Marine Weather and Tide Forecast for Moncks Corner, SC

NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/
Surface high pressure will slowly shift offshore through the remainder of the afternoon. Temperatures were able to reach into the upper 50s to low 60s, with conditions expected to cool off heading into the evening hours. Cloud cover will continue to increase ahead of an approaching upper level trough. Associated with the upper level trough a low pressure system will develop in the northern Gulf, approaching the forecast area late tonight and into the early morning hours. Just offshore a weak inverted trough is forecast to develop. Isolated showers are possible, associated with the coastal trough, however the current forecast keep shower activity offshore. As the low pressure approaches the region from the SW showers will begin to enter the southernmost portions of the forecast area right around daybreak. Overnight lows are forecast to dip into the upper 30s inland with mid to upper 40s along the coastline.

SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY NIGHT/
Wednesday: Aloft, the flow remains zonal initially until h5 vort energy begins to ripple across the local area mid-late morning. The energy will help promote a coastal low to develop along an inverted trough just off the coast, especially as a h25 jet core becomes favorably positioned across the Southeast. Light rains/showers are expected to develop by mid-late morning hours across southern areas, eventually spreading across Southeast Georgia into Southeast South Carolina by the afternoon. Moisture amounts are modest with low pressure passing south of the region across the Gulf and a northerly wind occurring along the western edge of the coastal low taking shape across the western Atlantic. Temps will remain below normal for the day, peaking in the mid 50s along the coastal corridor and only into the upper 40s inland.

There are some concerns in the forecast heading into Wednesday night with a northerly wind anticipated to hold on through much of the night and drive colder sfc temps into northern areas late evening and after midnight. The key will be how long moisture/light precip holds across the local area heading into overnight hours as latest model soundings and increasing HRRR probabilities indicate a non- zero potential for light freezing rain (trace to 0.01 inch), mainly along and north of a line drawn from Jamestown, SC to Moncks Corner, SC to Reevesville, SC where sfc temps dip to around 30 degrees for a few hours before precip shifts offshore late night. At this point, confidence is low in ice accumulations given some uncertainty in overall precip chances after midnight and especially given soil temps are generally around 50 degrees and likely to limit ice accumulation on the ground. However, there is at least some risk of light freezing rain on elevated surfaces, such as bridges and overpasses and perhaps on trees across northern Berkeley County.
Should winds become light overnight, there is also a non-zero risk of black ice developing prior to daybreak, but again warmer soil temps should limit this overall concern. Elsewhere, including the Charleston metro area, precip is expected to remain in the form of rain/showers.

Thursday and Friday: Colder air arrives late week as the region becomes positioned along the base of a mid-upper lvl trough while dry sfc high pressure is reinforced across the Southeast. Although precip-free conditions are expected, Thursday night/early Friday temps will become chilly (dipping into the low-mid 20s). The combination of these temps and a light northwesterly wind should result in wind chill values in the upper teens across many areas, and likely result in the need for a Cold Weather Advisory prior to daybreak Friday. Despite full days of sunshine, afternoon highs will struggle to reach the mid-upper 40s north to around 50 south, some 15-20 degrees below normal.

LONG TERM /SATURDAY THROUGH TUESDAY/
Saturday will see the aforementioned surface high pressure slide onto the Atlantic, with warmer southerly winds already bringing the region back up into the 50s and lower 60s. Deterministic guidance begins to diverge on the timing of the exiting surface high which propagates through the mid-levels, with ensemble clustering showing the main factor being the strength of the trough along the east coast. At this time, conditions look to remain dry this weekend with high pressure continuing across the region while weak sfc low pressure attempts to develop offshore. Otherwise, the main story is the return of warmer temps in the 60s and 70s to start off next week.

AVIATION /00Z WEDNESDAY THROUGH SUNDAY/
KCHS/KJZI: VFR conditions will prevail tonight and Wednesday morning. While there could be a few showers around in the morning, the better chance for steady rains and flight restrictions will occur thereafter, as low pressure develops off the coast of the Southeast. This far in advance we prefer to not go any lower than MVFR conditions, although IFR is likely, and will re addressed, as necessary in later forecasts.

SAV: VFR conditions will prevail tonight into Wednesday morning, before light to moderate rains develop late morning, and continue into the evening. This will take place as low pressure develops offshore, leading to at least MVFR conditions, and likely even IFR. It's too soon to show any IFR conditions, but later shifts have the option to, if trends continue to look that way.

Extended Aviation Outlook: TEMPO flight restrictions are possible at CHS/JZI/SAV terminals Wednesday night with passing rain/showers and low clouds associated with a coastal low passing just offshore. VFR conditions are then expected at the terminals through late week.

MARINE
A coastal trough will develop over the marine waters tonight. A slight enhancement of winds is expected with a pinched pressure gradient in the vicinity of the inverted trough, with NE gusts around 15 or 20 kt. Seas will average 2 to 3 ft.

Wednesday through Sunday: Latest guidance suggests a coastal low developing just off the Southeast Coast Wednesday as h5 shortwave energy passes over an inverted trough axis nearby. The pressure gradient will strengthen in response to the changing conditions, potentially leading to marginal Small Craft Advisory level conditions (~25 kt wind gusts) across northern SC waters off the Charleston County and outer Georgia waters mid-late Wednesday afternoon/evening. High pressure should then become reinforced across local waters Thursday, building seas upwards to 3-5 ft across most nearshore waters and 4-6 ft across northern SC waters off the Charleston County coast as well as across outer Georgia waters.
Additional Small Craft Advisories could be needed Thursday afternoon and night. High pressure will then prevail this weekend with winds/seas expected to remain below Small Craft Advisory levels.

CLIMATE
Record Low Maximum Temperatures:

February 21: KCHS: 47/2020

Record Low Temperatures:

February 21: KCHS: 22/1958

CHS WATCHES/WARNINGS/ADVISORIES
GA...None.
SC...None.
MARINE...None.