MESOSCALE PRECIPITATION DISCUSSION 0726
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1052 AM EDT FRI AUG 25 2017

AREAS AFFECTED...MIDDLE TX COAST

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

VALID 251451Z - 252051Z

SUMMARY...HURRICANE HARVEY'S CENTRAL DENSE OVERCAST (CDO) IS
EXPECTED TO MOVE ASHORE THE MIDDLE TX COAST SHORTLY.  HOURLY RAIN
AMOUNTS TO 3" WITH LOCAL AMOUNTS TO 6" ARE EXPECTED.

DISCUSSION...HURRICANE HARVEY CONTINUES MOVING NORTHWEST AT 10 MPH
PER THE LATEST NHC ADVISORY.  THE SYSTEM HAS RECENTLY EXHIBITED A
DOUBLE EYEWALL STRUCTURE WITH THIRD NEARBY INNER SPIRAL BAND
EVIDENT, AND THE LEADING EDGE OF ITS CDO LIES WITHIN AN HOUR OF
THE COAST.  PRECIPITABLE WATER VALUES ARE ~2.5" PER RECENT GPS
DATA.  INFLOW AT 850 HPA IS CYCLONIC NEAR THE COAST AT 30-50 KTS
PER VAD WIND PROFILES.  ML CAPE VALUES OF 500-2500 J/KG LIE FROM
THE COASTLINE OFFSHORE INTO THE GULF OF MEXICO.  THE LEADING EDGE
OF A BROAD DEW POINT DISCONTINUITY EXTENDS JUST OFFSHORE THE
MIDDLE TX COAST.

THE MESOSCALE GUIDANCE APPEARS SOMEWHAT SLOW WITH THE
PRECIPITATION PROGRESSION OF THE CDO.  THE BROWNSVILLE TX RADAR
SHOWS OCCASIONAL HOURLY RAIN TOTALS UP TO 2" OFFSHORE, BUT AMOUNTS
COULD BE AMPLIFIED ONCE ONSHORE DUE TO FRICTIONAL CONVERGENCE AND
A REINFORCEMENT OF THE BOUNDARY NEAR THE COAST CAUSED BY THE
RAINFALL ITSELF (A RAIN-INDUCED WEDGE SITUATION), WHICH WOULD MOVE
SLOWLY NORTHWEST AHEAD OF THE STORM'S CDO.  SHOULD THE SYSTEM NOT
COMPLETE ITS EYEWALL REPLACEMENT CYCLE, THE OUTERMOST EYEWALL
COULD REACH THE COAST AT THE END OF THE MPD HORIZON.  HOURLY RAIN
TOTALS UP TO 3" WITH LOCAL AMOUNTS UP TO 6" ARE EXPECTED.  THIS
SHOULD LEAD TO FLASH FLOODING, PARTICULARLY WITHIN URBAN AREAS.

ROTH

ATTN...WFO...BRO...CRP...EWX...HGX...

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

LAT...LON   29679565 29099503 28799545 27949682 26829744
            27409789 28069793 28779756 29449662