Marine Weather and Tide Forecast for Oak Island, NC

NEAR TERM /THROUGH TONIGHT/
Although it's still dry down here at the surface with dewpoints in the 30s and lower 40s, changes are occurring aloft. A shortwave sweeping northeastward across KY this morning is bringing a swath of warm advection northward across the Carolinas and Virginia. We're on the southern edge of where enough isentropic lift and mid level moisture will coexist to generate measurable rainfall. A few hundredths of an inch are possible this morning mainly before 10 AM north of a line from Florence to Whiteville to Wilmington. Behind this shortwave clouds may thin enough for some breaks in the clouds, especially east of I-95 where temperatures could rise well into the 60s again.

A moist subtropical jet originating from the Pacific and southwest flow off the Gulf will combine to push precipitable water values up to 1.5 inches by tonight. This is about two-tenths of an inch above the 90th percentile values for December but not in record territory for the Charleston upper air site. Another shortwave will approach tonight in the broad southwest flow off the Gulf. Although much weaker than this morning's disturbance, this one should move directly across the Carolinas. HRRR ensembles show a large number of members painting 40+ dBZ echoes where positive CAPE exists, implying precipitation will be convective in character. Small convective instability is also noted in both GFS and NAM forecast soundings, although it remains shallow enough in depth that thunder appears unlikely. Forecast Pops range from around 50 percent in Georgetown to 70-80 percent across across the I-95 corridor eastward to the Cape Fear area.

SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/
A cold front will move through the area this period, pushing well offshore of the Carolinas by Wednesday night. Initially, offshore ridging will help to keep the winds aloft more westerly, which helps keep some of the drier continental flow in place. While scattered showers are still expected Tuesday and Tuesday evening, I don't think it'll be quite as widespread as I once thought. The shortwave energy has slowed down just a tad, which brings the ticket to richer southwesterly flow, and therefore more moisture.

This energy finally arrives before dawn Wednesday, and that dry layer aloft gets filled in with moisture. Precipitable water values are still slated to shoot up towards 1.25-1.50", with the upper quartile suggesting even closer to 1.75". The timing of the upper energy matches up just about perfectly with the frontal passage, which is where we really cash in on the rain through late Wednesday afternoon. Several areas stand a good chance at capturing over an inch of rain, particularly closer to I-95, where the shortwave energy is a bit stronger. Depending on training of the rainfall, it is even possible that some isolated spots could hit 1.5-2.0 inches.
The majority of the area is in a D1 "Moderate Drought," so this rain is certainly needed. Since soils are so dry, and the rain will be occurring over several hours, I'm not really worried about flooding.
At worst, there could be some minor flooding in low-lying spots and poor drainage areas. I also took out any mention of thunder. The stout marine layer will be in place, so any rumbles would be from elevated instability. However, while the forcing aloft looks pretty good, the 95th percentile of MLCAPE doesn't even touch 200 J/kg.

The front races towards the coast and offshore by early Wednesday evening. Winds in the lower levels quickly shift to the west and then northwest, which cuts off the moisture and ends the rain chances. Highs Tuesday and Wednesday generally in the lower 70s for most spots. Lows Tuesday night in the lower 60s, mimicking more like early October than mid-December. That'll change quickly by Wednesday night though, as the northwesterly flow turns on the cold air advection. Lows that night dip below freezing inland, near or just above freezing at the coast.

LONG TERM /THURSDAY THROUGH SUNDAY/
High pressure comes in from the north, bringing back more sunshine and cold temperatures. Highs Thursday and Friday in the upper 40s to lower 50s. Widespread lows in the mid-to-upper 20s Thursday night tick up 3-4 degrees by Friday night. That high pressure moves up towards Quebec by the weekend, which may help to introduce a classic cold air damming setup. Guidance doesn't completely line up with this idea, so we'll have to see how this evolves over the next several days. In general, temperatures looks to moderate throughout the weekend.

AVIATION /06Z MONDAY THROUGH FRIDAY/
VFR conditions will continue through at least 00Z tonight, perhaps longer along the coast. A wave of mid level moisture will spread across the area beginning around 10Z inland and 12Z at the coast. Ceilings averaging 7000 feet AGL and some light rain are possible, and this activity should exit to the northeast by 14Z. A second wave of deeper moisture should arrive late this afternoon into this evening, potentially dropping ceilings below 3000 feet. More showers accompanying this moisture could also negatively impact visibility, particularly inland. The odds of MVFR conditions developing are moderate to high at KFLO and KLBT mainly after 03Z.

Extended Outlook...High potential exists for MVFR conditions inland late Monday night into Tuesday morning. There is a moderate potential ceilings and visibility could both drop to IFR for a period as well. Another potential for MVFR to brief IFR conditions will develop Wednesday as convective showers develop along an eastward-moving cold front.

MARINE
Through Tonight...High pressure will remain centered near Bermuda through tonight while low pressure slowly weakens across the Great Lakes. The pressure gradient between these two systems will maintain a light to moderate southwest wind across the Carolinas, peaking at near 15 knots south of Cape Fear late this afternoon through this evening. The dominant wave will be short period wind chop averaging only 4-5 seconds. When combined with a small 9 second southeast swell, total seas are expected to average 2-3 feet in height.

A little patchy light rain is possible this morning across the beaches and coastal waters, mainly north of Myrtle Beach. Better chances for more substantial showers will develop tonight.

Tuesday through Friday...SSW winds and seas build ahead of a cold front Tuesday, easily hitting Small Craft Advisory criteria. Some of the probabilities for gale force gusts peak up over 80% over the coastal waters from Murrells Inlet to the South Santee River out 20 nm by Wednesday afternoon. However, this looks rather brief, so I'm not sure if a Gale Warning would be warranted. At their peak, seas may escalate to 5-7 ft at the coast, and 8-10 ft 20 nm from shore. Front moves through the waters Wednesday evening, allowing the winds to decrease and veer northwesterly. Advisory criteria should fall away by Thursday morning. From there, northwesterly winds eventually become northeasterly by Friday, with sustained winds at 15-17 kts. Seas drop down to 2-3 ft initially on Thursday, increasing to 3-4 ft by Friday afternoon.

ILM WATCHES/WARNINGS/ADVISORIES
NC...None.
SC...None.
MARINE...None.