Post by greysrigging on Feb 13, 2024 20:14:35 GMT -5
Why is it so wet during an El Nino ?
(source: Tony Auden Meteorologist )
Amongst a Spring and Summer of weather extremes, one question remains for many people, “why is it so wet during an El Nino?”
Well.. This current El Nino looks and feels very different to any that have come before it.
Here’s my analysis of what is happening, and a look towards what we can learn from this current climate setup.
Comments below each picture.
Back in Winter 2023, many international weather agencies had declared El Nino. This is based primarily on water temperature way out in the Pacific Ocean, in what’s called the “Nino 3.4 region”, in the box on the map here.
Once water there reaches 0.5C above normal for an extended period of time, that can be the main trigger for other parts of the world to declare El Nino, and they did.
But for Australia, it’s more complex. We rely moreso on atmospheric circulations working with this ocean pattern, to generally starve the nation of moisture.
If you remember back, the Bureau of Meteorology was slow in declaring El Nino, mainly because the atmosphere wasn’t linking up with the oceans in our part of the world.
They declared El Nino on 19 September 2023, in what was the driest August to October on record for Australia, with devastating fires across southern Queensland.
Then the switch flicked, and storms started in November, and have continued right through until the end of January.
Throw in a couple of cyclones (so far) and a few rain events, and we’ve seen flooding, instead of fires, over the past 3 months.
o what’s going on? Well here’s a quick summary.
El Nino and La Nina are not absolute in the weather conditions they bring, they merely sway the odds towards wet or dry conditions. Australia has an extremely variable climate, but, we can still generally get some useful information out of tracking El Nino/La Nina from season to season.
Amongst this variability, other climate factors are at play:
- The Indian Ocean Dipole “IOD” drove most of the record dry, and horrible fire conditions, in 2019. It was also in a dry “Positive IOD” phase this year. This is where cold water off Indonesia/Western Australia starves passing cloudbands of moisture before they move across Australia.
- The Southern Annular Mode “SAM” can also impact moisture levels over eastern Australia. This index tracks the paths of cold fronts from the Southern Ocean. It’s been in a positive phase for the past couple of months (before recently dropping back to neutral), allowing humid easterly winds to push in from the Tasman Sea and feed rain and storms.
- The tropics, monsoon and waves like the Madden Julian Oscillation (MJO) can also play a part. While monsoonal weather has picked up in the past few weeks, and will drive a lot of rain over the rest of the northern wet season, tropical climate drivers had minimal impact early on in the season.
Now to drill down into the anatomy of this El Nino.
Normally this is driven by a pool of warm water well out in the Pacific (in the Nino 3.4 region), and cooler than average water near Australia.
But over the past year, the global climate and oceans have seen a huge spike in heat. This is due to a combination of climate change, the developing El Nino itself, and some much smaller factors (like the Tongan volcanic eruption in 2022, and reduction in aerosols in shipping fuels).
So rather than having a gradient of warm to cold water, we now have VERY warm water out in the Pacific, while the oceans near Australia are also still warmer than average.
Here’s a great article looking into this in more detail.. www.swellnet.com/.../11/30/el-nino-not-the-others
Warm water nearby generally increases the moisture available to feed rain and storms.
Now to assess how I’ve communicated El Nino over the past few months.
To be clear, my main experience is in short term forecasting. But I’ve continued to study and improved my knowledge of Australia’s longer term climate drivers over the years.
I’ll happily change my day to day forecasts away from the official ones (I’m checking the latest info sometimes only seconds before going on air), but I’ve been wary of going against the official CLIMATE OUTLOOKS… so far.
So here’s what I said at the start of the season..
- El Nino generally leads to hotter and drier conditions across eastern Australia from Spring into early Summer, but it’s not everywhere and all the time.. it just changes the odds. (In reality I thought this season could potentially be hot and wet, but didn’t trust myself to go against the official outlooks). ❌ (but not completely wrong)
- Temperatures and humidity are very likely to be above average, and much hotter than the past few La Nina years. ✅
- We’re in for a much more active storm season. Thunderstorms need heat and some dry air to get going. ✅
- While the official stats suggest cyclones are less likely on the QLD coast during El Nino, it only takes one cyclone to do a lot of damage, and I think we’re due based off how warm the water is. ✅
I can only promise that I’ll learn as much as possible from this season (with plenty still to come) in order to best forecast and communicate the risks in future.
(source: Tony Auden Meteorologist )
Amongst a Spring and Summer of weather extremes, one question remains for many people, “why is it so wet during an El Nino?”
Well.. This current El Nino looks and feels very different to any that have come before it.
Here’s my analysis of what is happening, and a look towards what we can learn from this current climate setup.
Comments below each picture.
Back in Winter 2023, many international weather agencies had declared El Nino. This is based primarily on water temperature way out in the Pacific Ocean, in what’s called the “Nino 3.4 region”, in the box on the map here.
Once water there reaches 0.5C above normal for an extended period of time, that can be the main trigger for other parts of the world to declare El Nino, and they did.
But for Australia, it’s more complex. We rely moreso on atmospheric circulations working with this ocean pattern, to generally starve the nation of moisture.
If you remember back, the Bureau of Meteorology was slow in declaring El Nino, mainly because the atmosphere wasn’t linking up with the oceans in our part of the world.
They declared El Nino on 19 September 2023, in what was the driest August to October on record for Australia, with devastating fires across southern Queensland.
Then the switch flicked, and storms started in November, and have continued right through until the end of January.
Throw in a couple of cyclones (so far) and a few rain events, and we’ve seen flooding, instead of fires, over the past 3 months.
o what’s going on? Well here’s a quick summary.
El Nino and La Nina are not absolute in the weather conditions they bring, they merely sway the odds towards wet or dry conditions. Australia has an extremely variable climate, but, we can still generally get some useful information out of tracking El Nino/La Nina from season to season.
Amongst this variability, other climate factors are at play:
- The Indian Ocean Dipole “IOD” drove most of the record dry, and horrible fire conditions, in 2019. It was also in a dry “Positive IOD” phase this year. This is where cold water off Indonesia/Western Australia starves passing cloudbands of moisture before they move across Australia.
- The Southern Annular Mode “SAM” can also impact moisture levels over eastern Australia. This index tracks the paths of cold fronts from the Southern Ocean. It’s been in a positive phase for the past couple of months (before recently dropping back to neutral), allowing humid easterly winds to push in from the Tasman Sea and feed rain and storms.
- The tropics, monsoon and waves like the Madden Julian Oscillation (MJO) can also play a part. While monsoonal weather has picked up in the past few weeks, and will drive a lot of rain over the rest of the northern wet season, tropical climate drivers had minimal impact early on in the season.
Now to drill down into the anatomy of this El Nino.
Normally this is driven by a pool of warm water well out in the Pacific (in the Nino 3.4 region), and cooler than average water near Australia.
But over the past year, the global climate and oceans have seen a huge spike in heat. This is due to a combination of climate change, the developing El Nino itself, and some much smaller factors (like the Tongan volcanic eruption in 2022, and reduction in aerosols in shipping fuels).
So rather than having a gradient of warm to cold water, we now have VERY warm water out in the Pacific, while the oceans near Australia are also still warmer than average.
Here’s a great article looking into this in more detail.. www.swellnet.com/.../11/30/el-nino-not-the-others
Warm water nearby generally increases the moisture available to feed rain and storms.
Now to assess how I’ve communicated El Nino over the past few months.
To be clear, my main experience is in short term forecasting. But I’ve continued to study and improved my knowledge of Australia’s longer term climate drivers over the years.
I’ll happily change my day to day forecasts away from the official ones (I’m checking the latest info sometimes only seconds before going on air), but I’ve been wary of going against the official CLIMATE OUTLOOKS… so far.
So here’s what I said at the start of the season..
- El Nino generally leads to hotter and drier conditions across eastern Australia from Spring into early Summer, but it’s not everywhere and all the time.. it just changes the odds. (In reality I thought this season could potentially be hot and wet, but didn’t trust myself to go against the official outlooks). ❌ (but not completely wrong)
- Temperatures and humidity are very likely to be above average, and much hotter than the past few La Nina years. ✅
- We’re in for a much more active storm season. Thunderstorms need heat and some dry air to get going. ✅
- While the official stats suggest cyclones are less likely on the QLD coast during El Nino, it only takes one cyclone to do a lot of damage, and I think we’re due based off how warm the water is. ✅
I can only promise that I’ll learn as much as possible from this season (with plenty still to come) in order to best forecast and communicate the risks in future.