Azerbaijan National Academy of Science

largest supermoon of 2017 will be felt by Earth, in the sense that it will strongly affect earthly tides in days following May 25.

Astronomers sometimes call the year’s nearest perigee moon a proxigee moon.

How close will this May new moon supermoon be? The 2017 proxigee, or closest perigee, moon will lie 357,207 km (221,958 miles) away. That gives 2017 another first since 2009. It’ll be the first time since 2009 that the centers of the Earth and moon will not come closer than 357,000 km (221,830 miles).

Why do we have no proxigee full moon in 2017? It’s because – like so many things in the heavens – proxigee full moons happen in predictable cycles. They tend to recur in periods of 14 lunar months (413 days, or 14 returns to full moon), which is considerably longer than one calendar year. The last proxigee full moon came late in the year in 2016. Thus there’s no proxigee full moon in 2017, and the following proxigee full moon will arrive in early 2018.

http://earthsky.org/astronomy-essentials/no-proxigee-full-moon-in-2017