Fresh hopes for rain to follow the dry spring

Fresh hopes for rain to follow the dry spring


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Typically, during a positive IOD the easterly trade winds strengthen along the equator, which pushes the warm water towards the African continent.

Typically, during a positive IOD the easterly trade winds strengthen along the equator, which pushes the warm water towards the African continent.

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Typically, during a positive IOD the easterly trade winds strengthen along the equator, pushing warm water towards Africa.

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October was forecast to be drier than average, and so far, it has proven to be the case in most parts.

November too is likely to be drier than usual across Victoria.

Much of the recent and forecast dry signal for Victoria is coming from the positive Indian Ocean Dipole (IOD).

The positive IOD is forecast to break down in early summer.

Once this occurs, there are prospects for more neutral rainfall outlooks.

Typically, during a positive IOD the easterly trade winds strengthen along the equator, which pushes the warm water towards the African continent.

This change in the winds also encourages cool water to rise up from the deep ocean in the east.

This sets up a temperature difference across the tropical Indian Ocean with cooler than normal water in the east near Indonesia, and warmer than normal water in the west.

Generally, this 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 Australia's west, which often results in less rainfall and higher than normal temperatures across parts of Australia during winter and spring.

One of our other major climate drivers, the El Nio-Southern Oscillation (ENSO), is neutral.

And international climate models forecast neutral ENSO for the remainder of 2019, and into early 2020.

When ENSO is neutral, it has little effect on Victorian rainfall and temperature patterns.

The current outlooks for October and November both show a low chance of above average rainfall for the state.

However, the chance of low rainfall reduces when we compare the three-month outlooks for October to December and the outlook for November to January.

This suggests that as the IOD breaks down in December, the likelihood of above average rainfall will start to rise.

The three-month temperature outlooks show days will likely remain warmer than average, except in the south of the state where chances gradually reduce to around 50 per cent.

At the same time, there is no strong push towards warmer or cooler than average nights for western and southern Victoria.

For more information, visit http://www.bom.gov.au/vic/forecasts/

  • Jonathan Pollock is a climatologist for the Bureau of Meteorology.
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