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Area Forecast Discussion (AFD)

Issued by Houston/Galveston, TX (HGX)

FXUS64 KHGX 160446

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1146 PM CDT Sun Sep 15 2019

Expecting to see periods of SHRA/TSRA increasing over the next several
days with the approach of the slow moving Gulf system. Hard to pinpoint
when best shot of activity will be for this TAF package (forecaster
confidence is low), but generally expect to see greatest concentration
and possible MVFR conditions near the coast during the late night and
morning hours, then spreading a little bit inland as the day progresses.
NE to E winds during the day tomorrow with higher speeds near the coast.

PREV DISCUSSION... /ISSUED 356 PM CDT Sun Sep 15 2019/ 

SHORT TERM [Monday Through Tuesday]...
Broad mid/upper level low off the La/Tx coasts will continue its 
very slow trek toward the coastal Bend on Tue. Look for shra/tstms
to redevelop and expand in coverage offshore tonight...with some 
bands gradually making their way to around, or slightly north, of
the I-10 corridor later Monday afternoon with daytime heating. 
Precip should taper off Monday evening, then follow the same 
pattern described above late Mon night & Tue. Difference will be 
higher areal coverage further inland during the day Tue as 
available moisture increases. This should be much needed and 
welcome rainfall. Few, if any problems are anticipated, though one
can never rule out the typical very localized street flooding 
associated with higher rain rates. 47

LONG TERM [Tuesday Night Through Sunday]...
Though there is high confidence that there will be good chances of
precip Tuesday night thru Thursday across the region, but overall
confidence in the specific details is low. Guidance shows the 
mid/upper low drifting to the north and into western parts of se 
Tx during this time period. Closer to the surface, models also 
show either a surface trof or weak surface low developing - also 
moving into the area from the south. How organized, or unorganized,
this feature becomes will go a long way in determining the 
potential for either continued steady welcome rainfall, or the 
risk of a more prolonged heavy rainfall event associated with  
training convective banding (in the case of a more organized 
system). There is generally a split between models in regards to
its evolution. PW's do increase to 2.2-2.5" which are close to 
the upper end that've been recorded this time of year, so moisture
won't be a problem. That being said, we will be closely watching 
things, but for now there is somewhat concerning signal for a 
potentially heavy rain and flash flood threat developing late Tue
night and Wed for areas generally along and south of I-10 and 
west of I-45. We'll see what future models have to say, but will 
go ahead an start the mention of locally heavy rainfall wording 
there for now. 

Chances of precip will continue into Wednesday night & Thurs with
the trof/low and PW's aoa 2" continuing a slow move north thru the
area. Rain chances taper down Friday and into the weekend. 47

The large, broad cyclonic circulation brought on by a western-moving 
north central Gulf upper low will maintain a tight enough pressure 
gradient on its northern periphery to produce moderate easterly 
winds. These Caution level east to southeasterly Gulf winds will 
generally be the dominant wind through late tomorrow. Periods of 
showers and thunderstorm rotating in from the east will temporarily 
create strong gusty winds and agitate seas. The low should move 
onshore sometime late Tuesday into early Wednesday. More persistent 
precipitation, possibly heavy, may occur across the local bay and 
Gulf waters from Tuesday on through mid week as lift along with the 
northeasterly sector of this low taps into high moisture.  31

Rivers and bayous are well within banks and should remain that way
through at least through the day Tuesday. The ground is dry and
should be able to handle a good bit of rainfall. This of course 
will continue to be monitored as we head into the midweek time 
period as there is considerable forecast uncertainty in regards to
the potential for some localized higher rainfall rates and 
accumulations across portions of the region.  47

Another day...another record in Galveston. Tied a 119 year old record
high of 94 previously set in 1900.  47


College Station (CLL)      75  98  75  94  73 /  10  10  10  50  30 
Houston (IAH)              75  94  75  90  76 /  20  30  30  50  50 
Galveston (GLS)            81  90  79  86  80 /  50  60  70  70  80 


     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.