Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 241139

Area Forecast Discussion
National Weather Service Charleston SC
739 AM EDT Thu May 24 2018

High pressure will remain to the east through Friday while a
trough of low pressure lingers to the west. Developing low
pressure over the Gulf of Mexico will slowly move north toward
the central Gulf Coast this weekend, possibly lingering through
early next week. This pattern will maintain higher than normal
rain chances across the area.


Today: Deep moisture and the mid level eddy across east central
GA will be the stimulus for another round of diurnally enhanced
convective rains across much of our area along and to the west
of I-95. A secondary MCV which had been responsible for
overnight convection to the west will likely become absorbed
with the mid level vort max this afternoon and this feature will
likely be a significant factor in the pattern of convective
rains later today. Mid levels are warm and not very unstable
with the deep moisture environment responsible for weak
downdraft CAPEs. In fact, the updraft potential appears weaker
today, especially with more clouds to start off the day in our
western zones. We have POPs ranging from 65-75 percent adjacent
to east Central GA with likely POPs extending northward to
border the southern SC midlands. Locations west of a line from
Ludowici and Springfield GA to around Allendale SC stand the
better chances of seeing both some locally heavy downpours and
some thunder this afternoon. There could be some localized 2-3
inch plus rains somewhere over eastern GA but the mesoscale
looks too complex for placing highest QPF prior to convection
onset. Storm motions appear quite slow and heaviest rains well
inland will likely be the result of multicell mergers. Very
localized excessive rains cannot be ruled out in our far western
GA zones.

In the Charleston area today, we lowered POPs to trend with even
more stable mid levels and some distance from the deeper
moisture. Many of 00Z models suggest a dry day is possible to
the east of Highway 17 with lowest POPs on the beaches. The sea
breeze will probably generate at least isolated convective
rains. A backdoor front lurks just north with convection most
likely to develop from the southern Pee Dee into the central SC

Highs will range from the mid to upper 80s across then entire
area today with fairly light onshore flow.

Tonight: Not much change to the pattern. Deeper moisture lingers
over the region with evening convection inland dwindling and
a slight chance for showers many areas for the overnight with
lack of any instability and only weak speed convergence in
the boundary layer. There may be areas of inland stratus with
some localized patchy fog not out of the question. We do not
have any mentions of fog in the forecast since clouds look to
prevail many areas.


Atlantic high pressure will prevail through the end of the week.
Meanwhile low pressure is expected to slowly organize over the Gulf
of Mexico and move north toward the Gulf Coast. The track and
strength of this low is a bit uncertain but models generally agree
the low will make landfall anywhere from around New Orleans, LA to
Apalachicola, FL. Either way a tropical air mass will remain in
place with rain chances generally staying above normal, mostly
during the afternoon and evening each day. In general we think the
highest chances will be inland near the better moisture, instability
and forcing, especially Sunday. However there is some uncertainty
for Saturday as there may be a break in the rain. Some spots will
likely pick up over an inch through the period. No significant
flooding or severe weather is anticipated at this time. Temperatures
will generally be above normal except for Sunday when it will
likely be below normal given the abundant rain coverage.


Not much pattern change through the period with deep low pressure
persisting to the west and Atlantic high pressure to the east. This
will maintain a tropical air mass across the area and lead to higher
than normal rain chances, with not much more preference for higher
rain chances during the day than at night. Temperatures should
stay near to above normal.


KCHS: Mainly VFR. Isolated showers possible this morning with
sea breeze convection more likely inland by this afternoon.

KSAV: We have introduced a tempo SHRA to trend toward more
confidence in scattered convective rains closer to deepest
moisture anchored over the eastern half of GA. A few tstms
may develop around the area later today. Tonight, shower chances
to small for TAF mentions at this time with low clouds possible
inland from the terminal late (especially if some breaks in the
clouds occur).

Extended Aviation Outlook: A persistent tropical air mass will lead
to higher than normal rain chances into early next week, mainly each
afternoon. Thunder chances will be low however given the limited
instability. Some restrictions will also be possible from morning
low clouds and/or fog as well.


A light southerly flow early on today will become more onshore
with a very weak coastal trough developing tonight along the SC
coast. Winds will be on the weak side, less than 15 kt and
below 10 kt much of the time. Seas 2 to 3 ft through early

Friday through Tuesday: The area is expected to remain on the
western edges of Atlantic high pressure as a low pressure system is
expected to develop over the Gulf of Mexico and track north toward
the Gulf Coast. Depending on the strength and track of the low will
determine how much of a wind/sea increase there will be locally so
mariners should pay close attention to the forecast for this weekend
into early next week as Small Craft Advisories will be possible for
some or all of the marine area.




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