David Ward, of Dunedin, asks :-
For the past two years it seems to me to have been much windier in Dunedin. Is this impression supported by the data?
Andrew Tait, a climatologist at NIWA's National Climate Centre, responded.
Measuring wind is a complicated business, as it turns out. The type of instrument used (e.g. a cup or sonic anemometer) and the specific location of the instrument and its height above the ground all make a difference to the readings.
Wind speed and wind direction data have been collected at the Musselburgh Pumping Station site in Dunedin since 1981, however there have been some changes made to the instrumentation over these years and in 2006 there was a change in the location of the instrument from the roof of the pumping station to a new 10 metre tall mast. As such, it’s not possible to accurately compare the pre-2007 data with the post-2006 data. Nevertheless, we can look at and compare the average daily wind speed for every month from 2007 to 2012, which will help to answer your question. In the table you can see the average daily wind speeds (in km/hr) at Musselburgh for the last few years. 2011 and 2012 don’t particularly stand out as being significantly windier than previous years, although I note that June 2012 has the highest average daily wind speed for this month, compared with the previous five years. In saying this, 2012 has the lowest average daily wind speed for the month of July over the last few years.
Another way to examine the data is by comparing the number of days with wind gusts greater than or equal to 33 knots (61 km/hr), which is considered to be “gale force” on the Beaufort Wind Scale. There were 42 days in 2011 when the wind gust speed was at least this much, which is slightly more than previous years (37, 31, 27, 36 days in 2007, 2008, 2009 and 2010, respectively). In the first seven months of 2012 there have only been 10 such days – but mind you, the windy spring months are yet to come.
So, on balance, I’d have to say that based on recent comparable measurements the last couple of years in Dunedin haven’t been particularly windier than previous years, but perhaps the extra few “gale force” wind days last year made it seem so.