ENSO Update

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Bulletin July 2022 - Summary

Issue: August 2022 - "La Niña WATCH continues"

The ENSO outlook remains at La Niña WATCH, meaning there is around a 50% chance (double the normal likelihood) of La Niña forming later in 2022. This is a result of current observations and model outlooks. La Niña events increase the chance of above average rainfall across much of the country.

The Intertropical Convergence Zone (ITCZ) further east was close to its average July position but marginally suppressed near the Date Line. In the south Pacific, the South Pacific Convergence Zone (SPCZ) extended further east than normal and was enhanced over northern Papua New Guinea and northern Solomon Islands. Convection was suppressed in the vicinity of New Caledonia, Vanuatu, Fiji, Samoa and the southern Cook Islands.

The Madden–Julian Oscillation (MJO) is currently weak. Most models suggest the MJO is likely to remain weak or indiscernible over the coming week. The means it is likely to exert little or no influence on global tropical weather.

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Bulletin July 2022 - El Nino Oscillation

The 2021-22 La Niña has ended. There is a 50% chance of another La Niña event forming later in 2022.

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 July 2022 - 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 July 2022 - 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 July 2022 - Rainfall

With the La Nina-like conditions established, the country is most likely to experience above normal rainfall within the next three months, August to October 2022.

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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 July 2022 - SST

5-day sub-surface temperatures:

For the five days ending 17 July 2022, sub-surface temperatures along the equator were mostly close to average, with an area of warm anomalies in the east. In the eastern equatorial Pacific, temperatures were more than 3 degrees warmer than average between 50 m and 100 m depth in a region extending east of 130°W, and more than 2 degrees warmer than average at 100m in depth in the far western Pacific. Compared to two weeks ago, these regions of warm anomalies have decreased in strength. An area of weak cool anomalies has expanded in size in the central tropical Pacific between 100 and 150 m depth when compared to two weeks ago.

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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 July 2022 - 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 July 2022 - Model Outlooks

The El Niño–Southern Oscillation is currently neutral. However, some models suggest that La Niña may re-form during the southern hemisphere spring later in 2022.

Five of seven surveyed international climate models predict neutral but cooler than average temperatures in the central tropical Pacific to persist throughout the southern winter, while two show stronger cooling, reaching La Niña thresholds (−0.8 °C) by late winter. In October, four of the seven models indicate SSTs in the central equatorial Pacific Ocean will reach or exceed La Niña threshold values. Three of the seven models anticipate that the current ENSO-neutral state will continue through to at least November.

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Bulletin July 2022 - SPCZ

The Intertropical Convergence Zone (ITCZ) was active in the central equatorial Pacific, while the South Pacific Convergence Zone (SPCZ) was active and shifted southwest affecting southern PNG, southern Solomon Islands, Vanuatu and New Caledonia.

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