Brandolino said Niwa was keeping an eye on the potential development of a La Niña weather pattern, which could potentially bring high humidity and warmer temperatures to the region.
"There's likely going to be increased chances for more humidity.
"People could be running fans and air cons a bit more than usual and people may be going to the beach a bit more. It's going to be warm for October's standards and a bit of a humid week."
However, that did not mean there wouldn't be a "chilly day or two".
"We're expecting variability."
Meanwhile, a heavy rain watch was in place for the eastern ranges of the Bay of Plenty.
Rainfall amounts may reach "warning criteria" between 8am and 6pm tomorrow as a trough is forecast to move southeast across central and northern New Zealand.
According to MetService's national monthly outlook, spring had done its thing during the first two weeks of September.
A spokesman said the spring weather so far could not have been more contrasting.
"This is typical of spring weather but that doesn't make deciding when to put the winter woollens away any easier."
The outlook for October also included "classic indecisive spring weather".
"High pressure brings a fine and settled weekend with chilly mornings across the country to get October under way, but things don't stay that way for long.
"An area of low pressure becomes slow-moving in the southern Tasman Sea pushing warm, humid northwesterlies and repeated bouts of rain across the country through the first full week of the month.
"This likely leads to a wet week for most places, especially those exposed to the northerlies."
The bottom line for spring is low pressure dominates the first half of the month with warmer and wetter than average conditions, but, things calm down as high pressure moves in for the second half of October.
A MetService spokesman said it was set to be a wet start to the first week of the school holidays.
"It's going to be a bit showery ... but keep an eye on the skies as it shouldn't be too bad."
The spokesman said it was going to be an "unsettled" week ahead but the weather was expected to start to clear up on Friday.
However, he said Tauranga's temperatures would be "mild" and "slightly above average" for this time of year shifting between 19 and 21 degrees.
It was set to be a bit cooler in Rotorua with temperatures between 17 and 19 degrees forecast for the week ahead, he said.
The forecast, as of Sunday
Tauranga
Monday: Heavy rain, possibly thunder, changing northeasterlies. High of 19C, low of 12C.
Tuesday: Few showers, mainly afternoon, westerlies dying out. High of 20C, low of 13C.
Wednesday: Often cloudy, few showers, northerly breezes. High of 19C, low of 14C.
Rotorua
Monday: Heavy rain, possibly thunder, northeasterlies. High of 17C, low of 10C.
Tuesday: Early cloud, fine spells, few showers, light winds. High of 19C, low of 10C.
Wednesday: Cloudy, chance of showers, northerly breezes. High of 19C, low of 12C.
Source: MetService
