Looking towards substantial rainfall for SE Australia

[Supercellimpact]

That chart has La Nina writen all over it, looks like a carbon copy as last year, but of course this time it will be no where near as strong.

[crikey]

Just clicked on Anthony V's quote from a post he just made on another thread and was overjoyed to see how well Australia has done during an La Nina Period.
Looking towards substantial rainfall for SE was the title of this thread in 2009 and now we can say the rain came.
Have a look at this . It is a fantastic result. Thanks for that link Anthony V.
And lots of records broken for this 12 month period.
You will need to go to this link to view the whole map as it doesn't fit on my screen anyway
http://www.bom.gov.au/web03/ncc/www/awa ... t.hres.gif" onclick="window.open(this.href);return false;


EDIT: Made the image smaller - apocalypse

[droughtbreaker]

I don't see any correlation between the current events and what was happening at the same time last year, nor do I see this summer as panning out the same as last summer. There are no indications whatsoever that any La Nina that may develop this summer will be anywhere near as strong as last year. We have to remember that the previous La Nina was one of the strongest ever, if not the strongest. Statistically it is extremely unlikely to have two extreme La Ninas in a row. All indications are pointing to a weak La Nina this summer.

What this means is an increased chance of summer storms and systems of tropical origin making their way down here, but on the other hand it is all very hit and miss and a weak La Nina can often mean a hot summer down here and sometimes even dry (Black Saturday case in point).

If I had to make a prediction I would say that rainfall will be close to average over the period with a real mixture of stormy humid days, hot and dry days and perhaps one or two substantial tropical origin rain events.

Just to add...
We have had 123.1mm in the past 11 days here and it may seem very wet, but really that is typical of early/mid spring. September/October is the wettest time of year in central VIC.

[johnno]

Yeah I expect average rainfall the next few months mabye slightly above but nothing extreme thats for sure.. This weak to moderate La Nina at the moment looks exactly like the 2008/09 event and it didn't rain for 2 months down here (Jan and Feb) so just goes to show not every La Nina has a wet impact down here but in saying that I think we should get through a preety normal Summer... Last Summer was a freak and I will guranatee 99% that won't happen again this Summer.

[Supercellimpact]

Weatherzone 28day forecast has from the 17th to the 25th October. A high rainfall probability for the Northern Country, a trough hanging around maybe ??

[Jayman]

GFS has a moist northerly flow at that time, but it is a very long way out.

[Ken]

The 4-week forecasts from the EC ensemble currently suggests weak probabilities (very faint wet signal) of higher than normal rainfall extending down from the tropics through inland eastern Oz to Vic between the 17th and 24th of this month. Looking at its MSLP probability map, there's higher than normal pressures to the east and lower pressures to the west so it might be some moisture getting dragged down from the tropics into a trough or front.

[johnno]

By the sound of that Ken sounds like a period of above average temps coming up with only a slight chance of higher than normal rainfall?

[Ken]

Pretty much johnno. But would treat weak probabilities with caution at these ranges because it doesn't always mean there's no strong forcing synoptics for wet conditions. Sometimes you can have situations where just over half the ensemble's members could be going for very wet conditions and just under half are going for only slightly dry conditions. The 2-week EC ensemble meteogram for a sample point I selected near Melbourne is suggesting temps will probably warm up a fair bit (especially minimums) approaching mid next week (not this week but the week after) with moderate probabilities of winds coming from northerly quadrants before settling back down again.

[Anthony Violi]

Very interesting on that chart that the highest on record for Vic looks a lot like the shape of Italy...

Maybe this year we may see something different, like maybe....Russia? Or Jupiter?

[stratospear]

Long range GFS is predicting something big next week between Oct 18 -26:
http://www.wxmaps.org/pix/prec7.html" onclick="window.open(this.href);return false;

[johnno]

Elders updating Today looking into the climatic future next few months for Australia...


The rainfall outlook for the remainder of spring and summer is broadly consistent with that of recent months, while we now have concrete data showing we are moving into a true La Nina event. Sea surface temperature anomalies and temperature anomalies at depth through the equatorial Pacific are all meeting La Nina thresholds. Sea temperatures at depth were more than 5 degrees celsius below average at the end of September, which is a significant La Nina type anomaly. The NINO3.4 index, which is a measure of sea surface temperature anomalies, is also meeting La Nina type levels, with current values going past the required La Nina threshold of -0.5. For a La Nina to be declared by most weather agencies, we need this NINO3.4 value to be held be near or more negative than this -0.5 value for at least 3 months. We are now up to 2 months at or past this level and with no signs of any major changes in the next month, it is likely that most weather agencies worldwide will declare this as a La Nina event. Other data showing us to be in the midst of a developing La Nina pattern is the Southern Oscillation Index, which is a measure of the pressure difference between Tahiti and Darwin (typically lower than usual pressure in Darwin and higher than usual pressure over Tahiti). Consecutive months of +6 values on the SOI are an indicator of La Nina conditions. Having two consecutive months above this +6 value has a strong correlation with above average rainfall over eastern Australia during spring and summer, particularly over Queensland. The August value of the SOI was 2.1 and then increased to 11.7 for September. It is likely that our October value will come in above this +6 threshold, with the value for the first week of October holding above 10. This creates a strong likelihood of above average rainfall through many parts of northeastern Australia during the month of October. In fact, with the developing La Nina pattern, well above median rainfall would be likely through both Q4 and Q1 for northeastern Australia, which is reflected in the long-range modelling. There will be flooding risks for northeastern Australia during spring and summer with this La Nina pattern, although there are some factors that mean the risk is not quite as high as last year. Firstly, the La Nina indicators such as NINO3.4 and the SOI are still well short of the levels seen at the same time last year, meaning the enhanced atmospheric circulation across the Pacific (the Walker Circulation) is unlikely to be as strong through this coming spring and summer. This reduces the risk of flooding being as widespread across eastern Australia, but for northeastern Australia it is the wet season, so above average rainfall at this time of year can often mean flooding. Above median rainfall is not as likely for southeastern Australia through spring and summer, with nearer to median conditions favoured. We currently have a positive phase of the Indian Ocean Dipole, which is correlated with below average rainfall for many of the southeastern states. However, the developing La Nina pattern should conteract this to some degree through Q4 and Q1. This positive phase of the IOD is in stark contrast to the strong negative phase of the IOD seen at this time last year. This negative IOD played a significant role in producing heavy rainfall over eastern Australia last spring, especially when combined with the very strong La Nina event that was also in operation. In short, it is likely that northeastern Australia will see above median rainfall this spring and summer due to La Nina type conditions now being entrenched across the equatorial Pacific. It is worth qualifying that there are some differences in the climate drivers compared with last year, so while the risk of flooding remains, it is not expected to be quite as widespread or as extreme as seen last spring and summer. The correlation between La Nina and above average rainfall does decline for southern capitals, especially as you head west, so closer to median values are favoured for these areas


Issued 10 Oct 2011

[Geoff]

Now a chart like this could get a chap a tad excited!...

imageserver.jsp.png (83.12 KiB) Viewed 6090 times

[Anthony Violi]

I think a lot of people will get caught out this year, especially the BOM. What we are seeing is not normal, and nothing like we have seen for decades.

Already in the last 2 weeks the weather has transitioned, then had the westerly reinforce even further North than previous over the Indian, sending pulses of mid level troughs over the mainland, at latitudes that are most unusual. Shaping up as another big 6 months on the cards. Most climate models now starting to fall into line with my march prediction of a good la nina, and a long one. And indeed a worse one.

[stratospear]

The big change in the past two weeks has been the rapid shift in ocean temps in the Eastern Indian Ocean. Surface temps near Sumatra are now warmer than normal and the weak +ve IOD has basically disappeared. The atmosphere has responded accordingly.

Hold on for another wild ride this summer....

[Gordon]

The 4-week forecasts from the EC ensemble currently suggests weak probabilities (very faint wet signal) of higher than normal rainfall extending down from the tropics through inland eastern Oz to Vic between the 17th and 24th of this month. Looking at its MSLP probability map, there's higher than normal pressures to the east and lower pressures to the west so it might be some moisture getting dragged down from the tropics into a trough or front.

Nicely picked Ken, again.

[Supercellimpact]

The Current National satalite is amazing. Cloud is currently covering most of Australia ( most of it convective ). So this La Nina is just getting started, expect numerous events to drop nice falls and possible flooding and just you wait unitl the Tropical Cyclones get cranking !

[Anthony Violi]

Yeah been hideous falls of up to 1000mm through Northern Queensland...and good build up storms in Darwin and the top end.

One can only imagine when the monsoon gets cranking how much of a pasting we will cop.

[Jayman]

Well you guys have me pumped

[Geoff]

Well I've just had a look at EC, GFS and AccessG, and they all seem to indicate a cut off low moving in from the Bight interacting with tropical infeeds from both n/w WA and the NT from the 8th to the 10th Nov. Seems to me this could result in a big rain event for that period. Looks like the sort of setup to get Anthony excited and posting more regularly!