...um.

Okay.  Taking into account your giant insulating bubble suit, and that you did let the first primary wave go past you before jumping, and that it's a fucking tidal bore...

Let's call this a DC 15 Swim check, STR-based, unskilled possible, to avoid 1d3 nonlethal damage?  And if you fail by 5 or more, take 1d4 lethal damage instead.  Owing to the insulated suit, you'll only hit the surface rocks every two rounds, rather than getting tumbled into a new underwater impact every round.  Your STR is 10.

If you check that once per two rounds, starting from 87 hit points, it'll last you...

...around 60 rounds = 6 minutes, according to simulation?  During which time you'd travel 6km if you were going an average of 10 m/s, taking into account all the side motion and impacts.

...um.

Okay.  Taking into account your giant insulating bubble suit, and that you did let the first primary wave go past you before jumping, and that it's a fucking tidal bore...

Let's call this a DC 15 Swim check, STR-based, unskilled possible, to avoid 1d3 nonlethal damage?  And if you fail by 5 or more, take 1d4 lethal damage instead.  Owing to the insulated suit, you'll only hit the surface rocks every two rounds, rather than getting tumbled into a new underwater impact every round.  Your STR is 10.

If you check that once per two rounds, starting from 87 hit points, it'd last you...

...around 60 rounds = 6 minutes, according to simulation?  During which time you'd travel 6km if you were going an average of 10 m/s, taking into account all the side motion and impacts.