ODDS are still even for eastern Australia’s dreaded El Niño weather event forming, according to the Bureau of Meteorology (BoM).
But despite last week’s official forecast of a 50/50 chance for a dry, hot El Niño do not ask the BoM’s supervisor of climate prediction services, Dr Andrew Watkins, to bet against it.
“We haven’t changed the odds of an El Niño occurring, but we are certainly not going to downgrade either – based on what we’ve seen since the previous outlook forecast (on March 16),” Dr Watkins said.
After Tropical Cyclone Debbie’s deluge, the BoM’s April to June climate outlook forecasts drier than normal conditions for most of Australia except for eastern and northern coastal fringes, which are still being influenced by tropical airflows.
Sea surface temperatures off the coast of Peru are 3 ºC warmer than normal and up to 5 ºC in some places, while seven of eight international climate models indicate that sea surface temperatures will exceed El Niño thresholds during the second half of 2017.
El Niños typically bring eastern and northern Australia lower rainfall, higher day time temperatures, more clear nights and increased frost risk, fewer tropical cyclones and a higher fire danger in the south east.
But the BoM advised some caution over calling an El Niño now. While ocean temperatures had warmed, the indicators of an El Niño remained within neutral levels and models forecast with a lower degree of accuracy during autumn.
“It’s early days still, the indicators are nowhere near as strong as 2015, say. But we’re also not on the cusp of saying ‘forget about it’, put it that way,” Dr Watkins said.
“While it is too early to go into full El Niño mode, it’s time to have a plan in your back pocket.”
El Niño forms when the Pacific Ocean weather cycle that drives the easterly trade winds breaks down. This occurs when the eastern Pacific, along the west coast of south America, heats up and winds that usually blow cooling surface water from the chilly Peruvian coastline don’t pack their usual punch.
Under neutral conditions, in non-El Niño years, the sea surface temperature in the eastern Pacific is tempered by cold water upwelling to the surface. This cycle replaces the sun-heated surface water and fuels the trade winds, which blow into the central Pacific and toward Australia.
But as the trade winds break up, the central and eastern Pacific heats up and high pressure systems form over eastern Australia bringing hot, dry air.
Meanwhile, evaporation rises in the warmer central and eastern Pacific bringing more rain to the west coast of South America.
Tragically, hundreds of people were killed in mudslides in March in Peru and Colombia, precipitated by heavy rain.
South American are already calling the weather system driving the higher rainfall on their side of the ocean a coastal El Nino.
Visit: www.bom.gov.au/climate/enso/
Climate outlook
The BoM’s recently issued a climate outlook for April to June, which forecast drier than normal conditions for most of Australia, bar the northern and eastern coastline.
Rainfall is likely to be below average over the southern two-thirds of mainland Australia excluding the east coast, and above average for the far north.
April is likely to be drier than average across the south and southwest of Australia, but wetter for eastern NSW, southeast Queensland and far northern Australia.
Daytime temperatures for April to June are likely to be above average for most of Australia, except parts of eastern and northern Australia.
Night-time temperatures for April to June suggest a warmer three months for many parts of Australia, except northern Western Australia and the top of the Northern Territory, where cooler than average nights are more likely.
Southern WA, southern South Australia, eastern NSW and Cape York Peninsula have about equal chances of cooler or warmer April to June nights, the Bom said.
Tasmania, has there is a greater than 80 per cent chance of warmer than average daytime and overnight temperatures in April to June.