Forecasters are mostly confident about the predictions made for Christmas Day, but the following week has a big question marking hanging over it, if long range computer models are anything to go by says WeatherWatch.co.nz.

Two of the models we trust most to help prepare our long range predictions are both agreeing that a sub-tropical storm is forming to our north west – but what they can’t agree on is whether or not northern New Zealand will be hit.

Following two significant rain bands over the upper North Island in recent weeks, effectively reversing any potential droughts that were forming, more heavy rain isn’t needed just yet.

In fact in parts of Waikato the ground remains soggy more like early spring than early summer.

Head weather analyst Philip Duncan says it’s a typical battle of high air pressure verses low.

“Think of the sub-tropical low as evil and the high as good – this is a classic good verses evil set up”.

“If the high stays strong, many will consider that a good prediction.  If the low comes in and brings wind and rain to northern New Zealand I’d say it’s safe to say most will think that’s a bad forecast”.

Mr Duncan says the models show the low deepening to the north west of the country, near New Caledonia, around Christmas Eve then drifting south east towards New Zealand.  “Some long range maps show the high pushing back, trying to keep the sunny weather up for the last week of 2011, while other maps show the low winning, and pushing into the upper North Island in about 6 to 9 days time”.

WeatherWatch.co.nz says while there is a high risk the low will move near New Zealand, the chance of it hitting New Zealand remains low to moderate.

– WeatherWatch.co.nz