MESOSCALE PRECIPITATION DISCUSSION 0747
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
254 AM EDT MON AUG 28 2017

AREAS AFFECTED...SERN TX INTO SWRN LA

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

VALID 280651Z - 281100Z

SUMMARY...THE FOCUS OF THE HEAVIEST RAIN OVER THE NEXT 4-6 HOURS
WILL SHIFT EAST INTO FAR SERN TEXAS AND SWRN LOUISIANA WITH
ADDITIONAL RAINFALL TOTALS OF 5-10 INCHES THROUGH 12Z. THIS
COMBINED WITH AN ADDITIONAL 1-3 INCHES IN AND AROUND HOUSTON WILL
ONLY EXACERBATE ONGOING SIGNIFICANT TO CATASTROPHIC FLOODING OVER
THE REGION.

DISCUSSION...EXPERIMENTAL GOES 16 7.3 MICRON LOW LEVEL WATER VAPOR
IMAGERY SHOWED RELATIVELY DRIER AIR WRAPPING AROUND TROPICAL STORM
HARVEY TO THE SOUTH INTO THE HOUSTON METRO REGION AS OF 06Z. THE
DRYING IS REFLECTED WITH A MLCAPE GRADIENT NOTED IN THE SPC
MESOANALYSIS AND THE RAP. ON THE WRN EDGE OF THE INSTABILITY POOL
WAS A SOUTH TO NORTH BAND OF HEAVY RAIN WITH RAINFALL RATES OF 2-3
IN/HR OVER CHAMBERS COUNTY...JUST EAST OF GALVESTON BAY.
REFLECTIVITY FROM KHGX WAS RELATIVELY QUIET FOR COASTAL COUNTIES
ALONG AND WEST OF GALVESTON BAY WITH ONLY LIGHT SHOWERS APPEARING
DESPITE TOTAL PRECIPITABLE WATER VALUES OF 2.3 TO 2.5 INCHES AS OF
06Z.

OVER THE NEXT 4-6 HOURS...THE ONGOING BAND OF HEAVY RAIN...TIED TO
EXCELLENT LOW LEVEL CONVERGENCE NOTED IN WESTERN GULF OF MEXICO
STATION PLOTS...IS EXPECTED TO SLOWLY MOVE EAST INTO SWRN
LOUISIANA WHILE MAINTAINING RAINFALL RATES OF 2-3+ IN/HR. GIVEN
THE SLOW MOVEMENT OF THIS AXIS OF HEAVY RAIN AND ADDITIONAL
SCATTERED CONVECTION MOVING TOWARD THE NNW OUT AHEAD OF THE
LINE...AN ADDITIONAL 5-10 INCHES OF RAIN IS EXPECTED FROM ERN
CHAMBERS/LIBERTY COUNTIES IN SERN TEXAS TO VERMILION/JEFFERSON
DAVIS AND ACADIA PARISHES IN SWRN LOUISIANA. GIVEN 3-10 INCHES OF
RAIN OVER THE PAST 24 HOURS ACROSS THESE LOCATIONS...SIGNIFICANT
TO CATASTROPHIC FLOODING MAY EXPAND EAST FROM THE HOUSTON METRO
INTO BEAUMONT...PORT ARTHUR AND LAKE CHARLES.

FARTHER NORTH AND WEST FROM S-CNTRL INTO ERN TEXAS...REDUCED
INSTABILITY SHOULD LIMIT RAINFALL RATES TO THE 1-2 IN/HR RANGE BUT
GIVEN ONGOING FLOODING...AN EXPECTED ADDITIONAL 2-4 INCHES WILL
ONLY MAKE THE CURRENT SITUATION WORSE.

AS TROPICAL STORM HARVEY CONTINUES TO TRACK SLOWLY TO THE
SOUTHEAST THROUGH 12Z...RENEWED CONVECTION IS ANTICIPATED NEAR THE
MIDDLE TO UPPER TEXAS COAST...CONTINUING INLAND WITH RAINFALL
RATES OF 1-2 IN/HR BETWEEN MATAGORDA BAY AND GALVESTON BAY.

OTTO

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

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

LAT...LON   31639372 31339284 30739241 30089157 29289183
            29269266 29379330 29369393 28919493 28669542
            28619586 29169583 29539618 29439676 29229747
            29299780 29669791 30299755 31199634 31589512