Scientific Forecaster Discussion
fxus62 kchs 220826
Area forecast discussion
National Weather Service Charleston SC
426 am EDT Fri Sep 22 2017
high pressure will prevail through this weekend. The high will
weaken and shift inland as Hurricane Maria tracks northward off
the southeast U.S. Coast through the first half of next week. A
cold front could approach the forecast area late next week.
Near term /through tonight/...
pre-dawn: conditions tranquil this morning with calm winds and
generally clear skies. Patchy mainly shallow fog was developing
across the forecast area, especially across inland Georgia this
morning. No significant vsby restrictions are anticipated most
areas but stratus and fog to the south of I-16 was forming with
lower vsbys recently at Hinesville Georgia.
Today: surface high pressure will remain to the north while weak
synoptic flow remains onshore. In the mid levels, weak troughing
exists in a positively tilted fashion with a stagnant lobe of
vorticity at 500 mb extending across the forecast area. There
is a little pocket of -10c at 500 mb noted across the forecast
region this afternoon. Morning sunshine will give way to
cumulus/stratocu this afternoon with some high clouds mixed in
as well. In terms of convection, instability progs look just a
bit weaker than Thursday. Isolated showers and thunderstorms are
expected this afternoon. Some drier air aloft seen on soundings
however dcape values appear lower than yesterday and risk of
isolated strong storms appears really low-end. Highs will not
be as warm today many areas with upper 80s most common.
Tonight: isolated early evening convection is possible well
inland but mainly prior to sunset. Skies will be clear to
partly cloudy with lows in the mid to upper 60s. Patchy fog is
possible once again, especially inland from the U.S. 17
Short term /Saturday through Monday/...
dry high pressure will settle over the forecast area. On Saturday,
relatively higher ambient moisture will support a slight chance for
shower/thunderstorm activity mainly across Georgia zones, with South
Carolina zones appearing mostly dry based on the latest guidance.
Sunday and Monday appear too dry to support mentionable precipitation
over land zones in the forecast. Above normal temperatures are
expected, with highs in the mid to upper 80s and lows in the mid
to upper 60s, around 70 at the beaches.
Long term /Monday night through Thursday/...
inland high pressure will persist through early next week while
Hurricane Maria is forecast to remain offshore of the southeast U.S.
Coast as it tracks north through the middle of next week. While some
showers could skirt coastal areas early next week as Maria passes
by, persistent, weak negative vorticity advection under high pressure should help
mitigate precipitation chances. For much of the week, mainly dry
conditions are anticipated with temperatures likely remaining
Aviation /08z Friday through Tuesday/...
shallow ground fog likely nearing sunrise. We maintained mifg
at both sites roughly 08-09z through daybreak, but kept
conditions above MVFR thresholds for now but MVFR conditions
are certainly possible at either terminal.
Extended aviation outlook: mainly VFR conditions expected. Low
probability for brief flight restrictions in early morning fog
and/or low clouds Saturday morning at either terminal. Low
probability for brief restrictions due to isolated shower and
thunderstorm Saturday afternoon/evening, primarily affecting
high pressure from the Ohio Valley to the mid Atlantic region
will be our dominate synoptic feature through tonight. Gradients
will not be tight and wind speeds will continue to be less than
15 knots. We will begin to see building swells from Hurricane
Maria but suspect the initial wave guidance may be a bit too quick
given recent episodes of arriving swells with prior tropical
cyclones this year. Overall, we made just small timing adjustments
based on recent trends and maintained the Small Craft Advisory timing for hazardous
seas over our 20-60 nm Georgia waters that initiates at mid afternoon
today. Seas should build to 4-5 feet across near shore waters
by late tonight.
Saturday through tuesday: seas 6 ft and building are expected to
push into nearshore waters by early Saturday morning due to swell
from offshore Hurricane Maria. A prolonged period of small craft
advisories is expected. Generally NE winds 10-15 knots with some
gusts to 20 knots are anticipated through early next week.
Rip currents: swell from offshore Hurricane Maria will slowly build
at the beaches. This results in a moderate risk of rip currents
today and will we likely maintain moderate to high risks through
early to mid next week.
powerful surf created by offshore Hurricane Maria will drive
significant wave run-up, which could cause further beach erosion
this weekend into early next week. High surf advisories may be
required. Also, the potential for shallow salt water flooding
will persist through early next week around the times of high
tide, particularly along the South Carolina coast.
Marine...Small Craft Advisory for hazardous seas from 2 PM this
afternoon to 6 am EDT Wednesday for amz374.