Extreme Tides on May 26, 2009

Extreme tide levels in the nearshore waters around Puerto Rico were reported yesterday, May 26. The event was most notable along the southern coastline of the island and during low tide in the afternoon. The CaRA-CarICOOS offices received reports of extremely low tides from Parguera to Humacao. Fear arose when many confused these extreme tide events with the initial phases of a tsunami.

What happened yesterday?

Certainly it was not a tsunami. What happened was the occurrence of the lunar perigee in approximate synchronization with the New Moon. One or more New Moon or Full Moon events happen every month and each of these is called a plenilunium. Surface tides typically show maximum monthly amplitudes during plenilunium events. New Moon was on May 24th.

The distance between the Moon and Earth also partly determines the amplitude of tides; the closer the Moon is to the Earth (called lunar perigee) the larger the tidal amplitude will be. Yesterday's event corresponded to May's lunar perigee which roughly coincided with the New Moon (New Moon was 1 day and 15 hours before the perigee) thus generating the large amplitude tides. This is not an abnormal event as they occur at least twice a year.

Be on the lookout during June 23, July 21 and August 19 for similar tide levels will be occurring. July 21st's event should be the most extreme since the Earth-Moon distance will be at it's minimum during the year, the synchronization between the perigee and a New Moon event is almost exact, and the date is close to the summer solstice.

If you are close to the sea and observe a similar event where the sea floor becomes exposed in a extreme way and you are not sure as to what might be causing it, seek higher ground and stay on watch for news bulletins regarding the event!

For more information information on this event and other tide information visit the tides section and the Lunar Calculator here on CarICOOS.org