Pokémon GO players will have the opportunity to unlock a unique Moltres Day on September 8th, 2018 if they complete Professor Willow’s Global Challenge for September 1st, 2018 and September 2nd, 2018 which ties into the Safari Zone event in Yokosuka, Japan.

The Global Challenge requirements for this weekends event are:
GO Fest - Complete 100,000 Research Tasks
Europe - Complete 5,000,000 Research Tasks
Americas - Complete 5,000,000 Research Tasks
Asia Pacific - Complete 5,000,000 Research Tasks

Unlock Moltres Day during Professor Willow’s Global Challenge!

Trainers, The final challenge is here! It’s time to come together and work on the last round of Professor Willow’s Global Challenge, happening on September 1 and 2 during the Safari Zone event in Yokosuka, Japan. If certain areas of the world can meet the challenge requirements,they’ll unlock bonus Stardust for catching Pokémon and hatching Eggs—including a guaranteed 3,000 Stardust for every raid—starting September 3 at 1:00 P.M. PDT. Also, until September 10 at 1:00 P.M. PDT, Trainers can unlock a bonus to earn Star Pieces that will last for one hour!

If the challenge is completed, Trainers worldwide will receive up to five free Raid Passes for Moltres Day, which features the Legendary Pokémon Moltres! On September 8, Moltres will be available in Raid Battles around the world for a three-hour period and will know the Flying-type move Sky Attack. If you’re lucky, you may be able to encounter a Shiny Moltres!

So, get ready to GO! See you out in the field, Trainers!

Source: https://pokemongolive.com/en/post/moltresday2018sep/