Charleston Harbor Marine Forecast
|Tonight...Ne Winds 5 Kt, Becoming E Late.|
|Thu...Se Winds 5 To 10 Kt, Increasing To 15 To 20 Kt With Gusts To 25 Kt In The Afternoon. Waves 1 To 2 Ft. Showers With A Chance Of Tstms In The Afternoon.|
|Thu Night...S Winds 15 To 20 Kt, Becoming Sw 10 To 15 Kt After Midnight. Waves 1 To 2 Ft. A Chance Of Tstms. Showers.|
|Fri...Sw Winds 10 To 15 Kt With Gusts To 20 Kt. A Slight Chance Of Showers.|
|Fri Night...W Winds 10 To 15 Kt. A Slight Chance Of Showers In The Evening.|
|Sat...W Winds 10 To 15 Kt With Gusts To 20 Kt.|
|Sat Night...W Winds 10 To 15 Kt.|
|Sun...W Winds 10 Kt.|
|Sun Night...Nw Winds 5 To 10 Kt.|
|Mon...Ne Winds 5 To 10 Kt.|
|Mon Night...Ne Winds 5 Kt. Mariners Are Reminded That Winds And Waves Higher In And Near Tstms. Unless Otherwise Noted, Waves 1 Foot Or Less. Charleston Harbor Water Temperature 73 Degrees.|
| Area Forecast Discussion|
National Weather Service Charleston SC
736pm EDT Wednesday Oct 27 2021
A low pressure system will impact the region Thursday through the end of the week. High pressure will return early next week.
Near Term - Until 6am Thursday Morning
No significant changes were required with the early evening update. We did drop winds down to calm across many inland communities, and if the increase in the higher level clouds is slower than originally anticipated, we may need to drop min temps a bit.
Guidance provides mixed signals on when the leading edge of any convection will reach the southwest part of the forecast region. For now we have left any Probability of Precipitation greater than 14% outside the forecast through 6 am, with just slight chance Probability of Precipitation far interior Georgia arriving closer to sunrise.
Previous discussion... The mid-levels will consist of a narrow ridge, with its axis stretching from approximately the Great Lakes Region down into the Southeast this evening. The ridge will gradually shift to the ENE with time. At the surface, weak high pressure will move offshore this evening and overnight. Meanwhile, a warm front will approach from the southwest overnight. Though, the front is not expected to reach our area by daybreak Thursday. The high will continue.nue to bring our area dry conditions for most of the night. However, moisture will be increasing across our area, in advance of the front. Some of the models indicate a few showers could reach the Altamaha River and vicinity just before daybreak Thursday. Therefore, we have slight chance POPs there. Everywhere else is expected to remain dry. Otherwise, high clouds will gradually increase across our area overnight, most notably across our GA counties. Temperatures will generally be in the upper 40s far inland. But they'll be warmer (generally the 50s) along the immediate coast due to the winds eventually coming off the warmer ocean, and closer to the Altamaha River and vicinity where there will be more clouds.
Short Term - 6am Thursday Morning Through Saturday
Thursday: An anomalously deep mid level trough/low and associated surface reflection will track across the Mississippi River Valley to the Tennessee and Ohio River Valleys during the afternoon/evening. As this occurs, a warm front will shift north across the local area by late day, followed by a cold front sweeping through the region overnight. Within the warm sector ahead of the cold front, a 40-50 kt low-level jet will help advect deep moisture into the local area with PWATs (Precipitable Waters) around 2 inches during the afternoon into early evening. Instability should remain marginal given a fair amount of cloud cover associated with isentropic lift and especially if ongoing convection from the previous night prolongs some stabilization across the local area during the day. However, latest guidance does suggest SBCAPE increasing to around 1000-1500 J/kg within the warm- sector late afternoon into early evening when impressive forcing/shear also coincide across the local area. Bulk shear (0- 6km) around 50-55 kt and helicity (0-1 km) between 300-500 m2/s2 in combination with forcing associated with an advancing h5 shortwave, upper level divergence with an h25 jet, and the approaching cold front suggest the potential for some thunderstorms to be strong and/or severe with damaging straight line winds and perhaps an isolated tornado or two across parts of southeast Georgia and southeast South Carolina, although the best potential for a tornado appears to be across the Quad County area where surface winds are slightly more backed closer to a front during early evening hours. Given cold temps (-20 C) associated with the large h5 low centered far northwest of the region, poor mid-level lapse rates across the local area, and expected convective mode (linear or clusters of thunderstorms), large hail will be a considerably less threat. The progressive nature of the event should also limit overall flooding potential, but isolated pockets of heavy rainfall could produce minor flooding along low- lying areas and roadways.
The greatest potential for severe weather should occur along and east of the I-95 corridor (currently outlooked with a Slight Risk by SPC) late afternoon/evening (4-10 PM), starting across southeast Georgia first, then advancing into southeast South Carolina. Further inland, a Marginal Risk for severe weather remains across the area as well, but the potential should remain somewhat more limited given less instability and the potential of ongoing convection from the previous night stabilizing the atmosphere during the day.
Outside the potential of strong/severe thunderstorms, atmospheric conditions will still favor breezy winds across the region mid-late afternoon through the evening. Highs should peak in the low/mid 70s, warmest along the coast. Chances of precipitation will decrease with cold fropa overnight, but some lingering showers are possible late night given lingering moisture and the large mid-upper level low positioned to the west-northwest. Lows should dip into the mid 50s inland to upper 50s/lower 60s at the beaches.
Friday And Saturday
An expansive mid-upper level low covering much of the East Conus will slowly shift toward the Eastern Seaboard this weekend. A few showers will be possible with lingering moisture and cooler mid-level temps on Friday, but moisture in the mid-upper levels will likely exit the area Saturday, favoring drier conditions. Temps will be cooler than normal, with highs generally ranging in the mid 60s inland to upper 60s/around 70 near the coast each day. Low temps should range in the upper 40s inland to mid-upper 50s closer to the coast Friday night.
Long Term - Saturday Night Through Wednesday
Models are in good agreement that a large mid-upper level low as well as surface low pressure will slowly advance off the Mid-Atlantic and Northeast Coasts late weekend and into early next week, while high pressure builds into the local area from the west, eventually becoming centered across the Southeast United States early next week. Drier air and a lack of significant forcing mechanisms will support a rain-free forecast through the middle of next week. Temps through the period will mostly be below normal, although will be moderating with time early next week. In general highs should peak in the lower 70s while a few middle 70s are possible across southeast Georgia. Lows should generally range in the mid-upper 40s well inland to upper 50s/around 60 near the coast.
Tonight: Weak high pressure will move offshore this evening and overnight. Meanwhile, a warm front will approach from the southwest overnight. Though, the front is not expected to reach our area by daybreak Thursday. These synoptic features will cause winds to be light and variable this evening, then shifting to the ESE and increasing to 5-10 kt by daybreak Thursday. Seas will be 1-2 ft within 20 nm and 2-3 ft for the GA waters beyond 20 nm.
Thursday through Monday: Conditions will deteriorate across coastal waters Thursday as a strong low pressure system tracks across the region. Outside showers and thunderstorms, some of which could be severe with damaging winds and waterspouts Thursday afternoon into Thursday evening, an enhanced pressure gradient will support Small Craft Advisories, starting across Georgia waters Thursday afternoon, then for the remainder of coastal waters outside the CHS Harbor late Thursday afternoon. There is a potential for small craft advisory level conditions in the CHS Harbor Thursday night, before conditions slowly improve heading into daybreak Friday. Elevated winds/seas will then persist across all other waters for much of Friday before additional improvement occurs Friday night into Saturday, when the last of Small Craft Advisories comes to an end. Conditions are then expected to remain below small craft advisory levels Sunday and Monday as high pressure expands across the area.
NOAA Charleston SC Office: Watches - Warnings - Advisories
Small Craft Advisory from 5pm Thursday to 8pm EDT Friday for AMZ352. Small Craft Advisory from 2pm Thursday to 8am EDT Saturday for AMZ374. Small Craft Advisory from 5pm Thursday to 8am EDT Saturday for AMZ350. Small Craft Advisory from 2pm Thursday to 8pm EDT Friday for AMZ354.