Seasonal Climate Outlook; November 2012 – February 2013.
Issued by Anthony Violi, on 22rd October 2012
Current Overview :
Currently, there are a lot of bizarre goings on with respect to climatic activity. There is currently a large displacement of moisture, pressure systems and rainfall patterns. This has forced the patterns to be slow to transition into late Spring like conditions. There is also a large seperation of airmasses that has been apparent for sometime now, with the Northern half of the country extremely warm, and the Southern half extremely cold. Usually by now, even in a neutral year, the pattern should have transitioned into Spring and we would see much more heat and inland troughs moving South. There are a few reasons for this.
The biggest factor is the Positive IOD, which is colder than normal water sitting off the NW coast of the country. Coupled with this, the air that was quite moist in the westerly wind flow has become dry in recent months, in conjuction with the record levels of Sea Ice in Antarctica. Its my belief both of these phenomenon have coupled together to prevent a breakdown of the positive IOD. In short, cold and drier air has moved up from the relentless barrage from the Southern Ocean, and been swept up through the inland and then NW out into the Indian Ocean. The effect is little moisture over the interior for at least 6 months, with little rainfall, and well above average temps.
This is because of the positioning of the high pressure systems, which have stayed well North. Something a lot like this for example, i have drawn the line of where the cold air comes up from and gets dragged across the Top End and out over the Indian Ocean.
Now, this pattern is a normal climate response after 2 years of record rainfall. Its dragging up cold air, and drying everything out. Usually, this happens most winters. However, this year, its taken it to new levels, the pattern is trying to break from what you see here but is struggling. By now we should have seen the high pressure system further South, allowing moisture to move South from the tropics and given most of the country some rain. The heat troughs over WA and QLD are moisture starved at the moment and are struggling to get moving, so its like a vicious circle. This has caused my forecast of a fairly wet October for some parts to not eventuate, and my belief is that the Antarctic Sea Ice at record levels has had an effect.
In any case, lets look forward to what is coming up. My outlook is almost unchanged.
As i have pointed out previously, the forecast El nino has failed to gain any semblance in the Pacific. The forecast of cool neutral appears well on track. All other indicators are well de-coupled from the oceans, in fact the oceans are starting to couple with the atmosphere at present.
Here is the current drivers for the Pacific Ocean region that i am seeing as influencing the climatic pattern.
Trades are still Easterly, consistent with a La Nada.
Note also though that the trades have weakend somewhat, so a stalemate is in progress. In short, it wont have an effect, it will be neutral year, it will only determine how much heat is released from the oceans, and how big next years La Nina will be.
Southern Oscillation Index is 2.2 for the 30 day reading, and -1.80 for the 90 day reading. By the end of November it should be at zero for the 90 day average as we lose the negative figures from August which was a -6 month. Again, a neutral tendency.
Here is the graph: The positives are La Nina tendencies, and the negatives are El Nino tendencies. The SOI is calculated as the difference in Sea Level Air Pressure between Darwin and Tahiti.
CFS, and the BOM, and all the other climate models, finally agree with my forecast from months ago that an El nino will not occur. It will be a neutral year, which is a good result for us after 2 record la Nina years. Here is the Nino 3.4 area, the centre of the Equatorial Pacific
Here is Nino 1 and 2, close to the South American coast. This is where the cooling of the oceans start as a result of upwelling of cold water.
Sea Surface temperatures continue to lose heat, here is the anomaly chart. I have drawn some indicators on here, and i wil leave up the sst chart from last month to see the difference.
So, the cold upwelling has now got stronger, in the red circle. This is colder than normal water being dragged up due to the strong SE trade winds near South America. In a neutral, or normal pattern, this occurs. The blue then spreads towards Australia as it sloshes westwards on these winds. In the black circle is the slightly warmer than normal water, at the moment there are no westerlies to push this water towards South America. It should move towards Australia with the Easterly trades, which will increase the moisture levels for the monsoon season, and provide more rainfall for much of the eastern half of Australia.
The biggest change is in the orange circle, which is the IOD region I mentioned earlier. Finally the pattern is starting to slacken and it has now warmed quickly at the surface. Note also that it warms every year in November, and stays warm until April. The IOD is only important from April – October, as was seen this year. In any case its warmed nicely now so we will start to see the effects of this warm water in the coming weeks and months.
Here is the last months Sea Surface Temperatures to see the changes.
Will definitely be a neutral, even though there is cooling and warming simultaneously it looks like a break even neutral, with neither side favoured. What is important is that the trade winds should bring enough moisture for good rainfall to the country. How much is the million dollar question?
As noted in previous forecasts, notice the warmth in the Central Indian Ocean, providing fuel for fronts and low pressure systems over the next few months with a great moisture source. Once both areas are warm in tandem, which is now occurring, I think it lines us up for an enormous summer rainfall problem again for most of the country.
Also of note is the heat due to the build up of cloudless days over the desert in the winter months. This heat cannot be ignored, and will move South in the summer months. There should be enough moisture by then to ensure we dont break records, and also enough cold air lurking to keep it at bay so any heat that does eventuate will not be long lasting events. Nevertheless, its possible that we could get some very hot weather, by the next update in November, I will have a much clearer picture on the heat and its effects for Southern areas.
Forecast for Spring: November 2012 to February 2013.
Northern Territory : Temperatures will be slightly above average through the forecast period, tending less so in January and February. Rainfall will be average through the Northern Territory areas for all of the forecast period, and will become above average for all areas through the monsoon season. There is also a risk of severe cyclone occurrence within the forecast area in this late forecast period. monsoonal rain will be above average again, particularly areas exposed to western coastal regions.
Queensland: Temperatures will be slightly warmer than average through the forecast period for all of Queensland except the far north. Rainfall in November will be average to slightly below average through all of Queensland, except the inland which will be below average. However during December through February rainfall will increase substantially for all areas of Queensland. Also, risk of cyclone activity cannot be ruled out this forecast period, though i will have a closer look at this in the update for Qld, in late November
New South Wales : Temperatures will be slightly above average for the forecast in NSW, and well above average in November and December for the two inland western districts. Temepratures will be about average for all districts after the Xmas period. Rainfall will be below average in the NW initially in November, then average for the remainder. The remainder of NSW will have average to above average rainfall this forecast period.
Victoria : Temperatures in Victoria will also be average to slightly above average for all of the forecast period, for Northern and NW districts. Southern areas will see average to slightly below average temperatures during the forecast period. Rainfall will also remain above average for all Southern areas, and below average for the Northern areas in November. However rainfall will increase through late November through Northern areas and be about average for the forecast period.
Tasmania : A continuation of the trend for Tasmania with average temperatures for the entire period and state. Rainfall will be variable, average in western areas and below average slightly in Eastern areas.
South Australia : Southern areas will be slightly above average for temperatures for the entire forecast period. Northern areas will see early above average temperatures through November, averaging out by December. Rainfall will also be highly variable, southern areas will see average rainfall tending wetter through the latter part of the period, Northern areas of SA will see below average rainfall until late November when rain will increase markedly.
Western Australia : Temperatures will be slightly above average in the forecast period, particularly through the Southern and inland areas. Early season records did occur as forecast, and may continue for another 4 weeks until mid to late November. After that the rest of the forecast period will see temperatures average out to normal. Rainfall will be average for the entire state through November, except Southern areas which will be slightly above average. However i expect rainfall to increase markedly through late November through February for most areas not coastal.
Notes: We did see early Spring warmth for most of the inland areas, moving South, as previously forecast. Humidity will increase from early November onwards, deep Easterly trades should ensure lots of moisture will be advected over the country. Also, the Indian Ocean has rapidly warm as previously suggested, this warming trend will stick around for the next 6 to 9 months and should ensure above average rainfall across much of the Northern half of Australia, and the SE states. I am also forecasting a much earlier build up season, and then earlier monsoon arrival than last summer. Probably mid December, as per my previous outlook.
Also the risk now of serious flooding is still significant. I cannot rule that out until a later period, in the next update I will have a close look at this as it is the question I get asked most. However, in another months time we can have a good look at the set up and the build up will be well and truly on. We will need a significant increase in the surface Dewpoints, and by then I will know one way or the other.
The position of the Long Wave Trough also puts us at significant risk this summer yet again for another deluge, this is another ace in the pack that didnt quite line up in the last 2 years despite record rainfall. This is the key element of the forecast, if the pattern of colder air does not retreat South in the next few weeks then it can have profound effects on rainfall and temperatures across the entire country.
As mentioned last month it could also be the ace in the pack that interacts with the moisture and delivers massive rainfall to southern states.
Warmer than normal temps will continue for another month in the North of Australia, average elsewhere. Then average temperatures will be fairly common for the remainder of the outlook. The general trend for the forecast period is for humidity to increase, along with rainfall for the entire country, except the Sw corner of the country, where the trend will be in reverse.
Next Update by November 20th 2012.