776
FXUS64 KMOB 211810
AFDMOB

Area Forecast Discussion
National Weather Service Mobile AL
110 PM CDT Sat Sep 21 2024

...New AVIATION, NEAR TERM...

.AVIATION...
(18Z TAFS)
Issued at 110 PM CDT Sat Sep 21 2024

VFR conditions are expected throughout the forecast with light
easterly winds becoming southerly near the coast this afternoon.
Winds become light and variable overnight. Light patchy fog could
be possible across interior areas. BB/03 &&

.NEAR TERM...
(Now through Sunday)
Issued at 110 PM CDT Sat Sep 21 2024

An upper ridge continues to build into the region today, with just a
modest weakening beginning Sunday night in response to an upper trof
progressing across the Plains. A surface ridge over the southeast
states favors a mostly easterly surface flow over the forecast area
today, with a sea breeze circulation developing near the coast in
the afternoon. The surface flow pattern will be similar on Sunday.
Subsidence associated with the upper ridge is expected to limit the
potential for convective development and have continued with a dry
forecast. Highs today and Sunday will be 90 to 95. Lows tonight
typically range from the upper 60s well inland to the lower 70s over
the southern portion of the area, and lows Sunday night range from
the upper 60s inland to the lower 70s at the coast. A low risk of
rip currents is expected through Sunday night. /29

SHORT and LONG TERM...
(Monday through Friday)
Issued at 441 AM CDT Sat Sep 21 2024

Dry and warm conditions continue through Tuesday as an upper-
level ridge slowly pushes eastward across the local region and an
expansive surface high pressure remains over the Appalachians.
Subsidence from the deep- layer ridging in place, along with lower
moisture values (PWAT values around 1.2 to 1.5 inches) should
keep rain out of the forecast for Monday and Tuesday (although a
very isolated coastal shower/storm cannot be ruled out late
Tuesday afternoon). Highs through Tuesday will generally range
from the upper 80s along the coast to the low 90s inland. Lows
will be in the upper 60s to low 70s inland to the mid 70s along
the coast. Moisture returns by midweek as troughing sets up to our
north, leading to an increase in rain chances and a decrease in
high temperatures to the low to mid 80s.

The biggest forecast challenge continues to revolve around an area
of low pressure that is slated to develop over the southern Gulf by
midweek. This eventual feature, which is expected to form off of a
developing Central American Gyre (CAG), now has a 60 percent chance
of developing into a tropical cyclone over the next 7 days.
Unfortunately, there still remains a lot of uncertainty when it
comes to the strength, timing, and trajectory of this system. The
biggest reason for this uncertainty is that the system has not even
developed yet. In fact, the larger-scale CAG is still very much in
its infancy stage as of this morning, so we still have to wait a few
more days before we can obtain a trackable feature that will help us
to narrow down the wide range of possibilities. There are a few
things, though, that guidance is beginning to agree upon, so I will
break down the remainder of the discussion into a "what we know"
section and and a "what we don`t know at this time" section.

What we know... Satellite imagery and model analysis suggests that
the CAG is beginning to form this morning over Panama, Costa Rica,
and Nicaragua. Over the next couple of days, this gyre will begin to
mature as is broadens out and expands across much of Central
America. From this, most operational models and a good majority of
the ensembles now suggest that a low pressure area will consolidate
over the western Caribbean, probably around the Tuesday timeframe.
This feature will likely cross over the Yucatan or move through the
Yucatan Pass thereafter, arriving in the southern Gulf on
Wednesday. At this point, the system will start to break off from
the CAG and will start feeling the steering effects of the upper-
level features to its north. The upper features at this point
include: the aforementioned upper ridge located over the southeast
US, a longwave trough digging into the central US, and an upper low
that cuts off from the main longwave trough over the south central
US. Once the system enters the Gulf, strengthening is definitely
possible due to the very warm Gulf waters and being located
underneath an upper-level anticyclone (giving way to low shear
values). Additionally, models are suggesting that whatever does
develop from this will be quite large, so even though the eventual
track of this system is quite murky (see the next section for more
details), marine, coastal, and even some rain and wind impacts will
likely be felt across a majority of the Gulf Coast region,
regardless of track. We will begin honing into the details of these
impacts as we get closer in time.

What we don`t know at this time... As stated earlier, the system has
not developed yet. When this lack of data gets inputted into the
various models and then we look out at the solutions 5+ days out,
this leads to a plethora of inaccuracies within each model run that
ultimately affects the model run`s output. This is why there has
been so much run-to-run and model-vs-model variability in the
overall strength, trajectory, and timing of this storm. Once the
system actually forms and models are able to latch onto a trackable
feature, we should start to see guidance begin to converge on a most
probable solution. Additionally, questions with regards to the upper-
level features listed in the above section also begin to arise, such
as 1) How long will the ridge linger over the southeast US? 2) How
deep will the longwave trough be as it pushes into the Great Lakes
region, and how fast will it be moving? 3) What role will the cutoff
upper low play to its northwest? Once again, I think that once a
trackable feature develops, we`ll be able to pinpoint which steering
features will play the greatest role in its eventual track. By then,
we will also have a better idea as to the strength and locations of
these upper features. But, as alluded to earlier, it is important
not to focus on the precise location of the center as impacts will
likely be felt far removed from the center of the system. We will
continue to monitor trends closely and we urge residents and
visitors across the entire Gulf Coast to continue to monitor the
forecast over the coming days. /96



&&

.PRELIMINARY POINT TEMPS/POPS...
Mobile      71  92  69  91  70  90  73  89 /   0   0   0   0   0  20   0  30
Pensacola   74  90  73  90  74  89  76  88 /   0   0   0   0   0  20  10  30
Destin      74  89  75  89  76  88  77  88 /   0   0   0   0   0  10  10  20
Evergreen   68  94  67  94  68  92  70  90 /   0   0   0   0   0  10  10  30
Waynesboro  69  93  67  93  68  92  69  91 /   0   0   0   0   0  10  10  20
Camden      69  93  68  93  69  93  70  90 /   0   0   0   0   0  10  10  20
Crestview   68  93  68  93  68  92  70  91 /   0   0   0   0   0  20  10  30

&&

.MOB WATCHES/WARNINGS/ADVISORIES...
AL...None.
FL...None.
MS...None.
GM...None.
&&

$$

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