Nintendo finally announced that Splatoon 3 has a planned launch window of Summer 2022, but one of four seasons doesn't really narrow it down all that much. The main focus of the recent Splatoon 3 gameplay trailer was showing new enemies and bosses for players to fight in the next iteration of the Salmon Run co-op mode, but just an indication of when the game is planned to come out will likely grab more attention. Nintendo has only provided the broad "Summer 2022" release window, though, which is probably purposefully unspecific so that the final stretch of development has some leeway.
Although seasons are usually associated with their distinct weather, there is a defined, astronomical measurement for the beginning of summer. In the Northern Hemisphere, the Summer solstice - the longest day of the year - falls on June 21, 2022, coinciding with the beginning of summer. Summer officially ends on September 22, 2022, when day and night are the same length during the Autumnal equinox. This gives Splatoon 3 exactly three months to hit its Summer 2022 release window.
Splatoon 3's release window was revealed during the February 2022 Nintendo Direct, and while the new gameplay looks rather polished, Nintendo seems keen on waiting for a more specific release date until the game is ready. For the Splatoon series historically, this release window at least tracks, though the previous games really have no bearing on the third's launch. The first game released in May of 2015 (late Spring), and the sequel dropped in July 2017. Those really wanting to speculate might put stock in the fact that the Direct was focused primarily on games releasing in the first half of 2022, which could put Splatoon 3's release date before July 2, but there's no corroborating evidence for this assumption.
There was a quick turnaround between the original game and the sequel, but it's now been five years since Splatoon 2 released (or four counting from the Octo Expansion). Splatoon 2 had a very good launch, but picked up even more steam during its lifetime, and was even being listed fifth in a recent poll of Japan's best games of all time, with Zelda: Breath of the Wild in the top spot. The series seems to be bigger in Japan than the West, but that's quite the honor for a comparatively recent series. Splatoon has gained a lot of notoriety with only two releases, becoming a Nintendo mainstay franchise, and the excitement for 3 seems to be building quite well.
Nintendo already has quite the Switch release slate for Summer 2022, including Fire Emblem Warriors: Three Hopes, Mario Strikers Battle League, the port of No Man's Sky, a long-awaited localization for Live A Live, and potentially Xenoblade Chronicles 3. Splatoon has sort of become Nintendo's primary shooter series, though, and a Summer release for the third entry gives it some space from the annual holiday shooter releases. There's still no exact date for Splatoon 3's release, but the Summer 2022 window at least narrows down how long the wait will be.
