A slow-moving front may bring heavy rain to the West Coast of the South Island from Sunday evening through to Monday morning, while a trough brings areas of heavy rain to the upper North Island with thunderstorms and localised downpours possible.
Meanwhile this weekend has seen some very high temperatures including some breaking 30C - it was 31C in Kawerau at midday Sunday, according to MetService.
But for Monday, MetService have issued heavy rain watches for Northland, Auckland, Great Barrier Island and Coromandel Peninsula from 3am, and the Bay of Plenty and Rotorua from 6am, until 6pm Monday.
Heavy rain watches are also issued for the Grey District and Paparoa Range from 6pm on Sunday through to 8am on Monday.
MetService warns there is high uncertainty over where the largest rain accumulations will be.
All watches have a moderate change of upgrading to a warning.