The word ‘storm’ is frequently misused in the media and colloquially, almost as much as the misuse of the term ‘weather bomb’*. In the strictest meteorological sense, a ‘storm’ is only a storm if accompanied by storm-force winds, which are defined by the Beaufort scale as having an average speed of over 47 knots (88 km/h). However, there are several other types of storm which don’t require storm-force winds.
An explanation of wind speeds and the Beaufort Scale
Sometimes in MetService forecasts, you will see a forecast for “fresh northerlies”. But what exactly does the word ‘fresh’ mean? For many people, the word ‘fresh’ carries connotations of cool or clean air (eg the phrase ‘fresh air’). However, the word ‘fresh’ also has a more technical definition, that comes from the Beaufort Scale.
Mean Wind Speeds vs. Gust Speeds
Besides the coastal waters, the MetService forecasting team produces marine forecasts for a number of smaller areas where there is a lot of recreational boating activity. These forecasts are routinely issued four times every day; they are monitored continually and updated more frequently if conditions warrant it.
MetService's forecasting team produces marine forecasts for New Zealand coastal waters. These forecasts are routinely issued four times every day; they are monitored continually and updated more frequently if conditions warrant it.
Forecasts for coastal waters cover the area from the coastline to 60 nautical miles (about 100km) out to sea. The New Zealand coast is divided into 18 areas, as shown in figure 1:
Written by John Law, Meteorologist
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?
In August 1961 my Dad took me to see my first test match. All Blacks versus France at Wellington’s Athletic Park, although with hindsight it was more like New Zealand and France combined versus the weather.
Not that wind and rain were a negative for my ten-year-old self. That seemed to be one of the great things about rugby: it was so important that you were allowed to play in the rain. There was even some thought that the muddier you got the better you had played, the more heroic your effort.
We've just had some very strong winds over NZ, so I'm writing this short post to give some background to it. First of all, check out these peak northwesterly wind speeds from the morning of Wednesday 4 November:
mean wind (including gusts and lulls) strongest gust South West Cape (Stewart Island) 143 km/h183 km/hCastlepoint (Wairarapa coast)109 km/h161 km/hPuysegur Point (bottom of Fiordland)100 km/h144 km/h
Written by Chris Webster, Meteorologist