Returning Raid Event
On August 16th, 2019, Niantic announced that they will be hosting the return of the Water Festival from August 23rd to 30th. During the middle of the event on August 28th, the Legendary Raid Hour would be returning with a special trio of legendaries: Azelf, Mesprit, and Uxie, the Lake Trio Pokemon.
These Lake Trio Pokemon are the only regional legendaries in the game, and they will be keeping their regional status during the event. During the 6 PM to 7 PM scheduled raid hour:
- Azelf will spawn in the Americas and Greenland
- Mesprit will spawn in Europe, the Middle East, and Africa
- Uxie will spawn in Asia, Australia, and New Zealand
Trainers will find their respective Lake Trio regional in every gym as a raid available starting from 6 PM today.
The Legendary Raid Hour has been going on for almost 6 months now, with the first one happening March 13th of this year. That event was set for 12 PM to 1 PM and was dubbed the "Legendary Lunch Hour". The timing of the event proved difficult for many players who only have exactly an hour or less during their midday meal break.
The change from 12 PM to 6 PM happened in late April and early May.
None of the three bosses are particularly meta-relevant to Pokemon GO; Azelf is a decent Psychic-type attacker, and Uxie has some utility in PvP. You can find the meta-analyses for these Pokemon at the link below.