Tauranga's overnight low tonight will match our forecast daily high tomorrow.

WeatherWatch.co.nz says tonight's overnight low is 17C, while Tauranga's high tomorrow is...17C.

The humid sub-tropical flow is moving down across the upper North Island with thick cloud, limiting how warm the days get but significantly increasing the overnight lows, says head forecaster Philip Duncan.

A bit like how closed curtains can stop the sun from warming your home - but also at night can keep that daytime warmth trapped inside.

'Tauranga's low of 17 tonight and high of 17 tomorrow is a great example of this.

'Whangamata, further north in the Coromandel Peninsula, also has a low of 17 tonight and high of 17 tomorrow.

'Auckland has about a two degree difference from overnight tonight to Thursday's maximum temperature, as does Thames.

Whangarei has a 3 degree difference.”

Philip says further down NZ and in Napier tonight's low is 16, tomorrow's high is 19 - a three degree difference.

New Plymouth on the other coastline has a low of 16 tonight and a high of 18 on Thursday, only two degrees separation.

Images: WeatherWatch.co.nz

Wellington has a three degree difference from night to day - although Wellington often has a smaller margin between daytime highs and overnight lows due to windier weather overall keeping temperatures fairly steady - not too hot, not too cold.

'Only three degrees separates Nelson and Greymouth's overnight low tonight with Thursday's high (15C & 18C).

'But the eastern South Island has more ups and downs. Sunny nor'westers in Christchurch means the low gets down to 12 and tomorrow's high is 24, maybe even a few degrees higher than that in some suburbs.

'At least 12 degrees difference between night and day.

'In fact by Thursday night Dunedin also has just three degrees between overnight low and daytime high - but this is due to a cooler change that comes through. Thursday's low is +7C and Friday's high is only 10C at this stage.”