Scientific Forecaster Discussion
fxus64 khgx 180904
Area forecast discussion
National Weather Service Houston/Galveston Texas
404 am CDT Wed Sep 18 2019
the remains of Imelda with the low level circulation centered just
west northwest of Tomball but the center pressure is filling and
the circulation center becoming more muddled. Mesoanalysis
indicating the strong convergence is focusing from around Victoria
to Bay City to Freeport to Galveston to Chambers County and then
turning north into eastern Liberty County. Intense rainfall rates
of 3-3.5"/hr have been seen in the stronger storms in this band
mainly on the immediate coast. Storms further inland have still
been putting down 1-2"/hour rates up into northern
Brazoria/southeast Harris counties. Storms have occasionally been
been taking on supercell characteristics with the storms over the
coastal waters and this will likely extend up into
Bolivar/Chambers County today.
The circulation center should wobble north then slow near
Huntsville. The models diverge with the track after that this
afternoon. Most drifting very slowly either west or north or east.
Leaning more towards the northwest and then west with most of the
models pinging on the southern counties with an east to west or
southwest to northeast line forming. This fits with the
destabilization that should occur in the southwestern counties and
feed into the convergence zones that sets up on the southeast
flank of the circulation. Have expanded the Flash Flood Watch up
into Trinity/Walker counties and extended it through 7 am
Thursday. At that point it can adjusted to probably focus over the
eastern counties. During the afternoon storms will be expanding
out over the area and but do expect a band to set up and then
gradually shift east and northeast into tonight. Convergence
should weaken somewhat tonight and wind profiles weaken so perhaps
lower the rainfall rates but by that point the soils will have
taken on a lot of water so flooding threat will certainly remain.
Thursday the remains of the circulation should be centered
somewhere in the Crockett to Tyler area generally drifting slowly
north still. Southeast Texas will still be dealing with abundant moisture
over the area and instability and acceleration southwesterly flow
feeding into the system and maintaining the potential for heavy
rainfall and another band or two of storms to form and focus heavy
rains. Thursday night the remains lifting north a bit faster and
then heavy rainfall threat should start to diminish significantly.
May get storms again Friday though with less coverage and after a
lull a chances for the rivers to recover.
Needless to say it should be relatively cool over the central and
northeastern counties today thanks to all the rain. Could get
pretty steamy down around Jackson County today and Thursday.
The weekend expecting widely scattered to scattered showers and
thunderstorms as band of drier air finally spreads back into the
area. The deep tropical moisture feeding into Humberto sloshes
south and then west and into the Gulf possibly surging up into the
western portions of the Gulf Monday into Tuesday though it may
struggle to get very far into southeast Texas with weak steering winds and
ridging nosing in from la even though a brief upper shortwave
passage may ripple by to the north and introduce slightly cooler
air aloft. Temperatures
N area of low pressure over southeast Texas will move into East Texas today.
The pressure gradient remains tight and will issue an Small Craft Advisory for the
Gulf waters this morning with winds gradually decreasing this
afternoon. A scec will be required for the Gulf waters in the wake
of the Small Craft Advisory. A scec will also be needed this morning for the bays. A
moderate onshore flow will persist through early Sunday before the
pressure gradient finally begins to relax by Sunday afternoon. A
light onshore flow and lower seas are expected for the first half of
Tide levels are continuing to run about 1.5 to 2.0 feet above
normal. At Galveston Bay entrance, tide levels are still forecast to
peak between 3.0 to 3.4 feet above MLLW during high tide. Tide
levels will remain elevated through Saturday and water levels could
possibly reach 3.5 feet. The strong onshore flow will also increase
the risk for strong rip currents along Gulf facing beaches. Due to
the multiple beach hazards in place, will re-issue the beach hazards
flash flooding threat remains high and Flash Flood Watch in effect
southeast of a line from Wharton to Groveton to the coast. Much
of the southeastern 1/3 of the region has had soaking rains of
1-3 inches with a notable band of 5 to 9 inches from near Sargent
to Angleton to Friendswood to Deer Park and over across Chambers
County. Rivers and bayous have risen and hardest hit has been the
Clear Creek basin and lower coastal basins. With the expected
rainfall later today anticipate that some of Harris County
watersheds and up into the San Jacinto/Trinity basins having at
least minor impacts. 43/45
Preliminary point temps/pops...
College Station (cll) 86 74 90 75 89 / 50 40 40 50 50
Houston (iah) 82 76 86 77 87 / 100 80 70 40 60
Galveston (gls) 84 80 86 81 86 / 100 70 60 30 50
Texas...Flash Flood Watch through Thursday morning for the following
zones: Brazoria islands...Chambers...coastal Brazoria...
coastal Galveston...coastal Harris...coastal Matagorda...
Fort Bend...Galveston Island and Bolivar Peninsula...inland
Brazoria...inland Galveston...inland Harris...inland
Liberty...Polk...San Jacinto...southern Liberty...Trinity...
GM...small craft should exercise caution until 10 am CDT this morning
for the following zones: Galveston Bay...Matagorda Bay.
Small Craft Advisory until 10 am CDT this morning for the
following zones: coastal waters from Freeport to Matagorda
Ship Channel Texas out 20 nm...coastal waters from High Island
to Freeport Texas out 20 nm...waters from Freeport to
Matagorda Ship Channel Texas from 20 to 60 nm...waters from
High Island to Freeport Texas from 20 to 60 nm.