What do Irene, Osai, Tam and Xavier all have in common?

How do I understand a tropical cyclone track map?

Sitting out in the middle of the ocean, New Zealand is vulnerable to weather extremes from all directions, from the remains of tropical systems barreling in from the north, to cold winter southerlies bringing a blanket of snow.

Sitting out in the middle of the ocean, New Zealand is vulnerable to extremes of weather from all directions; from the remains of tropical systems barrelling in from the north, to cold winter southerlies bringing a blanket of snow.

As New Zealand’s designated national meteorological service to the World Meteorological Organisation (WMO), it is MetService's responsibility to provide clear, concise and timely warnings of severe weather that is likely to affect New Zealand.

What defines severe?

This article relates to weather experienced in late September 2010  

MetService issues severe weather warnings to New Zealanders whenever widespread heavy rain, heavy snow or damaging winds are expected. There are formal criteria that events have to meet or exceed for the forecast to be called a success; the wind criteria are in a previous post, while the rain and snow criteria relate to the total falls required within set periods.

Written by Bob McDavitt, Meteorologist

Today’s weather map shows how this cold southerly is being produced by a combination of a HIGH or anticyclone in the Tasman Sea, and a LOW or depression between Canterbury and the Chatham Islands. For want of a better phrase, we could call this an eggbeater southerly.