The ridge is expected to spread on to central New Zealand on Wednesday, then remain slow-moving east of New Zealand during Thursday and Friday.
But according to MetService modelling, rain or showers are forecast for most of the places marking Auckland Anniversary Weekend.
"Although it's quite possible that could change - people should keep checking the MetService website as we get closer to the weekend."
WeatherWatch forecaster Philip Duncan said although the picture for the long weekend appeared "messy", people should not be putting off outdoor plans.
"It's a very tricky forecast to completely lock in, but it does look as though there's a chance of rain on Sunday. We are seeing more drier than wet weather for the long weekend - especially if you are south of Auckland."
The weather has pushed soil conditions in many parts of the country to extreme levels of dryness, according to the latest Niwa data.
Anniversary Weekend forecast
Auckland:
Saturday to Monday: showers with northeasterlies, daily highs 24C.
Whangarei:
Saturday and Sunday, showers with northeasterlies, daily highs 24C, Monday, showers with little wind and 26C high.
Tauranga:
Saturday, showers with northeasterlies, 25C high. Sunday to Monday, showers with light winds, high 26C.
Hamilton:
Saturday, showers with little wind, 27C high. Sunday to Monday, showers with little or light wind, highs 28C and 27C respectively.
Extended forecast based on modelling and may improve later this week. Source: MetService
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