It's likely to be a wet Waitangi Weekend in Northland with the possibility of heavy rainfall in parts today.

The MetService said a deepening low over the north Tasman Sea was expected to move slowly eastwards and should weaken as it passed north of New Zealand during the weekend.

A strong, moist northeast flow ahead of the low is forecast to bring periods of rain to northern New Zealand from today through to early Sunday. Some heavy falls are likely about Northland, Auckland, Coromandel Peninsula, western Bay of Plenty and eastern Waikato over this period.

A period of heavy rain is expected during today, with amounts possibly reaching warning levels.

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Further showers are likely during the weekend, which may put a dampener on the 30,000-plus people expected to descend on the Bay of Islands for Waitangi Day commemorations.

MetService said the temperatures in the Bay would hold up, with highs of 24C expected today, 27C tomorrow and 25C on Sunday and Monday.