How Low Does It Go?

Look at this remarkably low tide we had back on December 20th.  Those exposed sand flats are where summer guests happily paddle in a couple feet of water. Why was the tide so low in Rhode Island on the 20th?  There were a number of factors.


  • The greatest influence on the tides is the moon. On December 21st the moon was at perigee, the point in the moon’s orbit when it is closest to Earth – on this day, a mere 227,000 miles away. The perigee also corresponded with a waxing Gibbous moon that was about 80% illuminated or, in other words, getting close to full.


  • The orbit of Earth around the sun is also elliptical and, believe it or not, Earth is closest to the sun in early January. This is called the perihelion. 


From an astronomical standpoint, we were approaching the full moon (which produces more extreme tides), and the sun and the moon were at, or near, their closest point to Earth. Combine these factors and the gravitational effects on the tides were notably stronger.


But wait, there’s more! You can see from the picture that it was a beautiful, clear day – a byproduct of a high-pressure system sitting over us. High atmospheric pressure can actually push down on the water and squeeze it out towards the sea. Furthermore, the strong and sustained northwest winds that ushered in the high pressure also worked to push water off shore during the falling tide and hinder its return on the rising tide. 


Put these factors all together and you get an exceptionally low tide… and a striking photo.