Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 300003

Area Forecast Discussion
National Weather Service Charleston SC
803 PM EDT SUN MAY 29 2016

Tropical Depression Bonnie will meander over southern SC through
Monday before gradually lifting northeast away from the area. A
cold front will then approach the region late week.


Surface observations, satellite imagery and radar continue show
the broad circulation of Tropical Depression Bonnie over southern
Charleston County as of early this evening, actually sliding to
near the Atlantic coast. The system is trapped beneath a weak
negatively tilted trough over the southeast, so not much change in
strength and/or location is forecast through the night. Recent
satellite pictures showing that Bonnie may actually be starting to
loop counter-clockwise, very close to a consensus forecast of the
GFS, NAM, RAP, HRRR and SREF that shows the system only in the
vicinity of Moncks Corner by late tonight, maybe finally starting
to show a little better movement northeast around the low and mid
level ridge in the Atlantic by that time.

Given PWAT of 1.8-2.0 inches or between the 90th and 100th
percentile, co-located with sluggish moving Bonnie and it`s
associated low level convergence/forcing, heavy rains will
continue to be the main weather hazard with the tropical
depression. Since Bonnie will undergo some diurnal fluctuations
this evening and given that there isn`t too much in the way of
instability to begin with, we don`t show heavy rains any longer
than during this evening, mainly from Colleton and Beaufort
counties to the rest of the SC zones bordering the Savannah River,
and also over sections of GA in some places near and north of
I-16. Savannah will likely escape the heavy rains at least for the

As the night progresses and Bonnie starts to lift a little north-
northeast, some of the heavier and steadier rains that have been
absent from parts of the Charleston tri-county district should
start to arrive. For now we have only mention of moderate rains,
but given the excessive moisture and associated forcing, heavy
rains are certainly possible in and near these areas as well.

Much of the region south of I-16 will get by with no more than
slight chance to low end chance Pops.

We have made significant adjustments to the temp curve based on
rain-cooled conditions over much of the central CWFA, but lows for
tonight still on track into the mid and upper 60s.


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.


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.


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: We have extended the ongoing Small Craft Advisories for
the Atlantic waters outside of Charleston Harbor until at least
late this evening or overnight. This is in response to an ongoing
and fairly tight cyclonic pressure pattern around TD Bonnie,
located in Dorchester County as of early this evening. Bonnie will
continue to meander around through the night, and it`s possible
that the advisories may need to be extended further in time since
little change in strength is forecast in that system as per
guidance from NHC. Coverage of showers and t-storms is forecast to
increase during the late evening and/or overnight hours as Bonnie
could slip a little closer to the coast for a short time.

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 11 PM EDT this evening for AMZ352-
     Small Craft Advisory until 2 AM EDT Monday for AMZ350.


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