Heavy rain and cloudy periods are being forecast for the Bay of Plenty this week as a number of volatile fronts move across the country.

The MetService warns that these fronts will herald an unusually late cold spell as the week progresses.

Volatile fronts are expected to bring heavy rain and possibly thunderstorms to the Bay of Plenty this week.

'The temperatures this week will be well down for this time of the year, with gales, hail and thunderstorms thrown into the mix,” says meteorologist Rob Kerr.

Temperatures in the Bay will sit around the 20 degree mark for daily highs and drop down to around 10 degrees for overnight lows.

Rob says several cold southwest changes march northwards over the next few days.

'This highly unstable air brings a risk of thunderstorms for many areas,” adds Rob.

'A showery southwesterly flow covers all of New Zealand from Wednesday, with a few showers off-and-on throughout the week.” Rob says the weather is expected to settle down for Friday and remain mostly fine and dry for early Saturday.

But he warns another swift moving front is expected during Saturday and Sunday.