Catch-up rainfall outlook mixed across Australia by Dave McRae. DPI Centre for Climate Applications
GroundCover™ Issue: 45
BASED ON the recent pattern of the SOI, the chance of getting above the long-term May-July .median rainfall for a large proportion of the southern grainbeJt of Queensland remains low at around 30-40 per cent. For much of central and western Queensland though, the chance of getting above the long-term May-July median rainfall is higher at around 50-70 per cent.
For the Northern Territory, the northern half of SA and parts of both the northwest and south-west of WA, the chance of getting above the long-term median rainfall for May-July remains at around 60-80 per cent.
These probabilities are lower (20-40 per cent) for much of the north-east, central and south-east of NSW. The chance of getting above the long-term median rainfall across the rest of Australia for May-July is around 40-60 per cent.
As always when dealing with a probability-based forecast system, it is important to consider the alternate view. For example, currently there is an 80 per cent chance of getting above 60 mm at Dalby, Qld, for May-July. This also means there is a 20 per cent chance of not getting above 60 mm.
Another way of looking at this is that in eight years out of 10 (or slightly more than three-quarters) with the current SOI pattern, Dalby has received more than 60 mm for May-July. Therefore, in two years out of 10 (or slightly less than one-quarter) with the current SOI pattern, less than 60 mm has been recorded at Dalby.
Longer-term modelling posits neutral sea temperature pattern coming up
Sea-surface temperature data suggest that the El Nino system has weakened significantly, although areas of remnant warm water 'stubbornly' remain in the central equatorial Pacific near the international dateline. The low-level westerly wind bursts that largely drive the El Nino system have also generally dissipated in the equatorial Pacific.
Given current ocean and atmospheric conditions, our policy remains not to 'sound the all-clear' regarding the complete breakdown of the El Nino system until the end of May.
Ocean and coupled ocean/atmosphere forecast models (GCMs) give an indication as to likely ENSO development out to nine months. Of 11 models that forecast to September 2003, nine indicate the development of a neutral sea temperature pattern, one indicates an ongoing El Nino (or warm) sea temperature pattern and one indicates the potential development of a La Nina (or cold) sea temperature pattern.
Of the nine models that forecast to December 2003, eight indicate the development of a neutral sea temperature pattern while one indicates the development of a La Nina sea temperature pattern.
It is positive news that the majority of these GCMs show a breakdown in the El Nino pattern. However, while the CPC model continues to show a 'persisting' El Nino (warm) sea temperature pattern, we will maintain an 'El Nino watch'. For more information on GCMs, try www.bom.gov.au/climate/ahead
Due to the size of the areas covered, the information provided in this column is of a fairly broad nature. For those readers who require more specific climate information for their location, we recommend referring to Australian Rainman, the latest 'Climate Note' at www.dpi.qld.gov.au/climate or contact us at the DPI Centre for Climate Applications on 07 4688 1459.