[Aegypticus]

The same guys that leaked the water event have shown an image of what they say is the next event. It's all in Spanish, but here's the English translation:

Trainers,

With summer quickly approaching in the Northern Hemisphere and winter approaching in the Southern Hemisphere, we couldn’t think of a better way to celebrate the upcoming solstices than with a Fire-type and Ice-type Pokémon GO event.

From 1:00 P.M. PDT on June 13 to 1:00 P.M. PDT on June 20, 2017, Trainers around the world will discover more Charmander, Cyndaquil, Growlithe, Houndour, Ponyta, Swinub, Vulpix, and their Evolutions. You’ll also want to keep an eye out for Sneasel, Magmar, Cloyster, and other Fire types and Ice types!

It’s time to perfect your Poké Ball throws, Trainers! Throughout the event, you’ll receive huge XP bonuses for successfully catching Pokémon with Nice, Great, and Excellent Throws, as well as Curveballs and First Throws. Additionally, as you walk around your neighborhoods or discover new sights, you’ll earn even more XP for hatching Eggs. To help you take advantage of these awesome XP bonuses, Lucky Eggs will be 50% off in the in-game shop.

Get ready to explore the world around you—there are even more exciting updates coming your way soon!

—The Pokémon GO team