Tuesday, August 25, 2015

Special Report: What the heck is a perigean spring tide?

(corrected text, because I was informed I didn't know what month it was!  Thanks, Pat.)

They dropped this term on The Weather Channel this morning.  Dang, we had to look that up!  The moon has something to do with the tides, right?  (Go ahead.  Look it up.  I'll wait.)  During the full moon (twice a month), the tidal range is greater (or high tide is higher and low tide is lower)--that's called spring tide.

When the moon is closest to the earth, it is called a lunar perigee.  The gravitational pull of the moon is the strongest.

Three to four times a year, the lunar perigee and full moon coincide.  This is the perigean spring tide (or unofficially, the supermoon or "king tide" in New Zealand) and can affect tides up to 20 percent (usually just a few inches).  Apparently, we experienced this once in Annapolis--when it's perigean spring tide, wind blows onshore from the bay and it storms (barometric pressure drop), they get flooding downtown.  

If you're still reading this, the next perigean spring tide in August 29th (this Sat), and it coincides with the possible arrival of Hurricane Erika on the Atlantic coast.  Yikes.  The Weather Channel specifically mentioned Charleston.

Here's more info:

Don't get me started on neap tides and apogees.


  1. Thanks, Professor Bonnie. Can I buy you an apple?

    Currently in Nova Scotia on a particularly hot day. Stay well!