-- Discussion containing changed information from previous version are highlighted. --
848
FXUS62 KCHS 271018
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
618 AM EDT Fri Sep 27 2024

.SYNOPSIS...
-- Changed Discussion --
Helene will pass to our west and then northwest today into
tonight. Multiple impacts are expected across our area this
morning. Drier weather then arrives later this afternoon and
should persist into next week.
-- End Changed Discussion --

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
This Morning: The upper air pattern features a large cutoff low in
the vicinity of the Middle Mississippi Valley area, while a strong
anticyclone is across the western Atlantic, centered west of
Bermuda. The southerly flow between these two features will steer
Helene north over Georgia.

Given the speed of Helene, strong winds are expected further inland
than typical. Wind fields have remained large, producing impacts
well east of its center. For this reason, a Tropical Storm Warning
remains in effect for the entire forecast area, including nearby
waters. The latest forecast will keep Southeast Georgia and
Southeast South Carolina along Helene`s eastern side during the
morning with multiple hazards to the immediate area. For full
details, please refer to weather.gov/chs and the Hurricane Local
Statement (HLS).

Tornadoes: A Tornado Watch remains in effect until 8 AM for portions
of Southeast Georgia and all of Southeast South Carolina counties,
and includes all coastal waters. Long, looping hodographs continue
across areas northeast and east of Helene`s center. 0-1 km SRH as
much as 250-400 m2/s2 and impressive STP/SCP values persist this
morning. There is all dry air wrapping around the southern side of
Helene, which could enhance the tornadic risk. Additionally, the
HREF indicates updraft helicity tracks supportive of tornadic
waterspouts that shift onshore, coinciding with rainbands associated
with Helene that slowly progress across into Southeast South
Carolina. Have a tornado plan in place in case a warning is issued.
Keep in mind that tropical tornadoes can form with little advance
warning, move very quickly (potentially in excess of 35 to 45 mph),
and will be hard to see due to the potential that they will be rain-
wrapped.

Winds: A Tropical Storm Warning is in effect for the entire forecast
area. Tropical storm force winds are expected to occur across
Southeast Georgia and expand into Southeast South Carolina and
adjacent coastal waters tonight. Wind speeds should peak late
tonight as the center of Helene moves across central Georgia. Gusty
winds as high as 45 to 65 mph could produce downed and/or uprooted
trees, isolated to scattered power outages locally, with greatest
impacts anticipated during the night.

Flooding Rainfall: Multiple rounds of showers/rainbands and a few t-
storms in association with Helene will impact the area early
morning, before considerably drier air wraps around the southern
edge of departing Helene and overtakes the entire forecast area by
late morning. Additional rainfall amounts of 1 to 2 inches are
possible, mainly across the Charleston Tri-County Area, with locally
higher amounts possible in heavy rainbands. Minor flooding of low-
lying and poor drainage areas is likely in some locations with
isolated flash flooding possible. Urban flooding is also a
possibility. Area rivers and creeks will rise in response to the
rainfall, with some flooding possible, even after the rains come to
an end.

Storm Surge: The latest forecast maintains storm surge values in the
1 to 3 foot range. Additional information can be found in the
Tides/Coastal Flooding section below.

This Afternoon through Tonight: A broad cutoff low will be centered
across Tennessee, with the circulation of Helene migrating north
through northwestern Georgia and becoming absorbed by the cutoff
low. Strong subsidence and dry air wrapping along the south and
southeast side of Helene will likely lead to dry weather conditions
across all local areas by the afternoon. However, tropical storm
force wind gusts could linger into early afternoon hours, before
diminishing to 20-30 mph through the remainder of the day. Breaks in
clouds are expected and skies should become mostly sunny by mid-late
afternoon allowing for ample sfc heating. In general, sfc temps
should peak in the mid-upper 80s. Overnight, conditions improve
considerably with light southwesterly winds expected and lows
ranging in the mid-upper 60s inland to low-mid 70s closer to the
coast.
-- End Changed Discussion --

&&

.SHORT TERM /SATURDAY THROUGH MONDAY/...
-- Changed Discussion --
The mid-levels will consist of a rex block over much of the U.S.
A ~565 dam cut-off Low will be over western TN Saturday morning
while a ~594 High will be located off the Southeast U.S. The Low
will gradually weaken, becoming ~575 dam by late Monday, while the
~592 dam High will shift closer to the northern Bahamas. At the
surface, the remnants of Helene will be located to our northwest,
roughly over western TN Saturday morning. A stationary front will be
located just off our coast at the same time. The remnants of Helene
will weaken as time progresses, becoming a broad disturbance located
well to our north by late Monday. Meanwhile, the stationary front
will remain just off our coast. There will be a pocket of drier air
between these two synoptic features. However, it doesn`t mean our
forecast will be completely dry. Saturday, the synoptic models and
long-range CAMs have light showers over the coastal waters moving
onshore during the afternoon. Therefore, we have slight chance POPs
mainly over our coastal counties. These should persist into the
evening, then shift offshore overnight. Sunday, the models keep most
of our area dry, except for maybe a few showers moving onshore along
the GA coast in the afternoon. Additionally, showers could move
onshore along the entire coast late at night. Monday, most of our
area is dry, except for maybe a few showers moving onshore along the
far southern GA coast in the afternoon. High temperatures will be in
the mid to upper 80s each day. Low temperatures will range from the
mid 60s far inland to the lower 70s along the immediate coast.
-- End Changed Discussion --

&&

.LONG TERM /MONDAY NIGHT THROUGH THURSDAY/...
-- Changed Discussion --
A stationary front will be located just off our coast Monday night.
It`ll shift away late Tuesday as a dry cold front approaches from
our northwest. The dry cold front should move through our area
Wednesday night. Following that, High pressure will build in from
the northwest and north on Thursday. Conditions should remain dry.
High temperatures will be a few degrees above normal Tuesday and
Wednesday, dropping to near normal on Thursday.
-- End Changed Discussion --

&&

.AVIATION /10Z FRIDAY THROUGH TUESDAY/...
-- Changed Discussion --
KCHS/KJZI/KSAV: Numerous to widespread showers and a few TSRA
associated with Helene will impact all terminals tonight,
before rapid drying takes place on Friday. Flight restrictions
will occur through the tonight timeframe as rounds of showers
and some thunderstorms move through, generally down in the MVFR
range for both cigs and vsbys. IFR conditions remain possible
at times, especially during heavier rains.

SE winds will steadily as we go through tonight, peaking as
high as 35 or 40 kt sustained with gusts of at least 50 to 55 kt,
with the peak winds occurring largely between 06Z and 14Z Friday.
Higher wind gusts are possible. Winds will veer around to the S
or SSW during the day on Friday, with winds still as high as
20-30 kt through the day. During the night, S or SSW winds
should gradually decreasing to the 10-20 kt range.

Finally, LLWS remains at all three terminal sites, although
given the strong gusty surface winds, LLWS may not truly come to
fruition.

One side note is that conditions remain favorable for isolated
tornadoes across southern South Carolina and southeast Georgia
through tonight.

Extended Aviation Outlook: Mainly VFR. Though, radiational fog
could bring brief flight restrictions late each night and early
each morning.
-- End Changed Discussion --

&&

.MARINE...
-- Changed Discussion --
This Morning: Dangerous conditions continue to impact the Atlantic
waters and Charleston Harbor as Helene continues to track north
across Georgia. Wind fields remain large surrounding Helene, with
gusts up to 45-50 kt across local waters. Tropical Storm Warnings
remain in effect for all local waters as a result. These winds will
allow for seas to build as high as 10-15 feet on the waters out 20
nm, and up to 17 feet on the Georgia waters beyond 20 nm from shore.

Mariners are also alerted to the risk for waterspouts through much
of the night, as convective bands move through the area in
association with helene. Some of these will be tornadic waterspouts,
moving much quicker and producing much stronger winds than most
waterspouts in our area.

This Afternoon and Tonight: Conditions will improve as Helene shifts
further away from the area. Gusts up to Tropical Storm strength are
possible into early afternoon, but conditions should remain below 25-
30 heading into the night. Thereafter, wind speeds will slowly
diminish to about 15-20 kt after midnight. Seas will also be
subsiding through the day and night, lowering to 5-7 ft across local
waters during the overnight period.

Extended Marine: A stationary front will persist off our coast.
This will yield winds mainly from the SW through early next week.
Seas will start out in the 2-4 ft range on Saturday, subsiding to 2-
3 ft on Sunday, then 1-2 ft on Monday.

Rip Currents and High Surf: Conditions at the beach will be
dangerous through today, as winds and seas remain high/large while
Helene tracks across the interior Southeast. A High Risk of Rip
Currents will be in effect for all beaches today, and breakers of at
least 5 feet in height will persist in the afternoon and/or
evening. Areas of significant beach erosion are also likely
during this time. For Saturday, remnant swell and changes in the
beach bathymetry from Helene will yield a Moderate Risk at all
of our beaches.
-- End Changed Discussion --

&&

.TIDES/COASTAL FLOODING...
-- Changed Discussion --
Latest trends indicate approximately 2.5-3.0 ft departures in
the Charleston Harbor and at Ft Pulaski. These departures along
with the continuation of strong onshore winds favor minor to
moderate coastal flooding during the current high tide this
morning. As a result, a Coastal Flood Advisory has been issued
for the entire coast through 7 AM this morning.
-- End Changed Discussion --

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
GA...Tropical Storm Warning for GAZ087-088-099>101-114>119-137>141.
     Coastal Flood Advisory until 7 AM EDT this morning for GAZ117-
     119-139-141.
     High Risk for Rip Currents through this evening for GAZ117-119-139-
     141.
     High Surf Advisory until 8 PM EDT this evening for GAZ117-119-
     139-141.
SC...Tropical Storm Warning for SCZ040-042>045-047>052.
     Coastal Flood Advisory until 7 AM EDT this morning for
     SCZ048>051.
     High Risk for Rip Currents through this evening for SCZ048>051.
     High Surf Advisory until 8 PM EDT this evening for SCZ048>051.
MARINE...Tropical Storm Warning for AMZ330-350-352-354-374.
-- End Changed Discussion --
&&

$$

NEAR TERM...
SHORT TERM...
LONG TERM...
AVIATION...
MARINE...