ENSO Update

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Bulletin February 2018 - Summary

The El Niño-Southern Oscillation (ENSO) remains in La Niña with the Bureau's ENSO status at LA NINA. However, it is a relatively weak event and may have peaked in recent weeks.
An active phase of the Madden Julian Oscillation (MJO) strengthened as it moved across the western Maritime Continent in recent days. The pulse of the MJO will track further eastwards into the western and central Pacific region in the coming week while maintaining its strength.
The Intertropical Convergence Zone (ITCZ) was generally weaker than average and disorganised from its normal January position. In contrast, the SPCZ was more active than normal with some evidence of a shift to the southwest. The behaviour of both convergence zones is in line with the La Niña event.
Seasonal rainfall outlooks for February to April favour below average rainfall for Papua New Guinea highlands region, Kiribati, Nauru, Tuvalu and the northern Cook Islands, while above-normal is most likely for the Marshall Islands, FSM and Palau in the northern hemisphere and for the Solomon Islands, northern Vanuatu, Fiji, Tonga, and Niue in the southern tropics. The outlooks are more mixed for southern Tuvalu and Samoa.


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Bulletin February 2018 - El Nino Oscillation

A weak La Niña continues in the Pacific Ocean, but may have peaked in recent weeks. Sea surface temperatures in the central tropical Pacific have warmed slightly since late December, with most models now forecasting that La Niña will end in the southern autumn.

Indicators of the El Niño Southern Oscillation (ENSO) continue to reflect La Niña. Sea surface temperatures show a weak La Niña pattern, with the coolest waters concentrated in the eastern Pacific Ocean. Likewise, atmospheric indicators such as trade winds and cloudiness show clear La Niña characteristics. The Southern Oscillation Index (SOI) is also at La Niña levels, though has fluctuated during the summer season due to the passage of tropical weather systems.

In order for 2017-18 to be classed as a La Niña year, thresholds need to be exceeded for at least three months. Five of the eight climate models surveyed by the Bureau suggest this event is likely to last through the southern summer, and decay in the early southern autumn of 2018. With indicators hovering near thresholds since December, it remains to be seen if 2017-18 will be classed as an official La Niña year.

The Indian Ocean Dipole (IOD) is currently neutral. IOD events are unable to form between December and April.

The approximate 30-day and 90-day Southern-Oscillation Index (SOI) values to 29 January were +9.5 and +6.5 respectively.

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Bulletin February 2018 - MJO

An active phase of the Madden Julian Oscillation (MJO) strengthened as it moved across the western Maritime Continent in recent days. Climate models are in good agreement that the pulse of the MJO will track further eastwards into the western and central Pacific region in the coming week while maintaining its strength. An enhanced rainfall pattern for northern Australia is typically associated with an MJO located over the Maritime Continent at this time of the year. As the MJO moves further east, the focus for the heaviest rainfall becomes the Southwest Pacific, including countries such as the Solomon Islands.

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Bulletin February 2018 - Cloud

The January 30-day OLR and TRMM anomaly maps suggest the ITCZ was generally weaker than average and disorganised from its normal January position. In the south Pacific, the SPCZ was more active than normal with some evidence of a shift to the southwest between about 180°E and 155°E.

Note: Global maps of OLR below highlight regions experiencing more or less cloudiness. The top panel is the total OLR in Watts per square metre (W/m2) and the bottom panel is the anomaly (current minus the 1979-1998 climate average), in W/m2. In the bottom panel, negative values (blue shading) represent above normal cloudiness while positive values (brown shading) represent below normal cloudiness.

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Bulletin February 2018 - Rainfall

Rainfall over Vanuatu in the last 30days have been above normal. The outlook for the next three months will above normal for Vanuatu.

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Bulletin February 2018 - SST

Sea surface temperatures (SSTs) were cooler than the long-term January average near the central and eastern Pacific from 180°E to the South American coast. It was a classic, although rather weak La Niña signal. The strongest anomalies were in the –1 to –2 °C range. Apart from Kiribati and the northern Cook Islands, most countries in the southwest Pacific experienced weak positive SST anomalies. The strongest anomalies in the region (strongest for the Globe in fact) occurred in the south Tasman Sea where January SSTs were three to four degrees above the monthly mean.

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Note: Due to frequent images update from source provider, the quoted Sources might not give the same images as shown

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Bulletin February 2018 - MSLP

The January mean sea level pressure (MSLP) anomaly map shows negative anomalies of less than zero in the equatorial Pacific. Positive anomalies of zero or greater were evident in Fiji to Coral Sea region.

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Bulletin February 2018 - Model Outlooks

All international climate models surveyed by the Bureau indicate that the current event is likely near its end.

Equatorial Pacific sea surface temperatures are likely to continue to warm over the coming months, although three of the eight surveyed models maintain values close to La Niña thresholds well into the southern hemisphere autumn. All models predict neutral NINO3.4 values for the southern hemisphere winter.

In order to consider 2017–18 a La Niña year, NINO3 or NINO3.4 values at least as cool as −0.8 °C need to be present for three months or more.

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Bulletin February 2018 - SPCZ

In the south Pacific, the SPCZ was more active than normal with some evidence of a shift to the southwest between about 180°E and 155°E.

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