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Saltwater tide tables

Saltwater Tide predictions for the United States Coast. This system will allow you to obtain tidal predictions for tidal stations around the entire United States coastal waters. Once your state is selected - click a red tide marker on the map to get your tide charts. You may then select predictions for 1 day or for up to 90 days. Save the chosen tidal location for easy access later.



Tides and Currents - NOAA

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What are Tides? What Causes Tides?

Tides are one of the most reliable phenomena in the world. As the sun rises in the east and the stars come out at night, we are confident that the ocean waters will regularly rise and fall along our shores. The following pages describe the tremendous forces that cause the worlds tides, and why it is important for us to understand how they work. Basically, tides are very long-period waves that move through the oceans in response to the forces exerted by the moon and sun. Tides originate in the oceans and progress toward the coastlines where they appear as the regular rise and fall of the sea surface. When the highest part, or crest of the wave reaches a particular location, high tide occurs; low tide corresponds to the lowest part of the wave, or its trough. The difference in height between the high tide and the low tide is called the tidal range. A horizontal movement of water often accompanies the rising and falling of the tide. This is called the tidal current. The incoming tide along the coast and into the bays and estuaries is called a flood current; the outgoing tide is called an ebb current. The strongest flood and ebb currents usually occur before or near the time of the high and low tides. The weakest currents occur between the flood and ebb currents and are called slack tides. In the open ocean tidal currents are relatively weak. Near estuary entrances, narrow straits and inlets, the speed of tidal currents can reach up to several kilometers per hour. The Highest Tides on earth A view of the tides at Halls Harbour on Nova Scotias Bay of Fundy. This is a time lapse of the tidal rise and fall over a period of six and a half hours. During the next six hours of ebb the fishermen unload their boats on the dock. That's a high tide every 12 and 1/2 hours! There are two high tides every 25 hours

There are some extreme cases: the Bay of Fundy, on the east coast of Canada, features the largest well-documented tidal ranges in the world, 16 metres (53 feet), because of the shape of the bay. Southampton in the United Kingdom has a double high tide caused by the flow of water around the Isle of Wight, and Weymouth, Dorset has a double low tide because of the Isle of Portland. Ungava Bay in Nunavut, north eastern Canada, is believed by some experts to have higher tidal ranges than the Bay of Fundy (about 17 metres or 56 feet), but it is free of pack ice for only about four months every year, whereas the Bay of Fundy rarely freezes even in the winter. There are only very slight tides in the Mediterranean Sea and the Baltic Sea due to their narrow connections with the Atlantic Ocean. Extremely small tides also occur for the same reason in the Gulf of Mexico and Sea of Japan. On the southern coast of Australia, because the coast is extremely straight (partly due to the tiny quantities of runoff flowing from rivers), tidal ranges are equally small.

What are the different types of Tides?

When the sun and moon are aligned, there are exceptionally strong gravitational forces, causing very high and very low tides which are called spring tides, though they have nothing to do with the season. When the sun and moon are not aligned, the gravitational forces cancel each other out, and the tides are not as dramatically high and low. These are called neap tides. Spring Tides When the moon is full or new, the gravitational pull of the moon and sun are combined. At these times, the high tides are very high and the low tides are very low. This is known as a spring high tide. Spring tides are especially strong tides (they do not have anything to do with the season Spring). They occur when the Earth, the Sun, and the Moon are in a line. The gravitational forces of the Moon and the Sun both contribute to the tides. Spring tides occur during the full moon and the new moon. Neap Tides During the moons quarter phases the sun and moon work at right angles, causing the bulges to cancel each other. The result is a smaller difference between high and low tides and is known as a neap tide. Neap tides are especially weak tides. They occur when the gravitational forces of the Moon and the Sun are perpendicular to one another (with respect to the Earth). Neap tides occur during quarter moons

Gravity is one major force that creates tides. In 1687, Sir Isaac Newton explained that ocean tides result from the gravitational attraction of the sun and moon on the oceans of the earth. Newton s law of universal gravitation states that the gravitational attraction between two bodies is directly proportional to their masses, and inversely proportional to the square of the distance between the bodies. Therefore, the greater the mass of the objects and the closer they are to each other, the greater the gravitational attraction between them. Tidal forces are based on the gravitational attractive force. With regard to tidal forces on the Earth, the distance between two objects usually is more critical than their masses. Tidal generating forces vary inversely as the cube of the distance from the tide generating object. Gravitational attractive forces only vary inversely to the square of the distance between the objects. The effect of distance on tidal forces is seen in the relationship between the sun, the moon, and the Earths waters. Our sun is 27 million times larger than our moon. Based on its mass, the sun's gravitational attraction to the Earth is more than 177 times greater than that of the moon to the Earth. If tidal forces were based solely on comparative masses, the sun should have a tide-generating force that is 27 million times greater than that of the moon. However, the sun is 390 times further from the Earth than is the moon. Thus, its tide-generating force is reduced by 3903, or about 59 million times less than the moon. Because of these conditions, the suns tide-generating force is about half that of the moon.

Most coastal areas, with some exceptions, experience two high tides and two low tides every lunar day. Almost everyone is familiar with the concept of a 24-hour solar day, which is the time that it takes for a specific site on the Earth to rotate from an exact point under the sun to the same point under the sun. Similarly, a lunar day is the time it takes for a specific site on the Earth to rotate from an exact point under the moon to the same point under the moon. Unlike a solar day, however, a lunar day is 24 hours and 50 minutes. The lunar day is 50 minutes longer than a solar day because the moon revolves around the Earth in the same direction that the Earth rotates around its axis. So, it takes the Earth an extra 50 minutes to catch up to the moon. Because the Earth rotates through two tidal bulges every lunar day, coastal areas experience two high and two low tides every 24 hours and 50 minutes. High tides occur 12 hours and 25 minutes apart. It takes six hours and 12.5 minutes for the water at the shore to go from high to low, or from low to high.


FRESH WATER True tides, changes in water level caused by the gravitational forces of the sun and moon, do occur in a semi-diurnal pattern on the Great Lakes. The investigations of the U.S. Coast and Geodetic Survey indicate that the spring tide, the largest tides caused by the combined forces of the sun and moon, is less than 2 inches (5cm) in height. These minor variations are masked by the greater fluctuations in lake levels produced by wind and barometric pressure changes. Consequently, the Great Lakes are considered to be essentially non-tidal. The moons lunar force is nine million times weaker than the force of Earth's gravity at the Earth's surface. If the Earth's surfaces were completely submerged by an ocean of unvarying depth and if the Earth were to face the Moon at all times, there would be tides two feet high. In addition to rivers, lakes are also affected by the lunar tide action. These are effects usually easier to detail. Lake high tides are opposite the Moon when the Moon is below the horizon. If the Moon is up, the water of the lake follows the Moon around the shore. Low tide goes along the opposing shore. Lake Michigan, for example, has a tidal difference of 1 and 3/4 inches.

What causes tides?

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