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ENSO neutral, but tropical Pacific waters continue to cool, says BOM

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ENSO

MELBOURNE, Australia – Sea surface temperatures (SSTs) have steadily cooled over the central and eastern tropical Pacific for the past two months, but remain well within the neutral ENSO range.

Temperatures at and below the surface are now slightly cooler than average. Other indicators of ENSO, such as the Southern Oscillation Index (SOI), cloudiness near the Date Line and trade winds also remain at neutral levels.

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Most international climate models surveyed suggest the tropical Pacific Ocean may cool further, but persist at ENSO-neutral levels for the rest of 2017. Two of the eight models approach La Niña thresholds around the end of the year, which is typically when ENSO events reach their peak.

The Indian Ocean Dipole (IOD) is neutral, though index values have generally been weakly positive for the past five months.

Most climate models suggest the IOD is likely to remain neutral. However, two of the six climate models surveyed suggest a positive IOD may develop during spring.

If a positive IOD eventuated it would likely be short-lived as IOD events typically break down by December as the monsoon trough moves south towards Australia.

Positive IOD events are typically associated with below average spring rainfall, and increased spring–summer fire potential over central and southern Australia, while La Niña-like patterns tend to promote above-average spring rainfall in the south and east.

Hence Australia faces some competing, though weak, climate drivers in the months ahead.