Downpours and gales are expected for the upper North Island later this week

MetService has issued a heavy rain watch for Northland, Auckland, Great Barrier Island and the Coromandel Peninsula from 6am Wednesday until Friday.

It's also put out a strong wind watch - with gales expected to threaten powerlines, trees and unsecured structures.

Metereologist Lewis Ferris says there's a chance it could be worse than expected.

He says it looks like there could be more watches issued - which could be upgraded to warnings.