It's the last long weekend of summer and it looks like raincoats will be needed ahead of togs.

Metservice says a deepening low over the north Tasman Sea is expected to move slowly eastwards and should weaken as it passes north of New Zealand during the weekend.

But a strong, moist northeast flow ahead of the low is forecast to bring periods of rain to northern New Zealand from Friday through to early Sunday, with some heavy falls likely about Northland, Auckland, Coromandel Peninsula, western Bay of Plenty and eastern Waikato during this time.

On Friday the heavy rain in Northland could see amounts possibly reaching warning criteria (for example 80mm falling between Friday morning and Friday night). Further showers are likely during the weekend.