Weather experts argue over forecast, rain radar

The North Island has been drenched in bad weather, but forecasters seemingly cannot agree on the details. Photo / Greg Bowker

With wild weather obviously battering the North Island, forecasters seemingly cannot agree on the details - thunder? No thunder?

The MetService today issued a severe thunderstorm watch as an active front slowly crossed over Auckland, western Waikato, Waitomo and the Coromandel Peninsula.

Forecaster Gerard Barrow said there was a possibility that one or two thunderstorms could be severe, with a risk of damaging tornadoes and squally winds gusting up to more than 110km/h.

The gusts and tornadoes could cause structural damage, including to trees and power lines, and would make driving hazardous. Any tornadoes would affect only very localised areas.

But WeatherWatch forecaster Philip Duncan said although there were the right ingredients for isolated tornadoes, the chance of thunder in Auckland was low and any related activity would be isolated.

Mr Duncan said 95 per cent of the thunder activity today had been offshore and the main front was expected to clear Auckland by 6.30pm.

The MetService thunderstorm watch would remain in place until 11pm, while WeatherWatch said it was unlikely to issue more updates today.

The state-owned MetService and privately owned WeatherWatch services are split on more than just their forecasts, with another storm brewing over public access to rain radar images.

Mr Duncan today criticised the MetService for making only one of its rain radar image available to the public every hour, unless users were willing to pay.

That compares with Australia, Canada and the United States, where up to 20 images an hour were freely available to the public.

Mr Duncan said unless the rain radar updates were updated regularly they were "basically useless".

"A severe thunderstorm can come and go without even being detected in an hourly update. But with updates every 3 or 4 minutes the public can track particular rain bands and see if their property is at risk," Mr Duncan said.

"It is a significant tool used by the public all over the world for protecting life and property - except here in New Zealand."