Meteorologist’s ‘jaw dropped’ when BoM gave the all-clear as mini cyclone neared

The Bureau of Meteorology may not have seen the mini cyclone that was about to hit flood-ravaged northern NSW with more than 400mm of rain this week — but others did.

It was a once-in-a-lifetime flood — twice in one month — which caught most off guard.

On Tuesday afternoon, residents in Lismore were told they could go home with caution as an earlier evacuation order was lifted, only to be ­reinstated at 3am Wednesday morning.

The Bureau of Meteorology got its forecast wrong, and Acting Premier Paul Toole defended the failures, saying “no one could have predicted” the catastrophic weather — but one meteorologist could see what was coming: a hybrid cyclone.

“My jaw dropped last night when I saw the ‘all clear’ message given for residents to return to evacuated areas with the low hurtling towards the NE NSW coastline,” meteor­ologist Anthony Cornelius, from independent meteorological group Weatherwatch posted online.

“As expec­ted, the low has generated further torrential rain. I don’t want to throw ­people under buses, but what we saw, we had this obvious low-pressure system that ­became dominant east of ­Brisbane and was tracking southwest.”

But it was not behaving like a traditional east coast low.

“There are two types of main systems we see along the east coast; you have your east coast lows that we are familiar with and you have your tropical cyclones,” Mr Cornelius said. “Hybrid cyclones are a cross between the two systems.

“The hybrid systems play by different rules.”

The BoM defended its earlier call and a spokeswoman said “the term ‘hybrid cyclone’ is not a defined term” at the bureau.

Fears of third straight La Nina

Drenched NSW residents have been warned of the possibility of a third consecutive La Nina event which could see no end in sight to the state’s record rain and destructive flooding.

La Nina is an oceanic and atmospheric phenomenon which sees higher sea water temperatures off the Australian northeast coast and stronger than normal easterly winds pushing heavy rain into eastern NSW and Queensland.

Sydney has endured the soaking consequences of two consecutive years of La Nina, and the city and flood-ravaged northern NSW may yet suffer under a rare third consecutive La Nina.

“There are certainly indications coming from the Pacific that we could see a third consecutive La Nina, although we won’t know for sure until we get into winter or even spring,” Sky News chief meteorologist Tom Saunders said.

“Sixty per cent of La Ninas become back-to-back events, so the chances of a third consecutive La Nina are high enough that it’s worth considering and planning for.”

A typical La Nina event will peak in late spring to early summer, will decay in late summer and break down in autumn. The current system was starting to break down in late January and early February, but restrengthened, bringing with it the floods and rain bombs of recent weeks.

“Even when La Nina does break down, perhaps later in autumn, the atmosphere often has a slight lag, so you can still have the impacts of a La Nina even when it is breaking down,” Mr Saunders said.

“So the short answer is we can expect more wet weather over the next few months.”

Sydney experienced some wild weather on Friday, with winds gusting up to almost 83km/h causing havoc across the city with fallen trees crushing cars, damaging homes and bringing down powerlines.

The Bureau of Meteorology’s outlook for the next three months predicts above-average rainfall for eastern NSW and 1.5 times the usual chance for rainfall in the top 20 per cent of historic records.

Last month was the wettest March on record for Sydney, with 554mm of rain falling, smashing the 1942 record, and also marked the wettest start to the year.