MEDIUM TERM MAY DRY OUT A LITTLE BUT SIGNALS SHIFTING BACK WETTER FOR THE EAST MID MONTH ON.

This will be something we will watch together over the coming week, will we see a drier picture develop for the flood impacted areas of the east or will the rainfall continue on with the persistent easterly winds?


There has been the idea on some of the climate model data relating to the SAM and the MJO that they may weaken and tend to a drier phase impacting Australia during the second week of March, but that idea has begun to soften in the past three updates, with the SAM not looking to go as negative as first thought and for not as long, which means we could see the positive phase return from mid month supporting the increased rainfall chances for eastern and adjacent inland QLD and NSW. Some of the members go for one of the strongest positive SAM events since last December when we saw those extreme floods around Gympie where 1000mm of rain fell. That does not mean it will happen again as such, but with the past positive SAM event we have seen 1000-1500mm fall west of Brisbane and Brisbane get close to their yearly rainfall achieved for 2022. This next couple of weeks will be interesting watching and I will have details on this climate driver in the coming days.

Over the north, there are signals that the MJO will be rotating through the tropics as forecast over the coming week or two, but the signal could weaken (contract back to the equator) leaving the north in a monsoonal break. Given the orientation of TC Anika over the northwest, there is a chance we could see the drier air from Central Australia being propelled northwards for a period through the week ahead reducing rainfall for the northern tropical areas. There could be renewed rainfall developing once the MJO moves into the Pacific Ocean in mid month which could influence moisture moving south and east through the nation again, and if it merges with a positive SAM phase, I am afraid the areas that are been under flood could see more flooding issues and the areas that have been dry, will remain dry. Something to consider for the medium term, but again more on this through the week.

18Z GFS - Surface Pressure Pattern and Rainfall Distribution - Next 2 Weeks

You can see that the events of this week connected to the positive SAM phase that is now starting to ease. The rainfall will ease this week over the southeast and east as a result, opening the door for a drier westerly change to move through by the weekend. But as quick as the SAM looks to turn negative, it turns positive, and the signal for rainfall and onshore conditions for eastern Australia starts to increase from mid month. So this will be an area to watch over the coming week as rainfall totals could escalate. Over northern areas, you can see that drier air moving north and the monsoon trough moving north of the nation reducing rainfall spread away from the TC. But more rainfall develops once we see the MJO move into the Pacific Ocean and a northwest monsoon becomes established again over the NT and QLD in particular. With the SAM turning positive, most of SA and WA remains dry which is not uncommon for March in the absence of tropical weather moving out of the north.

18Z GFS - Precipitable Water Values - Next 2 Weeks

Excessive moisture over the north and east with the MJO and the positive SAM will remain in place for the best part of this week leading to more rainfall and thundery weather. The moisture from Anika will spread through much of northern and central WA with widespread rainfall moving through the interior before the system is eroded by an upper high over southern Australia during the weekend. The moisture may be spread ahead of the weak front passing over the southern and eastern parts of the nation across the weekend. Then watch the moisture increase again as the SAM turns positive into mid month, so there is now a shorter window of drier air in the areas that do need a break from the torrential rainfall. Fingers crossed the modelling softens and settles down on this idea, but some of the signals are for heavy rainfall to redevelop for eastern Australia in particular. Seasonal moisture values most elsewhere increases through the medium term away from southern SA and WA.

18Z GFS - Rainfall Accumulation - Next 2 Weeks

Rainfall is excessive in the short term over the east and southeast regions of the nation and will ease later this week with a pattern shift. Widespread showers and thunderstorms over the tropics easing in coverage as drier air moves in. TC Anika will move into WA with increasing rainfall and thunderstorms with moderate to heavy falls leading to inland flooding. In the medium term, rainfall will ease for WA at this stage but increase once again for NSW and QLD, extending inland possibly to the ACT and through northern VIC. Interior parts under an upper ridge could stay dry for a fortnight, but it depends on the movement on tropical moisture, but that looks more likely to impact WA.

I will have more in the national wrap tonight and hopefully that rainfall in the east can ease, but this event over NSW and QLD has shown how upper level systems are volatile, hard to predict and can lead to extreme weather conditions when the ingredients are there to produce the 1/100 year events a little more often.


It is safe to say we are seeing more of these climate extremes.