The Tonga Meteorological Service says there is a highly likely chance of El Niño developing during the June to August 2026 period, with warmer-than-average ocean conditions expected to continue across Tonga waters.

In its Ocean Outlook released on 14 May, the service said average to above-average sea surface temperature anomalies are likely to persist over the coming months, while a moderate marine heat wave is expected to continue in the coming weeks.

Sea surface temperatures around Tonga have remained above average in recent weeks, affecting northern parts of Tonga, particularly the Niuas and parts of Ha’apai waters, with increases ranging from 0.8°C to 2.0°C above normal levels.

The outlook predicted mostly average to above-average sea surface temperatures across the country. The presence of warmer-than-average waters was expected to intensify stress on marine ecosystems and increase risks to fish populations and coral reefs.

Sea level height across most of Tonga is forecast to remain average to below average over the next three months. The report said this information could assist stakeholders in making decisions on protecting communities and infrastructure against coastal inundation, particularly during periods of extreme high tide.

Coral bleaching forecasts showed no stress for most Tonga waters during the outlook period, except north of the Niuas where conditions remain at watch level. The report noted that coral bleaching is a common signal of stress in coral reefs and marine ecosystems caused by warmer sea temperatures, and advised continued monitoring by fisheries and related stakeholders.

The outlook also noted that the boundary between warm and cold ocean waters, which is rich in nutrients and attracts tuna, is normally located far north of the Niuas. During the June to August period, however, the convergence zone is forecast to shift southward, although it is expected to remain north of Tonga. The information was highlighted as useful for stakeholders monitoring tuna distribution during the forecast period.

The next climate update is expected to be issued in the second week of June 2026 or earlier.