More hope for rain after Spring
October was forecast to be drier than average, and so far, it has been 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, pushing warm
water towards Africa. 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 northwest of
Australia. This changes the path of weather systems coming from Australia's west, often resulting in
less rainfall and higher than normal temperatures over parts of Australia during winter and spring.
One of our other major climate drivers, the El Niño–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 3-month outlooks
for October–December and the outlook for November–January. This suggests that as the IOD breaks
down in December, the likelihood of above average rainfall will start to rise.
The 3-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%. At the same time, there is no
strong push towards warmer or cooler than average nights for western and southern Victoria.
See the Bureau's rainfall and temperature outlooks for the weeks, months and seasons ahead.