What Is the Relationship Between Tides & Weather?

Hurricanes and strong weather can dramatically affect local tide levels.

Tides are caused by the gravitational forces of the moon and the rotation of the Earth. Tide levels can be changed significantly by nearby weather systems, which is apparent during storm surges and hurricanes. High- and low-pressure systems, wind, the rainfall effect and waves can all influence tide levels. Hurricane Katrina in 2005, for example, produced storm surges in excess of 27 feet.

Pressure systems

High-pressure systems cause water levels to lower out in the ocean, leading to sunny weather and lower-than-usual tides. Low-pressure systems cause water levels to rise, leading to cloudy, rainy days with higher-than-usual tides. Each inch of mercury drop in atmospheric pressure results roughly in a 13-inch rise in the water level.

Winds

Onshore winds force water to accumulate on the shoreline, causing a higher water level during low tide. Offshore winds carry water away from the coastline, exaggerating the low tide.

Rainfall effect

Extended amounts of rainfall can overflow into rivers that then dump into the ocean. Water piles up where the rainfall and ocean meet, leading to higher water levels.

Wave effects

Strong waves accompany powerful winds in the open ocean. The waves have considerable effects near the shore. This extra momentum can cause water to reach far up on the beach, especially during high tide.

References

• National Oceanic and Atmospheric Administration: What Affects Tides in Addition to the Sun and Moon?
• National Oceanic and Atmospheric Administration: D. Lee Harris - Characteristics of the Hurricane Storm Surge
• National Weather Service: Hurricane Katrina August 23-31, 2005