Indian Ocean the cause of drier August to October outlook

Indian Ocean the cause of drier August to October outlook


Weather
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The updated August-October climate outlook remains drier than average for Victoria.

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The updated August-October climate outlook, released last week, remains drier than average for Victoria.

Days are still likely to be warmer than usual in northern and central parts but in the south there's roughly equal chances of a cooler or warmer than average season.

There are slightly increased chances of warmer than average nights for most of the state.

With more cloud-free days and nights expected, there is an increased risk of frost in susceptible areas.

The outlook for August shows much of southern and central Victoria has no strong push towards a drier or wetter than average month.

Climate model accuracy changes across the year, there are times when it typically performs better or worse.

Historical rainfall outlook accuracy for August to October is low for much of Victoria, but accuracy for maximum temperatures is high.

However, most of our seasonal predictability, and climate model accuracy, comes from El Nino-Southern Oscillation and Indian Ocean Dipole events driving our climate.

And a positive Indian Ocean Dipole (IOD) is forecast for the remainder of winter and spring.

That typically means below average rainfall for much of central and southern Australia.

A positive IOD occurs when changes in the winds along the equator allow warm surface water to pile up in the western Indian Ocean while cooler waters rise to the surface in the east.

This pattern of cooler than average waters in the east and warmer waters in the west means there is less moisture than normal in the atmosphere to the north-west of Australia.

This changes the path of weather systems coming from the west, often resulting in lower rainfall and higher maximum temperatures for Victoria during winter and spring.

IOD events are typically active during the winter-spring months and then rapidly decay when the monsoon arrives in the southern hemisphere around the end of spring.

The positive IOD is likely to be the dominant climate driver for Australia during the next three months.

July rainfall was close to average for much of the state but parts of the centre and east, along with the Mallee were drier than usual, while parts of the south-west were wetter than average.

Temperatures were much higher than normal across Victoria for this time of year, ranking as one of the top five warmest July mean temperatures on record.

Root zone soil moisture for this time of year is close to average across much of the north, above average in the south-west and below average in central and east Gippsland, and the Mallee.

Victoria's total water storage level continues to rise, up 2.7 per cent over the last month to 47.4pc full.

The first look outlook for spring will be available on Thursday, August 15.

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