ENSO Update

Select Issue:
Bulletin September 2022 - Summary

The ENSO outlook has been raised to LA NIÑA.

Key atmospheric and oceanic indicators of the El Niño–Southern Oscillation (ENSO) show an established La Niña. Tropical Pacific sea surface temperatures have been cooling since June and are now at La Niña thresholds. Atmospheric indicators including the Southern Oscillation Index (SOI), trade wind strength, and equatorial cloudiness are also displaying patterns typical of a La Niña event.

Models indicate this La Niña event may peak during the September - November, and return to neutral conditions early in 2023. La Niña events increase the chances of above-average rainfall for Vanuatu.

The Madden–Julian Oscillation (MJO) continues to show a weak signal with most models suggesting it will remain weak for at least the next seven days. A weak MJO is unlikely to have much impact on Vanuatu climate.

Print this part
Bulletin September 2022 - El Nino Oscillation

ENSO Outlook has been raised to LA NIÑA.

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.

Print this part
Bulletin September 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.

Large view

Source

Large view

Source

Large view

Source

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

Print this part
Bulletin September 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).

Large view

Source

Large view

Source

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

Print this part
Bulletin September 2022 - Rainfall

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

Large view

Source

Large view

Source

Large view

Source

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

Print this part
Bulletin September 2022 - SST

5-day sub-surface temperatures:

For the five days ending 12 September 2022, sub-surface temperatures along the equator were mostly within 2 ºC of average. Compared to two weeks ago, cool anomalies in the eastern sub-surface expanded and strengthened, while the warm anomalies in the west contracted slightly. In the west, temperatures were more than two degrees warmer than average from around 125 m and 150 m depth between 160 °E and 175 °E, and in the east, temperatures were more than three degrees cooler than average around 125 m depth at 140 °W.

Large view

Source

Large view

Source

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

Print this part
Bulletin September 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).

Large view

Source

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

Print this part
Bulletin September 2022 - Model Outlooks

A La Niña event is under way in the tropical Pacific and the ENSO Outlook has shifted to La Niña.

All seven surveyed international climate models show NINO indices are expected to meet or exceed La Niña thresholds by October, with five persisting at these levels until at least the end of 2022. Most models indicate a return to ENSO-neutral conditions in early 2023, suggesting a relatively short-lived event; ENSO events typically decay during the southern hemisphere autumn (March to May).

While back-to-back La Niña events are not uncommon, and have occurred in approximately half of all past events since 1900, three La Niña events in a row is less common and has previously occurred only three times in the Bureau record since 1900: 1954–57, 1973–76, and 1998–2001.

Print this part
Bulletin September 2022 - SPCZ

The Intertropical Convergence Zone (ITCZ) was active and shifted north of the average July position in the central equatorial Pacific, while the South Pacific Convergence Zone (SPCZ) was largely suppressed in July.

Print this part