Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 170919

Area Forecast Discussion
National Weather Service Houston/Galveston TX
419 AM CDT Thu Aug 17 2017

A fairly complex pattern was in place over Southeast Texas early
this morning. An upper level low pressure trough at 200-300 mb
extended into the forecast area from the southern Gulf of Mexico.
A shear axis was in place over the western part of the upper
trough, mainly across the northern and central parts of the state.
This axis was co-located with a moisture axis where PWs
approached 2.4 inches. A secondary moisture axis was over
Southeast Texas where PWs approached 2 inches. Finally, an upper
level high pressure ridge extended across the northern Gulf of
Mexico to over the forecast area.

The main items of concern today include high heat index values and
chances for showers and thunderstorms. With the axis of higher
moisture just to the north and northwest, and with the secondary
axis overhead, dewpoints may stay high enough this afternoon for
the heat index to approach advisory levels (108 degrees). However,
model blends showed the potential for enough mixing for the heat
index to be a bit lower--mainly between 205 and 207 with an
isolated area of 108-109 here and there. It will be close, but am
not confident enough to issue an advisory at this time. Best
chances for showers and thunderstorms will be over the eastern
and northern counties. Isolated showers will be possible mainly
over the coastal counties and off the coast through mid morning.
May see the seabreeze get active later this morning and this
afternoon. Any storms that do develop will help alleviate the heat
at least temporarily. Enough moisture will remain overhead for
best rain chances over the eastern and northern areas once again
on Friday.

The models then show that the subtropical ridge aloft should build
over Southeast Texas; although, an approaching upper level trough
from over the Gulf of Mexico will help weaken the ridge on Sunday.
This should lead to diminished rain chances on Saturday and
Sunday. The upper level trough will then bring slightly cooler
temperatures and increase rain chances on Monday. The GFS and
ECMWF differ in the details but expected rain chances to persist
from Monday through the middle of the week as the upper level
trough shears out over or near Southeast Texas.



Again there is not much change in the forecast for the Upper Texas
Coast. Southerly winds should continue into the weekend. Winds have
increased to SCEC levels overnight and should continue this morning.
Winds should be decreasing Friday and into the weekend to closer to
10 knots. Seas currently running 4 to 5 feet and look for those seas
to slowly subside to around 2 to 4 feet for the weekend. Light winds
and low seas are expected for the start of next week.

Tide levels look to be near normal or a half foot above.



College Station (CLL)      99  76  99  76 100 /  10  10  10  10  10
Houston (IAH)              96  78  97  78  97 /  20  10  20  10  20
Galveston (GLS)            92  83  92  82  91 /  20  10  20  10  20


     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...Waters from Freeport to
     the Matagorda Ship Channel from 20 to 60 NM...Waters from
     High Island to Freeport from 20 to 60 NM.



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