They will occur on E3 Day -2.
Nintendo held the US finals for their Smash and Splatoon 2 tournaments today, and the champions will be advancing to pre-E3 weekend.
The 2019 World Championships for Splatoon 2 and Super Smash Bros Ultimate will be held in Los Angeles on June 8. The US champions will face teams from Europe, Australia and Japan in 4v4 Splatoon 2 and 3v3 Squad Strike play for Super Smash Bros Ultimate.
Mark the date everyone, the #SmashBrosUltimate and #Splatoon2 World Championships will take place on 6/8! Our #NintendoNAO19 Champions will be representing the US in all the action. Stay tuned for more info in the future. pic.twitter.com/o6zLbHlsaq
— Nintendo Versus (@NintendoVS) March 30, 2019
Tournaments for Splatoon 2 and Smash Ultimate were held last year around E3, with the Splatoon 2 tournament on Monday and the first Smash Ultimate tournament ever on Tuesday.