It may be November ... but it's 74 degrees in Honolulu -- so Alexis Ren decided to put on her tiniest bikini and hit the beach.
The "Queen of Instagram" (she's got more than 11 MILLION followers) was climbing all over some volcanic rocks ... and still managed to be the hottest thing on the island.
By the way, Ren is a 2018 Sports Illustrated Swimsuit Edition rookie ... and judging by the behind the scenes footage from her debut S.I. shoot -- she's gonna have a future in this biz.