Charleston Harbor Marine Forecast
|Tonight...Sw Winds 10 To 15 Kt.|
|Mon...Sw Winds 5 To 10 Kt.|
|Mon Night...Sw Winds 5 To 10 Kt, Becoming Nw After Midnight.|
|Tue...N Winds 5 To 10 Kt.|
|Tue Night...Ne Winds 5 To 10 Kt, Increasing To 10 To 15 Kt With Gusts To 20 Kt After Midnight.|
|Wed...Ne Winds 15 To 20 Kt. Waves 1 To 2 Ft. A Slight Chance Of Showers.|
|Wed Night...Ne Winds 15 To 20 Kt With Gusts To 25 Kt. Waves 1 To 2 Ft. A Chance Of Showers.|
|Thu...Ne Winds 15 To 20 Kt, Increasing To 20 To 25 Kt In The Afternoon. Waves 2 To 3 Ft. A Chance Of Showers In The Morning, Then Showers Likely With A Slight Chance Of Tstms In The Afternoon.|
|Thu Night...Tropical Storm Conditions Possible.|
|Fri...E Winds 15 To 20 Kt With Gusts To 25 Kt. Waves 1 To 2 Ft. Showers With A Chance Of Tstms.|
|Fri Night...Se Winds 10 To 15 Kt. Showers With A Chance Of Tstms Early In The Evening, Then Showers Likely With A Slight Chance Of Tstms In The Late Evening And Overnight. Winds And Waves Higher In And Near Tstms. Unless Otherwise Noted, Waves 1 Foot Or Less. Charleston Harbor Water Temperature 80 Degrees.|
| Area Forecast Discussion|
National Weather Service Charleston SC
430pm EDT Sunday September 25 2022
High pressure will persist tonight. A cold front will push across the region Monday before high pressure returns Monday night into Tuesday. Tropical low pressure could impact the region mid to late week.
Near Term - Until 6am Monday Morning
A mid level trough will encompass the eastern half of the country tonight. At the surface, high pressure over the western Atlantic will give way to a weak cold front approaching from the west. The front should be somewhere near our inland counties around daybreak Monday. There will be a narrow band of higher moisture that moves across the area, so a stray shower can't be ruled out, but probabilities remain too low to include explicit mention in the forecast. Low temperatures will be more mild than previous nights, generally ranging from the mid 60s across the interior to upper 60s closer to the coast. Beach locations and downtown Charleston will likely stay around 70/low 70s.
Short Term - 6am Monday Morning Through Wednesday
Monday: A cold front associated with low pressure centered in New England will sweep across the forecast area during the daylight hours. 12Z GFS (Global Forecast System) indicates that H85 Cold Air Advection and veering winds will not arrive over the forecast area until Monday evening. Using a blend of MOS, high temperatures are forecast to range from the low 90s across SE GA to the upper 80s across the SC Lowcountry. Conditions are expected to remain dry during the day, with a shower or two possible over the nearshore waters Monday night.
Tuesday: The cold front will slowly push east across the western Atlantic through the day. In the wake of the front, dry high pressure will build over the region from the west. Temperatures are expected to range close to normals, generally in the low to mid 80s.
Wednesday: Canadian high pressure will push from the Northern Plains to the Great Lakes Region, ridging south along the east facing slopes of the Appalachians. TC Ian is forecast to track north off the Gulf coast of the FL Peninsula. The pressure gradient across the forecast areas will steepen through the day, resulting in strengthening NE winds. The NE flow will keep the forecast area under dry air during the morning. However, moisture will build in from the east from the top-down. GFS indicates that a warm front will sharpen over the Gulf Stream, drifting towards the GA/SC coast. Isolated to scattered showers may reach the coast, especially the GA coast, Wednesday PM. High temperatures will be noticeably cooler from Tuesday, generally in the mid 70s.
Long Term - Wednesday Night Through Sunday
Thursday through Friday will be the primary period for any TC Ian impacts. On Thursday, the pressure gradient across the nearshore waters will tighten, GFS indicates nearly a 7mb gradient Thursday afternoon. Based on forecast soundings and blended models, tropical storm force winds and gusts are expected across the marine zones, possibly on the beaches. The warm front will near the coast Thursday night, likely leading to winds to gradually weaken. A thick band of moderate to heavy showers and thunderstorms are expected to develop over the Gulf Stream as the warm front pushes over the nearshore waters. The warm front is timed to reach the coast Thursday night, pushing inland during the day on Friday. The air mass east of the warm front will feature PWs in excess of 2.1 inches and deep surface based instability. The combination of deep frontogenesis, tropical moisture, and instability should yield periods of moderate to heavy rainfall rates Thursday night into Friday. Although this event well into the extended and hard to determine rainfall amounts, it would not be unexpected to see rainfall totals in the 5-7 inch range. The rainfall may overlap with periods of coastal flooding, exacerbating any fresh or salt water flooding. In addition, hodographs in the wake of the warm front are interesting, possibly resulting in a time window for tornadoes/waterspouts late Thursday night into Friday morning.
Refer to the National Hurricane Center for the latest Ian advisories.
Tonight: South to southwest winds will prevail tonight ahead of a cold front. Winds will increase a bit, but should top out in the 10-15 kt range. Seas will average 2-3 feet.
Monday through Friday: A cold front will sweep across the area on Monday, with high pressure building in from the west through Tuesday. Conditions should remain below Small Craft Advisory criteria through Tuesday. The marine zones will remain between high pressure ridging in from the north and Tropical Cyclone Ian Wednesday into Thursday. Conditions will deteriorate through the mid and late week. In fact, it is possible Ian may bring Tropical Storm conditions to the marine zones later next week. The current thinking is that seas will increase to around 5-9 feet across the nearshore waters out to 20 nm and 10-12 ft across the outer Georgia waters from 20-60 nm. Conditions will gradually improve on Friday.
Marine interests should stay informed of the latest official forecasts for Tropical Cyclone Ian through the upcoming.
Marine Impacts: Conditions mid to late week along all beaches may lead to High Surf, Beach Erosion, and an elevated risk for rip currents. The worst conditions are expect from late Wednesday night through Friday evening.
Tides / Coastal Flooding
The combination of astronomical forcing and gusty winds will likely lead to minor coastal flooding during both high tides on Wednesday. Winds may strengthen to near tropical storm force along the coast Wednesday night through Thursday. The gusty winds would likely increase tidal departures Wednesday into Thursday, possibly leading to moderate coastal flooding along the coast, especially for Charleston and Colleton Counties. In fact, surging winds ahead of arriving convection could lead to major coastal flooding, primarily mid-day Thursday.
NOAA Charleston SC Office: Watches - Warnings - Advisories