Oceanic indicators firmly exhibit an El Niño state. Central and eastern Pacific sea surface temperatures (SSTs) continue to exceed El Niño thresholds. Models indicate further warming of the central to eastern Pacific is likely.
Broadscale pressure patterns over the tropical Pacific reflect El Niño, with the 90-day Southern Oscillation Index (SOI) at −10.2. Trade wind strength over the past week has weakened in the far western Pacific, but is close to normal elsewhere. Overall, there are signs that the atmosphere is responding to the warm SSTs over the Pacific and coupling of ocean and atmosphere is occurring. This coupling is a characteristic of an El Niño event and is what strengthens and sustains an event for an extended period. El Niño typically leads to reduced rainfall for Vanuatu.
Climate models indicate this El Niño is likely to persist until at least the end of February. El Niño typically leads to reduced spring and early summer rainfall for eastern Australia, and warmer days for the southern two-thirds of the country.
The Madden–Julian Oscillation (MJO) is currently weak or indiscernible. About half the models indicate it is likely to remain weak or indiscernible, while the other half suggest the MJO may strengthen and progress into the Maritime Continent and western Pacific over the coming fortnight.
Bulletin September 2023 - El Nino Oscillation
El Nino El Niño Southern Oscillation (ENSO) is at El Niño levels.
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 central and eastern equatorial Pacific, 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 central and western equatorial Pacific, both at the surface and the sub-surface tends to WARM. 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 September 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 September 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 September 2023 - Rainfall
Seasonal Outlook for October to December 2023
On average, rainfall is slightly likely to be below normal for the central and southern islands, and normal elsewhere for the period of October to December 2023.
Note: Due to frequent images update from source provider, the quoted Sources might not give the same images as shown
Bulletin September 2023 - SST
For the 5 days ending 24 September 2023, sub-surface temperatures were warmer than average across the upper levels of the equatorial Pacific between the surface to around 125 m depth. Much of this region was more than 2 °C warmer than average, with anomalies more than 5 °C warmer than average in a small area of the eastern Pacific.
Compared to last week, warm anomalies in the eastern and central Pacific have increased.
Note: Due to frequent images update from source provider, the quoted Sources might not give the same images as shown
Bulletin September 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 September 2023 - Model Outlooks
Central and eastern Pacific sea surface temperatures (SSTs) currently exceed El Nino thresholds. International Climate models suggests some further warming of the central and eastern tropical Pacific ocean is likely. All surveyed models indicate SSTs will remain above El Nino thresholds until at least the end of the December to February 2024 period.
El Nino typically increases the chances of below normal rainfall with warmer than average days for much of Vanuatu.
Bulletin September 2023 - SPCZ
The ITCZ was active and displaced south from its normal position in August 2023.
