Marine Rescue NSW has urged those planning to take a vessel out on Sunday to check forecasts and sea conditions, and to take precautions as the change moves up the NSW coast.

The strong southerly change is predicted to move through south coastal waters in the morning, reaching the Hunter by late afternoon, into the early evening.

Marine Rescue NSW Commissioner Stacey Tannos said heatwave conditions along the coast over the weekend were expected to attract many boaters to the coast seeking relief from the oppressive conditions.

"Marine Rescue volunteers are frequently called to help boaters who find themselves in serious trouble after misjudging weather and sea conditions and not heeding weather warnings," he said.

"It's vital that you check weather and sea conditions before heading out and regularly throughout the day as conditions may change quickly.

"You can also call your local Marine Rescue base on VHF Channel 16 at any time for an update on current and forecast weather and sea conditions."

Commissioner Tannos said it was important for boaters to understand the limits of their vessel for the forecast conditions and to follow the simple advice: if in doubt, don't go out.

"We urge anyone heading out on the water to Log On with Marine Rescue NSW as they head out on VHF Channel 16 or the free MarineRescue App so our volunteers can keep watch. If you're not back safely as planned, we'll start to search for you.

"It's also vital to make sure everyone on board is wearing a lifejacket."

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