Dry spells take hold in South Island

Many areas in the South Island are tracking towards record dry spells as relatively warm, dry weather that began in mid-August continues.

A dry spell is defined as a period of 15 days or more with less than 1mm of rain on any one day.

NIWA climate scientist Gregor Macara says for some South Island places, the current period of fine weather is quite rare.

“Milford Sound generally only has a dry spell once every two years and seven months. The current dry spell in Milford Sound has lasted 22 days so far - if it lasts for another week it will become the longest on record, beating the 2001 record of 27 days,” Mr Macara said.

Queenstown’s record dry spell is 59 days that began on 21 July, 1952. The current dry spell there is now at 26 days. Queenstown, Alexandra and Milford Sound have all exceeded their average dry spell length during the present dry spell.

Dry spells are not particularly common in coastal areas of Otago and Southland but do occur more frequently inland. They typically occur when a persistent anticyclone becomes established over the South Island. Western ranges also provide sheltering for eastern areas so that dry spell conditions can persist in north or north-westerly airstreams.

Wanaka and Fairlie are leading the pack for the current dry spell, with both towns experiencing ongoing dry spells that have now reached 29 days each. This is still well short of the record for these towns of 55 days and 40 days respectively.

Timaru is on 28 days, Oamaru 26 days and Nelson 18 days.

“What we’re seeing is a particularly widespread bout of dry spells across the South Island, Mr Macara said.

Table 1.  Dry spell (at least 15 consecutive days with less than 1 mm rainfall per day) frequency and duration for selected locations, from all available data.

Table 2. Current dry spell information up to and including 9 September 2014.