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Area Forecast Discussion (AFD)

Issued by Houston/Galveston, TX (HGX)

                            
000
FXUS64 KHGX 171521
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1021 AM CDT Sat Aug 17 2019

.UPDATE...
Surface high pressure remains over the eastern/central Gulf with
lower pressures over eastern New Mexico. 12z CRP/LCH soundings
show 850 temps between 19-20 C which supports high temperatures in
the middle 90's this afternoon but considering the warm start to 
to today, will add a few degrees to that which matches values 
already in the forecast. Drier air is trying to work into the
western portion of the CWA and the CRP and FWD soundings show
quite a bit of dry air above 900 mb. Think there will be some
mixing this afternoon and lowered dew points out west and
subsequently lowered heat index values. Heat Advisory looks
marginal out west but still looks valid toward the coast. Will
maintain current Advisory as previously configured. Radar is 
showing scattered showers and thunderstorms along and east of I-69
this morning. PW values remain near or just above 2.00 inches over
the eastern third of the region. Convective temperatures are in
the upper 80's so shra/tsra should continue to develop with
additional heating and this is supported by HiRes guidance. Had
some reports yesterday of funnel clouds and waterspouts and
conditions look favorable for this to occur again today. Stay
alert if on the water today. Lastly, bumped wind speeds up a bit
for tonight over the Gulf waters and a SCEC will probably be need
over the western Gulf waters tonight. 43

&&

.PREV DISCUSSION... /ISSUED 641 AM CDT Sat Aug 17 2019/ 

AVIATION [12Z TAF Issuance]...

Currently some VCSH down along the GLS and LBX and some off and
on MVFR CIGs up towards CXO that will continue for the next few
hours. Showers and thunderstorms will again develop this
afternoon starting near the coast then move inland through the
late afternoon then dissipating after sunset. Activity will 
mainly impact along and east of the I45 corridor. VFR conditions
will mostly prevail through the period. Fowler

PREV DISCUSSION /Issued 420 AM CDT Sat Aug 17 2019/...

SHORT TERM (Today through Sunday)...
Isolated showers are popping up over coastal waters again early 
this morning, but we will head into a lull in activity towards the
late morning. Satellite derived PWAT has a surge of PWATs of 
around 2.1 inches across the region, which is slightly lower than 
yesterday. However there is enough moisture that showers and 
thunderstorms will pick back up in the afternoon hours. CAM 
guidance mostly shows these showers staying on the eastern half of
the CWA, which is where I left the higher PoPs. Activity settles 
down after sunset, but isolated to scattered showers make a return
on Sunday. 

Yesterday, heat indices at Sugarland got to 110, at Galveston to 
109, and both Houston and Huntsville got to 107, with today
looking very similar if not a couple of degrees higher. That, 
plus it being the weekend, have decided to put out a Heat Advisory
beginning at noon and lasting until 7pm. Increased cloud cover 
and the increased chances of showers over the eastern counties may
prevent them from hitting criteria (which is 108 or greater), but
with the isolated nature of these showers have decided to just 
put the advisory out for the entire area. Heat indicies will again
climb to similar levels on Sunday, but will wait to see how today
goes before we re-issue any future advisories. Fowler

LONG TERM (Sunday Night through Saturday)...
No change in next week's weather pattern, at least from late
Sunday through Friday. A typical summertime pattern as the 
region remains under the influence of Desert SW to Southern Plains 
593-ish dam upper ridging. The general mid layer steering flow 
will out of the east with periodic lobes of higher moist NW Gulf 
air (1.9 to 2.1 inch pwat range) traversing southeastern Texas. As
these air masses pass through they will increase the occurrence 
and areal coverage of showers and thunderstorms, especially if 
their arrival is during the afternoon. A near 95 F noon convective 
temperature should be achieved each mainly clear to partially 
cloudy week day. Due to suppression brought on by the ridge, 
background weak southerlies should prevail and allow for the local 
mesoscale breezes to become more of a player as it relates to 
afternoon convective focus. Low to moderate early day (southern 
CWA) streamer showers transitioning to afternoon shower and 
isolated storm cluster activity will all be dependent upon sea/bay
breeze and outflow interaction behavior. 

A general height weakness channel across the western Gulf will
support the northern advancement of weak Bay of Campeche-based 
tropical waves that will skirt the coastline from Friday into 
Sunday. Model ensembles are all pointing to a general inverted 
trough feature but the member consensus is not wanting to close 
off anything. So, as of this morning, expect higher coastal and 
maritime rain/storm chances a week from now...the impetus from a 
large scale tropical trough with weak embedded waves within greater
than 2 inch pw air introducing periods of marine and coastal zone
moderate precipitation. Southern third forecast area thicker 
overcast and periodic precipitation will regulate weekend warmth 
to the 80s. 31

MARINE...
Very similar conditions compared to yesterday for today with 
mainly light to occasionally moderate onshore flow with slightly 
higher wind speeds during the overnight and early morning hours. 
Isolated to scattered showers and thunderstorms are expected in 
early morning hours today and tomorrow. Winds may become gusty 
and erratic near any thunderstorms that do form. Seas will 
generally be 2 feet or less today, but will be gradually 
increasing to around 4 feet by tomorrow. There will be marginal 
SCEC conditions due to both wind speeds and seas tonight into
Sunday morning. High pressure building into the region through 
next week will bring more relatively quiet weather. Fowler

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      99  78 100  78  99 /  10  10   0  10  20 
Houston (IAH)              97  81  96  81  97 /  40  10  20  10  60 
Galveston (GLS)            93  85  92  85  93 /  40  20  20  20  50 

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...Heat Advisory until 7 PM CDT this 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...NONE.
&&

$$

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