A King Tide is the informal term used to describe the highest predicted high tides of the year. These exceptionally high water levels offer coastal communities a preview of what daily high tides could look like in the future due to rising sea levels. Understanding the forces behind these events is important for coastal residents and visitors in North Carolina, as they lead to frequent high-tide flooding in low-lying areas.
The Astronomical Cause of King Tides
The term “King Tide” is a non-scientific moniker for what oceanographers refer to as a perigean spring tide. Tides are primarily caused by the gravitational pull exerted by the Moon and, to a lesser extent, the Sun. The largest tidal ranges of the month, known as spring tides, occur twice monthly when the Sun, Moon, and Earth align in a straight line, a configuration called syzygy. This alignment happens during both the full moon and the new moon, combining the gravitational forces to create higher-than-average high tides.
A King Tide occurs when this Sun-Earth-Moon alignment coincides with two other orbital factors that maximize the gravitational pull. The Moon travels around the Earth in an elliptical orbit, and its closest approach point is called perigee. When the Moon is at perigee during a spring tide, its gravitational force is at its strongest, significantly increasing the tidal bulge.
The third factor involves the Earth’s orbit around the Sun, which is also elliptical. Once a year, typically in early January, the Earth reaches perihelion, its closest point to the Sun, which further enhances the Sun’s tidal influence. When the Moon is at its closest (perigee) and the Sun is at its closest (perihelion) during a new or full moon, the resulting gravitational synergy produces the highest tides of the year.
Predicting the Highest Tides in North Carolina
King Tides are highly predictable because they follow the regular cycles of the Moon and the Sun’s orbits. In North Carolina, the highest events often occur during the late fall and early winter months. This timing is partly due to the Earth moving closer to perihelion, which occurs in early January, making the winter King Tides often the largest.
Forecasting these events relies on precise data collected by the National Oceanic and Atmospheric Administration (NOAA) through its network of tide gauges. Local efforts, such as the North Carolina King Tides Project, utilize this data to predict specific dates and times when the highest water levels are expected. However, while the astronomical forces are constant, local geography and temporary meteorological conditions can amplify the actual water level.
The physical characteristics of North Carolina’s coastline, including the shallow continental shelf and the expansive sounds like the Pamlico Sound, influence the magnitude of the tides. Non-tidal factors such as persistent onshore winds, low atmospheric pressure from weather systems, or even the subtle effects of the Gulf Stream can push water toward the coast. When a King Tide coincides with one of these weather-related forces, the resulting water levels can be substantially higher than predicted by astronomy alone.
Visible Effects on NC Coastal Areas
The impact of a King Tide is often described as “sunny day flooding” or “nuisance flooding,” because it can occur even when the weather is calm and clear. Water frequently backs up through stormwater systems and spills out onto coastal streets and low-lying public spaces.
In North Carolina, towns like Beaufort and Morehead City regularly see streets and docks inundated during these events. The Outer Banks are particularly vulnerable, with King Tides often causing ocean overwash that impacts transportation arteries. Portions of NC Highway 12, the primary road connecting the barrier islands, frequently become impassable, leading to temporary closures from both water and sand pushed across the dunes.
Unlike storm surge, which is caused by the wind and pressure of a hurricane or nor’easter, King Tide flooding is predictable and not wind-driven. However, when a minor storm or strong onshore wind does converge with a King Tide, the resulting flood can be severe, causing temporary business closures and property damage. Repeated exposure to saltwater can cause corrosion to infrastructure, including roads, bridges, and underground utilities.
Protecting Property and Ensuring Safety
Residents and visitors should be proactive by monitoring local alerts and tide prediction resources like the North Carolina King Tides Project for upcoming high-water events. A primary safety measure is to avoid driving or walking through any standing saltwater. Even six inches of moving water can be hazardous, and floodwater may contain contaminants or hide hazards.
Property protection involves moving vehicles parked in low-lying areas to higher ground. If a vehicle encounters saltwater, it should be thoroughly washed, especially the undercarriage, to remove corrosive salt residue. To prevent damage to homes, valuable items, important documents, and electrical equipment should be moved to upper floors or elevated storage.
Homeowners in flood-prone areas may also utilize temporary barriers, such as flood gates or shields, across doorways and garage entrances. Staying informed by checking North Carolina Department of Transportation (NCDOT) traffic maps is advisable for anyone traveling on coastal roads like NC Highway 12 during these events. Ultimately, recognizing that King Tides are a consistent hazard allows for necessary preparation and mitigation efforts.