Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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764
FXUS64 KHGX 261626
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1126 AM CDT Fri May 26 2017

.UPDATE...
A more humid morning as higher moisture moves in from the west.
Overcast skies beginning to break up closer to the coast...
expecting very dry air to begin mixing down as more efficient
surface heating works on the stout 800-900 mb cap. Afternoon
ambient temperatures reaching the lower 90s...with lower 70 dew
points...equates to heat indices topping out in the 99 to 102 F
range for a few hours. This is a good time to reiterate that
strenuous outdoor activity should be limited and that proper
hydration through the day is key to avoiding heat-related illness.
May near or reach Saturday morning high minimum temperature
records. Research has found that it is the consecutive days of
excessive heat...with little (cooling) relief during the overnight
hours...that have the most impact on the increased frequency of
heat-related health issues.

A Beach Hazard Advisory is in effect through Saturday evening for
strong rip currents and elevated tides. The unofficial start to
summer is typically the Memorial Weekend weekend and traditionally
population spikes at local area beaches during this holiday
weekend. A couple of days of a persistently moderate onshore
fetch has generated rougher surf and stronger rip currents. If
entering the water...ensure to swim in the proximity of a
lifeguard and avoid swimming near jetties...groins or piers. 31

&&

.PREV DISCUSSION... /ISSUED 409 AM CDT Fri May 26 2017/

DISCUSSION...
Hot and humid conditions are expected to settle in across
Southeast Texas over the next few days. 00Z upper air analysis
showed mid-level ridging building into Texas from Mexico with a
shortwave trough lifting across Kansas and Nebraska. As a surface
cyclone ejects across the Southern Plains today in response to the
Kansas/Nebraska shortwave, associated breezy 10-20 MPH southerly
winds will draw Gulf moisture back into the region. CIRA Layer
Precipitable Water satellite estimates show a tongue of 1.2-1.3
inch precipitable water air jutting into the Texas Coastal Bend
early this morning, with this moisture expected to rapidly
surge inland through the day.

Stout capping in place around 890 mb (also evident by the
anomalous propagation evident over the Gulf this morning) should
prevent any rain chances today and will play a critical role in
cloud cover, which will affect afternoon high temperatures. NAM
and GFS Bufr soundings show moisture remaining trapped beneath
this inversion through the day (leading to persistent cloud cover
and lower high temperatures), but with elevated near-surface winds
and daytime heating providing some turbulent mixing should see
some scattering this afternoon. This would allow for high
temperatures to again climb back to near 90 degrees inland today.

Mostly dry conditions are expected tonight through Sunday morning
as ridging over Texas amplifies as an upper level disturbance
over southern Idaho on early morning water vapor imagery slides
southeast. Increasing heights aloft associated with this ridging
will result in high temperatures climbing into the low to mid 90s
on Saturday, with peak heat index values climbing into the 100-105
degree range. While this is technically below Heat Advisory
criteria, early season heat is incredibly dangerous as people are
not acclimatized to it and anyone participating in Memorial Day
Weekend activities are urged to drink plenty of water and make
sure they have a cool place to go to if they become overheated.
Also of note will be the very warm (near to record) morning lows
on Saturday and Sunday. Cannot rule out speed convergence may
produce an isolated shower or two along the coast both Saturday
and Sunday mornings with the northern counties possibly being
grazed by a decaying thunderstorm complex moving out of North
Texas Saturday night, but rain chances during this time are 20
percent or less.

By Sunday, the disturbance now near Idaho reaches the Southern
Plains and sends a cold front into the region as it swings towards
the east. Loss of upper level forcing with the departure of this
disturbance is expected to result in the cold front stalling
somewhere near (or within) the region by Monday morning. There`s
still some uncertainty on where exactly this frontal boundary will
stall as it outruns its upper level support, but 00Z model
guidance has been fairly consistent with the boundary reaching
somewhere between the Interstate 10 corridor and the coast by
Monday. A few even show the cold front pushing just off the coast
before lifting inland as a warm front. Regardless, periods of
showers and thunderstorms are expected from late Sunday through
the middle of next week, first along the approaching frontal
boundary and then along it wherever it stalls as disturbances
override it in the weak southwest to west flow aloft.

While the severe weather threat does not appear to be
particularly high during this time given the weak flow, will have
to monitor for at least an isolated heavy rain threat as
precipitable water values peak between 1.6-1.9 inches at times in
a weakly forced environment. This would offer very little in terms
of overall storm motions, with rain chances (and highest rain
totals) focusing along either the remnant frontal boundary or
other mesoscale boundaries that develop from previous showers or
thunderstorms. Interestingly, CIPS Analog guidance shows a signal
for widespread rainfall exceeding one inch in the Monday/Tuesday
timeframe with another signal for even higher rainfall amounts
late next week. The main takeaway here is that several rounds of
rainfall will be possible throughout the next week, but will
likely be driven by features that are too far out in the forecast
to resolve at this time. 14

&&

MARINE...
Moderate to strong onshore flow this morning. Winds 15-20kts int
he far waters and increase to 20-25 in the nearshore and lower
bays. Wind profile showing the S25-30 knots at 1000ft this
morning. Expect that winds in the bays and nearshore should
gradually diminish between 7-10am to a more manageable 15-20
knots. SCA all waters through 10 am then can probably dialed back
to SCEC. The persistent moderate WAA continues through Saturday
night into Sunday morning before relaxing. A weak cold front moves
into SETX Sunday night but may be preceded by a prefrontal trough
that further relaxes winds in the bays and nearshore by Monday
morning. Frontal boundary gets diffuse and will likely be driven
by mesoscale rain events Monday possibly pushing an outflow into
nearshore waters Monday or Monday night. Showers and thunderstorm
chances increasing Sunday and Monday across the coastal waters. By
Tuesday afternoon winds should be more consistently southeasterly
and continue so through Thursday. May be experiencing some light
sea haze again Sunday through Thursday.

Tide levels on the increase with the WAA pattern and stronger
winds today and Saturday which will lead to increasing rip tide
strength and elevate levels to Gulf facing areas. May flirt with
2.5-3ft by this afternoon and again Saturday afternoon. Lighter
winds Sunday afternoon and Monday should scale back tide levels
but rip tides may be slower to improve. 45


AVIATION...
MVFR deck spreading eastward across the area and should fill in
to the east fairly quickly in the next few hours. 1200-2500ft deck
should scatter out this afternoon with winds on the increase by
15z. LLJ lined up from SW to NE across the region this morning and
afternoon and strengthens which should help boost winds by late
morning pushing gusts in the 18-28kt range. Overnight expect ST
deck to return and likely earlier than it did given slightly
richer moisture streaming in from the Gulf. 45

CLIMATE...
Near to record high minimum temperatures are possible at all of
the first order climate sites on Saturday and Sunday mornings. A
listing of the current records is provided below.

May 27
LOCATION           RECORD HIGH MINIMUM     YEAR
City of Houston           80               1996
Houston Hobby             78               1996
College Station           77               1924
Galveston                 80               2000

May 28
LOCATION           RECORD HIGH MINIMUM     YEAR
City of Houston           81               1996
Houston Hobby             79               1996
College Station           77               1996
Galveston                 81               1996

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      91  76  94  76  90 /  10  10  10  20  30
Houston (IAH)              92  78  93  78  90 /  10  10  10  10  20
Galveston (GLS)            85  80  87  80  85 /  10  10  10  10  20

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...SMALL CRAFT SHOULD EXERCISE CAUTION until 7 PM CDT this evening
     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.

&&

$$

Discussion...31/43



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