 31719184 31139169 30659162
            30349170 30309202 30319236 30429263 30259301
            29739329 29549381 29589415 29679446 29939471
            30369487 31099481 31839413 32389333