As El Niño intensifies, weather in the South is expected to go from one extreme to another over the next three months.
Niwa National Climate Centre forecasting principal scientist Chris Brandolino said the weather could swing between heavy rainfall and flooding, to long hot dry spells with risks of wildfires.
He said there was an 80% chance El Niño would continue through to next autumn, maintaining an important influence on New Zealand’s climate.
On the West Coast, Southern Alps and foothills, inland Otago, and Southland, temperatures were about equally likely to be above average or near average, and rainfall totals were most likely to be above normal, he said.
"Strong lows will occasionally impact the western and lower South Island, delivering heavy rainfall and a risk for flooding.
"However, the first half of November looks drier than normal. A hot spell looks likely during the second half of November."
Despite the contrasts, soil moisture levels and river flows were most likely to be near normal, he said.
In coastal Otago, temperatures were most likely to be above average.
"Frequent west-to-northwest winds will likely lead to a higher frequency of hot days with temperatures greater than 25˚C, such as in the second half of November.
"Rainfall totals are equally likely to be below normal or near normal, but an increased frequency of west-to-northwest winds will likely lead to longer dry spells.
"For inland and southern Canterbury and east Otago, periodic wetter-than-normal conditions may occur when rain bands may spill over the main divide.
"But soil moisture levels and river flows are equally likely to be near normal or below normal."
He said the Niwa outlook came with two cautions for the weather over the next three months.
"Seasonal wind strength is forecast to be above normal across most of the country because of a stronger than normal pressure gradient near New Zealand.
"This will come with a higher-than-normal risk for periods of damaging winds."
He also warned of the rising fire danger - particularly in eastern parts of the country.
"As of late October, fire danger was low across the country.
"Despite this, normal or above normal wildfire activity is expected to eventuate, particularly in northern and eastern areas of both islands during periods of hot, windy weather."
