Transcript Of Monthly Climate Update - November
Date: 5TH NOVEMBER 2010
MR GRAY: Well, good morning everybody. My name is Dale Gray from the Department of Primary Industries at Cobram, and welcome to November's Climate Update where the weather currently, and climate, is partly sunny with some cumulous cloud blowing in from the south-west.
Now to the October monthly summaries: first of all, to rainfall, where you can see that over large amounts of Australia there's been very much above average rainfall. In fact, there is the highest on record in some areas, and also characterised by an area of pretty much below average rainfall here in the south-west of WA, which is not very funny for their wheat crop.
Here in Victoria, you can see the north-central area and into the north-central hills, we had some above-average rainfall, and a sort of a patch of lower average over here in the Limestone Coast and other sort of small patch in central Gippsland, as well as some lower rainfall in Tasmania. So, even though it's been good in some parts, it's certainly not been good everywhere.
In terms of the greenness index at that moment, where things are greener than normal over the country of Australia, we can see once again this very large amount of abnormal greenness through the lower part of the Northern Territory, most of Queensland, Western Australia, and even the Mallee area of Victoria now showing greener than normal. Compared to last month, we now have south-western Victoria returning to some degree of normality, but there's some dryness sort of showing up down there in parts of Gippsland where things are not as green as they would normally be for this time of the year.
In terms of temperatures, well, both maximum and minimum temperatures in Victoria this month are pretty close to normal; marginally sort of below normal here and marginally above, but essentially normal. The real outlier, of course, is this real depression of temperature that occurred through the centre of the Northern Territory, Alice Springs having very, very, low temperatures compared to normal, and I think there's some records going on there.
Looking at the current sea surface temperature anomaly chart, we can see a number of features. We can see our La Nina still appearing quite strongly through the central equatorial Pacific and the temperatures here at Nino 3 are -1.18 degrees, cooler than normal. Here at Nino 3.4 in the green box -1.4 degrees below normal, and the purple box, Nino 4, at -1.25 degrees, and all those temperatures are well above the La Nina thresholds of roundabout the 0.7 degrees.
So, La Nina is still steaming on quite nicely in the Pacific. You can see that the oceans to the north of Australia here and the Coral Sea, particularly here off the Indian Ocean off the Western Australian coast, are much warmer than normal, and you can see some warmness here sort of off the island of Java and Sumatra.
In terms of the Indian Ocean dipole, we have had in the previous month a weak Indian Ocean dipole negative event, but the most recent data from the BoM suggested that that's now returned to about neutral. The IODDMI measurement is sitting at around about zero. So, there has been a slight warming in this area and some slight cooling in here, which is sort of helping to perhaps remove that DMI. So, it's certainly showing some signs of weakening recently. But, nonetheless, we have had that combination of IOD negative and La Nina, which has certainly been helping to give us some of the rainfall that we've been experiencing in Victoria.
Looking at the changes to the sea surface temperature chart over the last month, no real major thing is happening. Mainly through the equator there has been some slight cooling, more over here in the NINO 3 area which has been a bit slow to sort of cool down, a patch of slight warming here, but it tends to be not much happening through that whole region of the equatorial Pacific. You can see a major area of cooling that's happened here up in the Timor Sea and parts of the Arafura, and this real area of rapid warming that's happened here off the Exmouth coast off WA.
But, in terms of Sumatra and off the coast of Kenya, slight warming here and slight cooling here, which is perhaps helping to nullify some of that IOD negative.
Looking at the undersea temperatures now as taken by the Tao/Triton boyo rays, to depth, 400 metres in depth in fact, you can see here that through the month of October, we still had this very large amount of cool water in the ocean to depth, and we're not really seeing any real propagation of these warmer water in the west back underneath that at this stage yet, which we would usually see when we would start to see the La Nina disappearing or you know, soon to show some signs of decay. So, this warm water is persisting in its usual spot, and the cold water here for the month of October, is certainly still keeping the temperature down, so to speak, for the coolness that's at the surface.
Looking at the world cloudiness chart as brought to us by the satellites, outgoing longwave radiation, so where we have the purple and pink dots is where there is a large amount of cloud, and where there's the black and brown and orange there's a lack of cloud compared to normal, and this is for the last month. So, we can see here at the international date line a lack of cloud, and a real lack of cloud to the west of there. This is indicative of what we would expect for La Nina conditions, with the cool water through this area here not devolving a lot of moisture up into the atmosphere and forming cloud. More typically of La Nina though, we would expect a large amount of cloud over Indonesia and that still continues, and has for many months now.
It's interesting, now you can see a large amount of cloud evolving over that warm part of the ocean which is off the coast of Java and Sumatra. We would normally see a rough sort of horseshoe shape of cloud through this area here with the tongue of cold water and the lack of cloud through the centre, and that's roughly observable there. Pretty much cloud in Victoria though has been pretty close to normal, and you can see in WA there has been a lack.
Now moving on to the tradewinds, we can see that the tradewinds for the month of October as once again taken by the Tao/Triton buoys floating out there permanently, showing that the tradewinds have been pretty much stronger in the Western Pacific. The Eastern Pacific it has been pretty close to normal, so once again as is indicative of La Nina, the tradewinds blow a lot stronger and anywhere you see an arrow here, the wind has been blowing in that direction much stronger than what we would expect normally for this time of the year. And so the tradewinds still picking up there, still pushing – well, helping to upwell some of the cold water to form the La Nina, and also helping to keep that warmer water to the north of Australia and through Indonesia by blowing and holding it there, and not letting it come back out into the more sort of mid Pacific area.
Looking at the southern oscillation index now, it's started to take a dive after remaining quite high for most of October. It's still dropping down but it's still very strongly positive, -17.7 the most recent 30 day figure. So, the ocean and the atmosphere are still totally fully coupled up, which we would like to see for a fully developed La Nina, so this shows the - - really the SOI of course being a measurement of the strength of the Walker circulation, the high and low pressure systems along the equator, and they're behaving as we would expect for La Nina conditions.
Looking at air pressure now, mean sea level pressure over Australia and the oceans around us, we can see here through this line that I've roughly drawn through the high-pressure systems, that the subtropical ridge for the month of - that should read October - was in fact in a reasonably normal position. So, at this time of the year, we would expect the position of the subtropical ridge to be retreating from its winter position at the top of the bite to its summer position around Melbourne, so this is roughly indicative that that was happening for this month. Of course, what you do see though is the predominance of some high-pressure out here in the Tasman Sea and this high-pressure here out off the Western Australian coast. So this pressure here in particular in the Tasman has been allowing moisture to trough down on the back of that, which has allowed some of that tropical moisture to come down into Victoria and much of those areas through central Australia and Queensland and New South Wales as well.
Looking at the pressure anomalies, looking at the differences to normal pressure for the month of October, you can see that the pressure over Victoria was up to 4 hPa above normal, which is actually quite a bit higher than normal, but the good thing was the positioning of this, as I said, this very high pressure out over in the Tasman Sea, which was much higher than normal there, which really allowed some of that moisture to trough down on the back of it. So once again you see high pressure off the coast of WA here which has really been stopping the frontal activity coming through then much for the month of October.
We had one good, or one significant rainfall event through the month, around the middle of the month, where we have sort of two or three days of rain in many parts of Victoria. That was in part helped by this blocking high out here, which prevented that low formation from getting away.
Looking at the southern annual amode now, the measure of what the winds and the frontal systems are doing around Antarctica, affecting southern Victoria, the southern annual amode has been spending most of its time in the positive territory for most of the year. We had some sort of retreating at the end of September. That's gone back up into the positive once again, and for most of October it was in fact positive, and this has allowed south-western Victoria in some respects to dry out. But, it probably hasn't been helping Gippsland at all given that most of those fronts that had come through Victoria had been quite low down, and with the rainshadow effect and then moving south, Gippsland has tended to miss out on much of that frontal range. Given that a lot of the rain has also been tropping in from the north, that doesn't necessarily help Gippsland either with the rainshadow effect.
So, the 7, 10 and 14 day NOAA predictions suggest a return to 0 for the southern annual amode and then sending positive once again, although at this time of the year it really does start to lose its influence in terms of giving us the rainfall, as most rainfall really needs to come from the north, but as a result of a trigger in terms of those frontal systems and low pressures that might be coming in in the south.
Looking at the NOAA storm tracks here now, we can really just look for any existence of the worm lines, which showed the existence of low pressures through the previous months, and you can see there this yellow line and this purple one, that we did in fact have two of those low pressure systems, and they did bring us most of the significant rain through the month of October.
Looking at the Madden-Julian oscillation here now, which starts to become more important as we come through the tropical summer periods and with the monsoon season, it was very strong through the month of October, as you can see here and where we like to see it in position 5, which is when it's sitting here to the north of us. Much of our rain happened around that 4th, 15th and 16th period of the month, where the Madden-Julian oscillation was in position 6, where much of that convective moisture was sitting here off the eastern coast of Papua New Guinea. That has since now returned back into an incoherent sort of form, where it is here on the second of the month and really not very noticeable and not doing anything, and it's proving to be reasonably weak by the next 14 days, at least by the NOAA people, so not expecting to see any tropical moisture coming in north of Australia as a result of the NJO any time soon in the next fortnight.
Now looking at the model summary runs that I recently crunched a couple of days ago for most of the - - some of the coupled circulation models around the world and some of the ensembles and some of the statistical systems that exist, just about everyone - - in fact, everyone is in agreeance that we have a cool La Nina in existence, and that is likely to remain there for the next three months. Interestingly, the warmer and slightly warmer ocean off the coast of Western Australia and off into the Timor Sea is predicated to stay at least warm or slightly warm for the next three months as well. So, both of these two events here are likely to keep warm oceans to the north of Australia, which at least means that moisture sources are going to be quite high from the tropics this year.
In terms of summer rainfall, La Nina's don't always provide summer rainfall to Victoria, in particular. A number of models though suspect that or are suggesting that this could be the chance this year. In fact, there's a bit of average sort of stuff going on here, particularly in the west of the state and the east of the state and a number of models here sort of predicting the whole state to be wetter as well. My assessment for most of that is that slightly wetter is still a possibility for the next three months, which is probably not what anyone harvesting grain is going to be looking for.
In terms of summer temperatures, well, many of the temperatures have been predicted to be warmer over the last three months. That hasn't eventuated, and last month a number of the models really couldn't - - there was no real consensus, and this month it is certainly the same as that, so we have some models predicting slightly warmer conditions due to those warmer oceans to the north, and a number of models predicting slightly cooler conditions, probably because of the amount of cloud and all the rainfall that might be going to happen, and some sitting on the fence on average. So with temperature, I'd say anything was probably possible.
Looking into the autumn period now, which is really the crystal ball gazing, many of the models are still predicting that La Nina to be quite strong and hanging around. Our own bureau's POAMA model is about the only model that is really showing - or what I looked anyway - that's showing some slight weakening of fact.
Interestingly enough, the Indian Ocean for the next three months in autumn is going to totally change from its warm and it will be either neutral to slightly cool. The rainfall, interestingly enough, though, is still predicted by many of these models to be still happening, and particularly in the east of the state once again, so my consensus of those is that it would be still slightly wetter, and once again, the temperatures for those months are predicted to be pretty much all over the shop. There's probably a few more slightly warmers there than slightly cooler, so it's still nonetheless quite mixed.
Just looking at the 0 to 14, and 14 to 28 day POAMA predictions here, essentially not showing a lot of joy if you're looking to make hay and having grains to be drying down. So, it looks like to be more moisture evolving and coming down from the north potentially for the coming months.
And, that's all folks. Thank you very much for listening, and we look forward to the end of - - start of December sort of predictions for the Christmas holidays, next month. Thank you.
