Earlier this evening WeatherWatch.co.nz described the storm as “unusual” – Philip Duncan explains why:

Most of the warnings and predictions of this storm were made well before the low was even a blip on the satellite maps. Even tonight it’s hard to easily detect, as the storm is still around 12 to 18 hours before reaching it’s full depth – and keep in mind a “weather bomb” takes 24 hours to go from basically nothing to becoming a fierce storm.

So it’s a bit like flying blind – making such big predictions without any storm on the map to look at.

You might say that is normal – forecasters trust and use models all the time – but that’s mostly for long range predictions. Within 24 hours forecasters can usually see a lot more about what is happening – this time, all forecasts were heavily based on the models. This a huge test of the capability of computer modelling – but every model we use points towards the predictions made today by all forecasters.

It’s also unusual to have a low deepening as it crosses the country – because of this, the storm will likely peak as it crosses into the Pacific.  This is why there seems to be higher confidence of more severe weather in south eastern areas of the North Island – because this is where the low will reach it’s depth and full strength.

– Philip Duncan