I will make a note about the Indian Ocean today as we are seeing little influence on the rainfall in recent weeks and continuing to see minimal impact over the coming week or so.
The issue that I am seeing at the moment surrounds the placement of high pressure over the Basin.
The warming over the Basin is not overwhelming at the moment but the guidance is for it too warm up further but the persistent southeast winds and drier is limiting the convection over Java at the moment. This may change as the build up returns earlier this year and that may be what we rely on for the IOD to be seen to influence the nation's rainfall.
SSTs Forecast - Euro - Valid for September through November 2021.
The forecast SST forecast continues to show a warmer than normal IOD region for the remainder of the year which is expected to peak during October with the anomalies peaking ahead of the shift to the monsoon season during December. This is where the influence will be at its greatest. So really from September to November is when we should feel the full impact this year, but modelling keeps things quiet in the shorter term as you can see in the analysis.
Rainfall Forecast Anomalies - Euro - Valid for September through November 2021.
The model still suggesting the convection and rainfall in response to the elevated SSTs and the negative IOD throughout the coming months, leads to widespread above average rainfall that spills over from Indonesia, through northern Australia and into the southeast inland of the nation. Having a higher chance of above average rainfall through the southeast of the nation, which is the wettest time of the year, is significant.
Lets have a look why it is quiet in the short term and the charts look bare in the regions that are slated to see above average rainfall.
You will note in the movement of the weather over the Basin, that the high pressure is ultimately blocking moisture coming into northern parts of WA. The moisture is having some modest impacts on frontal weather passing through the southern ocean during the coming week. You can see that clearly on the simulated satellite data below.
Simulated Infrared Satellite Imagery - Next 10 days
Note the moisture associated with the bump in monsoonal conditions over the Indian Sub Continent and through parts of Southeast Asia. That extends across the northern Indian Ocean and some of this moisture is what is fed via the jet stream into stronger cold fronts moving eastwards. The area that we need to see the moisture pass through and build up further is northwest of Australia and through Java for larger rainfall events to develop. Also I want to point out the northwest moving low pressure system through the Central Basin, that is then pushed west by strong high pressure southwest of WA. This is what is keeping the moisture away with the moisture being propelled west through towards the western Basin and leaving dry air over much of the eastern Basin towards Australia. This is not because the ocean is cooler, it is due to surface pressure pattern prognostics.
This illustrates the movement of high pressure and how it is deflecting the moisture away from the Australian region, the only influence of moisture is coming via the frontal weather passing through. For larger rainfall events, we need to see convection increase over Java and for this period it is relatively quiet, hence why we see the drier trends for northwest Australia. This needs to shift in the coming weeks to verify the climate model guide that the IOD is increasing in strength through September and October.
When it all comes together, you can see how the moisture from tropics is drawn south. You can see how far south that is pulled from the equator.
Again my two week temperature forecast and rainfall forecast reflect the current trend but I am still leaning towards more widespread rainfall building in the weeks.
Rainfall for the coming 2 weeks.
Temperature Anomalies for the next 2 weeks.
The seasonal rainfall and temperature outlooks below were prepared last week and will be updated again next week. You can read about it here. Make sure you refer to the climate section of the blog by choosing the drop down menu where you get all the climate posts and forecasts which are archived for reference.
Rainfall outlook for Spring 2021
Temperature Outlook for Spring 2021.
I will have more updates coming up on this Friday.