TRANSCRIPT OF OCTOBER CLIMATE UPDATE WEBINAR
Date: 5TH OCTOBER 2010
PRESENTER: Well, good afternoon everybody and welcome to the October Climate Update. My name is Dale Gray from the Department of Primary Industries at Cobram, where we have a partly cloudy, warm day. It's quite glary.
Anyway, on to the summary for September. You can see that the rainfall decile map for Australia out looks entirely very blue, with lots of very much above-average rainfall through Australia.
The story for Victoria, however, is a little bit different. It's essentially average for much of Victoria, a little bit of above average rain through the Central Highlands, and once again the Gippsland region sort of missing out for the month of September. Also you'll notice that the month of September wasn't so good for our compatriots over in Western Australia either, where it was very much below average.
Looking at the greenness, how much the NDVI, how much greenness there is compared to normal, we can see once again a large amount of vegetation growing through this southern Northern Territory area and into Queensland, and down into New South Wales and through the Mallee area of Victoria as well.
Most of Victoria, however, is pretty much normal, except there is a section down in the south-west here which I am presuming may be looking in fact yellow because of waterlogging rather than a - - so the greenness is coming from waterlogging rather than a lack of growth per se, because, there's certainly been enough water down there. So, in terms of locust food, there's plenty going on up here in these areas at the moment.
In terms of temperature, temperatures were cooler. Most people probably thought they were cooler for September. They certainly were by a couple of degrees in Victoria, although the interior of Australia was quite significantly cooler than normal, although the very top end was slightly warmer.
In terms of minimum temperatures, well, they were pretty much normal for Victoria, maybe just a touch cooler, and a patch up here in the Riverina, which was definitely 1 to 2 degrees cooler. But, you can see vast amounts of the top end and Queensland being significantly warmer than normal.
Looking to the latest seasurface temperature anomaly chart, where we can see that the Nino 3 section here is at -0.72, so that's just slightly below La Nina threshold of 0.8. The Nina 3.4 section is well and truly cooler than that at -1.39, well and truly over the threshold, and the Nino 4 section here as at -1.31 which is also very much over the threshold. You can see the classical shape of a horseshoe normal than normal warmer weather, which you get from a La Nina.
Interestingly, after the change which we alluded to last month, the DMI, the measurement of the Indian Ocean dipole here, is at -0.98, which is very much indicative of an IOD negative as shown here by the warm water around Sumatra, and this cooling patch of water hanging off the Kenyan coast.
Now, looking at our change in sea surface temperature chart for the month courtesy of the Bureau of Meteorology, you can see here that the change for the month, there's been some slight cooling going on in this Nino 3.4 region here, but essentially the Pacific didn't do much for the month of September. You can see there's been a little bit of warming out here in the Coral Sea, a little bit of warming out here in the sort of Arafura, Timor seas, and the really strong point is this warming that's happened off Sumatra, but you can't see that there's really been much going on over here over on the coast of Kenya.
In terms of the Tao/Triton Boyo Ray (?), giving us the ocean to depth, we can see for the month of September that there was a cooling intensification in the water to depth below the current La Nina down to sort of 150 to 250 m deep, yes, being you know up to at least 4° cooler than normal, so there's still no change in that, but there's large amounts of cool water which is helping to keep that La Nina cool at the surface.
In terms of world cloudiness as measured by the satellites and outgoing longwave radiation, we would normally expect a lack of cloud around the international dateline for La Nina and we're still seeing this, although that anomaly is sort of moving sorts of more westwards away from the international dateline. We still see a vast amount of extra cloud currently over the Indonesian continent and much of that cloud is actually now promulgating out here into the Indian Ocean.
You can also see that the north-west cloud bands that have been constantly coming through in the last month, have been missing Victoria, down here, and you can see that lack of cloud also in Gippsland. So, we're still awaiting for a change in the pattern which allows some of that north-west cloud band to really come down into Victoria.
Once again, looking at the winds, the winds through the Pacific Ocean as taken by the Teyo Triton buoys, we can see here that for the month of September once again that Western Pacific area has had trade winds much stronger than normal, and really pushing that warmer water and keeping it over the Indonesian continent, and really helps to form that classic horseshoe shaped warm water, but over here in the eastern Pacific we're not seeing anything terribly strong there. We did in the previous month see some pickup in the winds, but that's pretty much returned to much like normal at the moment.
The southern isolation index has maintained its strong positive value here at +24.7, which is a very strongly positive value for the FOI, and you can see that it's been like that now for a number of months. So, this is really indicating to us that the Walker circulation out there along the equator is behaving as we would expect for a La Nina, which means the cloud and the pressure through the equator is behaving like La Nina, and we currently have a really well fully coupled situation where the ocean temperature has been cool, talking to the atmosphere and the clouds and the pressure above the ocean, so they're working together in harmony.
Going on to the subtropical ridge now, and the September air pressure, this is just a mean September air pressure from the MSLP chart, conglomerated together for the month of September. We can see that the high pressure was essentially situated over the south-west of Western Australia. The actual level of that subtropical ridge is probably lower than you would like to see, but at the moment the subtropical ridge should be in transition from its winter position up here at the Bite, down to its summer position in Melbourne, so essentially reasonably normal for positioning. And, you can see here that the prevailing winds coming on average were sort of just clipping the south-west of Victoria, and there were numbers of fronts south of the divide, but there were very few frontal systems that got through north of the divide, and we had that one major low pressure system at the very early start of the month, which brought us most of the rain.
Looking at the anomaly for pressure, position was normal, but certainly the anomaly is very interesting. Really dominated by this large area of very, very high pressure south of the Western Australian tip, and that was really assisting to totally block weather patterns coming particularly into northern Victoria. Once again, there was some frontal system coming up here and getting to the coast and shifting away quite rapidly, but really blocking any activity coming in either from Shark Bay and down, which we would normally like to see this time of the year.
Looking at the southern annual amode, which as people might remember has been in this very strongly positive phase for a fair bit of this year, through the month of September, there was actually some weakening of that and we actually saw some forays into the negative which we really hadn't seen a lot of. It's currently still up in the positive, slightly positive sort of area.
The Noah predictions for 14 days sort of show that it's possibly going to come back down to neutral in the next fortnight. The really issue though is the southern annual amode starts to lose its influence over Victoria in spring. It really has its major influence over winter, although it clearly can in spring if it's strong enough, actually either improve or remove the ability for frontal systems to come in from the Southern Ocean.
Looking at the Noah storm track here, we're really looking for the prevalence of some of these wiggly lines through the state, and we did just have that one low pressure system at the start of the month, so you know I think the previous month we might have had two coming through. This month we've only had one, so if we're not getting frontal activity, we're really needing some low pressure system to cut off lows to occur, which we were fortunate not enough to get at the start of the month. It caused a bit of flooding, but the fine weather since then has really allowed things to dry out quite nicely.
Looking at the Madden Julian isolation which has really been in no man's land for the month of September, looking pretty incoherent doing not much, really sort of sitting over in this area of Africa and not really developing, has just now though started coming into position three here with some intensity, so some of the models are predicting that that weather will actually progress forward into our favourite position five here sometime in the next couple of weeks. So, that might provide a potential moisture source for us, although at the moment, the ocean up there is very, very warm, anyway, providing plenty of moisture source, if only we can get the triggers down south to actually link through and pull some of that down.
Now looking at some of the coupled global circulation model runs for the coming three months, you can see here that the consensus of most of these models is that La Nina is likely to hang around for October, November, December. The Indian Ocean is predicted to stay warm or slightly warm and you know, four of the models here predicting IOD negative conditions to continue for the next three months.
So, not surprisingly, a number of models are all saying that the chances of rainfall for Victoria are slightly wetter, slightly higher to wetter because of these moisture sources here looking so good.
In terms of temperature, well, that's very mixed at the moment. The modellers are pretty unable to make up their mind whether it's going to be average, slightly cooler or slightly warmer. This is a bit of a change from previous months where a number of models have been suggesting it was going to be slightly warmer for some time, but we haven't really experienced those sort of conditions, and now some of them are sort of hopping on the cooler bandwagon.
Looking forward into the next three months after that, so January, February, March nearly - - well, all the models predicting the La Nina to be still in existence at that time and the Indian Ocean to return to neutral conditions. We would normally expect the Indian Ocean dipole to break down sometime in November/December if it is a late one like it is currently this year. Most Indian Ocean dipole events are happening earlier, in the winter time months, but this one is setting up much later.
The La Nina, interestingly, certainly can get right into our Autumn period, but the strength of La Nina actually having an influence on Australia's climate tends to decrease over those summer months, and really is more likely to influence the northern areas of Queensland. That's sort of obeying the historical record. But, a number of the models are still thinking that that La Nina is likely to give average at least to slightly wetter conditions over a lot of areas of Victoria through summer, which potentially wouldn't be so good if it's in the middle of harvest.
So, summer temperatures once again looking quite - - yes, slightly mixed in terms of their outlook. A few warmer ones, you know an odd average, and some thinking things might be slightly cooler.
So, looking at the last slide here, looking at the Bureau of Meteorology's POAMA model, looking at the 0 to 14 day run, and its 14 to 28 day run in the sort of medium-term, it's not really showing any strong signs of joy here, as this sort of a dry patch here off the Sydney coast is really influencing here. There's quite a strong blocking high in the Tasman Sea over New Zealand sort of stopping moisture feed coming into this area.
The 14 to 28 day forecast doesn't really show a great patch of green over Victoria, which we might be looking forward to by then, but, clearly, we will be looking for some average rainfall reasonably soon as a number of those crops are starting to tongue it, particularly in the Mallee as they're pumping a lot of water out, being as good as they are.
So, that finishes this for the summary for this month and the coming months, and I hope that's been useful to you, and we look forward to your presence next month. Bye.