Damaging Winds in South Carolina, July 6, 2016

Area Forecast Discussion
National Weather Service Wilmington NC
329 PM EDT WED JUL 6 2016

.SYNOPSIS...
Oppressive heat and humidity will build through Saturday with heat
advisories likely each day. Thunderstorm chances will be greatest
on Thursday beneath an upper disturbance, before falling into the
weekend. Temperatures will slowly drop back to more seasonable
levels by early next week, accompanied by increasing shower and
thunderstorm chances as a trough stalls near the area.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
As of 300 PM Wednesday...A slightly less hot and humid day
continues, but widespread 100-105 degree heat indices are still
making it quite uncomfortable this aftn. Heat will slowly abate this
evening, but the slow fall will lead to a very humid night once
again.

Severe thunderstorms have developed to our west across the Peachtree
City, GA CWA, and are racing eastward through Columbia and will
approach the western portions of our CWA this eve beneath a sharp
mid-level impulse. The Storm Prediction Center has raised a SLIGHT
RISK for extreme western portions of our area, and it is likely
these storms will impact our CWA in a few hours. Local tools suggest
convection first reaching Darlington/Florence counties around 5pm,
and then moving offshore the Myrtles by 9pm.

These storms are congealing into an MCS, which is likely to become
cold-pool driven as individual cells weaken and new ones develop in
a still very unstable environment ahead of the ongoing convection.
Latest SPC Mesoanalysis shows 2000 J/kg of SBCAPE, and most recent
CAE VWP has unidirectional wind with marginal shear through the
lowest 6 km. This points towards a rapidly moving complex of storms
(limited in speed by relatively weak forward propagating corfidi
vectors) but still strong enough to produce isolated damaging wind
gusts, primarily west of i-95 this evening. Although convection will
wane with loss of heating, do expect storms to reach the coast and
move offshore in a weakened state.

Min temps will be very tricky, and where rain cooled air occurs
tonight mins will likely fall below guidance as occurred last night,
while staying at or above elsewhere. Very tough to pinpoint this
even in the near term, but have shown the lowest mins, 73-74, across
the Pee Dee, warming to the upper 70s along the Cape Fear Coast.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY NIGHT/...
As of 300 PM Wednesday...If the 3 most important words in real
estate are "location, location, location," then the 3 words most
important for this forecast are "hot, hot, hot." Temperatures are
expected to approach record values on Friday, and heat advisories
are a near certainty both days.

Starting on Thursday, Bermuda high will begin to gradually intensify
and expand across the Southeast. The true potential of the heat will
be moderated Thursday by shortwave energy moving overhead and
dampening the ridge amplitude. Still, with W/SW winds and 850mb
temps climbing to 20-21C, highs will soar well into the 90s, which
will combine with dewpoints in the low-to-mid 70s to produce heat
index values of 100-105 across the area. A heat advisory will
likely be needed for eastern portions of the CWA once again, but will
hold off on the NPW until the current HT.Y expires. This heat will
drive a very unstable environment, and the aforementioned shortwave
progged to move overhead in the evening and into Thursday night will
likely help drive convection. Currently SPC has just a general risk
for tstms Thursday, but with such an unstable environment and the
shortwave creating PVA and increased instability aloft, a strong
wind gust /downburst/ will not be out of the question. Convection
will likely persist, at least in weakened form, after dark as the
shortwave energy persists overhead, but will wane by Friday morning.
Mins Thursday night will hover around 80 degrees as the extreme heat
continues.

Friday is then set to, almost literally, roast. The ridge across the
southeast amplifies further with 591-594 heights moving overhead the
eastern Carolinas. This occurs in the wake of Thursday's shortwave,
which creates subsidence and dries out the column such that
convection is unlikely, and may just occur in a very isolated
fashion despite extreme heat. As the ridge axis builds west of the
area, downsloping will maximize with NW flow enveloping the lower
half of the column, and this is the type of flow that usually causes
our hottest temperatures, especially near the coast. 850mb temps
climbing to 22-23C would be a record for the date compared to both
CHS and MHX sounding climatology, and highs will likely reach triple
digits in many locations. Record highs will be approached Friday,
they are:

Wilmington, NC: 100, Forecast: 99
Florence, SC: 105, Forecast: 100
North Myrtle Beach, SC: 97: Forecast 96

These temperatures combined again with high dewpoints (although
fortunately some mixing out will occur during the aftn) will again
allow heat index values to rise above 105 and a heat advisory will
again be needed, this time for the entire CWA. Mins Friday night
will show little cooling, falling again only to around 80 degrees.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
As of 230 PM Wednesday...Hot temperatures will continue into the
extended period, with the hottest readings expected during
Saturday. Max temps Saturday could push 100F at many locations
across the forecast area and in the least a Heat Advisory will
likely be required. Other than the heat concerns could see
convection each day, but think coverage would be isolated to
widely scattered during Saturday, with increasing coverage as
we head into next week.

&&

.AVIATION /20Z WEDNESDAY THROUGH MONDAY/...
As of 18Z...Basically looking at high pressure across the
Southeast States ridging across the region. At the same time, the
NE to SW oriented Piedmont trof will exist across the central
Carolinas. Another mesoscale sfc feature will affect the area is
the diurnally driven coastal seabreeze. With wind speeds in the
lower levels, up to 700mb, from the west in the 20 to 30 kt
range, the sea breeze will be somewhat pinned closer to the coast.
The seabreeze may not even reach the ILM terminal or if it does it
will be late in the day. The same goes with MYR, as was the case
yesterday when the sea breeze took until 2100Z to push thru MYR.

The seabreeze, Piedmont trof and an upper level disturbance,
across Ga at the moment and tracking to the east, will all aid
tstorm initiation. Area of convection with the upper level
disturbance is already ongoing and will approach the fa from the
west during this evening. The mentioned sfc boundaries will also
have active thunderstorm development, more-so with the Piedmont
trof then the sea breeze. Will include VCTS for the coastal terms,
and the inland terminals will include tempo groupings.

For winds, the sfc pressure pattern will provide wsw to w wind
directions. In the wake of the pinned sea breeze, expect a sw
wind direction. The sfc pg will remain tightened this aftn and
evening with speeds of 10 to 15 kt with g20+ kt. Winds will
diminish to less than 10 kt by 01z, and 5 kt or less by 04z. If
winds are able to drop to less than 3 kt, then mvfr fog will be
possible especially terminals that receive rainfall. By Thu mid-
morning winds will only ramp up to around 10 kt from the west.

EXTENDED OUTLOOK...Mainly VFR. Possible brief MVFR/IFR from
scattered convection each day. Possible brief MVFR from fog each
morning.

&&

.MARINE...
NEAR TERM /THROUGH TONIGHT/...
As of 300 PM Wednesday...SW winds around a ridge axis extending from
a Bermuda high across Florida will persist overnight. Speeds have
been around 15 kts, and even the locally backed near-shore sea
breeze has struggled to rise much above those speeds. Winds will
become SWly throughout again this evening with loss of diurnal
heating, with speeds of 15 kts expected into Thursday morning. Seas
will be most heavily influenced by a 5-6 sec SW 4-5 ft wave,
producing seas of 3-4 ft.

A cluster of thunderstorms moving east through SC will likely enter
the waters this evening after 8pm. The SC waters are forecast to be
most heavily impacted by these weakening storms, but all the waters
may see tstms this evening into early tonight, which would produce
locally higher seas and winds, along with lightning and
briefly torrential rainfall.

SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
As of 300 PM Wednesday...More of the same through the end of the
week as Bermuda high pressure extends back across Florida and
strengthens, maintaining W/SW winds across the local waters. Of
course, this will be modified in the near shore waters by the
backing sea breeze each aftn. W/SW winds will be 10-15 kts during
the day, slightly higher in the sea breeze, and then increase to
around 15 kts each night beneath a LLJ and better mixing over the
warm waters. No hazards or cautionary statements are expected, as
seas will be 2-4 ft much of the period, with a few 5 fters possible
on Friday.

LONG TERM /SATURDAY THROUGH MONDAY/...
As of 230 PM Wednesday...Offshore flow at the onset will back to
a southwesterly direction by Saturday afternoon as an inland trof
develops. The pressure gradient will increase during the day and
evening, prior to the trof shifting off the coast. The offshore
flow in the wake of the trof will be short-lived as another
inland trof takes shape re-establishing the southwest flow across
the waters by Sunday night. Seas will average 4 ft away from the
coast Saturday afternoon-evening, then 3 ft during Sunday into
Monday.

&&

.ILM WATCHES/WARNINGS/ADVISORIES...
SC...Heat Advisory until 7 PM EDT this evening for SCZ032-033-039-
     053>056.
NC...Heat Advisory until 7 PM EDT this evening for NCZ096-099-
     105>110.
MARINE...None.

&&

SYNOPSIS...JDW
NEAR TERM...JDW
SHORT TERM...JDW
LONG TERM...SRP
AVIATION...DCH
MARINE...JDW/SRP

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