UPDATED 10.12AM: A severe weather watch for heavy rain has been issued for the Bay of Plenty.

The MetService warns rainfall amounts could reach warning thresholds, for example 70mm in 12 hours, in Taupo and the eastern ranges of the Bay of Plenty on Sunday.

The glass like sea seen in the Tauranga Harbour earlier this week has been replaced by choppy waters.

A strong, moist northwest flow covering the country is expected to remain until an active trough moves up the country during Saturday and Sunday, bringing a colder southwest change.

The Port of Tauranga reports winds are gusting about 22 knots in a northerly direction and wave are reaching a maximum height of about 1.9 metres.

According to the Whakatane Heads Surf Forecast, winds are gusting about 30km/h in a north westerly direction and wave heights are reported to be about 1.5 metres.

The MetService says while the watch is only in effect for the Taupo region and now the Eastern Bay of Plenty, people should be aware that further areas may be included as the day progresses.

'The watch could also be upgraded to a warning as this event progress,” says a statement from the weather organisation.