A gale warning is in force for the Marine area of the Bay of Plenty this morning as strong winds and rain hit the region.

Northwest winds of up to 64 km/h are forecast this morning, turning south west to 55 km/h this evening.

Heavy rain has already lashed parts of the Bay of Plenty today. Photo: File.

The sea is expected to become very rough, with a northerly swell of one metre predicted. Poor visibility due to rain is also forecast, some of which could be heavy and thundery at times.

Port of Tauranga's wave recorder at A Beacon is recording a maximum wave height of 2.1 metres over a swell of 1.2 metres.

The onshore forecast is for less wind, forecast to peak in Tauranga this morning at 42km/h before backing to the west at 35km/h.

In addition to the rain accompanying the active trough crossing the country today, the MetService is warning that temperatures will drop because of a burst of cold air originating from the Antarctic ice sheet.

Unseasonably cold temperatures, strong winds and snow to low levels are expected over the South Island, where this event is likely to have a high impact today and tomorrow.

Livestock could be affected and it will probably have an effect on higher roads where significant snow accumulations may make driving conditions difficult and could lead to some road closures.

Showers around higher parts of Desert Road (SH1) are likely to turn to snow for a time overnight on Monday and early Tuesday, with two-to three centimetres possibly accumulating on the road above 900 metres during this time.

The coldest air is expected to make its way to the North Island on Tuesday, bringing strong winds and unusually low temperatures.

In addition to the strong winds and cold temperatures on land, large south to southwest swells are expected to affect much of the New Zealand's coastline on Monday and Tuesday.

When strong-to-gale southerly winds combine these swells, waves greater than six metres are likely – possibly reaching eight to 10 metres along the east coast for a time on Tuesday.

Image: Metvuw.com.