Weak La Nina set to stay through summer

Weak La Nina set to stay through summer | The Outlook


An active trough of low pressure moving in from SA during this coming weekend is likely to briefly break this pattern


LOCAL synoptic weather patterns continue to dominate weather developments and these are providing fairly stable conditions.

An active trough of low pressure moving in from SA during this coming weekend is likely to briefly break this pattern.

Despite the majority of the climate indicators still pointing to a wetter than normal end of the year, these current synoptic set-ups look likely to bring drier than normal weather for much of the remainder of September.

The developments in the Pacific Ocean continue to be interesting and show a continuation of the trend towards a full La Nina event by later in October.

La Nina conditions normally bring above average rainfall to large areas of eastern Australia.

The developing La Nina event is favoured to be a fairly weak one so this could "dampen" the hopes of rain a little bit but it is also favoured to persist well into summer which increases the chances of summer rainfall as well.

Currently the so called El Nino Southern Oscillation conditions are neutral but the Southern Oscillation Index is in the La Nina range already with the 30-day running mean sitting around +9

To the west, the important Indian Ocean Dipole is slightly negative mainly due to large areas of warmer than normal sea surface temperatures stretching from around south-east of India to north-west Australia.

However, the synoptic conditions referred to above have not been encouraging for areas of tropical storm development off north-west Australia so there has been no north-west cloud bands coming our way in recent weeks.

This has the potential to change in the coming month but it must be remembered that the influence of the IOD on south-east Australian rainfall diminishes significantly in summer.

To the south, the Southern Annular Mode is close to neutral and looks likely to become positive in the next few weeks.

This would allow a synoptic pattern to develop which has more easterly winds flowing into eastern Australia - thus increasing rainfall potential especially in Queensland and eastern and northern NSW.

In the longer term, a La Nina is favoured to persist in the Pacific into next year before neutral conditions return.

A neutral pattern is then likely for many months, probably through winter of 2021 after which developments become a little unclear.

However, the good news is that there appears to be little or no chance of an El Nino returning in the foreseeable future.

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