Brisbane
Grey skies are gonna clear up
It's been many days now that we've been back in Brisbane waiting for the weather to clear. Apparently it will let up on Wednesday and we should be able to get out. In the meantime I guess we'll just sit it out and complain about the weather.
Brisbane's climate is Subtropical Oceanic. It has very mild, dry winters from June to August. During winter the daytime temperatures are generally around 20 degrees and it is mostly sunny.
Springtime here is September and October. It is usually pleasantly warm, but the rains start to make their presence felt.
Summers are long in this part of Queensland, lasting from November until March. It is hot and muggy as a rule, however there is usually a nice sea breeze, especially in the afternoon. The weather can be quite good; it can also be quite bad. Especially in La Niña years.
La Niña (the little girl) and El Niño (the little boy) are two phases of the El Niño Southern Oscillation - the ENSO cycle. The winds and sea surface temperatures in the tropical Eastern Pacific Ocean warm up and cool down in an irregular cycle, and as they do, they greatly affect the weather patterns over much of the tropics and subtropics all around the world. When the temperatures are normal, the ENSO system is said to be Neutral. When the temperatures are warmer than normal, the system is said to be in an El Niño phase. When the temperatures are a bit cooler then it is La Niña.
The reason a La Niña results in cooler surface temperatures in the Eastern Pacific is that the Equatorial Trade Winds from South America have driven the warmer waters towards the Western Pacific, where we find ourselves at the moment. These warmer tempeartures generally result in increased rainfall for Eastern and North-Eastern Australia. They can also increase the risk of a tropical cyclone and bring an early monsoon season.
The La Niña of 2010-12 was an exceptionally strong and long lasting event. It coincided with a negative phase in the Indian Ocean Dipole, which is another major factor in the weather of Australia. And there were a number of notable cyclones, including Cyclone Yasi, one of the strongest in Australian history. Together, these individual factors added up to devastating floods and the wettest period on record.
Until now. The current La Niña is considered to be weakening. The Indian Ocean Dipole is in a neutral phase. The Bureau of Meteorology predicts only an average to a slightly-above-average number of cyclones for the 2020-21 season. And yet the rains have come. For the last four days there has been a convergence of four factors: a La Niña, weakening though it may be; a tropical low north of Australia; a dip of the Southern Polar Jet Stream towards the equator; and high pressure over the Tasman Sea. Together these have all created a weather bomb.
The weakening La Niña has infused a great deal of moisture into the air. By itself, this would result in a few rainy days. But the addition of two pressure areas - a low to the north and a high in the south, changes the intensity a great deal. In the Northern Hemisphere, winds flow clockwise around a high pressure system and counter-clockwise around a low. This is due to the Coriolis Effect, and it is reversed south of the Equator. That means a low to the north of Brisbane would cause an increase in wind speed blowing moisture in from the ocean. And so would a high to the south. A double whammy. But even this would merely result in a day or two of rain. Unless you factor in the jet stream. Ordinarily, the South Polar Jet Stream flows from west to east at around sixty degrees south and helps to blow pressure systems out of any one area. But from time to time the east-west stream dips towards the equator - a south-north orientation. This has the tendency to lock pressure systems in place for days. And this is what has happened.
A few days ago they were calling this weather bomb a once-in-twenty-year rain event. Then they were calling it a once-in-fifty-year event. It was sixty for a while but now some are calling it a century event. And it isn't quite over.
All along the eatern coast of Australia, in Queensland and mostly New South Wales, there are evacuations, mudslides, washed out roads and bridges, overflown rivers and reservoirs on the brink. Some parts of New South Wales resemble an inland sea. There have been more than 700 rescues of trapped people. In one such rescue, a family of six and their three cats, the rescuers could not put the children in the raft until they had first removed the snakes, spiders and insects that had jumped in to escape the water. Right here in Brisbane, there are sharks and crocodiles swimming in the flooded streets.
The current wet is a stark contrast to last summer - the Black Summer. During the summer of 2019-20 a completely different set of atmospheric conditions were at play, resulting in the worst bushfire season ever seen in Australia. Then, 186,000 square kilometers, 5,900 buildings, 34 people and an estimated three billion critters were victims to the wildfires that ravaged the country. These dramatic weather events are naturally attributed to global warming, and are expected to worsen.
For now, though, Brisbane is starting its fall season. March to May is a good time to visit Brisbane, as the temperatures are generally between 15 and 25 degrees and there is little humidity. And with that, almost no rain.