Edisto Beach, SC to Savannah, GA Marine Forecast
|Today...Ne Winds 10 To 15 Kt With Gusts To 20 Kt, Becoming E. Seas 2 To 3 Ft, Building To 3 To 4 Ft This Afternoon. Isolated Showers And Tstms This Morning, Then Scattered Showers And Tstms This Afternoon.|
|Tonight...E Winds 15 Kt With Gusts To 20 Kt. Seas 3 To 4 Ft. A Chance Of Showers And Tstms In The Evening, Then Showers Likely With A Slight Chance Of Tstms After Midnight.|
|Mon...E Winds 15 Kt With Gusts To 20 Kt. Seas 3 To 4 Ft. Showers. A Slight Chance Of Tstms In The Morning, Then A Chance Of Tstms In The Afternoon.|
|Mon Night...E Winds 10 To 15 Kt With Gusts To 20 Kt. Seas 3 To 4 Ft. A Chance Of Tstms. Showers.|
|Tue...Se Winds 10 Kt. Seas 3 To 4 Ft, Subsiding To 2 To 3 Ft In The Afternoon. Showers. A Slight Chance Of Tstms In The Morning, Then A Chance Of Tstms In The Afternoon.|
|Tue Night...Se Winds 5 To 10 Kt. Seas 2 To 3 Ft. A Chance Of Tstms. Showers.|
|Wed...S Winds 5 To 10 Kt. Seas 2 To 3 Ft. Showers Likely With A Chance Of Tstms.|
|Wed Night...W Winds 10 To 15 Kt. Seas 2 To 3 Ft. A Chance Of Showers And Tstms.|
|Thu...Nw Winds 10 To 15 Kt. Seas 3 Ft. A Slight Chance Of Showers.|
|Thu Night...N Winds 10 To 15 Kt. Seas 3 To 4 Ft. Mariners Are Reminded That Winds And Seas Higher In And Near Tstms.|
| Area Forecast Discussion|
National Weather Service Charleston SC
1016am EDT Sunday September 19 2021
A wet weather pattern will prevail into the middle of the week. A cold front will move through the area Wednesday evening into early Thursday, followed by high pressure prevailing through the weekend.
Near Term - Through Tonight
Morning analysis reveals sharp mid level ridging through the Great Lakes this morning, overtop a short-wave circulation across the lower Mississippi River Valley. Sounding like a broken record, but deep tropical moisture plume remains entrenched across the Deep South ahead of the circulation, particularly the Gulf Coast states. Morning CHS sounding shows a PWAT (Precipitable Water) value of 1.68...down a little from last evening but still running above seasonal norms.
At the surface, strong high pressure is across the eastern lakes into New England and nosing down along the east coast, maintaining our persistent and increasing northeasterly flow across our area. Convection is active in the coastal and outer waters. Well defined coastal and just offshore convergence axis is noted south of Sapelo Island to JAX and offshore, bringing persistent heavier showers and some thunder into those areas. Persistent heavy rainfall has already setup in far southern McIntosh county where KCLX radar rainfall estimates show 1 to 2 inches of rainfall in the last 6 hours already.
Through the day: Strong convergence along the GA shoreline will relax some this afternoon, as daytime heating continues and the land breeze breaks down. But strongest moisture convergence/forcing is looking to remain focused through SE Georgia counties into the JAX area through the day. Going forecast already had higher probability of precipitation and Quantitative Precipitation Forecast amounts through that area, but I have increased both. And given the rainfall amounts we have already seen, I am becoming concerned that heavy rain and localized flooding may be possible down that way. Will highlight the threat in the HWO.
Further north, much less coverage of showers/storms anticipated particularly through the SC counties.
Tonight: A well defined H9-H7 confluence moisture axis extending from Tennessee southeast into Florida will slowly propagate northeast into Southeast Georgia by daybreak Monday as a H5 trough across the lower Mississippi Valley nudges east. Although convection may wane a bit after sunset as instability diminishes with the loss of insolation, convection is expected to increase in coverage by late evening and especially overnight as forcing for assent begins to intensify and H8-H7 moisture transport rapidly strengthens. By daybreak Tuesday, mean RH throughout the lower Troposphere should average >90% across Southeast Georgia. This coupled with some instability advecting inland from off the warmer Atlantic and additional low-level convergence associated with the formation of a weak coastal trough along the coast will likely support a large band of showers with few tstms across much of Southeast Georgia and possibly into far southern South Carolina. This activity could pose a risk for urban flooding in the Savannah Metro Area as PWATs (Precipitable Waters) climb to 2.20-2.35 inches and will have to be closely watched. Overnight probability of precipitation will range from 20-30% across the Charleston Tri- County area to 60-80% across Southeast Georgia, highest along the Georgia coast. Lows will range from the lower 70s inland to the upper 70s along the beaches.
Short Term - Monday Through Wednesday
Monday and Tuesday: Aloft, a broad ridge will extend across the Southeast United States while a mid-upper level low shifts north along its western edge across the Midwest and Great Lakes region. At the sfc, high pressure strengthening and extending south along the East Coast will set up a fairly strong onshore flow across the local area, reinforcing deep moisture with PWATs (Precipitable Waters) approaching 2.25-2.50 inches Monday and Tuesday. Given ample moisture in place and subtle mid-level energy drifting across the area aloft, numerous to widespread showers along with few/scattered thunderstorms will be possible each day with peak precipitation coverage anticipated late morning into early evening hours across southeast Georgia Monday, before the bulk of activity drifts north into southeast South Carolina Tuesday while enhanced moisture convergence occurs with a developing coastal trough along the Southeast Coast. At this time, convective activity is expected to remain sub-severe, although many locations could experience heavy downpours from showers/thunderstorms each day. Should the bulk of rains occur closer to the coast around the evening high tides, minor flooding issues are possible. Flood Advisories could eventually be needed.
Extensive cloud cover each day should limit overall heating potential. Highs should be near or a few degrees below normal, generally peaking in the low-mid 80s each afternoon. Overnight lows should remain mild, generally ranging in the low-mid 70s away from the immediate coast.
Wednesday: High pressure extending south along the East Coast is expected to weaken considerably as a coastal trough shifts north across the Carolinas early in advance of a mid-level trough shifting across the Midwest toward the Northeast and Mid-Atlantic region. Scattered to numerous showers along with a few thunderstorms should shift north with the coastal trough, before another round of showers and thunderstorms develop during the afternoon as the area remains somewhat warm-sectored and moist in advance of a cold front approaching the region late day into the evening. A few stronger and/or perhaps severe thunderstorms can not be ruled out late day, especially if the front arrives by early evening. Regardless, convective activity could produce heavy downpours while PWAT (Precipitable Water) values around 2.0 inches remain across the area ahead of frontal passage. High temps should generally range in the low-mid 80s, warmest across southeast Georgia.
Long Term - Wednesday Night Through Saturday
A cold front associated with the high amplitude trough is expected to shift through the area by early Thursday, likely bringing an end to a wet pattern as drier and cooler high pressure spreads across the Southeast into early next weekend. Along the front, deep moisture characterized by PWATs (Precipitable Waters) around 2.0 inches will support at least chances of showers/thunderstorms Wednesday night, some potentially strong before shifting offshore. Once frontal passage occurs, conditions will be noticeably drier and cooler with high pressure dominating the pattern and a northerly wind in place through next weekend. High temps should average in the upper 70s to lower 80s Thursday to Saturday, then gradually warm a degree or two Sunday. Low temps in the mid-upper 60s Wednesday night should dip into the mid-upper 50s away from the coast during the weekend.
Through Tonight: An easterly wind regime will hold in place through tonight as high pressure holds to the north. Winds will increase to 15-20 kt through the day, possibly just a few knots lower across the Georgia waters, as the pressure gradient tightens over the local marine area. These elevated winds will linger through tonight, especially across the South Carolina waters. Seas will average 2-4 ft.
Monday through Friday: High pressure will become reinforced by stronger high pressure building south along the East Coast Monday into Tuesday. While this process unfolds, a coastal trough will attempt to develop off the Southeast Coast Tuesday, before shifting north of the area well in advance of a cold front approaching the region late Wednesday into early Thursday. Given the setup, the pressure gradient will be somewhat enhanced initially with 15-20 kt easterly winds across local waters and seas averaging between 2-4 ft. Winds should then veer more south Wednesday before a cold front shifts through the region Wednesday evening into early Thursday. Strong cold air advection in wake of the front could push northerly winds upwards to 20-25 kt and build seas up to 4-6 ft, leading to a period of Small Craft Advisories across local waters Thursday night into Friday.
Modest onshore winds coupled with a 2 ft swell with 8-10 second periods generated by Odette over the past few days will support a moderate risk for rip currents at all beaches today. The moderate risk will linger into Monday.
Tides / Coastal Flooding
Shallow coastal flooding is possible along the coasts of Charleston and Colleton Counties with the evening high tide. A Coastal Flood Advisory could be needed. Coastal flooding is not expected along the Georgia and far southern South Carolina coasts as tides at Fort Pulaski are expected to remain below 9.5 ft MLLW. The risk for minor coastal flooding will linger through at least mid-week.
NOAA Charleston SC Office: Watches - Warnings - Advisories