Niwa National Climate Centre forecasting principal scientist Chris Brandolino said the El Nino weather phenomenon which was bringing much of our weather from the west at present, was dissipating and was expected to ease to ENSO-neutral by the end of this month.
The El Nino-Southern Oscillation (ENSO) is a recurring climate pattern involving changes in the temperature of waters in the central and eastern tropical Pacific Ocean, which impact on our weather.
"However, global atmospheric patterns favour a continuation of higher-than-normal air pressure around New Zealand, particularly near the North Island.
"That means May is expected to feature rounds of chilly, southerly quarter winds before a transition to milder, westerly quarter winds from late in the month into June and July."
On the West Coast, the Southern Alps and foothills, inland Otago and Southland, temperatures were equally likely to be near average or above average over the next three months, and rainfall totals were most likely to be near normal, he said.
"However, May looks drier than normal. The region may be exposed to strong fronts and lows on occasion, particularly later in the season.
"Soil moisture levels and river flows are most likely to be near normal."
Coastal Otago temperatures were also about equally likely to be above or near average.
"However, cold, southerly air masses are expected during the first half of May.
"More frequent westerly winds in June and July may cause milder temperatures.
"Rainfall totals are most likely to be below normal and May has an elevated chance of being drier than normal.
"Soil moisture levels and river flows are most likely to be below normal, so soil moisture deficits will be slow to be alleviated."
He said Oceanic La Nina conditions (which bring weather from the east) might develop in late winter at the earliest, but it was more likely to arrive later in spring.
"There is expected to be a meaningful lag between La Nina developing in the ocean and the atmosphere responding in a La Nina-like fashion, particularly in a New Zealand context.
"In other words, moist, northeasterly winds are not expected to be a dominant flavour in New Zealand’s weather patterns for at least the next 3-6 months."
