Somewhere in the North Island today there could be a deluge similar to the one that swamped parts of Wellington two days ago - but forecasters cannot predict where it will happen.

The capital was swamped by 53mm of rain on Thursday night - half the normal rainfall for the whole of January.

Tauranga was also hit by thunderstorms, and the roof of a home caught fire after it was hit by lightning.

MetService forecasters say "the recipe is just right" for similar downpours today.

And if the rain was not enough of a headache, the moist summer has spawned an explosion in mosquitoes.

Napier testing laboratory New Zealand Biosecure reports a 10-fold increase in the number of mosquitoes caught in traps in the upper North Island.

The laboratory's taxonomist, Mr Mark Disbury, said the population of adult insects had exploded in recent hot weather after a wet December which gave plenty of puddles for hatching.

Traps at ports showed an increase particularly in the native species known as "Vigilant".

"We usually get at this time 60 to 70 adults in a sample taken every few days but this year it is 150 to 200 more per sample," Mr Disbury said.

"On December 31, we got a sample with more than 1000 of the native species in it.

"We have never had numbers like that before."

Mr Disbury said lots of an aggressive exotic species were showing up in port traps set to detect undesirable imports.

They came from Australia about 150 years ago and thrived near homes in gardens, watering cans and pot plants where there was pooled water for breeding.

In the present warm conditions, they could grow from egg to adult fly in a week.

Mr Disbury said even family pets were not safe from mosquito attacks.

"They go for any warm-blooded animal and some reptiles too," he said.

The native Vigilant was more focused on biting birds.

The Auckland medical officer of health, Dr Virginia Hope, said people who had a bad reaction to a bite, or had a bite which did not heal, should see a doctor because it could become infected.

MetService forecaster Janet Tyme said "storm cells" could develop anywhere in the North Island today, but where they would finally dump their build-up of moisture was anyone's guess.

Storm cells are towering cumulus clouds with an updraught of air which sucks up moisture.

Once the cloud gets too heavy, the moisture rapidly becomes heavy rain, sometimes with lightning.

"The recipe is just right, with lots of moisture around, light winds and unstable weather conditions," Ms Tyme said.

Otherwise, the North Island will be showery with fine periods and improving tomorrow.

The South Island's east coast could be in for a battering today and tomorrow. The MetService has issued a severe-weather warning for the Kaikoura coast and North Canterbury ranges. Southeasterly winds could gust up to 45 km/h.

But the West Coast of the South Island is the place to be today, with lots of sunshine forecast.

Tomorrow, rain will persist in eastern areas of the South Island but fine periods will increase.

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