ENSO neutral conditions are expected to continue over the next couple of months, but La Niña is slightly favoured over ENSO neutral during October-December.
Trade winds have been enhanced in the tropical Pacific and thunderstorm activity has favoured the western Pacific, both signs of a La Niña-like atmosphere. Despite this, sea surface temperatures (SSTs) in the central equatorial Pacific Ocean were around +0.3˚C above average over the last month. However, a new measure of central Pacific SSTs, called the relative oceanic Niño Index, has ranged from -0.3˚C to -0.5˚C over the last month and is more aligned with the La Niña-like atmospheric conditions.
As of 21 July, the 30-day Niño 1+2 Index anomaly was -0.35˚C, within the neutral range. The 30-day NINO3.4 Index anomaly (in the central equatorial Pacific) was +0.32˚C. The relative 30-day oceanic Niño Index was -0.29˚C.
The Southern Oscillation Index (SOI) was in the neutral range during May-July (+0.1), but the July value was -0.7 (in the El Niño range).
The subsurface equatorial Pacific continues to be 4˚C to 6˚C cooler than average just below the surface in the east of the basin.
Meanwhile, above average oceanic temperatures persisted in the central and western parts of the basin, with the West Pacific Warm Pool showing a distinct warming trend. This signature is reflective of an oceanic transition, possibly towards La Niña in a few months.
The South Pacific Convergence Zone was very close to its climatological normal position during July.
During August-October, model guidance favours an enhancement in convective forcing over the western Pacific and Maritime Continent, consistent with a developing La Niña. This may lead to enhanced rainfall for some countries like Papua New Guinea and the Solomon Islands (based on the decile precipitation forecast for August and August-October; see pages 6-7 for more information).