Air flow travelling in from the sea hasn't had a chance to dry out or heat up,
meaning wet weather was likely.
''If the winds were westerly, we probably wouldn't have that same outcome.''
Mr Brandolino said the Bay of Plenty was typically a sunny region because it usually had westerly winds.
Mr Brandolino said the forecast was an overall estimate and while rain was likely to be near or above normal for that time of year, it didn't mean the Bay would be without sunshine.
''But you're unlikely to get a really dry weather pattern.''
Sea temperatures were also expected to be on the up.
MetService meteorologist Georgina Griffiths said seas to the north of the country were expected to remain warm.
"North of Taupo, you may expect more of a La Nina-like flavour, which would include some sub-tropical rain at times, long dry spells in between, and warmer, more humid, conditions. "So we may see quite a different season this year compared to last year and the year before.''
Ms Griffiths said people already planning Christmas camping holidays shouldn't panic.
"A climate forecast isn't particularly helpful from an 'am I going to get wet in my tent' point of view," she said.
"As always, you are just going to have to listen to the actual weather forecast across the core two-week holiday period."
The week ahead:
Today - Cloudy 20C high
Thursday - Cloudy, late showers 20C high
Friday - Showers 19C high
Saturday - Becoming fine 19C
Sunday - Fine 19C