However, above average temperatures could be expected north of Taupo.
Although Southland and Otago could expect a drier month, the cool weather would remain, said Ms Griffiths.
August got off to a wet start for the west and far south of the South Island, and the western and central North Island, said Ms Griffiths.
"The second half of the month saw higher pressures over the South Island, with mostly dry conditions seen there," she said.
Heavy rain hit the northeast of the North Island towards the end of August, and caused flash flooding near Rotorua and also around KeriKeri and Kaeo.
She said more cold weather was expected for the end of August, with rain forecast for eastern parts of Northland, Auckland, Coromandel and Bay of Plenty over the weekend.
Compared to the average September:
Auckland: Warmer and wetter
Hamilton: Wetter, near average temperatures
Tauranga: Warmer and wetter
Wellington: Cooler, a little wetter
Christchurch: Cooler
Dunedin: Cooler and drier