The sweltering heat has northern Coastguard volunteers on alert for a jump in calls this Auckland Anniversary Weekend.

The hot weather over the three-day weekend means tens of thousands of boaties are expected out on the water.

Coastguard operations manager Ray Burge said Auckland Anniversary is generally one of their busiest weekends, with Monday the most frantic of them all.

"There will be a lot of boats out there just keep a sharp lookout, just stick to the basics, you know the whole thing that we talk about tried and true, don't just take your life jackets wear them, wearing a life jacket never ruined a day on the water."

And with a heatwave coinciding with Auckland's Anniversary holiday, operations manager Ray Burge said weather forecasts and basic prep are even more important than usual.

"Probably something a little bit different for us is actually what that weather means for a lot of boaties out there, especially in the smaller boats the big thing at the moment is keep hydrated and keep plenty of sunscreen on, which is not the thing that we usually talk about, we usually warn about bad weather."

Burge said two forms of waterproof communication are also crucial.