ENSO neutral conditions are expected to continue over the next 2-3 months, but La Niña is favoured to develop during October-December.
Because of above normal trade wind speeds, an increasing Southern Oscillation Index, a shift in convective patterns, and an expectation for these conditions to continue, a La Niña Watch has been raised.
The 30-day Niño 1+2 Index anomaly was -0.79˚C, within the La Niña range.
The 30-day NINO3.4 Index anomaly (in the central equatorial Pacific) as of 21 June was +0.10˚C, in the neutral range. However, a cooling trend is continuing in the eastern and central Pacific.
The Southern Oscillation Index (SOI) was in the neutral range during April-June (0.0), but the June value was -0.7 (in the El Niño range).
During mid-June, the subsurface equatorial Pacific continued to be 4˚C to 6˚C cooler than average just below the surface in the east of the basin.
Meanwhile, above average temperatures persisted in the central and western parts of the basin. This signature is reflective of an oceanic transition toward a possible La Niña in a few months.
The South Pacific Convergence Zone was slightly south of its climatological normal position during June.
During late June and early July, a pulse of the Madden-Julian Oscillation may propagate across the Pacific. This may lead to a period of heavy rainfall with the potential for flooding, especially south of the equator in island groups such as the Solomon Islands, Tuvalu, Tokelau, parts of Fiji, Vanuatu, Wallis & Futuna, Samoa, and American Samoa (based on the decile precipitation forecast for July located on page 6).