South Santee River to Edisto Beach, SC Marine Forecast
|This Afternoon...Sw Winds 10 To 15 Kt. Seas 3 To 4 Ft. A Chance Of Showers And Tstms.|
|Tonight...Sw Winds 10 To 15 Kt, Becoming W 5 To 10 Kt After Midnight. Seas 3 To 4 Ft, Subsiding To 2 To 3 Ft After Midnight. A Slight Chance Of Showers And Tstms In The Evening, Then A Chance Of Showers And Tstms After Midnight.|
|Wed...Nw Winds 5 To 10 Kt, Becoming Ne In The Afternoon. Seas 2 Ft. A Slight Chance Of Showers In The Morning.|
|Wed Night...E Winds 5 To 10 Kt. Seas 2 Ft.|
|Thu...Ne Winds 5 To 10 Kt, Becoming E 10 To 15 Kt In The Afternoon. Seas 2 To 3 Ft.|
|Thu Night...E Winds 10 To 15 Kt. Seas 3 To 4 Ft.|
|Fri...E Winds 10 Kt. Seas 2 To 3 Ft.|
|Fri Night...E Winds 5 To 10 Kt. Seas 2 To 3 Ft.|
|Sat...Ne Winds 5 To 10 Kt. Seas 2 Ft. A Slight Chance Of Showers And Tstms.|
|Sat Night...E Winds 5 To 10 Kt. Seas 2 Ft. Mariners Are Reminded That Winds And Seas Higher In And Near Tstms.|
|Area Forecast Discussion|
National Weather Service Charleston SC
950am EDT Tuesday September 18 2018
Synopsis: A weak surface trough will slowly progress through the area today, then push offshore into early Wednesday. High pressure will then prevail over the region through the weekend and into early next week.
Near Term - Through Tonight
The forecast remains on track late this morning. GOES Total precipitable water values exceeding 2 inches are noted across much of the forecast area as marine showers/thunderstorms continue to push offshore. While a drier column will slowly advect to encompass the forecast area, this will not occur prior to best forcing and expected afternoon convective initiation. In fact, the intrusion of this drier air will serve to increase downdraft CAPE values from west to east. Under ideal conditions, areas where ongoing convection later this afternoon overlap with increasing DCAPEs would need to be monitored for potential strong to severe wind gusts. Fortunately, currently prognosed mid-level lapse rates don't look overly impressive, suggesting limited potential for deeper convection.
Previous discussion: For today: H5 ridging will build over OK and the Arklatex region, and this will steadily push both a surface and mid level trough associated with the remnants of Florence toward the coast by late in the day. Forcing from these features, plus the formation of the afternoon resultant sea breeze, will lead to additional scattered showers and t-storms developing. We expect a gap of several hours this morning between the ongoing convection that winds down and the diurnal activity that generally forms about about 2 pm. The highest chances look to be mainly over the eastern third to half of the CWFA due to the deep westerly flow. Provided the morning convection doesn't alter the overall thermodynamic environment too much, DCAPE is forecast as great as 1000-1200 J/kg, and this could be enough to produce some strong winds in a few of the taller storms. Frequent lightning and heavy rains with PWat over 2 inches will also occur in isolated storms.
H8 temps are as warm as 18-19C, or about 1-2 standard deviations above normal. This will support max temps as high as 93 or 94F inland from the immediate coast, which is about 6-8F above climatological norms. With the accompanying dew points in the lower and middle 70s, this will equate to heat indices of 100-104F prior to afternoon convection.
Tonight: Diurnal convection will fade in the evening, but until the surface and mid level trough push offshore after midnight, we still have isolated to scattered convection ongoing for much of the night. Winds will veer around to the NW and N by late tonight, and this will allow for min temps to fall about 2-4F lower than they are early this morning. Fog could form S of I-16 in GA, but signals aren't strong enough just yet to add mention to the forecasts.
Short Term - Wednesday Through Friday
Wednesday: The remnants of Florence will shift off the Northeast United States coast, helping a trough axis extending to the south/southwest and over the area to shift offshore early Wednesday. Expect most shower and/or thunderstorm activity to shift offshore by daybreak as much drier air enters the region within surface high pressure building from the north and a large ridge of high pressure expanding aloft. However, a small window for showers and/or thunderstorms is possible near coastal Southeast Georgia late Wednesday morning into the afternoon as PWATs near 1.50-1.75 inches coincide with the trough axis shifting slowly south and offshore. Overall high temps will peak in the upper 80s over Southeast South Carolina and to the lower 90s across Southeast Georgia. Wednesday night looks dry with overnight lows dipping into the low/mid 70s.
Thursday and Friday: A large/expansive ridge of high pressure will remain centered over the region aloft while an axis of surface high pressure extends from northwest Atlantic and south/southwest across the Southeast United States. This should lead to dry conditions over most areas late week, with the exception of an isolated shower or thunderstorm near the Altamaha River in Southeast Georgia each day while mid-level energy and moisture attempt to drift onshore along the southern edge of the ridge axis centered just to the north. Despite ample sun and the ridge aloft, a northeast-east surface wind associated with surface high pressure should lead to overall high temps a degree or two cooler through late week. In general, highs should range in mid/upper 80s over Southeast South Carolina each day while temps peak around 90 degrees over Southeast Georgia
Long Term - Friday Night Through Monday
A quieter weather pattern will persist through the weekend while a large ridge of high pressure remains over the Southeast United States. By early next week, the large ridge of high pressure will become slightly more compressed and centered over the western Atlantic as a front approaches from the north, but likely stalls well north/northwest of the region. Most shower and thunderstorm activity should remain offshore during the weekend or perhaps over parts of coastal Georgia where mid-level energy and an onshore wind advects moisture over land. Thereafter, some guidance suggests increasing chances of showers and thunderstorms Monday and Tuesday as a coastal trough shifts onshore. High temps will generally range in the mid/upper 80s across Southeast South Carolina this weekend and early next week. Some areas could touch 90 degrees across Southeast Georgia. Overnight lows should range in the upper 60s to around 70 degrees well inland to mid/upper 70s along the coast.
Today: High pressure is situated to the E-SE, while a trough associated with the remnants of Florence are found inland over the SE. This results in S or SW winds as much as near 15 kt, and seas of 3-5 ft (highest on the outer GA waters this morning).
Tonight: The inland trough will push into the waters after midnight, then clears most if not all areas late. This will allow for not only a lighter gradient, but also for winds to veer around to the W late. Seas will subside about a foot due to these changes.
Wednesday through Sunday: Winds/seas are expected to remain below Small Craft Advisory levels through early next week. A weak trough of low pressure is expected to shift offshore early Wednesday, turning winds north/northeast with increasing speeds through Thursday as weak cold air advection occurs aloft. Northeast-east winds could top out near 15-20 kts Thursday afternoon into Thursday night before diminishing to 10-15 kts and turning more directly onshore this weekend into early next week. Seas will generally range between 2-3 ft Wednesday, then build to 3-4 ft Thursday afternoon or night, before gradually subsiding through the weekend.
Rip Currents: There remains enough swell energy around 2 ft every 12 seconds that will impact the beaches today, and that along with a S-SW wind at 10-15 mph will result in a Moderate Risk of rip currents
NOAA Charleston SC Office: Watches - Warnings - Advisories
GA...None. SC...None. MARINE...None