-- Discussion containing changed information from previous version are highlighted. --
678
FXUS64 KMOB 222338
AFDMOB

Area Forecast Discussion
National Weather Service Mobile AL
637 PM CDT Sun Sep 22 2024

...New AVIATION...

.AVIATION...
-- Changed Discussion --
(00Z TAFS)
Issued at 637 PM CDT Sun Sep 22 2024

VFR conditions prevail across the forecast area through Monday.
Light winds around 5 to 10 knots this evening out of the south
becomes light and variable late this evening into the overnight
hours. A light southeasterly wind around 5 knots can be expected
for the day Monday. MM/25
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&&

.PREV DISCUSSION... 
-- Changed Discussion --
/issued 404 PM CDT Sun Sep 22 2024/

..New NEAR TERM, SHORT TERM, LONG TERM, MARINE...

NEAR TERM...
(Now through Monday)
Issued at 404 PM CDT Sun Sep 22 2024

Really not much to talk about in this period as attention turns
to the extended. High pressure over central Texas will flatten out
across the northern Gulf on Monday in response to a upper trough
digging into the central US. This will keep rather dry conditions
through Monday as winds slowly become more east southeasterly at
the surface by Monday night. With deep dry air in place, the only
real adjustments made were to lower afternoon dewpoints and bump
high temperatures up a degree or two as deep vertical mixing seems
likely. Rain chances will remain near zero for the time being.
BB/03

SHORT and LONG TERM...
(Tuesday through Sunday)
Issued at 404 PM CDT Sun Sep 22 2024

We continue to monitor 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 80 percent chance of developing into a
tropical cyclone over the next 7 days and a 40 percent chance of
developing in the next 48 hours. Unfortunately, there still
remains a lot of uncertainty when it comes to the strength,
timing, and trajectory of this system. I will once again break
down the remainder of the discussion into a "what we know" section
and a "what we don`t know at this time" section.

What we know... Satellite imagery and model analysis suggests that
the CAG is continuing to mature over Central America this morning.
Although activity is still rather scattered and sprawled out,
pockets of deep convection are now developing around this feature,
with a decent blowup of clouds and storms forming just off the coast
of Nicaragua and Honduras.  Whether or not this new convection will
eventually become the trackable feature is yet to be seen, however,
latest guidance is beginning to pick up on a more concentrated area
of low pressure developing near this activity by around the
Monday night timeframe. This feature will likely be steered north-
northwestward around the larger-scale CAG feature, crossing over
the Yucatan Peninsula or through the Yucatan Pass and 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
known upper features at this point include: an upper ridge located
over the southeast US and a longwave trough digging into the
central US. Yesterday, an additional cutoff upper low over the
south central US was mentioned, however, model trends over the
past day are beginning to drop this feature in favor of a more
vigorous upper trough. More about this trend in the next section,
as this change will likely play a big role in the storm`s
eventual path. As the system enters the Gulf, strengthening is
likely 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 this system will
be quite large, so even though the eventual track of this system
is rather murky, marine and coastal/surf 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... The feature still has not
developed yet. Although we are starting to see the signs that a
trackable feature may soon be forming, as of right now models are
still unsure of what to latch onto. As mentioned yesterday, when
this lack of data gets inputted into the various models and then
we look out at the solutions 5-7 days out, this leads to a
plethora of inaccuracies within each model run that ultimately
affects the model run`s overall output. This is why there
continues to be so much run-to-run and model-vs-model variability
in the overall strength, trajectory, and timing of this storm.
Once the feature finally develops in the next day or so, this
issue should start to resolve itself and we should start to see
guidance begin to converge on a most probable solution. The other
big uncertainty is with regards to the upper-level steering
features at play. There were a few notable changes in the recent
model suite that are different then what the models were showing
1-2 days ago. Previously, much of the guidance suggested that as
the upper longwave trough digs into the central US, a weak cutoff
low would break off from the main trough and travel into the
Texas/Oklahoma/New Mexico region. This led to the tropical system
feeling its influence and caused it to take a path more in the
western/central Gulf. Today, instead of a lobe breaking off from
the main trough, most guidance now suggests that the actual
longwave trough will strengthen and dig far enough south to break
off from the northern jet stream. This now results in an
anomalously massive upper low parking itself over the Mississippi
River Valley. The strength and eastward extent of this upper low
helps to break the ridge down a bit quicker, ultimately resulting
in an eastward shift in a good majority of model guidance over the
past day for the tropical system. With that being said, these
sudden changes in model guidance tells me that the upper features
at play are extremely complex and fickle and, at this time, any
one model run should not be taken at face value, especially since
we still do not have a trackable feature. Expect models tracks to
continue to shift back and forth a bit longer until guidance has a
better handle of the system and the upper features at play, and
by that time, we can begin focusing on our local impacts. As
stated earlier, even if the center does not directly impact our
CWA, impacts will likely be felt far removed from the center of
the system due to its expected size. 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

MARINE...
Issued at 404 PM CDT Sun Sep 22 2024

Light northeasterly winds become southeasterly Monday
afternoon, with an easterly to southeasterly flow following through
Wednesday. Seas and winds begin to build Wednesday through Thursday
as a potential tropical system strengthens in the Gulf. We will
closely monitor the progression of this system as it will likely
result in significant hazardous conditions for small craft. BB/03
-- End Changed Discussion --

&&

.PRELIMINARY POINT TEMPS/POPS...
Mobile      71  93  70  90  71  88  70  80 /   0   0   0  10  10  60  50  50
Pensacola   74  92  73  89  75  86  73  80 /   0   0   0  10  20  60  60  70
Destin      75  90  75  89  75  86  74  82 /   0   0   0  10  20  50  60  70
Evergreen   70  95  67  94  69  88  69  81 /   0   0   0  10  20  60  60  60
Waynesboro  70  94  67  92  68  87  67  79 /   0   0   0  10  30  60  50  50
Camden      70  94  69  91  69  86  67  77 /   0   0   0   0  20  60  50  60
Crestview   69  95  67  91  70  88  70  81 /   0   0   0  10  10  60  60  70

&&

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

$$

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