Written 12:52pm, Tuesday 18th Jan, 2011

A significant development is occuring in the skies above New Zealand this afternoon as two ex-tropical cyclones and a low that contributed to the flooding in Victoria merge.

WeatherWatch.co.nz forecasters say the merger of these three systems may actually help decrease the predicted severe winds over some parts of the country.

“The air pressure is falling across New Zealand and the area of low pressure is increasing.  That makes for unstable conditions but actually helps lower the wind speeds” says Mr Duncan.  “The energy of these three lows is being dispersed across an area that’s over 2500kms long”.

Yesterday Zelia’s destructive winds covered an area only about 100kms wide, making it a very small cyclone in size, but still an intense one.  It’s this narrow window of gales that make predicting landfall and areas worst hit so difficult.

But now a new low is forming, absorbing the energy of all systems and spreading that energy further afield.

Mr Duncan says it’s a bit like pushing your finger against an inflated balloon that’s leaking air – eventually the pressure lowers and the balloon goes flat and that’s similar to the air pressure over us.

However WeatherWatch.co.nz has maintained that wind would never be the main feature of these systems with Zelia continuing to rapidly fall apart, as predicted.

But Zelia and Vania may actually have a long term impact on New Zealand, with WeatherWatch.co.nz now predicting the sub-tropics will be lingering around the upper North Island for the rest of January.

“Zelia and Vania have help pulled the tropics down over the upper North Island so we can expect more muggy, wet weather this weekend and into the next 10 days”.

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Mr Duncan says it’s a bit like a bath of cold water with a hot tap running at one end – the ex-cyclones were the hands that helped scoop the hot water and spread it across the bath.

Humidity remains around 98% in Auckland with WeatherWatch.co.nz getting reports of 100% across a number of weather stations in the upper North Island.

Some computer models are picking more tropical storms in the Coral Sea in the coming 10 days.

Meanwhile the merger of the three depressions over New Zealand is leading to heavy rain moving into some areas.  Heavy rain is now pushing in to the Far North and the West Coast of the South Island. 

As this new, larger, low forms it is expected to deepen and become aggressive.

It’s the combination of these three systems that prompted the numerous wind and rain warnings by MetService.

As this new larger low moves off the east coast of the South Island tomorrow it is expected to intensify quickly, pushing a strong southerly up the country, however due to its fast departure a sunnier, calmer, day is predicted over New Zealand on Thursday.

By Friday and/or the weekend more sub-tropical developments will affect the upper North Island.

– WeatherWatch.co.nz