Seasonal Outlook
The latest on La Nina/El Nino, IOD, SAM and MJO - all things that drive our weather. A discussion on the Pacific and Indian Ocean's (whether they are in a seasonal phase where they encourage tropical moisture to be sent towards or away from Australia), as well as the long range indicators of how the pressure systems may behave to turn that moisture into rain.
The latest guidance using key indicators and forecasts to tell us if it is more likely to be wetter or drier in the weeks and months ahead.
In order for it to rain, we need two things: a feed of tropical moisture (from the Pacific or Indian Ocean), and low pressure (from troughs, lows, fronts). Where they meet up it rains. Conversely, if there is a lack of tropical moisture, it doesn't matter how many low pressure systems move through, they can't produce much rain.
Follow the maps below to see the latest. Automatically updated daily to weekly.
Starting with the next week...
CURRENT WEATHER MAP
Updates four times daily.
8 DAY OUTLOOK
Updates twice daily, around 8am/8pm AEDT
See day by day maps here.
The indices we look at...
SEA SURFACE TEMPERATURE ANOMALY
Updates daily (showing how much warmer or cooler than usual the water at the top of the oceans are)
Warm water in the boxes pushes tropical moisture away from Australia.
Cool water in the boxes pushes tropical moisture towards Australia.
Warm water around the top half of Australia helps push tropical moisture across Australia. Cool water around Australia means less moisture is available.
PACIFIC OCEAN INDEX (EL NINO/LA NINA)
Updates weekly on Monday evenings
The temperature of the Pacific Ocean box, and forecasts for a range of models over the next six months.
If the forecast enters the green area, the Pacific Ocean should push tropical moisture towards Australia (known as La Nina). When low pressure moves through it helps bring flooding rain, most felt in northern and eastern AUS.
If the forecast enters the brown area, the Pacific Ocean should push tropical moisture away from Australia (known as El Nino). This leads to drier than average conditions, even if low pressure is nearby, as there is less moisture available to feed them.
INDIAN OCEAN INDEX (IOD)
Updates weekly on Monday evenings
The temperature of the Indian Ocean, and forecasts for a range of models over the next six months.
If the forecast enters the green area, the Indian Ocean should push tropical moisture towards Australia (known as a negative Indian Ocean Dipole [IOD]). When low pressure moves through it helps bring soaking rain to southern AUS - this area has chances of a wetter Winter and Spring.
If the forecast enters the brown area, the Pacific Ocean should push tropical moisture away from Australia (known as a positive Indian Ocean Dipole [IOD]). This leads to drier than average conditions, even if low pressure is nearby, as there is less moisture available to feed them.
This index naturally decays to neutral each Summer, thanks to the monsoon.
SOUTHERN ANNULAR MODE (SAM)
Updates daily
SAM controls our weather systems.
Positive encourages lows and troughs that can be slow moving (and when they are fed by tropical moisture they bring significant rain for those in their path). Also encourages weaker cold fronts, making it drier than average along Australia's southern coast, unless a low can wander down and drench those nearby.
Negative encourages stronger cold fronts. This helps Australia's southern coast see rain, but it only spreads inland if high pressure doesn't block tropical moisture from the Pacific or Indian Ocean spreading through.
But...
- High pressure can 'get in the way' no matter what the signal is. We can't all be covered in low pressure, there are highs in between.
- Cold fronts only hit one area. If a strong front hits Perth, it won't do much for Melbourne... if a strong front hits Melbourne, it missed Perth.
- Slow moving troughs and lows are the ones that produce the big wet weather as bring rain for longer. But the location of the low or trough has a huge impact on who gets the rain. For troughs: on or east of the trough gets the rain, those to the west miss out. For lows: east and south of the low gets the rain, and if the low is just off the east coast, then heavy rain falls just south of the low, those to the north miss out.
MADDEN JULIAN OSCILLATION (MJO)
Updates daily
Weird graph, but bear with me! This shows the path of a pulse of tropical energy that helps push that tropical moisture around.
When in the green zone tropical moisture is pushed towards Australia. If you are affected by low pressure it helps intensify the rainfall even further. In the tropics it encourages periods of wet weather in the wet season.
When in the white zone there is no push either way.
When in the brown zone tropical moisture is pushed away from Australia. If you are affected by low pressure the falls can be lighter than usual. The Australian tropics generally enter a quiet period even if it is in the wet season.
Putting It All Together...
NEXT WEEK OUTLOOK
Updates daily in the late afternoon
The latest forecast from BoM.
Green and blue indicate above average rain. Orange and brown indicate below average rain.
Updates daily in the late afternoon
The latest forecast from BoM.
Red indicates above average minimum temperatures. Blue indicates below average minimum temperatures.
Updates daily in the late afternoon
The latest forecast from BoM.
Red indicates above average maximum temperatures. Blue indicates below average maximum temperatures.
FOLLOWING WEEK OUTLOOK
Updates daily in the late afternoon
The latest forecast from BoM.
Green and blue indicate above average rain. Orange and brown indicate below average rain.
Updates daily in the late afternoon
The latest forecast from BoM.
Red indicates above average minimum temperatures. Blue indicates below average minimum temperatures.
Updates daily in the late afternoon
The latest forecast from BoM.
Red indicates above average maximum temperatures. Blue indicates below average maximum temperatures.
FIRST MONTH OUTLOOK
Updates weekly on Thursday afternoons
BoM's forecast for rain.
Green and blue indicate above average rain. Orange and brown indicate below average rain.
Updates weekly on Thursday afternoons
The latest forecast from BoM.
Red indicates above average minimum temperatures. Blue indicates below average minimum temperatures.
Updates weekly on Thursday afternoons
The latest forecast from BoM.
Red indicates above average maximum temperatures. Blue indicates below average maximum temperatures.
SECOND MONTH OUTLOOK
Updates weekly on Thursday afternoons
BoM's forecast for rain.
Green and blue indicate above average rain. Orange and brown indicate below average rain.
Updates weekly on Thursday afternoons
The latest forecast from BoM.
Red indicates above average minimum temperatures. Blue indicates below average minimum temperatures.
Updates weekly on Thursday afternoons
The latest forecast from BoM.
Red indicates above average maximum temperatures. Blue indicates below average maximum temperatures.
