Bay of Plenty continues to be battered by heavy rain as the MetService issues a severe weather watch for the region.

The MetService says a deep low over the Tasman Sea should move slowly eastwards across the upper South Island Sunday and early Monday.

This low is expected to bring periods of heavy rain to many parts of central New Zealand from Saturday evening to Monday morning.

MetService duty forecaster Allister Gorman says this watch is for the possibility of rainfall accumulations reaching warning criteria for the eastern ranges of Bay of Plenty.

Today's forecast is a high of 18C and an overnight low of 13C. A strong northerly is also expected with periods of rain and the chance of heavy thunder in the afternoon.

Tomorrow's forecast makes for gloomy reading with rain and the chance of thunder easing to showers and a strong nor westerly with a high of 18C and an overnight low of 10C.