MetService is warning people in the upper North Island to wrap up for some below average temperatures this week.

It said rain was expected to hit to the west coast of both islands today, however a high pressure system would build from Tuesday.

That is expected to bring frosty conditions.

MetService forecaster Kyle Lee said to prepare for bitter temperatures.

He said Coromandel would drop to below average temperatures.

"Coromandel is one place where they're usually about seven degrees or eight degrees for their minimum and they're going down to like one or two degrees on Wednesday morning."

Mr Lee warned our biggest populated city to put on an extra layer.

"Aucklanders will feel it because they're around about five degrees below their average - so places that aren't used to the cold are definitely going to feel it."