Scientific Forecaster Discussion
fxus62 kchs 191709
Area forecast discussion
National Weather Service Charleston SC
109 PM EDT Tue Sep 19 2017
high pressure will extend south across the region into early
next week as tropical cyclone Jose moves north toward the
southern New England coast later this week and then stalls.
Meanwhile Hurricane Maria will near the Bahamas this weekend
before likely turning north just off the southeast U.S. Coast.
Near term /until 6 PM this evening/...
the current forecast is in good shape.
Deep layered ridging remains in place this morning with
regional 19/12z raobs sampling a pronounced subsidence inversion
around 700 hpa. Even as highs warm into the upper 80s to lower
90s this afternon, it appears the inversion will hold. The h3r
and NSSL-WRF do generate a few showers in a northwest-southeast
oriented axis just north of the Savannah River later this
afternoon, but suspect these models are picking up on a band of
thick cumulus that is expected to develop in this area. For now,
this scenario has been discounted. Only made minor adjustments
were made to hourly temperatures and sky cover for the late
Short term /6 PM this evening through Friday/...
tonight: 500 mb ridging should flatten out, yielding west to east
flow during the overnight hours. Thin cirrus should push across
deep south and southeast U.S. Overnight. Given the weak SW flow
and passing high clouds, low temperatures are forecast to favor
values around 70.
Wednesday through friday: high pressure centered over the
eastern Great Lakes/New England will continue to ridge southward
into the area while tropical cyclone Jose stalls near the
southern New England coast. Mainly dry conditions are expected
through Wednesday but increased moisture and upper troughing
will bring a slightly better chance for showers and maybe a few
thunderstorms especially by Thursday and Friday afternoons.
Temperatures will stay above normal through the period.
Long term /Friday night through Monday/...
inland high pressure will persist into early next week but the main
forecast concern is what will happen to Hurricane Maria which will
be near the Bahamas this weekend. Much will likely depend on what
happens to Jose which is expected to still be lingering off the
southern New England/mid-Atlantic coast. Just too much uncertainty
at this point so everyone is encouraged to pay close attention to
the forecast later this week into early next week. Best, albeit
small, rain chances look to be near the coast Friday night into
Saturday, assuming Maria tracks well offshore. Temperatures look to
stay above normal.
Aviation /17z Tuesday through Saturday/...
Extended aviation outlook: no significant concerns through sun.
today and tonight: tc Jose will continue to track north off the mid
Atlantic coast through tonight. Swells across the SC and Georgia waters
will gradually subside, aided by sfc winds shifting from northwest this
morning to SW this afternoon-tonight. Small Craft Advisory for
amz374 is scheduled to expire at 6 PM this evening. Overnight, wave
heights are expected to range between 1-2 feet within 20nm, to 2-3
feet across the outer Georgia waters.
Wednesday through sunday: no significant concerns before swells from
Hurricane Maria nearing the southeast Bahamas later this week begin
to impact the waters Thursday night or Friday. Advisories will be
likely for the offshore waters starting Friday and the nearshore
waters starting Friday night. Seas could build to 10 feet or more
near the Gulf Stream Saturday night into Sunday but seas and winds
will be worse if Maria tracks closer to the area than currently
Rip currents: although swells from Jose are diminishing,
astronomical influences will remain today. Conditions will support a
low-end moderate risk for all beaches today.
the combination of an upcoming new moon, 9/20, and continued
swell activity from distant tropical cyclone Jose will likely
elevate water levels above projected high tide this evening
along the SC and Georgia coast. The running residual level at the
chs Harbor and fort Pulaski gauges were around 1 foot this
Much of the coast remains vulnerable in the wake of Irma with
many dune lines either completely washed away or severely
compromised. Even if the tide gages at Charleston Harbor and
fort Pulaski fall short of shallow coastal flooding criteria,
some flooding problems are still likely with many of the natural
coastal protection systems compromised. Powerful swells from
hurricanes Jose and Maria will also drive significant wave run-
up, which could cause further erosion. Thus, the potential for
shallow coastal flooding will persist into early next week
around the times of high tide, mainly the late day high tides,
and particularly along the SC coast.
Marine...Small Craft Advisory for hazardous seas until 6 PM EDT this
evening for amz374.