The NINO3.4 Index anomaly (in the central equatorial Pacific) over the last month (through 31 July) was -0.34˚C (climatology: 1961-1990); the latest weekly anomaly was -0.43˚C, showing a late-month cooling trend. The index was -0.63˚C relative to the more modern 1991-2020 climatological period. The July monthly SOI was +0.9, which was near the La Niña threshold.
Large changes took place in the subsurface equatorial Pacific during July in response to much stronger than normal trade winds. The strong trades drove the development of an upwelling Kelvin wave, which will likely further cool the equatorial Pacific in the coming months.
At the end of July, substantially cooler than average subsurface waters (3˚C to 5˚C below average) were focused in the central Pacific, particularly at 100-150 m depth. The effect of the upwelling Kelvin wave will likely see cooler waters migrate eastward and toward the surface over the next 1-2 months, reinforcing the oceanic La Niña signal.
Trade winds across the equatorial Pacific were much stronger than normal during July, in some cases by as much as 10-15 knots – this qualified as near-record strength. This was associated with rapidly cooling sub-surface ocean temperatures across the central part of the basin. Strong trade winds are predicted to continue over the next month or beyond with cooling seas likely.
Taking these factors into account, La Niña conditions are most likely to continue during August-October (70% chance). During November-January, there is a 65% chance for La Niña and a 35% chance for ENSO neutral. During February-April, ENSO neutral is favoured at 65%. Overall, this implies that a “triple dip” La Niña (three consecutive La Niña events from 2020-2022) is likely.
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