MetService has issued an orange heavy rain warning and a heavy rain watch for parts of the Bay of Plenty ahead of expected severe weather tomorrow.

The area east of Whakatāne is under an orange heavy rain warning from 5pm today until 5am tomorrow, with 70mm to 90mm of rain forecast. Peak rainfall rates of 20mm to 30mm an hour are expected about the ranges.

Thunderstorms are possible, with the heavy rain likely to cause rapidly rising rivers and streams, surface flooding and slips.

Residents are being urged to clear drains and gutters, avoid low-lying areas and take extra care on the roads.

MetService said there was a low chance the warning could be upgraded to a red warning.

A heavy rain watch has also been issued for areas west of Whakatāne from 2pm until 11pm tomorrow.