Queensland put on La Nina alert
Increased chance of more cyclones and floods for Queensland.
The BoM’s latest advice is that the likelihood of a La Nina weather pattern forming this year had increased to 70%, which is about three times more than usual.
BoM Manager of Climate Operations Dr Andrew Watkins said a La Nina event usually saw above average rainfall in winter-spring, particularly across eastern, central and northern regions of Australia.
"It typically also brings cooler and cloudier days, more tropical cyclones, and an earlier onset of the first rains of the wet season across the north," Dr Watkins said.
"The cooling of surface temperatures in the tropical Pacific Ocean and an increase in the strength of the Pacific Trade Winds indicates the chance of La Nina has risen.
“When these two changes occur at the same time, at this time of year, we see a greatly increased chance of a La Nina forming and persisting through spring.
"Climate models suggest that further ocean cooling and intensification of trade winds may occur over the coming months, which has triggered the bureau to shift from a La Nina watch, issued on 26 June, to a La Nina alert.”
The six wettest winter–spring periods on record for eastern Australia occurred during La Nina years.
The last significant La Nina event was in 2010-11, which was the Australia's wettest two-year period on record beating the previous record from the La Nina years of 1973-74. The impacts of La Nina often continue into summer and in eastern Australia, the average December-March rainfall during La Nina years is 20% higher than the long-term average, with eight of the 10 wettest such periods occurring during La Nina periods.
La Nina facts
FloodingThe presence of La Nina increases the chance of widespread flooding during summer, particularly during summer months. Of the 18 La Nina events since 1900 (including multi-year events), 12 have resulted in floods for some parts of Australia. Parts of northern Australia experience flooding during La Nina because of the increase in tropical cyclone numbers.
There are typically more cyclones in Australian during La Nina, with twice as many making landfall than during El Nino years on average and the first to cross the coast tends to be earlier in the season.
The only years with multiple severe tropical cyclone landfalls in Queensland have been La Nina years. This means an increased likelihood of major damage and flooding related to strong winds, high seas and heavy rains from tropical cyclones.
MonsoonThe date of the monsoon onset in tropical Australia is generally two weeks earlier during La Nina years than in El Nino years. This means that rainfall in the northern tropics is typically above average during the early part of the wet season for La Nina years but only slightly above average during the latter part of the wet season. The onset of the wet season is defined as the date when rainfall accumulated after 1 September is at least 50 mm.
Source: Bureau of Meteorology