What are Ocean Tides Called at Their Lowest?

Tides are among the most predictable of natural phenomena; the gravitational pull of the sun and moon, along with weather conditions, cause the oceans to rise and fall twice each day. While water levels are always considered lowest at "low tide," some low tides are lower than others, and a specific vocabulary has developed to describe these tidal conditions.

Daily Low Tides

Every day, most coastal areas around the globe experience two tide cycles. The main source of these tides is the gravitational pull of the moon, which causes the oceans around the earth to shift. The point in each tide cycle at which water levels are their lowest is known simply as "low tide." Because there are two daily tide cycles, coastal locations experience two low tides per day. Typically, however, the magnitudes of these daily low tides are slightly different from one another.

Monthly Low Tides: Spring Tides

Because tides are influenced by gravitational forces, tidal swings become larger when the sun and moon are in certain positions, namely, when the sun, earth and moon all form a straight line. This alignment occurs twice per month --- during the full and new moons --- and causes high tides to be higher and low tides to be lower. These more extreme tides that take place each month are known as "spring tides."

Yearly Low Tides: Perigean Spring Tides

Several times per year, the spring tides cause even lower tides. This happens whenever the spring tide occurs at the same time that the moon's orbit brings it closer to the earth. Because this point in the moon's orbit is know as the "perigee," these larger spring tides are known as "perigean spring tides." The effect of the perigean spring tides, however, is often minimal, and low tide may only be a few inches lower than a normal spring tide.

Other Factors Affecting Low Tides

Other factors besides the sun and moon may affect tide levels. Winds that are blowing in an offshore direction can push water away, creating a lower low tide than normal. The shape of the coastline also has a significant impact on tides. Funnel-shaped bays typically magnify tidal swings, while inlets with broad expanses of shallow water often minimize tidal variation, meaning that low tide is often not much lower than high tide.