As “very strong” El Nino conditions continue to strengthen their influence on New Zealand’s weather patterns, coastal Otago is expected to become warmer and drier than average, while Southland and inland Otago will continue to be wetter than usual.

Earth Sciences New Zealand weather and seasonal forecasting chief scientist Chris Brandolino said El  Nino’s influence on New Zealand’s weather patterns was becoming increasingly apparent, and it was expected to be “a dominant driver” of climate patterns over the next three months.

“Very strong El Nino conditions are now present in the tropical Pacific and are expected to strengthen further.

“It’s expected to favour more frequent westerly airflows over New Zealand, along with increased wind strength and gustiness.

“This pattern is likely to bring more frequent fronts to western and southern areas, while increasing the potential for dry, warm foehn conditions in eastern regions.”

Mr Brandolino said the pattern may be disrupted at times, by stratospheric influences favouring a positive Southern Annular Mode (SAM), which could partly counteract the circulation patterns associated with El Nino.

“Additionally, it’s important to remember that El Nino does not prevent short-lived departures from the typical El Nino pattern, including occasional northerly flows that may result in heavy rainfall for parts of the country.

“Despite the overall warmer outlook, temperatures are expected to be more variable than usual, with pronounced swings between warm and cold conditions.”

He said El Nino was expected to peak in late spring or early summer, with the potential for “significant impacts”.

“The event is likely to rank among the strongest on record, as anticipated over recent months.

“The Relative Oceanic Nino Index (RONI) has already exceeded 1997 values for this time of year, and has undergone the most rapid warming on record.”

On the West Coast, the Southern Alps and foothills, inland Otago, and in Southland, temperatures were about equally likely to be near average or above average.
However, rainfall totals were most likely to be above normal, and there was an increased potential for heavy rain events and unusually strong winds, he said.
Soil moisture levels and river flows were most likely to be near normal.
Along coastal Otago, he said temperatures were most likely to be above average, but “greater-than-usual variability” was expected.

“Strong westerly wind episodes may bring short-lived warm, foehn-like conditions to eastern areas, interspersed with cooler changes as fronts move across the country.”
Rainfall totals were equally likely to be below normal or near normal, and as a result, soil moisture levels and river flows were also equally likely to be below normal or near normal.

john.lewis@odt.co.nz