ENSO Update

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Bulletin April 2020 - Summary

Issued: 29 April 2020. Next Issue: 12 May 2020.

The El Nino Southern Oscillation (ENSO) remains Neutral for the whole Pacific. Neutral conditions will likely remain through the southern hemisphere winter (June-August 2020).

Madden-Julian Oscillation (MJO) is currently inactive, and has no influence on rainfall over the country at this time.

Cloudiness was above average over Vanuatu for the last 30days ending 7th April.

Vanuatu to expect below normal rainfall over the central and southern islands during May 2020. Normal rainfall is forecasted for other parts of the country.

Day & night-time temperatures are expected to be warmer than average over the northern and central islands during May 2020.

Sea surface temperatures (SSTs) have been warmer than average during late March into the beginning of April. Tropical Cyclone Harold caused SSTs to drop back to normal on April 7th. Waters over Torba, Sanma and Penama are expected to reach 28.0 - 30.0 degree Celsius in May 2020, while temperatures below 28.0 degrees Celsius are expected elsewhere.

The South Pacific Convergence Zone (SPCZ) shifted over Vanuatu during the previous month.

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Bulletin April 2020 - El Nino Oscillation

ENSO update: ENSO remains Neutral for the whole Pacific.

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

During an El Niño, ocean surface tends to warm in the CENTRAL and EASTERN tropical Pacific Ocean. Countries in this region would receive extreme rainfall, while countries in the western tropical Pacific (like Vanuatu) would experience extreme dry conditions.

During a La Niña, ocean surface tends to warm in the CENTRAL and WESTERN tropical Pacific Ocean. Countries in this region (like Vanuatu) would receive extreme rainfall, while countries in the eastern tropical Pacific would experience extreme dry conditions.

During a Neutral phase, ENSO indicators are generally normal. Neither an El Niño or La Niña is active.

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Bulletin April 2020 - MJO

MJO Update:
A weak pulse of MJO was active over the Maritime Continent from March 31st to April 4th, and is currently located over the western Indian Ocean. At this time, MJO has little influence on rainfall patterns over Vanuatu.

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 related rainfall from 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 April 2020 - Cloud

Cloud Update:
Cloudiness for the 30 days ending in 7 April was above normal over Vanuatu, indicating enhanced convection over the country for the past 30 days.

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.

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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 April 2020 - Rainfall

Rainfall Update:
Rainfall has been generally normal in March as the South Pacific Convergence Zone (SPCZ) shifted southwest over the country from its previous position in February.

Rainfall Forecast (May 2020):
As the country progresses into its dry season which begins in May, islands over Sanma, Malampa, Shefa and Tafea have 50% chance of experiencing below normal rainfall. Elsewhere, normal rainfall is likely.

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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 April 2020 - SST

Sea Surface Temperature Update:
There are signs of cooling along the equator in April. The extreme warming of sub-surface temperatures over the past months have tremendously decreased, resulting in enhanced cooling, visible at 150mm below sea surface.

Top Image - Monthly Sub-surface Temperatures:
This diagram shows temperatures below the sea surface along the equator. During an El Nino, extreme warming of sub-surface temperatures will be evident in the eastern Pacific (RED color will shift and intensify towards the right side of the diagram). While during a La Nina, extreme cooling of sub-surface temperatures will be evident in the eastern Pacific (BLUE color will shift and intensify towards the right side of the diagram). On the graph, Vanuatu is positioned between 166E and 170E.

Bottom Image - Weekly Sub-surface Temperatures:
This diagram shows sub-surface temperatures on a weekly basis. For the week ending on 8th April 2020 (refer to last diagram), temperatures directly below the sea surface (100m below sea surface) have dropped.

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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 April 2020 - MSLP

Mean Sea Level Pressure Update:
The March MSLP anomaly map shows the monthly atmospheric pressure over Vanuatu was normal; between 0 and +1 over most islands.

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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Source

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 April 2020 - Model Outlooks

There are currently 8 international climate models that are used by the bureau of Meteorology in Australia to monitor El Niño Southern Oscillation (ENSO events) in the Pacific. While most of these models indicate that ENSO will remain neutral until June to August 2020, one model shows a La Niña event is likely to develop during June 2020. Another two models show a likelihood of La Niña event by September 2020.

However, ENSO predictions made during this time of the year (March to May) tend to have lower accuracy than predictions made at other times of the year, therefore forecasts for this La Niña event may change beyond May.

ENSO events, that is, either El Niño or La Niña, typically begin to develop during March to May, before strengthening in June to September.

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Bulletin April 2020 - SPCZ

From the 30 days ending in 4th April 2020, the South pacific Convergence Zone (SPCZ) extended southeastward across the Solomon Islands, Vanuatu, Fiji, Tonga and the southern Cooks. The SPCZ looks to be west of its normal location.

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