ENSO Update

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Bulletin April 2019 - Summary

ENSO Outlook remains at El Niño ALERT since 19th March 2019.

Sea Surface Temperatures are within El Niño threshold.

Atmospheric indicators are yet to show El Niño-like response.

Climate Models show if an El Niño does develop, it is likely to be short lived and weak.

El Niño typically brings suppressed rainfall for Vanuatu with drier than average conditions. Vanuatu dry season is from May to October each year.

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Bulletin April 2019 - El Nino Oscillation

In keeping with MJO activity over the western to central Pacific since February, the SOI has dropped significantly over the past month, but is neutral for the last 90 days. The main contribution to the low SOI is high pressure over northern Australia in March.

SOI values below -7 indicate an El Niño event, while positive values above +7 indicate a La Niña event. Values between -7 and +7 indicate neutral conditions.

The SOI for the 30 days ending 14 April was −2.0, with the 90-day average −5.8. SOI indicates ENSO is currently Neutral.

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Bulletin April 2019 - MJO

The MJO is a pulse of atmospheric wave that enhances rainfall over the Indian and Pacific Ocean.

MJO is currently weak over the Maritime Continent (Vanuatu included) and has no influence on rainfall in the previous month.

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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 2019 - Cloud

Evidence of strong convection (purple shade) on or just north of the equator from western to central Pacific . A broad area of reduced cloudiness (brown shade) stretched east-west just south of the equator from the Solomon Islands to the central Pacific. The adjacent zonal regions of enhanced and reduced cloud was a most unusual pattern.

On average, Vanuatu experienced reduced cloudiness in a 30 day timescale ending in 7 April, which coincided with suppressed rainfall in the previous month.

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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 2019 - Rainfall

ITCZ evident just north of the equator across the Pacific, extending westward to a mass of convection west of the Date Line. Extending from this at an unusually sharp angle was a diffuse looking SPCZ, principally affecting Tuvalu and Fiji. This convective mass was displaced to the east from its normal location. There was also a line of convection just south of the equator from the central Pacific towards the South American coast.

Vanuatu rainfall detected by satellite shows there was reduced convection for the month of March 2019.

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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 2019 - SST

The NINO3.4 values for March was +8.0 compared to February values which was +6.0. This shows warming in late Feb increased by 0.2C into March. The latest weekly value ending in April 14th shows a sustained NINO3.4 value of +8.0 since March, which indicate SSTs already reached El Nino threshold.

SSTs are warmer than average across most of the tropical Pacific Ocean. Compared to two weeks ago, the surface of the ocean has cooled slightly in the west. Most of the tropical Pacific region is half to one degree warmer than average. SSTs over Vanuatu are up to half degree warmer average. Hence, Coral Bleaching outlook for the next 4 weeks is on WATCH over Torba, Sanma, Penama, Malampa and parts of Shefa, and No Stress for Tafea.

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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 2019 - MSLP

Sea Level Pressure anomalies for March have significantly increased compared to February. The slow moving TC Oma in mid-Feb has caused pressure to drop below 990 hPa over northern Vanuatu. In March, Mean Sea Level Pressure increased to 1010.0 – 1012.5 hPa.
High pressure typically brings less rainfall and normal weather conditions for Vanuatu in the previous month compared to February.

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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 2019 - Model Outlooks

While most climate models forecast El Nino-like warmth to persist throughout mid-2019, the ocean is likely to cool around winter (June, July, and August), leaving only 3 out of 8 surveyed climate models still forecasting El Nino-like warmth well into September/October. This could indicate that if El Niño does develop, it is likely to be short lived and weak.

Due to the natural cycle of ENSO, Model accuracy through autumn months (March, April, and May) is lower than at other times of the year. Forecast accuracy improves for outlooks after May.

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Bulletin April 2019 - SPCZ

ITCZ evident just north of the equator across the Pacific, extending westward to a mass of convection west of the Date Line. Extending from this at an unusually sharp angle was a diffuse looking SPCZ, principally affecting Tuvalu and Fiji. This convective mass was displaced to the east from its normal location. There was also a line of convection just south of the equator from the central Pacific towards the South American coast.

SPCZ shifted east away from Vanuatu, hence reduced convection was experienced in March.

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