Area Forecast Discussion
Issued by NWS Charleston, SC
FXUS62 KCHS 300227
Area Forecast Discussion
National Weather Service Charleston SC
1027 PM EDT SUN MAY 29 2016
Tropical Depression Bonnie will meander over or near the coast of
South Carolina through Monday before gradually lifting northeast
away from the area. A cold front will then approach the region
.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
Tropical Depression Bonnie was found just off the Charleston
County coast as of late Sunday evening, continuing with it`s
counter-clockwise movement from earlier. It is still stuck in a
nebulous pattern aloft under a weak and negatively tilted trough,
but will start to lift a bit further overnight to the
north/northeast as there becomes a little better flow between the
trough and the Sub-Tropical Atlantic Ridge. Little change in
strength will occur, despite the proximity to the ocean. Refer to
the official forecast from NHC.
The depression has been undergoing a large diurnal fluctuation to
a weaker system, with both the coverage and intensity of earlier
rains having dropped off considerably. There is little instability
and less hear and forcing than several hours ago, allowing for a
noticeable decrease in rainfall. Most model guidance was
suggesting this shrinkage to occur under these conditions.
If nearby waters were a little warmer then there might be a more
significant flare-up of rainbands. Plus the main tropical feed of
moisture, the so-called Atmospheric River has become shunted
further east of the area. So we feel that the heaviest rains have
ended. But with PWAT near 1.7-1.8 inches and the sluggish movement
to Bonnie, we held onto locally heavy rains in the HWO for late
tonight and Monday. But widespread heavy rains are done with and
maybe some drying out of Jasper County and other places that had
flooding rains can continue.
We maintained slight chance of thunder through the overnight and
made adjustments for radar trends, showing generally 20-30 Pops
south, 30-40 Pops north, with a few hours early on of 50-70
percent near the Savannah River.
Winds are basically not much of a concern, with the best winds to
occur over the Atlantic waters.
Temps won`t change too much through the night given extensive
cloudiness and already starting down in the upper 60s and lower
70s. But combined with the saturated conditions it will certainly
be a muggy night.
.SHORT TERM /6 AM MONDAY MORNING THROUGH WEDNESDAY/...
The remnants of TS Bonnie are expected to linger across eastern SC
through Monday before moving northeast into eastern NC through mid
week. The deeper moisture will shift northeast of the area with time
which will translate to generally lowering rain chances and warming
temperatures with time. However, heavy rainfall will be possible at
times, especially Monday across southeast SC. This could lead to
localized flash flooding given precipitable water values around 2
inches and generally weak steering flow.
.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
Weak surface pressure pattern will be in place Thursday into Friday
before a cold front approaches from the west over the weekend, and
potentially stalls near or over the area. Rain chances peak each day
in the afternoon with a relative minimum at night, with the better
chances occurring Saturday & Sunday. Upper ridge over the area will
boost temperatures a couple degrees above normal.
.AVIATION /03Z MONDAY THROUGH FRIDAY/...
MVFR or possible IFR conditions to impact the terminals tonight
into Monday, due to the proximity of Tropical Depression Boonie,
which will be in the vicinity of KCHS tonight, finally and
hopefully starting to pull away Monday. This should allow for at
least some improvement back to VFR at KSAV later Monday. While the
00z TAFs show only VCSH, occasional moderate or even heavy rains
can still occur tonight into Monday at KCHS, with light to
moderate rains at KSAV. Adjustments will be necessary pending
radar trends and the future movement of Bonnie.
EXTENDED AVIATION OUTLOOK...MVFR ceilings or worse are likely at
KCHS Mon night along with some showers/storms as the remnants of TS
Bonnie slowly lift northeast away from the area through mid week.
Thereafter...low risk for flight restrictions from mainly afternoon
showers/thunderstorms and early morning fog/stratus.
Tonight: For the late Sunday evening update we have dropped
mention of the Small Craft Advisory for AMZ350 and AMZ354, but
there is still a solid west-northwest flow around Bonnie to the
south across AMZ352 and AMZ374 for winds to still reach frequent
gusts to 25 kt and seas as high as 5 or 6 ft. Thus we have a
continuation of the SCA until 2 am for these waters. Bonnie was
found just off the Charleston County coast as of late Sunday
evening, and will gradually lift more north-northeast through the
overnight at a very slow pace. While a few rainbands can form,
there intensity and coverage should be somewhat restricted, so we
don`t anticipate anything more than scattered or maybe numerous
coverage of showers and a few t-storms.
Monday through Friday...Marine conditions expected to improve Monday
as the remnants of Tropical Storm Bonnie slowly move northeast near
the Carolina coast through mid week. Thereafter, no significant
winds/seas expected as a weak pressure pattern prevails before a
cold front approaches from the west late week and winds increase a
bit. Otherwise winds will mainly be 10 knots or less with seas 2-3
Rip Currents: An enhanced risk of rip currents is expected at all
beaches through at least Monday.
MARINE...Small Craft Advisory until 2 AM EDT Monday for AMZ352-374.