A severe weather watch has been issued for the Bay of Plenty as heavy rain is predicted for Saturday morning.

The MetService issued the warning reporting a broad complex low over the Tasman Sea is expected to move slowly east over the upper North Island on Saturday.

Wet, wet, wet is the forecast for today and tomorrow morning.

A series of active troughs are expected to bring heavy showers at times to northern parts of the North Island both today and Saturday.

Duty forecaster Hordur Thordarson says the watch is for the possibility a trough moving through the Bay on Saturday morning may produce local heavy rain for a time, which could cause surface flooding in isolated areas.

He says people are advised to stay up to date with the latest forecast in case the watch is upgraded to a warning.

Meanwhile, plenty of rain, some heavy falls, and a chance of thunder are what's on the cards for Tauranga today, with an estimated high of 17 degrees.