Wet, and not so wet?

Townsville Bulletin: Big summer rains forecast in North Queensland

PREPARE to get wet.
A ocean-atmosphere phenomenon associated with more rainfall and cooler conditions is taking place in the tropical Pacific Ocean.
The Bureau of Meteorology announced today that the El Nino-Southern Oscillation had been raised to La Niña.
The latest modelling shows the Pacific Ocean and overlying atmosphere have reached La Niña thresholds.

Observations suggest the ocean and atmosphere have coupled — which means they are reinforcing each other.
“It is therefore likely that the tropical Pacific will persist at La Niña thresholds over the southern summer; long enough for 2017-18 to be classified as a La Niña year,” a spokesman said in a statement.
“Climate models suggest further cooling of the tropical Pacific is likely during the early southern summer.
“Most models suggest a transition back to ENSO neutral by April 2018.
“Bureau climatologists will continue to closely monitor developments in the tropical Pacific over the next fortnight.”
It’s unclear how much the event will affect Australia but the outlook means there is an increased chance of rain for North Queensland, and Townsville.

There have been 18 La Niña events since 1900 and 12 have led to widespread wet conditions.
Australia’s wettest two-year period was during the 2010-12 La Niña.
Usually La Niña events develop in autumn or winter and have lasted two or three years.

They occur on average every three to seven years.
The new outlook comes with Townsville suffering through a dry period.
The bureau is predicting at least 522mm of rain will fall over the summer in Townsville.

Do you notice how the bit about increased chance of rain is not in quotation marks? Amateur weather sleuths may even think that the predicted precise to the millimetre  522mm minimum appears to be somewhat below both mean and median historical rainfall in Townsville over the summer months?

Australian Bureau of Meteorology: Weekly Tropical Climate Note

La Niña in tropical Pacific Ocean
The Bureau’s ENSO Outlook has been raised to LA NIÑA status, indicating that the tropical Pacific has reached La Niña levels. Climate models suggest this La Niña will be weak and short-lived, persisting until early southern autumn 2018. Most oceanic and atmospheric indicators show clear signs of La Niña. These include sea-surface temperature (SST) anomalies over the central tropical Pacific Ocean, the Southern Oscillation Index and cloudiness near the Date Line.
La Niña is typically associated with above-average rainfall during the northern wet season, average or above-average tropical cyclone numbers across the Australian region and an earlier onset of the Australian monsoon. Impacts associated with the current late-developing and relatively weak La Niña are not expected to be typical. Near-average SSTs are expected to persist across waters to the north and west of northern Australia (atypical during La Niña), and current rainfall outlooks do not indicate above-average rainfall for December to February for northern Australia.

Given that mostly the BOM outlooks are probabilities rather than predictions I would guess confidence may be lower around an atypical La Nina event?


Rainfall Probability




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