Seasonal Climate Outlook Message for June to September 2004

The bottom line

Outlook Improves for Southern Regions of Queensland 01/06/04

Based on the shift in value of the SOI from the end of April (minus 16.1) to the end of May (plus 13.0) the SOI is now in a "Rapidly Rising" phase. A rapidly rising SOI phase at this time of year creates a mixed seasonal outlook across Queensland.

Generally speaking, for a large part of the south east corner of Queensland and along the Queensland/New South Wales border there is a quite reasonable 60-80% chance of getting the long term June to August median rainfall.

Rainfall probabilities in the north west though are lower with only a 30-40% chance of getting at least the long term median rainfall through to the end of August. For the rest of Queensland there is no strong signal at present towards wetter or drier than 'normal' conditions through to the end of August.

The full story

Seasonal Outlook Improves for Southern Regions of Queensland 01/06/04

Based on the shift in value of the SOI from the end of April (minus 16.1) to the end of May (plus 13.0) the SOI is now in a "Rapidly Rising" phase. A rapidly rising SOI phase at this time of year creates a mixed seasonal outlook across Queensland.

Generally speaking, for a large part of the south east corner of Queensland and along the Queensland/New South Wales border there is a quite reasonable 60-80% chance of getting the long term June to August median rainfall. Rainfall probabilities in the north west though are lower with only a 30-40% chance of getting at least the long term median rainfall through to the end of August in this area. For the rest of Queensland there is no strong signal towards wetter or drier than 'normal' conditions at present through to the end of August.

The latest rainfall probability maps for Queensland, Australia and the world can also be found at www.dpi.qld.gov.au/climate or at www.longpaddock.qld.gov.au

When using probability based forecast systems it is important to consider the opposing view. For example, Tara currently has close to a 70% chance of getting at least its long term June to August median rainfall of 90mm. However, this also means that there is a 30% chance of not getting at least 90mm through to the end of August.

Another way of looking at this is that in 7 years out of 10 (or a bit under three quarters of years) with the current SOI pattern, Tara has received at least 90mm for June to August. Therefore in 3 years out of 10 (or a bit over one quarter of years), Tara has gotten less than 90mm for this period.

Many people like to follow the relationship between the SOI and rainfall patterns in more detail for their area. Finding out what conditions where like in your area for June to August in 1998, 1992, 1990, 1988, 1983, 1981, 1980, 1979, 1978, 1973, 1970, 1968, 1965, 1964 and 1962 and comparing it to your 'normal' rainfall for June to August could be useful.

More information on what rainfall patterns where like for June to August in those years can be found in Australian Rainman.

The late April/early May rain in many parts of Queensland was due, at least in part, to the Madden Julian Oscillation (MJO). The MJO is simply a band of low air pressure originating off the east coast of central Africa travelling eastward across the Indian Ocean and northern Australia roughly every 30 to 60 days.

Research has shown the MJO to be a useful indicator of the timing of potential rainfall events across much of Queensland. If its timing remains current it would next be expected to have an influence on our weather around mid to late June.

According to the Bureau of Meteorology "El Nino Wrap Up" www.bom.gov.au/climate/enso/ the Pacific Ocean remains in a neutral sea surface temperature (SST) pattern. However, there remains an increased risk of an El Niño developing this winter. It will be interesting to see if this develops and what impact, if any, this may have on our expected late winter/spring rainfall.

In my opinion the ongoing changes in the SOI phase and SST patterns still seem to be roughly following or similar to what happened in 1953, 1957, 1986/87 and 1992.

Part of the reason for the concern with the longer term outlook (3-6months) is because a strong westerly wind burst (WWB) in the second half of March initiated a Kelvin wave in the Pacific Ocean, which in turn has produced some subsurface ocean warming in the western Pacific. During autumn and winter Kelvin Waves can be considered to be somewhat of an early indicator that there is an increased risk of an El Nino developing. They take about two months to cross to the eastern Pacific, and can trigger warming of the subsurface ocean temperatures in the Pacific as they go.

However, it's too early to say just how strong this subsurface ocean warming in the Pacific will be, and how far east significant warming will be found. Sea temperatures remain cooler than average across the central to eastern Pacific for the time being.

Ocean and coupled ocean/atmosphere forecast models are used to show likely SST development out to 9 months. Of 11 models that forecast out to October, 9 indicate the continuation of a neutral SST pattern while 2 suggest the potential development of an El Nino (or warm) SST pattern.

While it is positive that the majority of these models highlight a continuing neutral SST pattern (rather than an El Nino), given current conditions our policy remains to recommend caution when considering the longer term outlook. This especially applies over March to the end of June as most models fall away in their forecasting skill.

It may therefore be useful for businesses that are adversely affected by El Nino events to consider now what risk management strategies they could use if the likelihood of an event increases. More details on these models can be found at www.bom.gov.au/climate/ahead/ENSO-summary.shtml

For more information feel free to give me a call through the DPI&F call centre on 132523 (Qld residents) or on (07) 46881459.

Last updated: 31 May 2004