Island Climate Update 277 - November 2023
El Niño continued during October and will likely intensify during the next three months. El Niño has around a 100% chance of persisting during through January 2024.
The monthly NINO3.4 Index anomaly (in the central equatorial Pacific) at the end of October was +1.60˚C, within the range of a strong El Niño (classified when the NINO3.4 Index is greater than 1.5˚C). The October 2023 NINO3.4 Index is exceeded by 2015, 1997, and 1982 with data back to 1981. From an oceanic perspective, this El Niño continues to rank with the most significant events in recent decades.
The Southern Oscillation Index (SOI) was near the El Niño threshold from August-October (-0.9) but on the El Niño side of neutral territory during October (-0.4), suggestive of an El Niño event that is displaying unusual atmospheric tendencies, which is unusual considering its oceanic strength.
Trade wind strength was was below or well below normal in the Pacific during October, particularly just north of the equator. In parts of the region, this qualified as a Westerly Wind Burst (WWB). This WWB will be responsible for the eastward propagation of warm sea water along the equator through the end of the year, via an oceanic Kelvin Wave.
In the sub-surface eastern equatorial Pacific Ocean, anomalies of +3˚C to +6˚C were occurring in the upper 100 metres in the east as of late October. A new area of anomalies greater than 3˚C developed in the west-central equatorial Pacific during the month, in response to a downwelling oceanic Kelvin Wave. This will transfer ocean heat eastward on the time horizon of the next 1-2 months, lending credence to the models that suggest a peak El Niño strength in early 2024.
The associated abnormally warm water, sitting near and north of both Vanuatu and Fiji, may be a common genesis zone for tropical cyclone activity in the months ahead. Extra vigilance around early tropical cyclone activity is encouraged.