October supermoon reinforces royal effect on coastal waters, ushering in minor King Tides

October’s full moon — the biggest, brightest and closest of four consecutive supermoons in 2024 — is having a royal effect on waters along Hawai‘i shores this weekend, ushering in minor King Tides throughout the islands.

The National Weather Service forecast office in Honolulu issued a coastal flood statement, saying peak monthly high tides will cause isolated minor flooding from late tonight through Sunday morning along island shorelines and in low-lying coastal areas.

Coastal flooding is expected around daily peak tide times on all isalands, which will occur in the early morning hours.

Click here for tide times in specific locations.

Areas that are most vulnerable include low-lying coastal roadways, docks, boat ramps and other coastal infrastructure.

The public is advised to:

• Avoid driving through flooded roadways. If you are forced to drive through salt water, be sure to rinse your vehicle with fresh water.
• Move electronics, vehicles or other valuables to higher ground.
• Monitor vessels to ensure mooring lines don’t get too tight.
• Watch out for overwash around boat ramps.
• Secure canoes or other watercraft stowed on beaches.

The higher than usual high tides could cause flooding of beaches that are normally dry, minor coastal erosion and saltwater inundation of the most vulnerable areas mentioned above.

King Tides is the non-scientific term often used to describe exceptionally high tides. They typically happen during a full or new moon, when it, the Earth and sun align.

Because of its eliptical orbit around the planet, when the moon is at its closest to Earth, it exerts a stronger tidal force on the planet.

During a full or new moon when it is at its closest to the planet, such as the case with this month’s supermoon, there’s an added kick, reinforcing the tidal forces of the moon and sun, resulting in higher high tides and lower low tides and causing the King Tides.

Those who get photos of the expected King Tides or coastal flooding are encouraged to submit them online to the University of Hawai‘i Sea Grant College Program’s Hawaii and Pacific Islands King Tides Project.

Big Island Now news reporter Nathan Christophel contributed to this report.