Marine Weather Net

Charleston Harbor Marine Forecast


REST OF TODAY

NE
WINDS
5 KNOTS

TONIGHT

E
WINDS
10
KNOTS

MON

E
WINDS
10
KNOTS

MON NIGHT

E
WINDS
5 - 10
KNOTS

The Marine Weather Forecast In Detail:
AMZ330 Forecast Issued: 944 AM EDT Sun Sep 23 2018

Rest Of Today...Ne Winds 5 Kt, Becoming E 10 Kt This Afternoon. A Slight Chance Of Showers, Then A Chance Of Showers This Afternoon.
Tonight...E Winds 10 Kt, Becoming Ne After Midnight. A Slight Chance Of Showers After Midnight.
Mon...E Winds 10 Kt. A Chance Of Showers With A Slight Chance Of Tstms.
Mon Night...E Winds 5 To 10 Kt. A Slight Chance Of Tstms. A Chance Of Showers, Mainly In The Evening.
Tue...Ne Winds 5 Kt. A Chance Of Showers With A Slight Chance Of Tstms.
Tue Night...Se Winds 5 Kt, Becoming S After Midnight. A Slight Chance Of Tstms. A Chance Of Showers, Mainly In The Evening.
Wed...Sw Winds 5 To 10 Kt. A Chance Of Showers And Tstms.
Wed Night...S Winds 10 Kt. A Chance Of Showers And Tstms.
Thu...Sw Winds 5 Kt. A Chance Of Showers And Tstms.
Thu Night...Sw Winds 5 To 10 Kt. A Chance Of Showers And Tstms. Mariners Are Reminded That Winds And Waves Higher In And Near Tstms. Unless Otherwise Noted, Waves 1 Foot Or Less. Charleston Harbor Water Temperature 83 Degrees.
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Area Forecast Discussion
National Weather Service Charleston SC
603am EDT Sunday September 23 2018

Synopsis: High pressure will weaken today as a stationary front gradually approaches from the north into Monday. Low pressure will approach from the Atlantic Monday night into Tuesday, then weaken as it moves northward. A cold front is forecasted to approach from the west towards the second half of the week and then possibly stall over the area. A second cold front is expected next weekend.

Near Term - Until 6pm This Evening
The forecast is pretty much on track. Made minor adjustments to hourly probability of precipitation over the marine area per KCLX radar trends. The rest of the forecast looks good.

H5 heigheights will rise today as the deep layered high pressure centered well offshore the Southeast U.S. begins to build west and influences from the weakening TUTT over the Gulf of Mexico wane. Despite the strengthening ridge aloft, the elongated surface high extending from eastern Georgia to north of Bermuda is weakening and becoming increasingly strung out ahead of a strong cold front that is moving farther offshore of the New England and Mid-Atlantic coasts this morning. This weakening of the surface anticyclone will allow deeper moisture to slowly advect north and northwest along the coast as the sfc-H8 flow slowly veers. PWATS are forecast to rise to 1.50 to 1.85 inches through the day and will be locally near 2 inches along the Georgia coast at times later this morning per latest RAP output.

Expect a larger areal extent of isolated shower activity today compared to past several days with activity generally remaining confined to the coastal counties until the afternoon sea breeze pushes inland. There is a potential for more scattered coverage along coastal Georgia later this morning where deeper moisture will be found, but am hesitant to increase probability of precipitation any higher than 20% at this time given the sea breeze geometry will favor more of a pure sea breeze. Pure sea breeze circulations typically have weak, ill-defined convergence fields associated with them and with strong capping still noted aloft in the absence of any upper-level forcing feature, there is just not enough evidence to justify higher probability of precipitation at this time. This will have to be monitored, however. Highs will range from the upper 80s/near 90 well inland to the mid 80s at the beaches.

Short Term - 6pm This Evening Through Wednesday
Tonight: Quiet conditions will persist. Another subtle coastal trough/surface perturbation will move west into the waters early Monday and may help to increase the risk for showers just before daybreak. Most of the night looks dry, however, with clouds increasing from off the Atlantic. Lows will range from the upper 60s/near 70 well inland to the upper 70s at the beaches.

Monday: The mid-levels will consist of high pressure off the Southeast coast in the morning, with it's western periphery barely stretching into our area. Additionally, a ridge will be over the Great Lakes Region. The ridge will move eastward through the day and into the night. This will help to strengthen the high off our and allow heigheights to rise over our area. At the surface, a broad area of low pressure will be far to our east Monday morning. Meanwhile, a stationary front will spread across NC. The front will slowly move southward during the day and into the night, weakening and then dissipating, possibly over our area. Meanwhile, the broad low will gradually approach from the Atlantic. Models have backed of on the PWATs a little, with amounts peaking ~2" in the afternoon. Though, Storm Prediction Center sounding climatology indicates this is still above the 90% moving average for CHS for this time of year. The lift and moisture will generate precipitation, with areal coverage initially along the coast and then moving inland during the afternoon, aided by the sea breeze. POPs are in the chance category. But it's not out of the question they may need to get raised more in some areas as the CAMs start to reach this time period. Instability, while in place is not overly impressive. Regardless, there is still a risk for thunderstorms. Steering winds won't be too strong, so some storms could produce locally heavy rainfall if they are slow moving or if there is back-building. Luckily, the precipitation will dissipate in the evening. However, more showers are expected to develop over the coastal waters overnight and move towards the coast. It's possible the POPs may be a little too high overland at night. Finally, heigheights and 850 mb temperatures are now hinting that temperatures may rise above normal, but before the precipitation begins.

Tuesday: The mid-levels will consist of high pressure off the Southeast coast. At the surface, the broad low initially approaching our area is forecasted start moving northwards and weaken. It is expected to get absorbed in the overall flow by the nighttime hours. PWATs appear to trend downward. But they may remain slightly above normal for this time of year. Models have the best rainfall potential over the Charleston Tri-County area and this is where we have the highest POPs. Instability is highest near the coast, then quickly lowering inland. Again, it's not overly impressive and the thunderstorm threat was capped at slight. The precipitation will quickly dissipate in the evening. However, more showers are expected to develop over the coastal waters overnight and move towards the coast in easterly flow, possibly making it to our coastal counties just before daybreak. Temperatures will be a few degrees above normal.

Wednesday: The mid-levels will consist of high pressure off the Southeast coast and long wave troughing over the Central U.S. The axis of the trough will slowly move eastward, which will push the high further offshore and cause our heigheights to lower. At the surface, a cold front will be approaching from the northwest. Most of the activity will stay fare away from us. But models at least show chance POPs and this is reflected in the forecast. Unlike previous days, the overnight hours will see more precipitation coverage as the front approaches. Heigheights and 850 mb temperatures will again lead to another day of above normal temperatures

Long Term - Wednesday Night Through Saturday
Wednesday night a cold front will be slowly approaching from the northwest. This trend will continue into Thursday. The front may then stall over or nearby our area Friday. Another cold front is then forecasted to approach from the northwest on Saturday. The rainfall potential will depend on the approximate location of the fronts. For now it appears to equate to above normal POPs. However, more adjustments to the forecast are expected.

Marine Discussion
Through Tonight: An easterly flow regime will hold through tonight. Winds are expected to tip to the northeast late as a coastal trough approaches from the east. Winds will remain less than 15 kt with seas 2-4 ft.

Monday through Thursday: A weakening stationary front to our north will slowly approach on Monday. Meanwhile, a broad area of low pressure will approach from the Atlantic. These two features will cause the pressure gradient to increase, causing winds/seas to trend upwards. However, no Small Craft Advisories are expected because the worst conditions will be far to our east. If anything, seas may reach 5 ft across portions of the Charleston waters and our outer GA waters during this time. The stationary front will dissipate across our area Monday night as the low continues to approach. The low is expected to weaken Tuesday, then move northwards before it gets to our area, getting absorbed into the atmospheric flow Tuesday night. A cold front is forecasted to approach from the west towards the second half of the week and then possibly stall over our area. No advisories are anticipated.

Rip Currents: Latest WW3 and NWPS output show swells dampening to 1 ft by the time they reach the beaches today with periods averaging 10-11 seconds. This typically supports a mid-range low risk for rip currents with winds remaining less than 15 kt despite increasing astronomical influences from the approaching full moon. A 2 ft swell with a similar period does tip the risk back into the moderate category, but a swell height of this magnitude reaching the beaches seems a bit of a stretch based on the latest model data. Ultimately decided to maintain a low- end moderate rip current risk given it is a weekend with good weather and to keep continuity from the previous forecast. This also blends better with the moderate rip current risk areas outlined by WFOs Wilmington and Jacksonville.

There could be an enhanced risk of rip currents early this week if swell associated with the tropical wave over the Atlantic makes it to our beaches

NOAA Charleston SC Office: Watches - Warnings - Advisories
GA...None. SC...None. MARINE...None

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