It appears that Community Day events in Pokemon GO are quite successful worldwide, as Niantic are announcing the next event days after the May event concluded. The event will take place on Saturday, 16 June 2018 and will feature Larvitar.
As per usual, Larvitar spawns will be increased for the duration of Community Day and players will likely have to evolve him into a Tyranitar before the event expires if they want to unlock the exclusive power. On that note, Niantic haven't actually confirmed what that power will be yet as they normally reveal it just before the event happens.
Triple experience for catching Larvitar and three hour lure duration will be present on June 2018 Community Day as well. There is just something about number three with Niantic and Pokemon GO, as on top of triple experience and three hour lures, the event itself lasts for three hours.
North American players will have the event from 11:00 to 14:00 PDT or 14:00 to 17:00 EST, European and African players can have a go at it from 10:00 to 13:00 CET and Asian players can go on Larvitar catching spree from 12:00 to 15:00 on Saturday, 16 June 2018.
After the June Community Day, European players will have two weeks until the large scale Safari Zone event kicks off in Dortmund, as a part of Pokemon GO Summer Tour 2018. American players will have a bigger pause in between, and even one more Community Day before Pokemon GO Fest happens in July 2018. The venue will be Lincoln Park in Chicago, with the name of the event being a play on words, since it's called "A Walk in the Park".
This is all still a fairly distant future though, but players will be able to fill their days in with catching the new Alolan forms of Gen 1 Pokemon, which should be coming up soon, as well as fighting the Raid Battles with the limited time Ho-Oh Pokemon in case they needed another fire-type monster.