Tom Brady's supermodel wife is down in Costa Rica for their family's off-season getaway ... and she decided to splash around and strike a few fun poses for a photog.

Gisele's looking every bit like the Brazilian bombshell who became the world's highest-paid model -- rocking her chocolate bikini top and animal print bottoms, and showing off her legs and perfectly toned abs. Yes, she's officially retired from modeling, but ... c'mon.

There's plenty of uncertainty about Tom these days -- no one knows where he's gonna play for the upcoming NFL season, after 20 years with the New England Patriots.