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Area Forecast Discussion (AFD)

Issued by Houston/Galveston, TX (HGX)

                            
000
FXUS64 KHGX 221137
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
637 AM CDT Sun Sep 22 2019

.AVIATION [12Z TAF Issuance]...
A mix of LIFR to VFR ceilings across the SE TX terminal this
morning, with most of the LIFR to MVFR ceilings impacting IAH and
northward. Ceilings should be on the rise through the morning
hours, with some MVFR decks developing south of I-10 as low level
moisture rises with daytime heating. Scattered showers and 
isolated thunderstorms will be possible today, starting earlier
along the coast and spreading inland. The best coverage of
precipitation should be to the east of the terminals. Otherwise
winds out of the southeast between 5 to 12 knots will be possible
today, becoming light and variable overnight. Lower ceilings again
look possible tonight into the early morning hours, with pockets
of patchy fog also possible.

Hathaway

&&

.PREV DISCUSSION /Issued 421 AM CDT Sun Sep 22 2019/...

.SHORT TERM [Tonight Through Tuesday]...
Radar imagery this morning shows decent coverage of showers over
the Gulf waters stretching north across the coastal counties
through Hardin and Orange counties to our east. Taking a look at
the GOES-16 total precipitable water imagery, 1.8 to 2.0 inches
prevail across the Gulf waters with a plume of higher precipitable
water values (PWs) closer to 2.0 inches stretching across the
eastern Gulf waters and into Hardin County where the best coverage
of showers is ongoing. This axis of better moisture should
continue to shift inland through afternoon hours and act as a
boundary for more widespread development of showers and 
thunderstorms. Convective temperatures should reach into the low 
to mid 80s, and with high temperatures expected to top out in the 
upper 80s to low 90s, isolated thunder will be possible with the 
help of daytime heating. NAM12 shows decent mid-level 
frontogenesis values across Chambers to Polk counties by the 
afternoon hours, which should also aid in convective development. 
Short term guidance such as the HRRR and RAP13 appear to have 
initialized best this morning, and show more scattered coverage 
this afternoon east of I-45 with more isolated development to the 
west. Along the axis of best moisture, a few brief heavy downpours
look possible, with the HRRR showing hourly rain rates between a 
quarter of an inch to an inch and a half per hour. That said, any 
additional rainfall over Liberty and Chamber counties
specifically, is only going to delay the recession of any 
lingering flooding. An areal flood warning remains in effect 
through 11 AM this morning, to account for those river and local 
tributary levels that remain high with very saturated soils. This
areal flood warning may need to be extended. Most of the 
convection should wane with the loss of daytime heating by the 
early evening hours. Tonight low temperatures should lower into 
the mid 70s to low 80s.

Hathaway

&&

.LONG TERM [Monday through Sunday evening]...
Overall, the early portion of next week will be characterized by 
quiet and dry conditions, with the chances of convective 
precipitation gradually increasing by next weekend. By Monday the 
upper-level ridge and surface high pressure continue to build in 
over the south-central CONUS, and the characteristic moderate 
onshore flow pattern across Southeast Texas continues. Generally 
weaker moisture transport throughout the beginning portion of the 
week will result in a reduced chance of diurnal showers and 
thunderstorms initiating over the coastal waters and progressing 
inland as we typically see in such a flow pattern. By Thursday, 
however, the ridge shifts eastward and an upper-level weakness 
within the prevailing zonal flow develops over the northwest Gulf 
of Mexico. Global model guidance shows a plume of enhanced 
moisture transport developing along with this feature, returning 
precipitable water values (PWs) across the CWA to the 1.75 to 2 
inch range. This will increase convective activity associated with
daytime surface heating to a more climatologically normal rate. 
Moisture transport further amplifies as we move into next weekend 
and PWs climb above 2 inches, bringing the potential for more 
widespread coverage of showers and thunderstorms. Despite this, 
precipitation amounts are not expected to be substantial enough to
produce further flooding impacts to areas recently impacted by TS
Imelda.

Cady

&&

.MARINE...
Small craft should continue to exercise caution at least through 
the early afternoon hours when the pressure gradient begins to 
slacken over the region. A Beach Hazard Statement remains in 
effect through early Monday morning to account for the risk for 
strong rip currents along Gulf facing beaches and elevated tide 
levels. At Galveston Bay Entrance, tide levels should peak between
3.0 and 3.5 feet above MLLW during times of high tide. Tide 
levels should fall around or even beneath 3.0 feet above MLLW 
late Monday evening.

Onshore flow around 15 knots should lower to 10 to 15 knots, later
this afternoon. Seas should also lower to 3 to 4 feet by Monday 
morning. Light to moderate onshore flow should prevail through a 
majority of next week, with seas remaining around 2 to 4 feet.
Moderate onshore picks back up by the weekend, increasing to 15 
to 20 knots.

Hathaway
 
&&

.HYDROLOGY...
We continue to see a gradual fall in river levels following the recent
flooding rains:
- The West Fork of the San Jacinto near Sheldon has fallen out of 
minor flood stage and is expected to continue to lower below action 
stage by Tuesday morning.
- The Trinity River at Moss Bluff has fallen below minor flood stage 
this morning and is forecast to continue to fall below action stage 
by Monday evening.
- Cedar Bayou near Crosby continues to hold steady in minor flood 
stage.

Cady

&&

.CLIMATE...
A daily record high minimum temperature was observed at Galveston 
yesterday. The minimum temperature of 83 degrees ties a record for 
the highest observed for September 21, which last occurred in
1992.

Cady

&&

.PRELIMINARY POINT TEMPS/POPS...

College Station (CLL)  94  75  92  74  92 /  10  10  20  10  10 
Houston (IAH)          89  74  90  73  90 /  30  10  30  10   0 
Galveston (GLS)        91  81  88  81  88 /  20  10  30   0   0 

&&

.HGX WATCHES/WARNINGS/ADVISORIES...

TX...None.
GM...SMALL CRAFT SHOULD EXERCISE CAUTION until 10 AM CDT this morning 
     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...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.


&&

$$

SHORT TERM/MARINE/AVIATION...08
LONG TERM/HYDRO/CLIMATE...12