Science and Technology

The sea breeze is probably the most influential local weather phenomena in our area. The sea breeze develops as the land heats up, air rises and is replaced by cooler air from over the adjacent water. The sea breeze can have a dramatic effect on weather parameters such as temperatures, winds and humidity along and sometimes well inland of the coast. In addition, the sea breeze can act as a trigger for thunderstorms to develop due to the convergence it produces. Forecasters at NWS Wilmington have classified several types of sea breezes through the years as shown below.

a picture of the beginning of a classic sea breeze

a picture of the beginning of a southwest resultant sea breeze

The Southerly Resultant Sea Breeze with Inflection is one of the most common types of sea breezes in our area due to the prevailing flow. This feature always has an inflection point which is displaced to the north or northeast. It generally stays confined to the coastal counties and can be accompanied by weak pulse storms.

The Southerly Resultant Segmented Sea Breeze partially mimics the coastline but stays close to the coast across the southern areas. There is no inflection point. This sea breeze often has little in the way of convection because the atmosphere is capped (i.e., stable - not prone to rising).

The Southerly Resultant Hybrid Sea Breeze remains confined to the coast across the northern and southern areas while moving inland toward the center.

The Northeast Resultant Sea Breeze with Inflection slightly mimics the coast. This feature always has an inflection point that is displaced to the west. The inland propagation is limited and with the prevailing northeasterly flow convection is usually limited because of poor instability.

The Northeast Resultant Segmented Sea Breeze partially mimics the coast and remains confined near the coast along the northernmost segments. This feature does not have an inflection point and usually inland propagation is limited.

Sea fog is an advection fog that forms in warm, moist air cooled to saturation as it moves over colder water. The colder water may occur as a well-defined current, or as gradual latitudinal cooling. The dew point and the temperature undergo a gradual change as the air mass moves over colder and colder water. The surface air temperature falls steadily, and tends to approach the water temperature. The dewpoint also tends to approach the water temperature, but at a slower rate. If the dewpoint of the air mass is initially higher than the coldest water to be crossed, and if the cooling process continues sufficiently long, the temperature of the air ultimately falls to the dewpoint, and fog results. However, if the initial dewpoint is less than the coldest water temperature, the formation of fog is unlikely. Generally, in northward moving air masses or in air masses that have previously traversed a warm ocean current, the dewpoint of the air is initially higher than the cold water temperature to the north, and fog will form, provided sufficient fetch occurs. The rate of temperature decrease is largely dependent on the speed at which the air mass moves across the sea surface, which, in turn, is dependent both on the spacing of the isotherms and the velocity of the air normal to them. The dissipation of sea fog requires a change in air mass (a cold front). A movement of sea fog to a warmer land area leads to rapid dissipation. Upon heating, the fog first lifts, forming a stratus deck; then, with further heating, this cloud deck breaks up into a stratocumulus layer, and eventually into convective type clouds or evaporates entirely. An increase in wind velocity can lift sea fog, forming a stratus deck, especially if the air/sea temperature differential is small. Over very cold water, dense sea fog may persist even with high winds.

Fair-weather waterspouts are small tornado-look circulations extending from the ocean surface up into a towering cumulus or cumulonimbus cloud. Fair-weather waterspouts occasionally occur during the warm season across North and South Carolina coastal waters and are a hazard to boaters and beachgoers. Wind speeds in large waterspouts can rival that of small tornadoes and sometimes reach over 100 mph. Fair-weather waterspouts can sometimes move onshore as a tornado, but normally weaken and dissipate within a minute of reaching shore due to increased surface friction and turbulence. However, given their small size and transitory nature, even advanced doppler weather radar can be of little use in the Tornado Warning decision process.

Fair-weather waterspouts are different than tornadic waterspouts which can form during severe thunderstorms involving extreme wind shear and a strong mesocyclone. Fair-weather waterspouts form in environments characterized by little to no vertical wind shear below 6000 feet in altitude, deep moisture, good instability (as measured by CAPE) and moderate to steep low-level lapse rates.

Research at other NWS forecast offices and qualitative observations locally seem to indicate that waterspouts form preferentially in the vicinity of morning land-breeze boundaries which push offshore overnight. These boundaries can be a focus for convergence and helicity.

Follow our seasonal Surf Zone/Beach Forecast which includes a forecast of the waterspout risk. More info about our Surf Zone/Beach Forecast can be found on our beach page.

Winds

Wind direction is very important to the occurrence of rip currents with winds blowing more perpendicular to the coast being more favorable than those blowing parallel to the coast.

Waves

The swell component of incoming waves also plays a significant role in the development and intensity of rip currents. Longer period swells, like those that emanate from distant hurricanes and other storm systems, push more water onto the coast. Also, swells coming in more perpendicular (i.e., directly onshore) are more favorable than swells coming in more parallel to the coast.

Tides

Follow our local tropical weather page the latest on the tropics.

Winter Weather

Although fairly rare, winter weather across southeast NC and northeast SC can be quite a forecast challenge given the many large-scale and small-scale factors involved in producing winter precipitation, the weather model limitations of the small-scale processes and the unique geography/topography of the area.

Sometimes colder and drier (more dense) air moves south on the eastern side of the Appalachian Mountains as high pressure builds from the north, which is known as "cold air damming". Meanwhile, warmer and moister (less dense) air can ride up and over the shallow colder air near the surface and the tug-of-war between these two air masses ultimately determines the areas that receive winter precipitation. More details on winter weather across the area can be found here.