Proxigean

Friday, 29 January 2010
Proxigean Tides
Dept of Learning Something Every Day:
I'd never heard of proxigean tides despite a lifelong love of long words, so it was delightful to come across the term at Frogma today. We are due for some over the weekend, with a height of 5.2m in Chichester Harbour on Tuesday, so it's floodboards and sandbags out, chaps.
A proxigean tide is an extreme spring tide that happens when the moon passes through a perigee, bringing it closest to the earth (about 365,500km, compared with the apogee at 406,700km). Perigees only coincide with springs every one and a half years or so, as you can see at AstronomyCafe.
Every 31 years the perigee is at its absolute minimum and coincides with a new moon, which means it is lined up with the sun for the maximum gravitational pull, and extreme proxigean tides occur. These can be very damaging. Luckily, one isn't due until 2026 apparently.

Thank you Chris ! and the Chepstow reporter (near me).