ENSO Update

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Bulletin March 2018 - Summary

The 2017–18 La Niña has ended. El Niño–Southern Oscillation (ENSO) indicators have eased back to neutral levels over the past several weeks. This means the ENSO Outlook has shifted from LA NIÑA to INACTIVE.

The end of the La Niña is clear in oceanic and atmospheric indices. Sea surface temperatures have warmed steadily since December, and are now in the neutral range. Waters beneath the surface have also warmed. In the atmosphere, cloudiness near the Date Line has returned to near-average levels, and trade winds are generally near average across the equatorial Pacific. Likewise, the Southern Oscillation Index (SOI) is well within the neutral range.

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Bulletin March 2018 - El Nino Oscillation

Most models indicate that ENSO-neutral is the most likely scenario through the southern hemisphere autumn and into winter. However, model accuracy during autumn is lower than at other times of year.

The 30-day Southern Oscillation Index (SOI) to 11 March was +3.2 (90-day value +0.9), which is within the neutral range. While the SOI fluctuates more during the southern hemisphere summer due to movement of tropical systems, it has spent most of 2018 to date within the neutral range.

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Bulletin March 2018 - MJO

The MJO has weakened considerably since the start of March and is currently approaching the unit circle. The Outlooks suggest it will remain weak or indiscernible for the rest of the month.

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Bulletin March 2018 - Cloud

ITCZ shifted northwards. SPCZ enhanced and shifted to the southwest (typical La Niña) in month of February.
In the last month, cloud cover has been close to normal over Vanuatu.

The outlook for the next three months the cloud cover will continue to be below normal cover.

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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 March 2018 - Rainfall

ITCZ shifted to the north, across the north Pacific, as has been the case for many months. SPCZ shifted to the northeast in keeping with the strong MJO and the weakening of La Niña. Rainfall strongly suppressed around the Solomon Islands and to a lesser extent around Vanuatu. The track of TC Gita is visible as a sweeping arc from south of Fiji, just south of New Caledonia and then recurving over NZ.

Rainfall over Vanuatu remained normal to below normal over the past month to three months.

The outlook for the next few months, rainfall over Vanuatu is expected to be above normal.

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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 March 2018 - SST

La Niña signal persisted in the sub-surface, with little change from January, but much weaker than December. Warm anomalies in the west clearly much stronger due to the effects of a strong MJO.

In Vanuatu, SST have slowly eased into cooler anomalies (weak positive anomalies) in the past month.

For the next three months, SST will continue to cool over Vanuatu.

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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 March 2018 - MSLP

The February mean sea level pressure (MSLP) anomaly map shows negative anomalies below 1 hPa across most of the southwest Pacific. Negative anomalies from 2 to 4 hPa were present around Vanuatu, Fiji, Tonga, Samoa and Niue. Positive anomalies were present in the far western Pacific.

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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 March 2018 - Model Outlooks

All eight of the surveyed international climate models indicate equatorial Pacific sea surface temperatures are likely to continue to warm over the coming months. Only one model anticipates NINO3.4 will meet La Niña thresholds for May, and all models predict ENSO will be in a neutral phase during the southern hemisphere winter.

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Bulletin March 2018 - SPCZ

In the South Pacific, the SPCZ displaced northeastwards. Rainfall was strongly suppressed around the Solomon Islands, southern Tuvalu and Niue.

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