Cyclone Prospects Warming Up
How many cyclones can you remember forming off Queensland this season? One.. maybe two?
It's been a quiet summer for tropical cyclone activity in the Coral Sea, especially with pre-season forecasts suggesting La Nina would bring a higher than average number of cyclones.
Tropical cyclones typically form during active phases of the Madden-Julian Oscillation (MJO). The MJO is a 'wave' of tropical activity that propagates eastward around the globe. It is simply a large area of low pressure and enhanced rainfall that moves around tropical latitudes on time scales of 30-60 days.
While tropical storms can form at any time during our summer and early autumn, the presence of the MJO moving through the Australian region greatly enhances the chances of tropical cyclone formation due to the increased instability and favourable atmospheric setup it creates. It provides the fundamental starting point for tropical storm formation by way of multiple areas of low pressure.
Combine the MJO with warm sea surface temperatures (as there currently are off north-west Western Australia and northern Queensland) and the likelihood of tropical cyclone formation becomes high.
The MJO 'wave' is currently moving across northern Australia and was last here during the end of January. If you remember TC Iggy which created the rare north-west swell for Western Australia, and then TC Jasmine which formed after a tropical low crossed into the Coral Sea from the Gulf of Carpentaria; these were related to the last time the MJO moved through the Australian region.
Once the MJO moves away to the east across the Pacific Ocean and beyond, tropical activity is usually suppressed across tropical Australia due to the establishment of a more stable weather pattern.
While the MJO increases the likelihood of tropical storms, it also varies in strength. The last two times it passed across Australia (around Christmas and then late January) it was relatively weak. This is one of the main reasons there's been a lower than average occurrence of tropical cyclones this season even though sea surface temperatures have been primed.
The MJO is back again and can be seen clearly on the satellite picture attached (Image 1 above), as a broad area of cloud and enhanced rainfall engulfing the northern half of Australia and surrounds. This time around though it's much stronger and as a result we can expect a flurry of tropical storm activity over the coming week. We have already seen Tropical Cyclone Lua form off north-west Western Australia and it's currently a category 2 system, but forecast to reach category 4 over the coming days.
With the MJO moving through the Coral Sea this weekend and into next week, coupled with high sea surface temperatures, the chance for cyclone formation will become very high and the weather models are indicating this.
A large swell is expected for the Australian East Coast during next week and this late season burst of tropical activity is all linked to the MJO. To forecast when the MJO is expected to come around and when there's an increased likely hood of cyclone activity you can use Images 2 & 3.
Image 2 (above) shows the current position of the MJO and it's track and strength over the last forty days, with Australia being positioned on the right hand side of the diagram (section 5) and the MJO travelling anti-clockwise.
What you can see is that during February the MJO was on the other side of the world and strongest in section 7 which is around Central America, with it re-intensifying as it crossed through the Indian Ocean during the start of this month. Image 3 (right) can be used to forecast the MJO 2 weeks ahead and currently indicates that it will weaken after passing across us and then restrengthen in the Western Pacific Ocean.
The MJO is likely to come around through our region again during the middle of April but as the seasons change it moves further north and will likely play no significant role until next summer.
But keep an eye on the East Coast forecasts over the next few updates as large swell event is highly likely with the last burst of the MJO moving through our region for the summer surf season.
1) The Madden-Julian Oscillation is an eastward tracking 'wave' of tropical instability around the globe with a period of 30-60 days.
2) The current MJO phase may help facilitate the formation of a tropical cyclone in the Coral Sea in the coming week
3) Once the MJO passes the likelihood of further tropical acitivty is suppressed until it comes around again.