Flash Flooding in Texas, August 31, 2003

SOUTHEAST TEXAS FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
920 PM CDT SAT AUG 30 2003

TROPICAL STORM GRACE MOVING SLOWLY WNWWD THROUGH THE WRN GULF THIS
EVENING. GRACE DOES NOT LOOK IMPRESSIVE ON SATELLITE AND HAS A BROAD
AND VERY DISORGANIZED CIRCULATION. CURRENT FCST TRACK TAKES CENTER
OF SYSTEM ONSHORE MIDDLE TX COAST SUNDAY EVENING. WITH ALL THE
SIGNIFICANT CONVECTION FAR REMOVED AND ON THE EAST SIDE OF THE
STORM...HEAVIEST RAINS ARE LIKELY TO IMPACT SE TX.

LOTS TO CONSIDER IN THE FCST TNGT. WILL LOWER POPS SOMEWHAT FOR
INLAND AREAS FIRST PERIOD WITH DIURNAL LULL EXPECTED. THE HEAVIEST
RAINS WILL SPREAD ONSHORE COASTAL COUNTIES TNGT AND ACROSS REST OF
CWA SUNDAY MORNING AS RAINBANDS GRADUALLY WORK THEIR WAY INLAND.
ALSO CONCERNED ABOUT THE MESOSCALE BOUNDARY LYING JUST WEST OF I-35
IN CENTRAL TX. THIS BOUNDARY SHOULD CONTINUE PUSHING EWD AND COULD
HELP TO FOCUS ANOTHER AREA OF VERY HEAVY RAINS OVER W/NW ZONES
SUNDAY. WILL KEEP THE 80-100% POPS ENTIRE CWA FOR SUNDAY.

THE #1 CONCERN WITH GRACE WILL BE HEAVY RAINFALL AND FLOODING WHICH
COULD REMAIN A THREAT FOR SE TX THROUGH MIDWEEK. LATEST GFS/ECMWF
MODEL RUNS INDICATE GRACE MAY DRIFT VERY SLOWLY AFTER LANDFALL WITH
REMNANTS AFFECTING SE TX UNTIL A STRONGER TROF PICKS UP SYSTEM UP
AND SWEEPS IT AWAY WED/THU. REMNANTS OF WEAK TROPICAL SYSTEM
COMBINED WITH STALLED FRONT OVER CENTRAL/EAST TX ARE A CLASSIC SETUP
FOR A PROLONGED HEAVY RAIN AND FLOODING EVENT.

35/40/38

.HGX... TROPICAL STORM WARNING HIGH ISLAND TO MATAGORDA SHIP
         CHANNEL.
        FLOOD WATCH ALL OF SOUTHEAST TX.

PREVIOUS DISCUSSION...
TD #11 UPGRADED TO TROPICAL STORM GRACE.

HIGH PW AIR OVER THE AREA THIS AFTERNOON 1.94-2.34 WITH DEEP
CONVECTION LIMITED MAINLY OVER THE COASTAL COUNTIES AND ALSO IN
TRINITY AND HOUSTON COUNTIES. LARGE MASS OF DEEP CONVECTION 110 NM SSE
OF GALVESTON. WINDS OVER THE LAND THIS AFTERNOON RUNNING 10 TO 20
KNOTS...CLOSER TO 20 KNOTS AT THE COAST...OVER THE WATER NNW 15KTS AT
42019 AND SE 10KTS 42035. GRADIENT SHOULD TIGHTEN UP QUICKLY TONIGHT
AND EXPECT WINDS IN THE TROPICAL STORM FORCE RANGE TO BE OVER THE
COASTAL WATERS BY 9 PM...GUSTS NEAR 40 MPH POSSIBLE NEAR THE COAST
AROUND 2 AM...INCREASING FURTHER AS IT NEAR THE COAST.  LANDFALL
EXPECTED BETWEEN MATAGORDA BAY AND GALVESTON 7-11 AM BUT STRONGER
WINDS AND HEAVY RAINFALL WILL BE DISPLACED FROM THE CENTER TO THE
NORTHEAST-EAST. THE UPPER LOW STEERING T.S. NORTH CURRENTLY NE OF
BRO/SE OF CRP AND DRIFTING WEST AND COULD FILL RELAXING THE SHEAR OVER
THE SYSTEM. THE MOIST AXIS SHOULD BE OVER THE REGION THROUGH MONDAY AS
GRACE MEANDERS NORTHWESTISH. ETA/GFS KEEP THE MOISTURE OVER THE AREA
OR SHIFT IT SLOWLY WEST TOWARD THE HILL COUNTRY NEAR THE APPROACHING
FRONT. IT STILL BOILS DOWN TO A LOT OF RAINFALL FOR THE AREA. HAVE A
FLOOD WATCH IN THE BREECH AND WILL FIRE IT OFF AROUND 4 PM. MARINE
SEAS OF 5 TO 10 TONIGHT/SUNDAY. TROPICAL STORM WARNINGS SETX COAST.
OBSERVED TIDES SHOULD PEAK AT 4 TO 5.5 TOWARD SUNRISE DURING THE
ASTRONOMICAL HIGH TIDE.

EXTENDED...WILL KEEP IT SHORT DUE TO LACK OF CONFIDENCE IN VERY
IMPORTANT ASPECTS OF THE SHORT TERM FORECAST IMPACTS LEADING
INTO THE EXTENDED. WILL LIKELY FLOAT THE FRONT SOUTH INTO THE FA LATE
TUESDAY BUT WILL PROBABLY BE WEAK IF AT ALL.

45/43/31

GMZ330-335-350-355-370-375-TXZ163-164-176>179-195>200-210>214-226-
227-235>238-311100-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
928 AM CDT SAT AUG 30 2003

...TROPICAL DEPRESSION 11 DEVELOPS IN THE CENTRAL GULF OF MEXICO...

...TROPICAL STORM WARNINGS IN EFFECT FROM HIGH ISLAND TO CORPUS
CHRISTI TEXAS...

...LOCALLY HEAVY RAINFALL POSSIBLE TODAY THROUGH SUNDAY...

THIS HAZARDOUS WEATHER OUTLOOK IS FOR SOUTHEAST TEXAS.

.DAY ONE...TODAY AND TONIGHT.
A TROPICAL STORM WARNING IS NOW IN EFFECT FOR MUCH OF THE TEXAS
COAST EXTENDING FROM HIGH ISLAND TO CORPUS CHRISTI. DEVELOPING
TROPICAL DEPRESSION 11 WILL STRENGTHEN TODAY AND TONIGHT AND IS
EXPECTED TO BECOME TROPICAL STORM GRACE. THE CENTER OF THIS STORM
IS FORECAST TO CROSS THE TEXAS COAST NEAR PORT OCONNOR EARLY
SUNDAY MORNING. SHOWERS AND THUNDERSTORMS ARE EXPECTED TO BECOME
WIDESPREAD THIS AFTERNOON WITH RAINFALL TOTALS OF 1 TO 2 INCHES
POSSIBLE AND ANOTHER 1 TO 2 INCHES TONIGHT. HEAVIER TOTALS ARE ALSO
POSSIBLE. PLEASE REFER TO HLSHOU FOR MORE DETAILS REGARDING THIS
DEVELOPING WEATHER SITUATION.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY.
TROPICAL DEPRESSION 11 OR MORE LIKELY TROPICAL STORM GRACE
WILL MOVE ACROSS TEXAS ON SUNDAY. LOCALLY HEAVY RAINFALL IS AGAIN
POSSIBLE ACROSS SOUTHEAST TEXAS ON SUNDAY AS DEEP TROPICAL MOISTURE
REMAINS IN PLACE. ANOTHER 2 TO 3 INCHES OF RAIN N IS EXPECTED ON
SUNDAY. IF THIS TROPICAL SYSTEM MOVES SLOWER THAN EXPECTED...THE
THREAT FOR LOCALLY HEAVY RAINFALL MAY CONTINUE ON INTO MONDAY. THE
CHANCE FOR RAIN WILL CONTINUE INTO TUESDAY NIGHT. DRIER WEATHER IS
EXPECTED TO BEGIN TO FILTER INTO SOUTHEAST TEXAS ON WEDNESDAY.

.SPOTTER INFORMATION STATEMENT...
EMERGENCY MANAGERS AND STORM SPOTTERS SHOULD BE PREPARED FOR
ACTIVATION. PREPAREDNESS PLANS SHOULD BE IMPLEMENTED.