Hank49
Contributor
We were at Turneffe Flats at the end of September. Water temp was a consistent 29 Celsius. Both of us were comfortable in full 3mm suits, but I would consider bringing a hood/hoodie if I were you.
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Sept has the warmest water of the year here. Even I only wear a hooded vest while free diving for 4-5 hours. But in Dec Jan through March, I'm in a full 3.5 mm suit with a 2 mm hooded vest underneath.