Flash Flood Warning 100, NWS Houston/Galveston, TX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
641 AM CDT Tue Aug 29 2017

.AVIATION...
Bad flight weather continues...strong northerly winds 20-30kts
today with gusts of 35-50kts...rain tapering off from west to east
with IFR/MVFR CIGS. Gradual improvement in CIGS to around 2000
feet tonight and early Wednesday as winds become more
northwesterly and diminish very slowly.
45

&&

.PREV DISCUSSION... /ISSUED 632 AM CDT Tue Aug 29 2017/

DISCUSSION...
Tropical Storm Harvey's position is about 100 miles east southeast
of Port O'Connor with the latest band of convection hitting
Bolivar and Galveston Island putting down 1 to near 2.5 inch per
hour rates. The persistent 20-25G40 kt (near coastal) wind has
maintained a near 4 foot water level on the bay side with web
cams currently showing Strand street flooding. This banding will
be commonplace today...dropping a quick 1 to 2 inches on their
east-to-west passage. As the broad center of TS Harvey moves by
Galveston Island through the day expect these bands to mainly
impact the southeastern forecast area or those counties surrounding
Galveston Bay. Much lower rainfall rates of between 1 to 2 inches
will equate to less of a flooding threat. 2 to 4 inches with
localized 7 to 8 inches are expected over these extreme southeastern
counties. The southeastern counties most impacted by Harvey's
catastrophic flooding (Harris, Fort Bend, Galveston) are forecast
to pick up another 2 to 3 inches today...and then another 2 to
possibly 3 inches tomorrow. Thus...we are not completely out of
the woods but we can see the light of coming out on the other
side of this unprecedented rainfall/flooding tropical event. The 3
to 4 day rainfall totals of greater than 40 inches (possible 50
inches in locations surrounding Santa Fe and Dickinson) are simply
mind-blowing that has lead to the largest flood in Houston-Galveston
history. From its rapid intensification from a wave to a Category
4 landfall in less than 60 hours to producing the most extreme
tropical storm flooding the Houston region has ever gone through...
this beast will be making landfall as a tropical storm along the
Texas-Louisiana coast tomorrow morning.

This historic flooding that has taken lives and will likely be the
largest economic U.S. natural disaster (certainly the costliest
hurricane) will transition from being a extreme flash flooding
event to a longer-lived (record level) river and bayou flooding
episode. Late week into Labor Day weekend weather becomes benign
with slight to low end chance POPs to account for redeveloping
precipitation left in Harvey's trailing trough. Highs will average
in the upper 80s...minimums in the low to mid 70s (low to mid 70
dew points to keep early September feeling like...well...early
September). I hate to even mention this feature but the GFS (and
Euro to a degree) develops and moves a tropical wave/low northward
into our waters through the weekend. Let's hope it's an aberration.
31

MARINE...
Tropical Storm Harvey is now 100 miles east of Port O'Connor and is
slowly moving east. Harvey will beginning moving northeast later
today. Expect seas to build today with winds increasing into the 30
to 40 knot range. Scattered showers and thunderstorms will continue
along with the threat of waterspouts. Harvey is expected to make
landfall Wednesday afternoon in southwest Louisiana.

Elevated water levels (2-4 feet above normal) will continue along
the immediate coast and in the bays into Wednesday. River and Bayou
drainage is causing water levels in the Houston Ship Channel to
continue to rise. 33

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      71  81  72  84  72 /  60  60  50  30  20
Houston (IAH)              72  79  72  84  73 /  90  80  60  40  30
Galveston (GLS)            72  83  73  85  75 /  80  60  40  30  30

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...Tropical Storm Warning for the following zones: Brazoria...
     Chambers...Galveston...Harris...Jackson...Liberty...
     Matagorda.

     Flash Flood Watch through late tonight for the following zones:
     Brazoria...Chambers...Fort Bend...Galveston...Harris...
     Liberty...Matagorda...Montgomery...Polk...San Jacinto...
     Trinity...Walker...Wharton.

GM...Tropical Storm Warning for the following zones: Coastal waters
     from Freeport to the Matagorda Ship Channel out 20 NM...
     Coastal waters from High Island to Freeport out 20 NM...
     Galveston Bay...Matagorda Bay...Waters from Freeport to the
     Matagorda Ship Channel from 20 to 60 NM...Waters from High
     Island to Freeport from 20 to 60 NM.

&&

31/33/11/43/45

Hazardous Weather Outlook
National Weather Service Houston/Galveston TX
752 AM CDT Tue Aug 29 2017

TXZ164-177>179-199-200-213-214-226-227-236>238-301300-
Brazoria-Chambers-Fort Bend-Galveston-Harris-Liberty-Matagorda-
Montgomery-Polk-San Jacinto-Trinity-Walker-Wharton-
752 AM CDT Tue Aug 29 2017

This hazardous weather outlook is for portions of Southeast Texas..

...FLASH FLOOD WATCH IS IN EFFECT TODAY....

.DAY ONE...Today and Tonight
Another day of spiraling bands coming onshore from Tropical Storm
Harvey will put down periods of one to two inches in the strongest
cores. Today and tomorrow's additional rainfall may only total 4
to 6 inches in most areas but may be enough to keep the worst flooded
locations under water for an extra day or two...hampering clean up
efforts.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday
The final bands of an exiting Harvey will come around and put down
a few more inches across the extreme eastern and northeastern forecast
area. These bands should not be initiate significant flooding but
may be a nuisance to regional clean up efforts.

A tropical wave in the western Gulf may need to be monitored for
possible development over the weekend.

.SPOTTER INFORMATION STATEMENT...
Spotters still need to be vigilant and monitor Harvey's rainfall
bands.

TXZ163-176-195>198-210>212-235-301300-
Austin-Brazos-Burleson-Colorado-Grimes-Houston-Jackson-Madison-
Waller-Washington-
752 AM CDT Tue Aug 29 2017

This hazardous weather outlook is for portions of Southeast Texas..

.DAY ONE...Today and Tonight
Another day of spiraling bands coming onshore from Tropical Storm
Harvey will put down periods of less than an inch within the strongest
cores. Today and tomorrow's additional rainfall may only total 4
to 6 inches in most areas but may be enough to keep the worst
flooded locations under water for an extra day or two...hampering
clean up efforts.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday
The final bands of an exiting Harvey will come around and put down
a couple of more inches across the western and central forecast
area. These bands will not initiate significant flooding but may
be a nuisance to regional clean up efforts.

A tropical wave in the western Gulf may need to be monitored for
possible development over the weekend.

.SPOTTER INFORMATION STATEMENT...
Spotters still need to be vigilant and monitor Harvey's rainfall
bands.

GMZ330-335-350-355-370-375-301300-
Coastal waters from Freeport to the Matagorda Ship Channel out
20 NM-Coastal waters from High Island to Freeport out 20 NM-
Galveston Bay-Matagorda Bay-
Waters from Freeport to the Matagorda Ship Channel from 20 to
60 NM-Waters from High Island to Freeport from 20 to 60 NM-
752 AM CDT Tue Aug 29 2017

This hazardous weather outlook is for portions of Southeast Texas..

.DAY ONE...Today and Tonight

Tropical Storm Warnings are still in effect with many early
Tuesday northeast wind observations registering 20 to 30 knots
with tropical storm force gusts. As Harvey's broad low tracks
across to the northeast ...seas are is still rough across the
upper Texas waters. Nearshore 7 to 8 feet...with near 10 foot
offhsore wave heights...through the day.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday
Winds and seas will significantly downtrend through early Friday
as Harvey moves well inland through late week. Late week light
southwesterlies over 3 to 4 foot average seas.