Seasonal Climate Outlook, Dec – Feb 2012/13.

Seasonal Climate Outlook, Dec – Mar 2012/13.

Issued January 1, 2013, by Anthony Violi

Current Overview :

Currently, the climate is beginning to respond to the inevitable push of the season change into a summer pattern. There has been a large displacement of moisture, pressure systems and rainfall patterns during the Spring, due to the positive Indian Ocean Dipole.. This has forced the patterns to be slow to transition into late Spring like conditions. In the last few weeks the IOD has broken down and gone into neutral conditions, meaning rainfall will increase from now on as moisture begins to increase from the NW corner of the country and moves South.

The top end is now transitioning from build up, into monsoon. As per my previous forecasts, cyclone activity and an earlier monsoon are tracking well. There still remains a large likelihood of a lot more cyclone and monsoonal activity. Given that SST are now very warm on the western coasts, and starting to warm for the Eastern coasts, all that stands in between us copping a deluge and a drier than normal summer is the Souther Annular Mode (SAM) keeping all the moisture and troughs to our north. its my thought that the monsoon will overcome the resistance and become dominant with an extraordinary amount of warmth off the NW coast.

Here is the current month rainfall for Australia, which is a big improvement, and signals the pattern is beginning to build as the wet season approaches.

dec 2102

Now let’s have a look at the climatic indicators.

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. Significant cooling is now reaffirming in the tropical equatorial Pacific Ocean.

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. Very little westerly winds are evident in this diagram, so its neutral all the way with consistent SE trade winds across the equator.

sst_wind_anom_5day_ps32

Southern Oscillation Index was flying along until a tropical Low went through Tahiti and caused a big drop in the figures. Its now at -7.0 for the 30 day average, which will recover soon once we get rid of mid Decembers readings.

soi30

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.

nino34Mon

You can see form the above forecast, the climate models show cooling in the central Pacific until April, then rebounding warmer than normal again for another warming phase of either neutral or weak El nino. This is no surprise because the models always forecast this every year, then react accordingly. Its still my forecast for a La Nina for 2013, but much water  (no pun intended) needs to flow under the bridge.

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.

nino12Mon

Again, a cooling off until April and then a rebound, we will keep a close on this into the New Year and see what eventuates.

Sea Surface temperatures are very interesting, very messy and all over the place, in line with a climate that is all over the shop. Here is the sea surface temperature anomalies on the 21st Nov.

So, now i can explain the crayon drawings! First off, in red, the cold waters have returned in the Bering sea near Alaska. These feed down the American coast and into the Equatorial basin. At the current time they are nowhere near as cold as a few months ago, however its starting to cool again with the onset of winter in the NH, so expect any warming to be short-lived in the Pacific.

So now, lets look at the comparison! I kept last months outlook in there for a good reason, and thats because its happened exactly as planned. The warmth has now moved towards the QLD coast, thanks to the strengthening of the trade winds, the cooling has accelerated in the Pacific, and the Indian is extraordinarily warmer than normal.

The green circle indicates warm water NW of the country has returned, as the IOD has now returned to neutral. This is why December’s rainfall has increased.  This will continue all summer and maybe into the autumn. Remembering that the IOD always warms up late October, its April to October period that needs to be warmer than normal for good Winter and Spring rains.

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 beginning to occur, 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 don’t 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.

Forecast for Summer : January 2013 to April 2013.

Northern Territory : Temperatures will be average through the forecast period, especially February through April.  Rainfall will be above average through the Northern Territory areas for all of the forecast period, and will become especially so 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 will be above average throughout the period January through to April. Also, the risk of heavy rains remains as I expect the SST of the Qld coast to warm as the warmth in the Pacific sloshes east. An impact from a cyclone, or maybe a couple of cyclones is a good possibility as well. The likelihood increases through February – April .

New South Wales : Temperatures will be slightly above average for the forecast in NSW, and well above average in January for the two inland western districts. Temperatures will be about average, to slightly below average for all districts after the end of January. Rainfall will be below average in the NW initially in early January, 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 average for all Southern areas, and average for the northern areas after mid January. Rainfall will increase in the early February for all districts.

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 : South Australia will see average conditions throughout for the temperature outlook. Initially temperatures in January will be slightly above average in the Northern districts, then will even out to average  to slightly below average after the middle of January. Rainfall will be average to slightly below average in the coastal regions, and average to slightly above average in the northern districts.

Western Australia : Temperatures will be slightly above average in the forecast period, particularly through the Southern and inland areas.  After that the rest of the forecast period will see temperatures average out to normal. Rainfall will be average for the entire state through December, except Southern areas which will be above average. However I expect rainfall to increase markedly through the forecast period for most areas not coastal, and will become above average to very much above average through the Northern half with the onset of a very active monsoon.

Notes:  Humidity is now beginning to increase across the country as the top end build up season has now transitioned into a monsoonal onset. It has been a great build up so far and has surpassed last years build up considerably.  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.

Also the risk now of serious flooding is still significant. In fact the Northern half of the country is quite likely to see significant monsoonal rainfall. Dewpoints are very high through the North, and now we starting to see the spill of moisture from the NW part of the country to the southern parts.

The position of the Long Wave Trough also puts us at significant risk, however its actually been doing the opposite by sitting in no mans land rather than drop away or stay very high. This has caused upper ridging and blocking for the southern half of the country, hot weather and little rainfall.  We are looking for a relaxing of the westerlies to allow the blocking and ridging to subside, and the troughs to become more active from the North. This should begin with monsoonal onset in early January.

Summary :

Warmer than normal temps will continue for another month in the North of Australia, average elsewhere. Then a cooling trend will emerge, and average to slightly below 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.

On a verification note, the pattern has moved much slower than in my previous forecast, my forecast is still unchanged. Late spring did not deliver the rains to the southern states, it did however deliver good rains to the northern states. The monsoon has seen a much better build up season, and the monsoon is much earlier than previous year.

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