An ill wind for warmer summers

An increasing trend towards more westerly weather patterns along Otago's coast does not bode well for future warm summers, climate scientist Jim Salinger says.

While summers were generally getting slightly warmer, in Otago the three-month period was known to be more unsettled, Dr Salinger said from Hobart, where he is on a visiting scholarship at the Institute of Marine and Antarctic Studies.

The region's summers, especially those along the coast from Dunedin south were most affected by westerly winds, known as the southern annular mode (Sam).

Sam provides an index of westerlies that lick the southern coast of the South Island, in particular coastal Otago. For the past 50 years southwesterlies have increased.

''The trend towards more westerlies or southwesterlies in summer has increased. That does not bode well for coastal Otago,'' Dr Salinger said.

He said the westerly winds made coastal Otago summers much more unreliable.

That had been highlighted by this summer's weather, as southwesterlies had cooled January and made for a relatively unsettled February along the coast.

''Dunedin has had a lousy summer but Central Otago has fared much better as this month there have been fewer southwesterlies.''

When westerlies were strong Central Otago was affected by the cooler weather but when they weakened the inland area escaped the cooling effect, as it had done this month, returning to warmer conditions.

''Central Otago jumps about a bit and North Otago is a different regime. It's sheltered from the southwesterlies.''

Sam had shown there was hope for the odd good summer to be mixed in among the bad, he said.

Looking at the index, there had been a spell of better summers in the 1960s and early 1980s when there had been fewer westerlies.

''Nineteen sixty-eight to 1969 were particularly good years but you're not going to get the same runs of good summers as there were 30 years ago or 50 years ago,'' Dr Salinger said.

The other influential ''climate drivers'' for Otago were the La Nina and El Nino weather patterns.

La Nina brings more easterly or northeasterly weather, meaning warm summers, while El Nino encourages more westerly or southwesterlies, and cool summers.

Together with Sam, either pattern tended to emphasise the weather pattern, he said.

''Together they can make quite a bit of difference.''

While this summer the weather pattern was neutral, Niwa was predicting an El Nino weather pattern to develop midyear.

- rebecca.fox@odt.co.nz