Fedaeff said Niwa was watching for the potential development of a La Nina weather pattern as ocean and atmospheric conditions in the Pacific Ocean trended toward that for the second consecutive year.
La Nina would bring warmer than average air and sea temperatures to New Zealand, and rainy conditions to northeastern areas of the North Island.
In its seasonal climate summary released on Friday, Niwa reported temperatures were 0.5C to 1.2C above average across most of New Zealand this winter with Bay of Plenty temperatures at the lower end of that scale.
Rainfall was 80 to 119 per cent of normal.
Record or near-record mean air temperatures for winter were recorded around the country including Taupō with a mean of 9C (its second-highest), Whakatāne with a mean of 11C (its fourth-highest) and Tauranga with a mean of 11.7C (its third-highest).
Rotorua and Taupō recorded their second-highest mean maximum air temperatures for winter on record - 13.6C and 13.7C respectively.
Rotorua also recorded its fourth-highest daily maximum air temperature for winter on August 28, reaching 18.4C.
The previous month it logged near-record low daily maximum temperatures in part due to low cloud leading to a lack of sunshine and low daytime temperatures.
Looking ahead to spring, Niwa forecaster Ben Noll said in a video analysing national climate trends, the first week of September would be warm but the second week could bring "brief periods of unsettled weather" with wind, rain and cooler temperatures.
Mid-September may bring warmer temperatures and dry weather again.
New Zealand's coastal sea surface temperatures ranged from 0.6C to 1.1C above average during August and are predicted to become more unusually warm by November.
Metservice made similar predictions and was forecasting "unsettled conditions" for the start of September followed by rain and lower temperatures then settled weather by mid-month.
Meteorologist David Miller said the Bay of Plenty could expect near-normal rainfall and average or slightly above average temperatures.
"It's looking like high pressure is mostly in charge. Next week is looking a little more unsettled and is the exception to the mostly settled outlook for September."
The forecast, as of Sunday
Tauranga
Monday: Cloudy periods, odd shower. Northeasterlies. High of 16C, low of 12C.
Tuesday: Rain developing, possibly heavy. Strong northerlies. High of 16C, low of 9C.
Wednesday: Scattered showers. Strong southwesterlies. High of 15C, low of 7C.
Rotorua
Monday: Cloudy periods and the odd shower. Northeasterlies. High of 13C, low of 8C.
Tuesday: Rain developing, possibly heavy. Strong northerlies. High of 14C, low of 7C.
Wednesday: Scattered showers. Strong southwesterlies. High of 13C, low of 3C.
- Source: Metservice
