Flash Flood Warning 18, NWS Houston/Galveston, TX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
851 PM CDT Thu May 9 2019

.UPDATE...
Storms fired as expected and quickly went severe over southeast TX
this evening, with -10c mid level temps atop mid 70f surface dew
points supporting strong instability and ripe airmass for large
hail given 35-45 kt of effective shear. Intense rainfall rates
also occurring with 4.5-5" having already fallen in western
Harris county thru 830p. These slow moving storms should
gradually become more organized/consolidate along and ahead of
surface cold front now pushing into sern TX between now and
midnight. Expect heavy rainfall and large hail will remain threats
as these storms finally move offshore by 3-4am. Damaging winds
could become added threat given surface based instability and
possibility of organized small lines or bow echoes.

Otherwise...forecast left unchanged from earlier.

Evans

&&

.PREV DISCUSSION... /ISSUED 248 PM CDT Thu May 9 2019/

DISCUSSION...
Forecast Highlights through the end of the week and through the weekend:

- A Flash Flood Watch is in effect for all of Southeast Texas through
  7 PM Saturday.
- Forecasted rainfall totals are still about 4 to 8 inches
  widespread, with isolated 9 to 12 inches possible. A lot of this
  rain could fall in a very short period of time which cold lead
  to flash flooding.
- Minor to moderate river flooding is ongoing and is expected to
  continue. Conditions could worsen significantly depending on
  where the heaviest rains fall.
- There is a Slight Risk of severe storms this afternoon and
  tonight across nearly all of Southeast Texas. The primary
  weather hazards are expected to be damaging winds, hail and
  isolated tornadoes.

Showers and thunderstorms have begun to develop off to our east
and off to our west, and it is only a matter of time until activity
begins to fill in across our area. Our developing storms will have
some strong/severe potential (slight risk per SPC's Day 1 Severe
Weather Outlook) with damaging winds, hail and isolated tornadoes
possible. Developing activity is expected to evolve into a
potential heavy rain event (rainfall rates of 2 to 4 inches per
hour or higher possible) as we head on into this evening and on
through the overnight hours, and then once again as we head on
into a Friday afternoon through Saturday time period. The
movement/placement of a slow moving frontal boundary in our area
could become a player as to where the heaviest rainfall sets up -
maybe more concentrated in/around the I-10 corridor or maybe more
concentrated near/along the coast. We will have to see how
everything evolves. Forecasted rainfall totals of 4 to 8 inches
are expected to be common for this event, and some locations could
see 9 to 12 inches before the heaviest rains come to an end some
time late Saturday or early Sunday.

The frontal boundary in combination with shortwaves, increasing lift
and building precipitable water values (>2 inches and getting close
to 2.5 inches) will be very supportive of the intense rainfall rates,
and if any of the activity is slow moving or trains, flash flooding
will be likely as lots of area grounds remain saturated from recent
rains.

River flooding (mainly minor to moderate right now) is expected to
continue. If the heaviest rainfall ends up in/around area basins,
creeks and bayous, conditions could worsen rather quickly and
significantly.

This could be a multi-day event, and every effort should be made
to closely monitor the weather/forecasts/warnings as everything
unfolds.  42

MARINE...
High pressure east of the region coupled with a weak trough of low
pressure over coastal Texas will allow the pressure gradient tighten
some tonight. Seas remain slightly elevated as swells propagate
toward the upper Texas coast. A weak cold front over North Texas
will sag slowly south tonight and may enter the coastal waters on
Friday before stalling out or possibly returning north on Saturday
as weak low pressure develops over the middle Texas coast. Have
issued a SCEC for the 20-60 NM waters tonight for slightly elevated
seas and an increasing E-SE wind. Have extended the Beach Hazard
Statement through 12z Friday due to elevated tide levels that will
again exceed 3.0 feet by 12z Friday and for the continued risk for
rip currents as swells propagate toward the coast. A series of upper
level disturbances will bring periods of thunderstorms to the
coastal waters through Saturday. Winds and seas will be higher in
and near these storms. The main threats from the storms will be high
wind gusts, heavy rainfall and lightning. Looking ahead, a general
easterly flow will develop next week as surface low pressure
develops off the middle Texas coast and high pressure remains over
the TN valley. 43

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      60  71  64  74  60 /  80  80  80  90  20
Houston (IAH)              67  76  69  78  64 / 100  90  80  90  40
Galveston (GLS)            72  77  74  80  71 / 100  90  70  90  50

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...Flash Flood Watch through Saturday evening for the following
     zones: Austin...Brazoria Islands...Brazos...Burleson...
     Chambers...Coastal Brazoria...Coastal Galveston...Coastal
     Harris...Coastal Jackson...Coastal Matagorda...Colorado...
     Fort Bend...Galveston Island and Bolivar Peninsula...
     Grimes...Houston...Inland Brazoria...Inland Galveston...
     Inland Harris...Inland Jackson...Inland Matagorda...
     Madison...Matagorda Islands...Montgomery...Northern
     Liberty...Polk...San Jacinto...Southern Liberty...Trinity...
     Walker...Waller...Washington...Wharton.

GM...SMALL CRAFT SHOULD EXERCISE CAUTION until 7 AM CDT Friday for
     the following zones: Coastal waters from Freeport to
     Matagorda Ship Channel TX out 20 NM...Coastal waters from
     High Island to Freeport TX out 20 NM...Galveston Bay...
     Waters from Freeport to Matagorda Ship Channel TX from 20
     to 60 NM...Waters from High Island to Freeport TX from 20
     to 60 NM.

&&

Hazardous Weather Outlook
National Weather Service Houston/Galveston TX
730 AM CDT Thu May 9 2019

TXZ163-164-176>179-195>200-210>214-226-227-235>238-300-313-
335>338-101230-
Austin-Brazos-Burleson-Chambers-Coastal Brazoria-
Coastal Galveston-Coastal Harris-Coastal Jackson-
Coastal Matagorda-Colorado-Fort Bend-Grimes-Houston-
Inland Brazoria-Inland Galveston-Inland Harris-Inland Jackson-
Inland Matagorda-Madison-Montgomery-Northern Liberty-Polk-
San Jacinto-Southern Liberty-Trinity-Walker-Waller-Washington-
Wharton-
730 AM CDT Thu May 9 2019

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

.DAY ONE...Today and Tonight

A Flash Flood Watch is in effect from 1 PM today through 7 PM
Saturday. Showers and thunderstorms should develop today along a
stalled frontal boundary by this afternoon. Heavy rainfall will
be possible and could result in flash flooding and additional
rises on rivers and bayous. Damaging winds, hail, and isolated
tornadoes will also be possible.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday

A Flash Flood Watch is in effect through 7 PM Saturday. Strong
storms are possible through the weekend. A series of upper level
disturbances coupled with a stalled front and abundant moisture
will create a favorable environment for heavy rain.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will be needed today. Emergency managers
should also prepare for activation at various times through the
remainder of the week.

TXZ436>438-101230-
Brazoria Islands-Galveston Island and Bolivar Peninsula-
Matagorda Islands-
730 AM CDT Thu May 9 2019

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

.DAY ONE...Today and Tonight

A Flash Flood Watch is in effect from 1 PM today through 7 PM
Saturday. Showers and thunderstorms should develop today along a
stalled frontal boundary by this afternoon. Heavy rainfall will
be possible and could result in flash flooding and additional
rises on rivers and bayous. Damaging winds, hail, and isolated
tornadoes will also be possible.

Elevated tide levels will approach 3.5 feet this morning. Minor
coastal flooding will be possible, potentially impacting
vulnerable locations such as Highway 87 and 124. A coastal flood
advisory may be needed. Strong rip currents will also be possible
along Gulf facing beaches.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday

Elevated tide levels near 3.5 feet will continue through the end
of the week. Minor coastal flooding will be possible, potentially
impacting vulnerable locations such as Highway 87 and 124. Strong
rip currents will also be possible along Gulf facing beaches.

A Flash Flood Watch is in effect through 7 PM Saturday. Strong
storms are possible through the weekend. A series of upper level
disturbances coupled with a stalled front and abundant moisture
will create a favorable environment for heavy rain.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will be needed today. Emergency managers
should also prepare for activation at various times through the
remainder of the week.

GMZ330-335-350-355-370-375-101230-
Coastal waters from Freeport to Matagorda Ship Channel TX out
20 NM-Coastal waters from High Island to Freeport TX out 20 NM-
Galveston Bay-Matagorda Bay-
Waters from Freeport to Matagorda Ship Channel TX from 20 to
60 NM-Waters from High Island to Freeport TX from 20 to 60 NM-
730 AM CDT Thu May 9 2019

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

.DAY ONE...Today and Tonight

Some showers and thunderstorms will be possible today, and could
produce heavy rainfall, gusty winds, and hail.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday

A series of upper level disturbances will bring periods of showers
and thunderstorms through the remainder of the week. Some storms
could be strong with gusty winds, hail and periods of heavy rain.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will be needed.

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
1122 PM CDT THU MAY 09 2019

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1115 PM     FLASH FLOOD      LEAGUE CITY             29.49N  95.11W
05/09/2019                   GALVESTON          TX   EMERGENCY MNGR

            MULTIPLE EMS REPORT IMPASSABLE ROADS AROUND LEAGUE
            CITY. THIS INCLUDES GULF FREEWAY BETWEEN FM-518 AND
            FM-646 AS WELL AS FM-518 AND HIGHWAY 3

&&

EVENT NUMBER HGX1900138

LUCHS

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
1133 PM CDT THU MAY 09 2019

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1113 PM     MARINE TSTM WIND 4 NNE SAN LEON          29.54N  94.91W
05/09/2019  M50 MPH          GMZ335             TX   BUOY

            WEATHERFLOW STATION IN GALVESTON BAY REPORTS PEAK WIND
            OF 50 KNOTS

&&

EVENT NUMBER HGX1900139

LUCHS

PRELIMINARY LOCAL STORM REPORT...CORRECTED
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
1134 PM CDT THU MAY 09 2019

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1113 PM     MARINE TSTM WIND 4 NNE SAN LEON          29.54N  94.91W
05/09/2019  M58 MPH          GMZ335             TX   BUOY

            WEATHERFLOW STATION IN GALVESTON BAY REPORTS PEAK WIND
            OF 50 KNOTS

&&

CORRECTED EVENT

EVENT NUMBER HGX1900139

LUCHS

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