Forecasters in New Zealand are writing and re-writing forecasts as Tropical Cyclone Wilma continues to move towards us.

The cyclone will become a category 4 cyclone by tomorrow morning.

Weather forecasts for Auckland provided by both WeatherWatch.co.nz and state owned MetService have literally gone from one end of the scale to the other within 24 hours.

The flip flop forecasting is a sure sign that something of tropical nature is coming our way.

Long range forecasts (beyond a couple of days) are incredibly hard to predict when a tropical system is involved, simply because the area of severe weather is so small compared to most lows that affect us.

A low of tropical origins has the severe weather wrapped tightly around its centre, whereas lows that form around New Zealand and south of us often have the rough weather spreading for hundreds of kilometres away from the centre.

Wilma is predicted to be a severe category 4 cyclone within 12 to 18 hours, something that is quite rare so close to New Zealand.

The eye of Wilma is just 1400kms north west of New Zealand – the same length as our county.

Forecast models, produced globally, are also having huge trouble predicting where Wilma will end up tracking but in the past few hours have started to align themselves, with the most likely track showing what will be a sub-tropical low passing over Northland and then East Cape during Saturday.

The good news is that it is likely to pass through quickly – so it may only be a 24 hour period of rain and wind, then sunnier weather returns.

WeatherWatch.co.nz is now picking that weather will start to improve rather than being wet for all three days of the long weekend.

As we’ve said all week, we thought by Wednesday evening we would have a fairly concrete idea as to what is happening, and the models are today finally starting to align themselves.