It may look like a beautiful day in the Bay today, but the MetService expects the weather to take a turn for the worse on Thursday.

A severe weather warning has been issued for both the Western Bay of Plenty and the Eastern Bay of Plenty.

Rain is expected to lash the Bay of Plenty tomorrow. Photo: File.

A trough embedded in a strong, moist north-west flow is expected to move slowly east over the country today and tomorrow before eventually moving out to sea during Friday.

In the meantime, heavy rain falls are expected in the Eastern Bay of Plenty ranges, where 100-to-150mm could accumulate.

The MetService says this rain could cause rivers and streams to rise rapidly, surface flooding and slips. It could also make driving conditions hazardous.

In the Bay of Plenty east of Whakatane, including the Raukumara Range, periods of heavy rain are expected on Thursday night before easing early on Friday morning.

Between 9am on Thursday until 6am on Friday, people are being warned to expect 60-to-90mm of rain to accumulate, but 100-to-130mm about the Raukumara Range.