October 8, 2010

Spring has sprung...a leak!

Between 40-80mm of rain has fallen since 9am around the Gold Coast, with the heaviest falls around Robina (56mm to 11pm at Boobegan Creek) and Springbrook (83mm to 11pm).

The archived 256km Radar Loop for Brisbane
(provided by theweatherchaser.com) shows a line of rain/storms whilst relatively isolated to the coastal strip made it's way north from about Southport at midnight with heavy falls continuing until it disapated north of Maroochydore around 6am.

The morning on the coast was relatively dry until more moderate to heavy falls moving north-west made landfall around 10-11am in the centre of the coast, with a further band of showers heading south-east.

As the radar loop shows, as these two fronts combined, further rain started developing to the north of the Gold Coast in an almost 'circular' pattern (similar to a swirling low or cyclone). Currently the heaviest falls are to the north of Brisbane, with a Flood Warning issued by the Bureau at 11:06pm for Sunshine Coast streams and rivers.

As far as my personal opinion goes along with years of experiencing weather patterns in south-east Queensland, getting this much rain in Spring is really out of the ordinary. Normally from about September onwards, the only real 'rainfall' that we experience is from thunderstorms or lighter coastal showers.

However, it appears that this year, the weather pattern has changed with seemingly continuous showers and rainfall that doesn't seem familar to me. Maybe it's just that I've live most of my life in a drought situation in Queensland and never saw (or had the tools to see) how weather patterns existing pre 1990.

From what I can see, the rainfall we are experiencing at the moment almost represents an East Coast Low situation that whilst they can occur at any time of the year, they are more prominent in autumn and winter. Additionally, the radar images show a 'circular' pattern which also appears to be related to a low pressure system, but normally the heavier rain falls occur on the southern side of the low. Tonight's weather pattern shows the heavier falls to the north.

In my mind, I can only assume that these weather patterns is because of La Niña climate phase. According to a BOM media release in June:

Historically, La Niña events have often, but not always, brought above average rainfall to much of Australia, particularly inland eastern and northern regions. Night time temperatures are also usually warmer than average. Tropical Cyclone risk for northern Australia also increases during La Niña events.

Widespread wet conditions and flooding events have accompanied a number of La Niña events in the past. Substantial flooding impacted NSW and Queensland in the event of 1998, while the event of 1988-89 saw flooding also occur in SA and Victoria.

In general, while La Niña events tend to be wetter than normal for Australia, no two La Niñas have exactly the same impact on local rainfall. So while some regions may experience the typical pattern of heavy rainfall, other regions may miss out altogether.

Actually, I do remember the flooding in 1998 - from memory there were actually two flooding events no more than about 1-2 weeks apart (this is when I was living on the Sunshine Coast). The second event started around 8:30 at night - as we were trying to watch 'Ally McBeal' on TV and because we had a tin roof, the rainfall got so heavy the TV wouldn't go any louder.

Throughout the night it just kept raining and raining, our backyard was under water, the street was under and the water came halfway up our driveway. We were lucky as our house was slightly higher than the other end of the street. Some of our distant neighbours had water lapping at their doors, with one house having raw sewerage coming out of the drains in the floors of the bathrooms because it had no where else to go.

Anyway, I'm interested to know for those of you who've lived here longer than I have, describe what your opinion of the weather patterns have been over the past month?