Mother Nature is proving to be slightly fickle this winter, prompting Niwa to make alterations to its forecast for the next three months.
Forecasting principal scientist Chris Brandolino said owing to La Nina-like tendencies in the atmosphere, the weather in this outlook was expected to show a wetter trend compared with last month’s outlook.
While wetter winter weather would not be celebrated by many southern people, it would be welcomed by hydro-power generators, he said.
"During June, convective forcing favoured the west-central equatorial Pacific, producing a La Nina-like response in the atmosphere.
"This was linked to a slow-moving pulse of the Madden-Julian Oscillation (MJO), which produced a La Nina-like circulation pattern in New Zealand.
"Such a pattern was quicker to develop than modelling had previously indicated."
During July, the MJO was once again forecast to track across the Pacific, particularly in the second and third week of the month, he said.
"This is forecast to be associated with lowering pressure north and west of New Zealand and may produce a spell of heavy rain.
"Because of a possible tropical moisture connection, there is an increase in the chance for flooding.
"Overall, this represents a trend away from the forcing patterns that produced abnormally dry conditions in several regions during the first half of the year.
"The MJO pulse may reach the eastern Pacific, Africa and the western Indian Ocean during late July, eventually producing more westerly flows and wetter conditions in the west of both islands, including in the South Island hydro catchments," he said.
On the West Coast, the Southern Alps and foothills, inland Otago and Southland temperatures were about equally likely to be above average or near average over the next three months.
"A lack of southerly winds may contribute to a reduced risk for frost."
He said rainfall totals were about equally likely to be near normal or above normal, and warned the region might be exposed to strong fronts and lows on occasion — particularly in mid-July.
Soil moisture levels were most likely to be near normal and river flows were about equally likely to be near normal or above normal.
In coastal Canterbury, the nearby plains and East Otago, temperatures were also about equally likely to be above average or near average, with a reduced risk for frost.
"Westerly-quarter winds will likely cause spells of milder temperatures, particularly in August and/or September."
Rainfall totals and soil moisture levels were most likely to be near normal, and river flows were equally likely to be near normal or below normal, he said.
"The models that are tracking closest to the observations suggest a La Nina of moderate intensity may develop later this year. Therefore, a La Nina watch continues."
