Dwyane Wade -- The Heat Is ON ... Wedding Will Be a Scorcher ... Save the Date

Dwyane Wade's wedding guests better pack flip flops -- TMZ Sports has learned, his upcoming nuptials to fiancee Gabrielle Union will take place on the surface of the sun ... aka Miami in August ... and we have the Save the Date.

The wedding is scheduled for August 30th -- and the Save the Dates just went out.

Dwyane's kids even make a cameo in the heart-shaped reminders, holding up signs that say, "Nickie, will you marry us?" (Nickie is Gabrielle's nickname ... her middle name is Monique.)

If all goes well, Dwyane will get more than one ring this year.