BOM: Strong El Niño and positive Indian Ocean Dipole persist

BOM, 27 October 2015

A strong El Niño in the Pacific and a positive Indian Ocean Dipole are dominating the climate of countries that border the Pacific and Indian oceans.

In the central tropical Pacific Ocean, sea surface temperatures (SSTs) continue to warm, but at a markedly slower pace than earlier this year. All NINO indices have now been above +1 °C for 11 consecutive weeks, equalling the previous record. Recent bursts of westerly winds in the tropics means some further warming remains possible. All models indicate that the strong El Niño is likely to persist until the end of the year, before a marked decline during the first quarter of 2016.

International climate models also suggest the positive Indian Ocean Dipole (IOD) will persist into November, but then decline rapidly once the monsoon trough shifts south, changing wind patterns over the IOD region. So far in October the IOD index has averaged over +1 °C—the last month that this occurred was in 2006.

El Niño is usually associated with below-average spring rainfall over eastern Australia, and increased spring daytime temperatures south of the tropics. A positive IOD typically reinforces the drying pattern, particularly in the southeast. During summer, El Niño’s influence on rainfall decreases, while warmer daytime and night-time temperatures tend to be more likely across the south and east.

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Indian Ocean Dipole

The positive Indian Ocean Dipole (IOD) event persists, with the weekly index value to 25 October strongly positive at +1.08 °C.

Sea surface temperatures (SSTs) in the Indian Ocean are warmer than average over much of the basin, while waters around the Indonesian archipelago and to Australia’s north are cooler than average.

Positive IOD events are often associated with lower rainfall in parts of central and southeastern Australia (see About the Indian Ocean Dipole). Positive IOD events are more likely to occur during El Niño, which also is typically associated with a reduction in winter–spring rainfall in eastern Australia.

All surveyed international climate models indicate this event is likely to begin to decay in late spring. IOD events typically decay by early summer.

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