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Area Forecast Discussion (AFD)

Issued by Houston/Galveston, TX (HGX)

FXUS64 KHGX 161027

Area Forecast Discussion
National Weather Service Houston/Galveston TX
527 AM CDT Mon Sep 16 2019

.SHORT TERM [Today Through Tuesday Afternoon]...

The radar currently is showing shower and thunderstorm activity 
filling in nicely in the Gulf waters. These storms are driven by the 
upper level low that has been meandering westward across the Gulf 
the past couple of days. These showers will continue to spread into 
the coastal counties later this morning, then up towards I-10 by the 
afternoon. The more scattered storms combined with more cloud cover 
will bring daytime temperatures closer normal levels (Galveston may 
see a day where it doesn't break or tie the daily record high, which 
it has the past 3 days). 

The threat of more widespread precipitation over the region 
increases beginning on Tuesday as the upper level low gets closer 
to the eastern Gulf. The GFS is driest of the solutions, while the 
EC and CAN have been trending wetter. There will be some concern 
that storms along near the coast will produce localized heavy 
rainfall rates and total, especially as we head into the later part 
of Tuesday, that raise the threat for flash flooding. Have kept off 
issuing any flash flood watches at the moment due to lack of 
confidence, but this could change later today. The threat of heavy 
rainfall continues to increase through the first part of the long 
term period. 


.LONG TERM [Tuesday Night Through Monday]...
Upper low should be sitting off the Matagorda coast with the
potential for tropical development Tuesday night into Wednesday
morning before it probably moves inland. NAM/ARW are something of
an outlier in developing the system faster and more intensely. But
that doesn't mean we are out of the woods. Many of the ensembles
show falling pressures after the surface low moves inland and
wind fields accelerating leading to very efficient rain processes.
The rainfall during the day Tuesday should do a great job of 
getting the soils wet across the southern half of the region. 
Tuesday night through Thursday afternoon puts SETX in a very 
favorable region for heavy rainfall with low pressures
aloft/tropical/PW 2.1-2.5" and moisture transporting winds
20-30kts. Thanks for the coordination WPC on upping the threat 
for excessive rain. The system is going to be a slow moving system
and widespread rainfall of 3 to 6 inches is going to be common by
Friday. Some areas are going to see amounts of 6-9" and isolated 
amounts in excess of 12" will be possible. Rainfall rates of
2-3"/hr are going to be common during the event. Difficult to 
narrow down a specific area but all the ingredients are in the mix
and will be needing to watch that models don't trend towards a 
nocturnal consolidating event. Ridging to the north is fairly 
strong and this system looks to be stuck underneath so 
wobbles/loops/meanders are probably going to come into play. 

A Flash Flood Watch looks like a given for Tuesday night and 
beyond and may be issued tonight or Tuesday morning.

On the bright side temperatures should be lower and closer to 
normal over even slightly below normal for highs with all the 
precip and cloud cover over the region. 

The system should start to lift out Thursday with focus for heavy
rainfall departing but SETX will still be in the moist axis
feeding the remnants of the system so will keep rain chances
higher than much of the guidance Thursday night through Saturday. 

Tide levels should remain elevated through Friday with strong rip
currents and possibly minor coastal flooding.



The very slow moving upper level low that has been in the central 
Gulf the past few days continues to meander westward inducing 
moderate easterly flow through tonight. Thus small craft should 
continue to exceed caution in the Gulf waters. The moderate flow 
will also create a continued threat of stronger rip currents today 
and bring the threat of minor coastal flooding. Will be issuing a
Coastal Flood Statement shortly. Onshore flow begins on Tuesday 
as the disturbance begins to enter the western Gulf/Upper Texas
coastal waters. Periods of showers and thunderstorm associated 
with this system will impact the waters beginning today and 
continue through midweek with some of these storms producing 
localized areas of very heavy rainfall and gusty winds. 



Galveston still setting records and yesterdays 94 degree high
temperature tied the old record from 1900. 



College Station (CLL)  98  74  94  75  90 /  10  20  50  20  60 
Houston (IAH)          95  76  92  76  88 /  40  30  70  60  80 
Galveston (GLS)        90  80  89  80  86 /  80  80  80  90  90 



GM...SMALL CRAFT SHOULD EXERCISE CAUTION through late tonight 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.