Preliminary Outlook for 2013-2014 Austral Summer

As of June 2013, a survey of existing climate indicators of both the atmosphere and ocean indicate an increased probability of above average rainfall for the upcoming austral summer in Northern Australia.  A current La Nina-like pattern is likely to have reached its peak and will return to more typically neutral conditions by spring 2013, possibly reaching weak El Nino thresholds by early 2014.  While El Nino would typically spell reduced rainfall potential in the SW Pacific, it is likely that the warm anomalous sea surface temperatures off NW Australia will persist, with increasing warm anomalies likely to develop along the Australian east coast contributing to increased rainfall potential along the eastern seaboard.  Anomalous warming of the Gulf of Carpentaria and Coral Sea is likely to increase the convective potential of these areas, thus contributing to a raised likelihood of severe cyclone development. 

 

Analysis of a range of atmospheric indicators from the past 20 years suggests that the 2008-2009 is the closest analogue for conditions in the upcoming season, with the Southern Oscillation Index (SOI), and the Quasi Biennial Oscillation (QBO), in a similar phase step and trend, as well as marked similarities noted for June 2008 and June 2013 for anomalous rainfall and temperature across Australia.  Image

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Above: Comparative analysis of June 2008 and June 2013 maximum temperature anomalies. 

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Above: Comparative analysis of June 2008 and June 2013 rainfall anomalies.  

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Above: Rainfall anomalies – northern Wet Season  2008-2009

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Above: Cyclones in the Australian Region, northern Wet Season, 2008-2009

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Upper Atmospheric Flow and the MJO

Analysis of historical 200 hPa analysis charts from the BOM website (www.bom.gov.au) and past MJO Monitoring Phase Diagrams (also on BOM’s site), has revealed a correlation between the two, with an identifiable pattern of upper atmospheric development accompanying the passage of the MJO.  For this analysis, I focused primarily on the development of upper features with the passage of the MJO through the Indian Ocean, through to the West Pacific, particularly due to its relevance to eastern Australia’s weather. As I have already commented about the similarity of atmospheric and oceanic characteristics between the current system and that of the 2005-2006 Wet Season (going back to November 2012), and the continuing similarities between the seasons, I chose to look at the upper atmosphere and the corresponding MJO signal from January to March 2006.  

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The above MJO phase diagram from January to March 2006 shows that through February 2006, the active phase of the MJO moved rapidly over the Indian Ocean into the Maritime Continent before weakening significantly in between Phase 4 and 5.  Below, a current forecast of the MJO as it is at present reveals a similar progression, with the MJO having crossed the Indian Ocean before a forecast weakening over the Maritime Continent, although not to the same extent as the weakening witnessed in 2006.  

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Below, are a series of upper analysis charts at the 200 hPa level.  Each image is annotated to indicate the MJO phase and what features have been noted on upper charts from other years.  

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The chart from 27 February 2006, at which time the MJO signal was focused over the east Indian Ocean shows an upper level trough approaching the east Australian coast.  

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The chart from 11 March 2006, when the MJO signal had moved through the Maritime Continent and become indiscernible, and shows an upper trough over the Coral Sea and West Pacific, with a large upper anticyclone over the Australian continent.  

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The chart from 20 March 2006, when the MJO was still indiscernible, shows that the amplitude of the long wave trough has decreased. It was this weakening of the MJO signal and the breakdown of the upper trough system that allowed Severe Tropical Cyclone Larry to move west and cross the North Queensland coast at Innisfail on this day.  Another cyclone – Wati – approached the Queensland coast immediately following Larry, but was eventually steered away from the coast as the MJO strengthened (as an upper level trough once again moved into play).  

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The chart from 30 March 2006, at which time the MJO signal had regained strength over the Maritime Continent, shows the amplitude of the longwave trough increasing once again, though not to the same extent as it was prior to the active phase of the MJO.  

Initial analysis of other years’ data shows a similar pattern, with upper level troughs increasing in eastern Queensland in the leading edge of the MJO, particularly during phases 3 and 4, before the amplitude decreases through phases 5 to 7.  I will be doing more research into this during the next few weeks, particularly as the MJO is moving through the phases that I am most interested in exploring.  

 

2013: A Brief Flirt with La Nina before El Nino Returns…?

Based on analysis of circumpolar waves, which bring alternating waves of warm and cool ocean temperatures around the Southern Ocean, it appears that the phase that has allowed La Nina conditions to dominate our weather patterns for the last few years may be about to give way to the next phase of El Nino, following a brief trip back into La Nina territory that should only last 3-5 months.Image

The current SST pattern in the Pacific appears set for warm anomalies in the northern and southern hemispheres to ‘work together’ to produce warmer than normal sea surface temperatures in the central equatorial Pacific later in 2013.  The previous brief period of above-average temps was shot down by cooler than normal waters in the northern hemisphere, but this time both sides of the equator are on the same side.  Fortunately for Australia’s east coast, which normally bears the brunt of the drier than average conditions during an El Nino event, it appears that the region will be surrounded by a warmer than average body of water currently sitting around Australia’s north west and into the Indian Ocean, which should allow for some decent rainfall despite the El Nino conditions, much like the 1997-1998 El Nino. 

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This seems to back up what I have said previously based on my own modelling of Nino3.4 temps, and I am looking forward to seeing if this pans out a

Enhanced South Pacific Cyclogenesis Potential from 26th January – 5th February

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As noted previously, the passage of the active phase of the MJO pulse is looking set to revive the cyclone potential of the South Pacific from about January 26th through to February 5th, with the possibility of a westerly track increased following the MJO.  Modelling is suggesting the persistent upper high over the continent to move west into the Indian Ocean, and an easterly steering flow to develop in the South Pacific mid-latitudes around this time.  The possibility of the Wet Season finally getting interesting is upon us. 

 

 

 

MJO Brings Enhanced Opportunities for Cyclogenesis in the Coral Sea

ImageBased on the Empirical Wave Propagation (EWP) model of MJO activity, an active phase of enhanced tropical convection is due over northern Australia as we speak.  This has already spawned a cyclone in the Indian Ocean, Tropical Cyclone Narelle, and is likely to bring similar conditions more conducive to cyclone development in coming weeks.  This active phase is likely to significantly increase the potential for cyclones to form, first in the Gulf of Carpentaria, then in the Coral Sea, followed by the Western Pacific (where development is most likely due to more favourable sea surface temperatures).  While the active phase of the MJO favours a SE path for such systems, the immediately following inactive phase favours a westerly path, which is more likely see some much needed tropical depressions or cyclones heading for the Queensland coast bringing some much-needed rainfall.  The most likely period for a Western Pacific LOW or tropical cyclone to make its way towards us would be from about January 25th to February 10th, which coincides with the usual arrival of the Australian monsoon around the Australia Day long weekend, which often results in flooded out backyard barbeques. 

Based on my own analysis of MJO development and movement, the next active phase towards the end of February and into early March is likely to see the peak of tropical cyclone activity in the Coral Sea/Western Pacific region, before the focus for cyclogenesis moves further into the Pacific.