International Surfing Day is the third Saturday of June, which in 2019 was on June 15. However I could find no other suitable international holiday on the date. It is International Refugee Day, but I’m saving that for my next title, 365 Atrocities a Year.
International Surfing Day is an unofficial, environmentally conscious, sports-centered holiday that celebrates the sport of surfing and the sustainability of ocean resources. One of the biggest venues is Huntington Beach, the self-proclaimed Surf City, USA. Activities include beach clean-up, competitions, and a half marathon.
Surfrider.org is a volunteer, activist organization dedicated to protecting coastlines. International Surfing Day accessories can be purchased at their website. The 2019 Theme is Protect & Enjoy.

Huntington Beach, California, USA.