The question of whether tides are higher in winter or summer does not have a simple answer, as the height of the sea surface is a complex product of competing forces. Tides are fundamentally the cyclical rise and fall of sea level caused by gravitational mechanics. However, the observed water height at the shore is also strongly influenced by seasonal meteorological and oceanographic factors. The true high water mark is a combination of consistent astronomical cycles and variable weather-driven effects.
The Primary Drivers of Tidal Range
The maximum potential range of the tides is set by the gravitational pull exerted primarily by the Moon and, to a lesser extent, the Sun. The Moon’s influence is about twice as strong as the Sun’s because of its relative proximity to Earth. When the Earth, Moon, and Sun align in a straight line, which happens during both the new and full moon phases, their gravitational forces combine to create a maximum tidal range known as a Spring Tide.
Conversely, when the Moon and Sun are positioned at a 90-degree angle relative to the Earth, their gravitational forces partially cancel each other out, resulting in the smaller tidal range of a Neap Tide. These Spring-Neap cycles occur approximately every two weeks and are the main drivers of tidal variability. The strength of these tidal forces is also modulated by the elliptical orbits of the Moon around the Earth and the Earth around the Sun.
The Moon’s orbit brings it closest to Earth at perigee, where the gravitational pull is strongest, and farthest at apogee. Similarly, the Earth’s orbit around the Sun brings it closest at perihelion (around January 3rd) and farthest at aphelion (around July 3rd). A Perigean Spring Tide, often called a “King Tide,” occurs when the Moon is at perigee while aligned with the Sun and Earth, producing the highest astronomical tides of the year. These astronomical high-tide mechanisms are governed by orbital and alignment mechanics, making them largely independent of the calendar seasons.
Seasonal Modifiers of Water Levels
While astronomical forces set the tidal rhythm, seasonal meteorological and oceanographic factors can significantly alter the observed water level. One major modifier is the inverse barometer effect, which relates atmospheric pressure to sea height. Low-pressure systems, often associated with winter storms, essentially “lift” the sea surface because there is less air weight pressing down on the water. Conversely, high-pressure systems, common in summer, push the sea surface down. This difference can change the mean sea level by several centimeters, often making winter water levels noticeably higher in northern latitudes.
Strong, sustained winds blowing toward the shore can physically push a large volume of water against the coastline, effectively raising the sea level (wind setup). In contrast, winds blowing offshore push water away, lowering the sea level. Water temperature also causes a seasonal change in the ocean’s volume; warmer water expands, leading to slightly higher mean sea levels in the summer, while colder, denser water contracts in the winter. The frequency and intensity of storm surges are perhaps the most dramatic seasonal modifiers.
Storm surges are created by the combined effect of strong onshore winds and low atmospheric pressure, raising water levels far above the predicted astronomical high tide. In many areas, the season with the most frequent and powerful storms, often winter or late autumn, experiences the highest observed water levels.
The Definitive Answer: Synthesis of Effects
The definitive answer is that the highest observed water levels are often a result of meteorological conditions, which frequently occur in winter, overwhelming the astronomical potential. While astronomical forces determine the maximum tidal range, seasonal weather patterns determine the maximum sea level that impacts the shore. In many coastal regions, the mean sea level is observed to be higher during the winter months, sometimes by as much as 0.6 meters, due to the prevalence of low-pressure systems and persistent onshore winds.
The astronomical factor of perihelion, where Earth is closest to the Sun, happens in early January, slightly increasing the gravitational pull and potential tidal range during the Northern Hemisphere winter. However, this subtle astronomical boost is frequently overshadowed by the dynamic effects of winter storms, which pile water against the coast through wind and reduced atmospheric pressure. Summer tides may benefit from thermal expansion, which causes the sea surface to rise slightly as the water warms.
Yet, the most extreme flooding events, which represent the true highest water marks, are typically caused by the rare coincidence of a maximum astronomical tide, such as a Perigean Spring Tide, with an adverse seasonal weather event like a severe coastal storm. Therefore, while the potential for an astronomical maximum exists year-round, the highest actual water levels are most often recorded during the season of peak storm activity.