Area Forecast Discussion
Issued by NWS Mobile, AL

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FXUS64 KMOB 231814

Area Forecast Discussion
National Weather Service Mobile AL
114 PM CDT Wed Aug 23 2017

.DISCUSSION...Updated for latest aviation discussion below.


18Z issuance...
Majority VFR conditions are expected through the forecast period.
Late afternoon scattered showers and thunderstorms could bring
MVFR ceilings along the coast. In addition the sea breeze could
also generate southerly winds this afternoon and evening, but the
main wind flow should be from the northeast. Patchy fog may occur
inland in the early morning hours prior to Sunrise. DJ/17


.PREV DISCUSSION... /issued 637 AM CDT Wed Aug 23 2017/

DISCUSSION...Updated for latest aviation discussion below.

12Z issuance...Scattered to broken higher based clouds will spread
northward off the Gulf with potential of shra/tsra developing
along the coastal terminals by mid AM. Cigs reduced to MVFR
categories, vsbys to IFR/MVFR categories in and near convection
today as well as brief strong convective wind gusts. /10

PREV DISCUSSION... /issued 358 AM CDT Wed Aug 23 2017/

NEAR TERM /Now Through Wednesday night/...Mid level ridge over
the southeast has shown signs of breaking down as lower geo-
potential heights aloft, associated with a long wave trof, moves
eastward over the Appalachians. Upper tropospheric trof forecasters
have been observing moving slowly westward over the Gulf the last
few days was positioned south of the Louisiana coast, mostly
unchanged from last 24 hrs. South of this feature, surface trof
associated with the remnants of Harvey has emerged off the western
coast of the Yucatan Peninsula. Thunderstorms have increased in this
area and environmental conditions will become conducive for a
tropical depression or tropical storm to form as the low tracks
slowly northwest. More on this in the long term section below.

For today, upper trof moving across the Appalachians and Tennessee
Valley will allow a surface front, draped from east of the Ohio
River Valley to the Mid-South, west into northern Texas this morning
to sink southeast, possibly moving into the far northern zones by
evening. The boundary is progged to continue southward to the coast
and possibly offshore by daybreak Thursday. As the boundary
approaches from the north, in combination with sufficient deep layer
moisture levels (PWAT`s ~ 2.0 inches) and daily instability,
scattered showers and storms are forecast to develop thru the day
over the land zones. Some of the storms likely to be strong at
times. Today`s highs in the lower half of the 90s north of the coast
and upper 80s/lower 90s closer to the beaches. Maximum heat index
values to range from 101 to 105 degrees.

Tonight, will maintain a small chance of mainly evening storms out
of respect for the southward moving front, with isolated to
scattered coverages shifting more south to the coast and offshore
late in the night. Overnight lows in the lower to mid 70s interior
to mid/upper 70s beaches. /10

SHORT TERM /Thursday Through Friday night/...An upper trof over
the eastern states gradually weakens during the period as an upper
ridge axis over the western Atlantic noses into the eastern Gulf
and as a tropical system is expected to move from the Bay of
Campeche area to near the Texas coast. This latter feature is the
remnants of Harvey and is nearly certain (90-100% per latest NHC
outlook) to have evolved into a tropical depression or storm
during the period. A weak stalled frontal boundary is expected to
be located near the coast of the forecast area Thursday morning
and drifts a bit inland during the day, but will held near the
coast on Friday due to gradually strengthening surface ridge over
the eastern states. A series of shortwaves move across the
forecast area on Thursday, then shift slightly more inland on
Friday with the weakening of the eastern states upper trof and
building of the upper ridge into the eastern Gulf. Precipitable
water values of 2.0-2.2 inches (125-135% of normal) generally
continue through the period, and with a weak steering flow
suggests that locally heavy rains will be possible with the
stronger storms that develop each day. Gusty winds and frequent
lightning will also accompany the stronger storms. For Thursday,
scattered convective development looks to be favored across the
entire area as the weak frontal boundary advances inland a bit,
whereas on Friday convective development will be more favored over
the southern half or third of the area due to the frontal
boundary being held near the coast. Rip current risk looks to
increase by at least Friday as long period swell begins to impact
the area. Highs on Thursday will be mostly in the lower 90s then
more around 90 on Friday. Lows Thursday night range from the upper
60s well inland to the mid 70s at the coast. Lows Friday night
will be mostly in the lower 70s with mid 70s at the coast. /29

LONG TERM /Saturday Through Tuesday/...While confidence in the
forecast during the long term period remains lower than normal,
the expectation continues for the tropical system (Harvey) near
the Texas coast to be absorbed into an amplifying upper trof
pattern over the eastern states. Increasing deep layer moisture
associated with this system still looks to flow into the forecast
area during the period, and there is at least some potential for
a heavy rain and/or severe weather event to occur over the
forecast area during the Monday into Tuesday timeframe - but this
is highly dependent on placement of a weak frontal boundary near
the area as well as the surface low from the anticipated remnants
of Harvey - and will just have to continue to monitor at this
point. An increased risk of rip currents is expected during the
period. Scattered to potentially numerous showers and storms are
expected through the period and will add more coverage detail as
confidence improves. /29

MARINE...A weak pressure pattern today results in a light wind
pattern thru tonight which becomes northerly late tonight into
Thursday with a frontal boundary pushing just off the coast.
Winds, waves and seas locally higher in isolated to scattered marine
storms. Away from storms, little change in seas. Meanwhile, the
National Hurricane Center calls for a high chance that the remnants
of Harvey will very likely regenerate into a tropical depression or
tropical storm today or tonight as it tracks  northwest around 10
mph across the western Gulf. Considering current forecasts, will
continue to call for an increased swell component which begins to
propagate northeast up over the coastal waters beginning late in the
week and may continue into the first of next week. Refer to latest
products from the National Hurricane Center and the local forecast
office in Mobile for further updates and status of the low to lift
up into the western Gulf end of the week. /10




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