South Santee River to Edisto Beach, SC Marine Forecast
|Today...E Winds 5 To 10 Kt, Becoming Se 10 To 15 Kt This Afternoon. Seas 2 Ft.|
|Tonight...S Winds 10 To 15 Kt, Increasing To 15 To 20 Kt Late. Seas 2 To 3 Ft, Building To 3 To 4 Ft After Midnight.|
|Thu...S Winds 20 To 25 Kt With Gusts To 30 Kt. Seas 4 To 6 Ft, Building To 5 To 7 Ft In The Afternoon. A Slight Chance Of Showers In The Morning, Then A Chance Of Showers With A Slight Chance Of Tstms In The Afternoon.|
|Thu Night...Sw Winds 25 To 30 Kt. Seas 6 To 7 Ft, Building To 6 To 8 Ft After Midnight. A Slight Chance Of Tstms. Showers Likely, Mainly In The Evening.|
|Fri...W Winds 20 To 25 Kt With Gusts To 30 Kt, Becoming Nw 15 Kt With Gusts To 20 Kt In The Afternoon. Seas 5 To 7 Ft, Subsiding To 4 To 5 Ft In The Afternoon. A Slight Chance Of Showers In The Morning.|
|Fri Night...Ne Winds 15 To 20 Kt With Gusts To 25 Kt. Seas 4 To 5 Ft, Building To 4 To 6 Ft After Midnight.|
|Sat...Ne Winds 20 Kt. Seas 4 To 6 Ft. A Slight Chance Of Showers.|
|Sat Night...Ne Winds 15 To 20 Kt. Seas 4 To 6 Ft. A Chance Of Showers.|
|Sun...Ne Winds 5 To 10 Kt. Seas 3 To 4 Ft. A Chance Of Showers.|
|Sun Night...Nw Winds 20 To 25 Kt. Seas 4 To 5 Ft. A Slight Chance Of Showers. Mariners Are Reminded That Winds And Seas Higher In And Near Tstms.|
| Area Forecast Discussion|
National Weather Service Charleston SC
428am EDT Wednesday Oct 28 2020
High pressure will linger through tonight. A large storm system will bring impacts to the region Thursday, followed by a cold front Thursday night. High pressure returns for the weekend. A dry cold front is expected early next week, followed by more high pressure.
Near Term - Through Tonight
Today: Aloft, the upper ridge and anticyclone will be gradually nudged to the east as the reflection of Zeta lifts northward toward the Louisiana coast. This will place the forecast area solidly within southwesterly flow between these features. At the surface, a subtle warm front will lift northward across the area this morning as high pressure slips off the North Carolina coast. East and even northeast low level flow this morning will become solidly southeast by the afternoon as the region starts to fall within the broader scale flow around Zeta over the Gulf of Mexico. Overall, we expect little to no shower activity through the day. The best chance for isolated showers will be across interior southeast Georgia which will be closer to the better moisture and forcing for ascent. Instead, it should be a rather pleasant day with highs topping out in the low to mid 80s across the forecast area. Such values would be on the order of 7-8 degrees above normal for late October.
Tonight: Zeta is forecast to have made landfall along the Louisiana coast and will be pushing inland across Mississippi and Alabama in the evening hours. Regardless, being displaced so far to the east of the system the overnight forecast looks pretty quiet. The precipitation shield should be closely associated with the center, and the forecast features essentially a dry forecast through sunrise Thursday. The main change overnight will be the increasing wind field around the periphery of Zeta, especially late. This will help keep lows very mild, with temperatures likely staying at or above 70 for much of the forecast area. Such temperatures would be around 15 degrees or more above normal for late October.
Short Term - Thursday Through Saturday
Thursday: A complex weather forecast is expected with the concern for multiple hazards. The mid-levels will consist of an strong trough and embedded low over the Southern Plains in the morning. These features will move eastward with time, passing over our region late at night. At the surface, the remnants of TC Zeta will have combined with a separate storm system in the morning, resulting in a large storm system that will bring impacts to the eastern third of the country. Models remain in good agreement keeping the bulk of energy with this system passing to our north during the afternoon and into the night. However, a cold front associated with this system will approach our area from the west during the day, then cross through our region during the evening, moving offshore after midnight. Lots of moisture originating from the Gulf of Mexico will be just ahead of the front. All of the models show a band of 2.25" PWATs (Precipitable Waters) crossing through our area in the afternoon and evening, with some hints of values reaching 2.5". These values are well above normal and are more typical of summer than late October. But despite all of this moisture, the strongest lift will be to our north. Also, the front may be entering a slight weakening phase as it moves through. Though, the models trended wetter. We use this term loosely because total rainfall may only reach 0.25", mainly fair inland, which is much less than what PWATs (Precipitable Waters) would support. Though, we did increase POPs across the region into the afternoon and evening.
One notable change is the tornado threat. Models now have stronger shear occurring earlier in the day. 0-6 km bulk shear approaches 50 kt in the afternoon. This shear appears to be associated more with the front than the remnants of TC Zeta, but it's still very strong. However, the limiting factor is the instability. MLCAPEs struggle to reach 500 J/kg, especially in what's expected to be a mostly cloudy regime. Showalter values are barely negative as well. But the concern remains, so Storm Prediction Center now has most of our area in a Marginal Risk. The greatest threat of a short-lived weak tornado appears to be late in the afternoon and early evening, mainly west of I-95.
Additionally, strong low-level winds are expected to partially mix down to the surface ahead of the front. This will lead gusty winds. A Lake Wind Advisory may be needed for Moultrie. But wind gusts don't appear high enough to warrant advisories elsewhere.
After the front, drier air and clearing conditions are expected to move in from west after midnight. Finally, this will be the last day of 80 degree temperatures for our area this week, which could put some record high temperatures at risk of being broken.
Friday And Saturday
A mid-level trough over the East Coast Friday morning will shift offshore into Friday afternoon. Zonal flow is expected to develop over our region Friday night and persist into Saturday. At the surface, the cold front will be offshore Friday morning and quickly moving away. Meanwhile, strong high pressure will become centered to our north. Drier air and subsidence associated with the periphery of this high will drive our weather. The result will be mostly dry conditions and mostly sunny skies both days. Though, some showers could develop over the coastal waters on Saturday and try to make a run for our coastal GA counties that afternoon. The most notable change will be the temperatures. Cold air advection within northwest veering to northeast surface winds will lead to much colder temperatures. Temperatures are forecasted to be near normal on Friday, then a few degrees below normal Friday night into Saturday.
Long Term - Saturday Through Tuesday
A long-wave trough is expected to move over the East Coast Sunday into Monday, then move offshore on Tuesday. At the surface, a dry cold front is expected to move through Sunday night, followed by continental high pressure. Expect temperatures well below normal Monday and Tuesday.
Today through tonight: Winds will gradually veer around to become southeasterly 10-15 knots this afternoon with seas 2 to 3 feet. Overnight, winds will steadily increase and become more southerly with time. By sunrise Thursday winds should be a solid 15-20 knots with seas 3-5 feet.
Thursday: The remnants of TC Zeta will have combined with a separate storm system in the morning to create one large storm system along the eastern third of the country. As a bulk of the energy passes to our north during the day, the surface pressure gradient will steepen. The result will be rapidly increasing winds and building seas Thursday. Small Craft Advisories will be needed for all of the waters, including the Charleston Harbor. The front is expected to cross through the region Thursday evening. The worst conditions are expected for a few hours around frontal passage. Gusts could exceed Gale force, especially across the Charleston waters and the GA waters beyond 20 nm. Gale headlines may be needed for these locations Thursday night. Additionally, expect steep wind-driven seas during this time period.
Friday through Monday: The front will be offshore Friday morning and quickly moving away. Meanwhile, high pressure will build in from the north and west, which will lead to a brief window of lower winds and seas Friday afternoon. However, conditions will deteriorate again Friday night as cold air advection increases and the pressure gradient steepens. These near gale conditions should persist through Saturday night. By Sunday the cold air advection slackens and the pressure gradient levels off, leading to lower winds and seas. A dry cold front is expected to move through the region Sunday night into Monday.
Record warmth possible Thursday, October 29:
KCHS: 85/1946 and 72/1984
KCXM: 82/1984 and 72/1984
KSAV: 87/1996 and 71/2019
NOAA Charleston SC Office: Watches - Warnings - Advisories
GA...None. SC...None. MARINE...None.