Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston SC
1003 PM EDT Fri Sep 30 2016
a stationary front will linger just offshore through the weekend
as high pressure builds South. Hurricane Matthew will move
northward across Cuba and the Bahamas through early next week and
remaining offshore of the southeast U.S. Coast by mid week. Refer
to the latest advisory on Matthew issued by the National Hurricane
Near term /until 6 am Saturday morning/...
convection off the northeast Florida coast along the stationary
front has been moving northward, and with small height falls aloft
around the large cyclone spinning from Kentucky toward Illinois
and Indiana there is a small risk that this activity could skirt
coastal sections well after midnight within a S-SW synoptic flow.
However, all model guidance suggests that any isolated showers and
T-storms will stay over the Atlantic.
Otherwise, debris clouds from that convection off northeast
Florida will spread north, but similar to the rain chances the
bulk of these clouds will stay over the ocean. Thus we anticipate
clear or mostly clear skies, and with a decoupled boundary layer
plus a dry atmosphere depicting pwat down to 0.78" at kchs and
1.04" at kjax per 00z sounding, this will equate to excellent
radiational cooling and a definite autumn feel to temps through
the overnight. We opened an even bigger range of temps based on
latest trends, now showing lower 50s near and west of US-301 in
Georgia, 55-60 most other places west of I-95 in the cwa, to
lower 60s near the US-17 corridor. The "warmest" locations will be
coastal South Carolina and in downtown Charleston where mid and
upper 60s will be common.
Short term /6 am Saturday morning through Monday/...
Saturday and sunday: weak stationary front will linger off the
coast through the period. Influence from the large cyclonic gyre
will gradually diminish through the weekend. The area will remain
along the drier, southwestern periphery of the cyclone so expect
dry conditions to prevail through the weekend. An isolated shower
can not be completely ruled out across the upper Charleston County
coast Saturday and along the far southern Georgia coast Saturday
night, so any mentionable pops will be in these areas.
Monday: the low-level flow will become a bit more onshore as the
outer circulation around Matthew begins to impact the synoptic
flow. 20-30% pops look reasonable for the coastal counties,
highest across coastal Georgia, to account for this.
Long term /Monday night through Friday/...
uncertainty higher than normal this period given the model
disagreement regarding Hurricane Matthew, so kept grids close to
NHC/wpc's coordinated guidance. The NHC/wpc forecast shows
Matthew moving from near Cuba at the start of the period north to
the Bahamas and then continuing east of the Georgia/SC coasts through
mid week. It is too soon to try and pin down specific impacts, if
any, to the region, but the latest data suggest tropical storm
conditions are possible as a reasonable worse case scenario even
through the storm could pass well offshore. This is mainly due to
a likely northward and westward expansion of Matthew's wind field
as the pressure gradient between it and high pressure to the north
Aviation /02z Saturday through Wednesday/...
VFR at both airports through 00z Sunday.
Extended aviation outlook: low clouds/showers are possible
Tuesday and Wednesday. Breezy/gusty conditions possibly Wednesday
dependent on the track of Hurricane Matthew.
tonight: quiet conditions will prevail across the local waters as
southerly winds early on turn more northwest and north with land
breeze circulations to develop overnight. Wind speeds will generally
be 10-15 knots or less through the night. Seas will range 2-3
feet. Isolated to scattered showers and thunderstorms will likely
develop across the waters overnight, mainly impacting areas 20 nm
or more offshore.
Saturday and sunday: there are no concerns as the stalled front
meanders near the local marine area. Winds 10 kt or less with seas
Monday through wednesday: solid northeast winds will prevail this
period with winds increasing quite a bit Tuesday night into
Wednesday as the pressure gradient between Hurricane Matthew and
high pressure to the north strengthens. In fact, tropical
storm/gale force winds will be possible, especially in gusts, by
Wednesday as Matthew meanders north of the Bahamas. Seas will
reach 6 ft by Tuesday evening for most waters and possibly
reaching as high as 10-15 ft by Wednesday. Small craft advisories
will likely be needed by Tuesday night.
Much will depend on the eventual timing, track and intensity of
Matthew has it moves north of the Bahamas next week. Even if the
core of the storm remains well offshore, the expanding wind field
could bring tropical storm conditions to the local marine area.
Rip currents: an enhanced risk for rip currents will exist next
week as breezy conditions and increasing swells generated by
Matthew impact the area.