MESOSCALE PRECIPITATION DISCUSSION 0741
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
235 AM EDT SUN AUG 27 2017

AREAS AFFECTED...S-CNTRL TO SERN TX

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

VALID 270634Z - 271200Z

SUMMARY...SLOW MOVING OR NEARLY STATIONARY TRAINING AXES OF HEAVY
RAIN WILL CONTINUE TO GENERATE VERY DANGEROUS AND LIFE THREATENING
FLASH FLOODING OVER PORTIONS OF SOUTHEASTERN TEXAS. LOCALIZED 6
HOUR RAINFALL TOTALS OVER 10 INCHES ARE EXPECTED THROUGH 12Z.

DISCUSSION...KHGX RADAR HAS SHOWN A NEARLY STATIONARY BAND OF VERY
HEAVY RAIN JUST WEST OF GALVESTON BAY WITH SEVERAL REPORTS OF 4-6
IN/HR AND OBSERVED THREE HOUR REPORTS RANGING FROM 12-15 INCHES
ALONG THE HARRIS/GALVESTON COUNTY LINE ENDING 06Z. EXTREME LOW
LEVEL CONVERGENCE/CONFLUENCE HAS BEEN IN PLACE TO THE EAST OF
TROPICAL STORM HARVEY...LOCATED OVER GONZALES COUNTY AT 06Z BY
NHC...WITH 40-60 KT 850 MB FLOW WRAPPING AROUND THE EAST AND NORTH
SIDE OF THE CENTER OF CIRCULATION. THE HEAVIEST RAINFALL RATES ARE
LOCATED...AND SHOULD STAY LOCATED WITHIN 75-100 MILES OF THE GULF
COAST GIVEN IT HAS BEEN THE SOURCE REGION FOR HIGHER INSTABILITY
AMID PRECIPITABLE WATER VALUES IN EXCESS OF 2.5 INCHES.

HARVEY IS FORECAST BY NHC TO CONTINUE A VERY SLOW DRIFT IN THE
SHORT TERM WHICH IMPLIES LITTLE MOVEMENT TO LOW LEVEL AXES OF
CONVERGENCE LOCATED FROM MATAGORDA BAY TO THE SABINE RIVER WITH
EXISTING BANDS PERSISTING OR SLOWLY MORPHING TO A NEARBY LOCATION
THROUGH 12Z. WHILE THE INFLOW BAND CONTAINING THE EXTREME RAINFALL
RATES IMMEDIATELY WEST OF GALVESTON BAY HAS SHOWN SOME SIGNS OF
REORGANIZING OVER THE PAST 30 MINUTES...A NEW STATIONARY BAND HAS
DEVELOPED OVER MATAGORDA BAY EXTENDING NORTH INTO WHARTON COUNTY
AS OF 06Z.

GIVEN LITTLE CHANGE IN FORCING MECHANISMS AND THE THERMODYNAMIC
ENVIRONMENT OVER THE NEXT 4-6 HOURS...LOCATIONS EAST OF HARVEY
WILL CONTINUE TO EXPERIENCE SLOW MOVING TO NEARLY STATIONARY AXES
OF RAINFALL RATES AS HIGH AS 6 IN/HR WITH 6 HOUR RAINFALL TOTALS
OVER 10 INCHES EXPECTED THROUGH 12Z. GIVEN THESE EXTREME RAINFALL
RATES ON TOP OF AN ALREADY SATURATED GROUND...VERY DANGEROUS AND
LIFE THREATENING FLASH FLOODING IS EXPECTED TO CONTINUE.

OTTO

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

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

LAT...LON   31579501 31539427 31109361 30359343 29609365
            29099412 28739483 28319555 27869622 27809629
            27899690 28329725 28829754 29189788 29699826
            30469800 30959747 31389618