Rain is in the forecast for the Bay of Plenty for most of the week, with heavy periods expected to hit the Western Bay later today.

The MetService has issued a severe weather warning for heavy rain this afternoon.

The Bay of Plenty will see heavy downpours throughout today and tomorrow.

A frontal system is expected to move slowly east over the country throughout today and tomorrow.

This front is preceded by a strong, moist northerly flow which will bring heavy downpours to the region.

The heaviest rain is expected in the Western Bay of Plenty, where a likely total accumulation of around 70-to-100mm of rain is expected in the WBOP and Rotorua.

Peak intensities of 15-to-25mm per hour are expected tonight.

The MetService is also forecasting the cold weather that started the week to gradually give way to rising temperatures as north-easterly winds persist for the next couple of days.

A front, which approaches New Zealand from the west, brings rain with some possibly heavy falls from this afternoon.

The rain will spread across the North Island on Wednesday, while eastern portions of the South Island are expected to remain mostly dry.

The front clears the country on Thursday, but showery conditions will remain as the flow turns more southerly.

A low pressure system deepens over the Tasman Sea towards the end of the week and moves over the North Island this weekend, bringing more rain, wind, and a return to colder temperatures across the country.