PORTLAND, Ore. (KOIN) — The last king tides of the season are forecast to periodically flood the Pacific Northwest’s low-lying shores between Jan. 20 and Jan. 22.

During a king tide, water levels can be half-a-foot or more above the highest daily tide average. KOIN 6 News Meteorologist Kelley Bayern reports that, at times, the tides will swell by more than 9 feet this weekend. Large 15- to-18-foot waves will also be possible in Northwest Oregon and Southwest Washington.

“Large waves plus high tides will cause hazardous conditions for beachgoers,” Bayern said.

Per the U.S. Environmental Protection Agency and the National Oceanic and Atmospheric Administration, king tides occur when the alignment of the sun and moon pull on Earth’s oceans, causing tides to swell. This astronomical alignment happens one to two times per year.

The sun and moon align to pull on earth’s oceans, causing king tides, also known as spring tides. (National Oceanic and Atmospheric Administration)

Western regions with the highest risk of coastal flooding include Friday Harbor, Port Angeles, Toke Point, South Beach and Humboldt Bay, Calif. Although hazardous, scientists say that king tides are also useful because they provide information on how the Earth’s rising sea levels will one day affect global shorelines.