Heavy rain and thunderstorms are predicted in parts of Northland later today and for most of this weekend as another low approaches the upper North Island.
The low is expected to track east, with the rain bands slowly spreading to the central parts of the North Island today.
"This rain will be a real concern for many, due to the ground being already saturated after this past weekend," MetService meteorologist Elke Louw said.
Eastern parts of Northland may experience localised downpours with rain of 25-35mm per hour, Ms Louw said.
She said rainfall of this intensity can cause flash flooding, especially around low-lying areas such as streams, rivers or valleys, and may also lead to slips.
Driving conditions will also be hazardous with surface flooding and poor visibility. There is a chance of small tornadoes, especially near eastern coasts.
The weather warning followed the release by the National Institute of Water and Atmospheric Research (Niwa) of the three-monthly weather outlook from September to November.
The outlook predicts temperature, rainfall, soil moisture and river flows in Northland and in all North Island regions are likely to be near or above average.
Cold snaps and frosts can still be expected in some parts of the country as we advance into spring.
Near or above average rainfall equates to between 100mm and 110mm while temperatures will hover in the higher teens.
Kerikeri was the wettest throughout the country yesterday afternoon at 11.4mm while Whangarei Airport recorded the sixth highest maximum temperature of 16.6C.
Northland had its second-wettest winter on record this year. This June to August was the second-wettest winter since records began for Whangarei in 1937, with about 840mm of rainfall recorded. The wettest was 1946, in which 1050mm fell between June and August.