Handy rain but seasonal deficit remains

Long way to go to make up for drought

Weather
Rainfall in the past week has delivered across much of eastern Australia but we are a long way from making up for the previous dry months.

Rainfall in the past week has delivered across much of eastern Australia but we are a long way from making up for the previous dry months.

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Climate drivers suggest patchy rainfall conditions will continue through another hot summer

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Another rain event brought handy rain to parts of NSW again this week and as previously indicated, there is a strong chance that the pattern responsible will persist for a little while yet.

Low pressure effecting the south east states, delivered north-west winds in Queensland with record November heat in central and northern parts of the state but this heatwave to the north will break down in the coming days.

Any rain events in coming months in NSW or Victoria are unlikely to be sufficient to overcome the deficiencies already established in 2018 – especially in Victoria and southern and central inland NSW.  This is mainly because the long term climate indicators are still trending towards conditions that decrease the chance of good and widespread rain events.  These indicators include the likely development of  an “El Nino”  in the Pacific (which is  still considered  around a 70 per cent chance)  and cooler than average waters in the tropical Indian ocean partially resulting in a  later than normal development of the “wet”  season  in the tropical Northern Australia.

So, overall in the Pacific, there remains the chance of a weak “El Nino” developing by the end of the year, which is later than originally expected because the link between the oceans and the atmosphere are not developing as expected. The sea surface temperature patterns in the tropical Pacific already exceed “El Nino” thresholds but the atmospheric patterns are not reinforcing this. If this set-up continues, then the effects of the developing “El Nino” will be minimal which would be good news for south east Australian farmers.

The situation in the west is also far from straight forward. The Indian Ocean Dipole (IOD) has been weakly positive for some months now and when the monsoon develops south of the Equator, the influence of the IOD will be minimal through until April next year. This then puts “more pressure” on the developing monsoon, which – as noted above – is undergoing a very slow start this season. This is resulting in very hot air over the north of the country with record November temperatures in parts of Queensland. The local synoptic patterns have so far prevented this hot air moving into the south east states but the potential is there and consequently, there remains a good chance that summer will again be warmer than normal this year.  A weak “El Nino” increases bushfire risk, increases slightly the chance of local severe storms in spring and early summer and decreases slightly the chance of tropical cyclone formation in the Coral Sea.

- Don White WEATHERWATCH

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