Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 221319
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
919 AM EDT Tue May 22 2018

.SYNOPSIS...
The region will remain in a warm and muggy air mass between
Atlantic high pressure to the east and low pressure to the west
into early next week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
A fairly active, wet day is expected for much of the day as the
region will remain pinned between broad mid-level troughiness
extending across the Deep South into Florida and subtropical
high pressure centered well offshore. Moisture being advected
northward out of the western Caribbean will remain in place
today with PWATS surging as high as 1.90 inches at times.
Forecast and observed soundings show fairly low convective
temperatures so with deep, tropical moisture in place aided
by some weak difluence aloft associated with an H25 shear axis,
expect scattered to numerous showers and some tstms to impact
much of Southeast South Carolina and Southeast Georgia through
sunset. It appears that the deepest band of moisture will setup
across Southeast Georgia so this should be where the greatest
rain coverage should occur, especially the afternoon sea breeze
begins its inland trek. Subtropical ridging looks to hold the
strongest over the Charleston Metro Area up into eastern
Berkeley and upper Charleston Counties so rain chances will be
considerably less there, which matches the latest trends noted
in the various CAMS. Locally heavy rainfall along with minor
flooding of low lying and poor drainage areas will be the
primary hazards today.

For the morning update, will increase pops to 70% across much
of interior Southeast Georgia and expand likely pops up to 60%
eastward into the Walterboro and Beaufort Areas. Pops will then
drop off quickly into the 20-30% range over eastern Berkeley and
upper Charleston Counties. Also lowered highs 1-2 degs across
Southeast Georgia where extensive cloud cover and shower
activity should limit temperatures.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY/...
Tonight: Diurnal showers and isolated thunderstorms are forecast to
gradually dissipate through the evening and overnight hours. I will
forecast SCHC PoPs for most areas, slightly greater over the marine
areas. Using a blend of MOS, I will forecast low temps from low 70s
across the beaches to the upper 60s inland.

Wednesday through Friday: The area will remain between Atlantic
high pressure to the east and low pressure to the west. A cold
front will approach from the north Wednesday night before
stalling out just north of the area. This pattern will maintain
the tropical air mass in place and lead to higher than normal
rain chances, especially each afternoon and evening. In general
we think the highest chances will be inland near the better
moisture, instability and forcing. Some spots could pick up over
an inch through the period. No significant flooding or severe
weather is anticipated at this time. Temperatures will generally
be near to above normal, especially lows.

&&

.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
Not much pattern change late this week into early next week with
high pressure remaining to the east and and low pressure to the
west. Will be watching for potential tropical cyclone development in
the south-central Gulf of Mexico. Models have been fairly agreeable
lately that the low will track toward the north-central Gulf Coast
region this weekend. This pattern will continue to maintain a
tropical air mass across southeast SC/GA and lead to higher than
normal rain chances. Temperatures should stay near to above
normal.

&&

.AVIATION /13Z TUESDAY THROUGH SATURDAY/...
VFR conditions expected at KCHS and KSAV through the 12Z TAF
period. Prior to the 12Z TAF, KCLX detected a cluster of
showers upstream of the KSAV terminal. Based on recent motion,
the showers will pass over or very close to KSAV between 12Z to
14Z, I will indicate MVFR conditions in a TEMPO. Otherwise,
steady south winds will develop during the daylight hours.
Showers are expected to increase in coverage this afternoon, I
will carry VCSH in each TAF. Tonight, shallow ground fog may
develop over areas that receive rainfall today.

Extended Aviation Outlook: A persistent tropical air mass will lead
to higher than normal rain chances through the weekend, 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.

&&

.MARINE...
Large high pressure centered over Bermuda will remain over the
region through tonight. Southeast winds will continue through today
and tonight, speeds remaining between 10-13 kts. Wave heights are
forecast to range from 2-3 ft within 20 NM to 4-5 ft beyond 20 NM.

Wednesday through Sunday: The area will remain between low pressure
to the west and high pressure to the east. A tropical cyclone may
develop in the central Gulf of Mexico later this week but models are
in good agreement it will remain far enough away to not have really
significant impacts locally. However, do expect an increase in winds
and seas later this week and we could see Advisory conditions this
weekend.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...None.

&&

$$


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