The Bay of Islands Beast participants will have natural obstacles and extra mud to navigate through thanks to the wet weather - but the rain is set to ease just in time for tomorrow's race.

While yesterday's weather was wet, MetService meteorologist Peter Little said by the weekend the rain would ease with a few showers across Northland tomorrow.

Azelia Parkinson, Bay of Islands Beast event team leader, had been setting up the 7km course yesterday and said it was looking "awesome".

"There's lots of natural obstacles and swamps and lots of mud in certain places," she added.

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Mr Little said participants might need to ensure they were wearing appropriate gear as cold south-easterly winds are expected this weekend.

"It will be quite cool so the main thing is to wrap up," he said.

On the east coast there would be large waves so anyone who was considering going out on the boat needed to be "well aware" of the conditions.

In Dargaville the expected high is 15C tomorrow and Sunday, 16C both days for Kaitaia, 15C for Kerikeri and in Whangarei the expected high is 16C tomorrow and 15C on Sunday.

Mr Snell said the lows for the weekend would be about 10C but towns on the east coast would be a bit colder.