It should be fine as long as you're in the water, plus you can always opt to push the hood back and not use it. You might roast while out of the water during the transfers by tender to dive sites though...worse on the way to dive sites than coming back to the liveaboard, but you can peel it down to your waist to get the breeze of tender movement. Darwin is a warmer site than everywhere else, however, so much of the dive is stationary and you can get cooler when you're still so it evens out. Feb and March are the two warmest months of the year so topside will be quite warm and sometimes, there is no breeze in Feb. Equatorial sun in a high temp with no breeze and humidity is hot. When you dive Cabo Marshal, Cousins, and Wolf, a 7mm is pretty much appropriate year round due to thermoclines. Surface water temps average 76-78 F.
