ENSO Update

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Bulletin June 2021 - Summary

Issue: July 2021

The El Nino Southern Oscillation (ENSO) remains neutral, with all oceanic and atmospheric indicators within the neutral range. This means there is currently no El Nino (prolonged dry period) nor La Nina (prolonged rainy period) in the region. Climate model outlooks show this neutral ENSO state is likely to continue until at least September to November 2021.

Sea surface temperatures in the western Tropical Pacific are forecasted to slowly increase over the coming six months. This warming pattern may be partly contributing to wetter than average climate outlooks for the country.

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Bulletin June 2021 - El Nino Oscillation

The 2020–21 La Niña is now INACTIVE. ENSO has returned to neutral.

El Niño Southern Oscillation (ENSO) is a single climate feature that has three states: El Niño, La Niña, and Neutral.

During an El Niño, sea surface temperatures in the Tropical Pacific Ocean, both at the surface and the sub-surface tends to WARM. Surface pressure changes across the Pacific; higher in the west, and lower in the east. Trade winds weaken and sometimes reverse. Cloudiness increases near the Date Line. El Niño events tend to develop in Autumn to Winter (March - August), and starts to decay in Summer (December - February). In Vanuatu, extreme below normal rainfall which results in drier conditions with warmer daytime temperatures are associated with El Niño.

During a La Niña, sea temperatures in the tropical Pacific Ocean, both at the surface and the sub-surface tends to COOL. Surface pressure changes across the Pacific; higher in the east, and lower in the west. Trade winds are much stronger than normal. Cloudiness decreases near the Date Line. La Niña events also tend to develop in Autumn to Winter (March - August), and finishes the following Autumn (March - May). In Vanuatu, above normal rainfall which results in extreme wetter conditions with cooler temperatures are associated with La Niña.

During a Neutral phase, all ENSO indicators (Sea surface temperatures, Southern Oscillation Index (SOI), trade winds, and cloudiness near the Date Line) in the tropical Pacific Ocean, remain within the neutral range. Normal climate conditions are experienced over Vanuatu during Neutral ENSO phase.

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Bulletin June 2021 - MJO

What is an MJO (Madden-Julian Oscillation)?
An MJO is a group of cloud and rain that circulates the globe near the equator, and usually occurs every 30-60 days. When an MJO passes over an area, it brings heavy rain with varying wind speed. During cyclone season, an MJO can help develop tropical cyclones by fueling any overlying low pressure systems.

The diagram below shows the track of the MJO for the past 40 days (coloured lines). [Click to enlarge the diagram]. When the lines are within the circle, MJO is weak and has no influence on rainfall. Outside the circle, the MJO is active and will usually move in an anti-clockwise direction. Vanuatu will most likely experience rainfall related to an MJO event when it moves over the Maritime Continent on the diagram.

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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 June 2021 - Cloud

The above maps show regions experiencing more or less cloudiness. The top map is the total outgoing long-wave radiation (OLR), and the bottom map is the cloud anomaly. Outgoing longwave radiation (OLR) is often used as a way to identify tall, thick, convective rain clouds. This means, a region which experiences lower outgoing radiation is an indication of more cloudiness over the area.

The purple shading indicates higher than normal, active or enhanced tropical weather (above normal cloudiness), while brown shading indicates lower than normal cloud or suppressed conditions.

Equatorial cloudiness near the Date Line typically increases during El Niño (negative OLR anomalies) and decreases during La Niña (positive OLR anomalies). 

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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 June 2021 - Rainfall

Although the country is in its second month of dry season, the country still experienced above normal rainfall last month, May 2021. All stations recorded above normal rainfall, except Port Vila which recorded normal rainfall.

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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 June 2021 - SST

Top Chart: Monthly Temperatures
The four-month sequence of the equatorial Pacific sub-surface temperature anomalies (to May) shows a pattern consistent with the return to a neutral ENSO state.

Bottom Chart: 5-day sub-surface temperatures
For the 5 days ending 6 June, sub-surface temperatures were close to average across most of the equatorial Pacific, consistent with an ENSO neutral state. Warm anomalies in excess of 2 °C exist between the depths of 25 m and 100 m in the eastern 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 June 2021 - MSLP

Regions of HIGH pressure anomalies (brown shades) are associated with lower rainfall, while higher rainfall are associated with regions of LOW pressure anomalies (purple shades).

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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 June 2021 - Model Outlooks

The El Niño–Southern Oscillation (ENSO) is currently neutral. All of the international climate models surveyed by VMGD anticipate sea surface temperatures will remain neutral until at least October.

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Bulletin June 2021 - SPCZ

A large convective region was centered over the Maritime Continent. The SPCZ shrink westward within the last 30 days ending 12 June 2021 from its normal position across the southern tropical Pacific. Higher convection was experienced over PNG, Solomon Islands, and the Micronesian countries.

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