ENSO Outlook has been shifted to El Niño ALERT, indicating a 70% chance of El Niño forming this year. This equates to roughly three times the normal chance of an El Niño forming. Central and eastern Pacific sea surface temperatures (SSTs) have warmed to El Niño thresholds. All models surveyed by the Bureau are forecasting the likelihood of further warming and that these SSTs will remain above El Niño thresholds at least into the southern hemisphere spring. Some atmospheric indicators such as the Southern Oscillation Index (SOI) have shifted towards El Niño thresholds, but wind, cloud and broad-scale pressure patterns indicate the Pacific Ocean and atmosphere are yet to reinforce each other, as occurs during El Niño events. El Niño typically suppresses rainfall in Vanuatu.
A weakening Madden–Julian Oscillation (MJO) pulse lies over the western hemisphere. Most models indicate the signal will become weak or indiscernible in coming days. While some models indicate a pulse will strengthen over the eastern Indian Ocean or western Maritime Continent region, north of Australia, in about a week, others maintain a weak or indiscernible signal. The MJO has little influence on Australian rainfall patterns at this time of the year.
Bulletin May 2023 - El Nino Oscillation
ENSO Outlook has been shifted to El Niño ALERT, indicating a 70% chance of El Niño forming this year. This equates to roughly three times the normal chance of an El Niño forming.
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.
Bulletin May 2023 - 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.
Note: Due to frequent images update from source provider, the quoted Sources might not give the same images as shown
Bulletin May 2023 - 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).
Note: Due to frequent images update from source provider, the quoted Sources might not give the same images as shown
Bulletin May 2023 - Rainfall
Rainfall Outlook for June 2023.
Rainfall is slightly likely to be above average for Malampa, Shefa, and Tafea provinces. The outlook offers little guidance for Torba, Sanma and Penama provinces, as the chances of above normal, normal and below normal are similar.
Note: Due to frequent images update from source provider, the quoted Sources might not give the same images as shown
Bulletin May 2023 - SST
For the five days ending 4 June 2023, sub-surface temperatures were warmer than average across the equatorial Pacific, at depths between about 25 to 200 m in the western and central Pacific, and between the surface to 100 m depth in the eastern Pacific. Anomalies were more than 1 °C warmer than average across the basin, increasing to more than 3 °C in the west and 5 °C in the far east.
Compared to two weeks ago, warm anomalies have increased marginally in strength in the west, while cooling slightly in the central Pacific.
Note: Due to frequent images update from source provider, the quoted Sources might not give the same images as shown
Bulletin May 2023 - 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).
Note: Due to frequent images update from source provider, the quoted Sources might not give the same images as shown
Bulletin May 2023 - Model Outlooks
Central and eastern Pacific Sea surface temperatures have warmed to El Niño thresholds. International climate models anticipate further warming of the central and eastern tropical Pacific Ocean is likely. By the end of June, six out of seven surveyed models indicate El Niño thresholds for SSTs will be reached with the seventh reaching the threshold during July. All models persist at these levels until at least the end of the southern spring. If the atmosphere responds to this warming, an El Niño event would be expected to develop.
El Niño typically suppresses rainfall in Vanuatu.
Bulletin May 2023 - SPCZ
The ITCZ and SPCZ were weaker than average in April 2023.
There is No Current Warning
