Summer arrives on June 21 and it doesn't end till the first day of autumn which is September 22. Summer does not end on Labor Day and it doesn't begin on May 26 or any day close to that.
Of course, Memorial Day is simply Memorial Day -- a day to remember our fallen heroes. And Memorial Day is May 30. For many years this day was known as Decoration Day. That term was coined to remind us to decorate the graves of those who died in service to our nation and all others that we wanted to remember. But hardly anybody seems to visit graves anymore so you never hear about Decoration Day these days.
Weather-wise, May is not a very reliable month. This year in these parts May has been unseasonably cool, damp, windy and rainy. So, don't expect the "unofficial start of summer" to be hot and sunny. It ain't July yet. Get it?