The Pokémon Company has announced the initial details for Pikachu Outbreak! 2019 which will take place from August 6th, 2019 until August 12th, 2019 in the Yokohama Minato Mirai area. The official translations follow:

Pikachu Outbreak! 2019:

There's going to be another Pikachu Outbreak this year in the Yokohama Minato Mirai area! A performance from Pikachu set against the Minato Mirai nightscape, boosted by technology!

Have a blast with over 2,000 Pikachu, our highest number of Pikachu ever!

What's more, we'll be hosting a ticketed Pokémon GO event “Pokémon GO Fest in Yokohama”(ticket raffle through advance application)!

Details will be announced at a later date!

Title: Pikachu Outbreak! 2019
Event Period: Tuesday, August 6 to Monday, August 12, 2019
Event Location: Minato Mirai area of Yokohama
Participation Fee: Free of Charge. Some content requires an admission ticket. Details will be announced at a later date.
Area stations:

• JR Sakuragicho Station
• Minato Mirai Station on the Minato Mirai Line
• Bashamichi Station on the Minato Mirai Line
• Nihon-Odori Station on the Minato Mirai Line

Source: https://www.pokemon.co.jp/ex/pika_event/en/