12 hours ago it dwarfed the North Island, now it’s a smudge of cloud to the east of the North Island. Ex-cyclone Atu has been downgraded and has weakened considerably today but the storm is not over yet.

It remained a powerful category 3 cyclone at the same latitude that Cyclone Wilma last month was a category 2. 

However, as expected, Atu transitioned into what is called an extra-tropical cyclone.  This term isn’t usually used to describe storms at our latitude but in fact that’s what they are.  The term is, however, commonly used when a cyclone leaves the tropics.

An extra-tropical cyclone is a storm that is outside of the tropics and has no tropical characteristics – in other words, it is fuelled by cold conditions, unlike cyclones which are warm at the centre.  These are the “everyday” storms that we get in New Zealand.

The transitions takes a huge toll on a tropical storm, they lose their eye, they lose their shape and they lose a huge amount of strength.  They also often lose that perfect circular shape which we see on the weather maps.

But once they get themselves sorted into an extra-tropical cyclone they can power back up again, often spreading their severe weather conditions further afield – and less concentrated around the centre.

Atu is predicted to do this in the coming 24 to 48 hours as it quickly slides into the Southern Ocean and well away from land.

Before it leaves it will continue to produce dangerous rips and beach conditions along the east coast of the North Island from Northland to Wairarapa, with conditions easing north west of East Cape tomorrow and elsewhere by Sunday.

Atu is still packing a punch – the crown forecaster says in their Marine Warning that Atu has sustained winds of 110km/h, although their most recent update was at 7:35am, one can assume those winds are now much lower.

– WeatherWatch.co.nz

Latest view of Atu looking north east towards East Cape in the distance / Google Earth