Graphic for MPD #0749

MESOSCALE PRECIPITATION DISCUSSION 0749...CORRECTED
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
627 AM EDT MON AUG 28 2017

CORRECTED FOR FLASH FLOODING LIKELY

AREAS AFFECTED...SERN TX INTO SWRN/S-CNTRL LA

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

VALID 281019Z - 281615Z

SUMMARY...AN ONGOING HEAVY RAINFALL AXIS OVER THE SOUTHERN
TEXAS/LOUISIANA BORDER IS FORECAST TO SLOWLY MOVE EAST WITH 4-9
MORE INCHES OF RAIN EXPECTED THROUGH 17Z INTO SOUTHWESTERN
LOUISIANA. RENEWED DEVELOPMENT BACK WEST OF GALVESTON BAY IS
POSSIBLE STARTING 15-18Z. ADDITIONAL RAINFALL WILL ONLY EXACERBATE
ONGOING CATASTROPHIC FLASH FLOODING.

DISCUSSION...TROPICAL STORM HARVEY WAS LOCATED OVER MATAGORDA BAY
AT 09Z WITH A SLOW SOUTHEASTWARD MOVEMENT OBSERVED SINCE THEN VIA
KCRP RADAR IMAGERY. THE STORM HAS BEEN STEADILY MOVING TOWARD THE
SOUTHEAST NEAR 3 KT SINCE 00Z AND THE 09Z NHC ADVISORY PLACES
HARVEY BACK OUT OVER THE GULF THROUGH 18Z. EXPERIMENTAL GOES 16
LOW LEVEL WATER VAPOR IMAGERY SHOWED A SIGNIFICANT AMOUNT OF DRIER
AIR PUSHING EASTWARD ACROSS SOUTH TEXAS INTO THE WESTERN GULF OF
MEXICO AND INFRARED IMAGERY SHOWED A STRONG BAND OF CONVECTION
EXTENDING FROM SOUTH TO NORTH AT THE LEADING EDGE OF THIS PUSH OF
DRIER AIR WITHIN AN AXIS OF GREATER LOW LEVEL THETA-E CO-LOCATED
WITH HIGHER MLCAPE SEEN IN THE LATEST RAP ANALYSIS. THIS BAND OF
HEAVIER RAIN HAS BEEN MOVING TOWARD THE EAST AT 5-6 KT OVER THE
PAST 4 HOURS BUT IS FORECAST BY SOME OF THE BETTER PERFORMING
HI-RES MODELS TO ACCELERATE TOWARD THE EAST AT ABOUT 15 KT TOWARD
17Z. HOWEVER...THIS MAY BE TOO FAST GIVEN CURRENT TRENDS...AND THE
HEAVY RAINFALL AXIS MAY BEGIN TO BREAK APART IF IT MOVES TOO FAR
AWAY FROM THE AXIS OF BETTER LOW LEVEL CONVERGENCE.

THE NORTHWARD EXTENT OF THE HEAVIEST RAINFALL RATES AS OF
10Z...RADAR ESTIMATED 2-3 IN/HR OVER JEFFERSON COUNTY IN FAR SERN
TX...HAS BEEN LIMITED BY MLCAPE DROPPING OFF RAPIDLY NORTH OF
COASTAL LOCATIONS. FORECASTS OF MLCAPE THROUGH 17Z KEEP THE
500-1000+ VALUES WITHIN ABOUT 50 MILES OF THE SOUTHERN LOUISIANA
COAST WITH MUCH WEAKER VALUES TO THE NORTH. ADDITIONAL 6 HOUR
RAINFALL TOTALS THROUGH 17Z ARE EXPECTED TO RANGE FROM 4-9 INCHES
FROM FAR SERN TEXAS INTO SWRN LOUISIANA.

FARTHER TO THE WEST...AS THE CENTER OF HARVEY MOVES BACK OUT OVER
THE GULF OF MEXICO...RENEWED CONVECTION WITH RAINFALL RATES OF 1-3
IN/HR MAY DEVELOP JUST EAST OF THE CIRCULATION CENTER WITH IMPACTS
TO LOCATIONS WEST OF GALVESTON BAY TO NEAR ROUTE 71...INCLUDING
THE HOUSTON METRO. THE TIME FRAME FOR THIS AREA OF NEW DEVELOPMENT
APPEARS TO BE IN THE 15-18Z TIME FRAME.

OTTO

ATTN...WFO...EWX...FWD...HGX...LCH...LIX...SHV...

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

LAT...LON   31399491 31359389 31069289 30989273 30599179
            30459152 30139103 29729099 29209116 29069149
            29209271 29169408 28799530 28999569 29359581
            29549607 29339664 29439697 29849705 30639657
            31079605


Last Updated: 627 AM EDT MON AUG 28 2017