Temperatures in some parts of Hawke's Bay are expected to reach 27C today.
But they are predicted to slump to 17C on Monday, with what is likely to be a fleeting nip in the air, according to the weather scientists.
Because of a cool southerly headed Hawke's Bay's way, Guy Fawke's Night is likely to be a rare fizzer in what the National Climate Centre is predicting to be a bright start to summer. In its seasonal climate outlook released this week, the regional predictions show a normal to dry summer between November and January, with average to above-average temperatures along the North Island's eastern areas.
Rainfall is expected to be average to below average, with soil moisture and river levels forecast to be below normal.
The driving weather forces behind the promising start to summer are warmer than normal sea surface temperatures in the west and central tropical Pacific.
A Niwa spokesperson said while the indicators showed conditions were on the threshold of an El Nino system, the atmosphere had yet to show any significant response to the warmer seas.
"The global forecast models indicate an approximately 50/50 chance of neutral versus weak El Nino conditions over the next three months."
El Nino conditions generally lead to eastern regions being drier than normal, due to prevailing westerly air systems.
The extended forecast for the Bay through to next Friday is for a fine start to the weekend but rain developing on Sunday and sticking around until late Tuesday. Fine weather is set to return on Wednesday.