Reunion Braces for Intense Heat and Erratic Storms as El Nino Strengthens

Reunion’s July 2026 temperature readings came in 1.4 degrees Celsius above normal, and the numbers have not improved since. The island is now entering a sustained period of above-normal heat and unpredictable rainfall as El Nino strengthens across the tropical Pacific and Indian Ocean basins, with the World Meteorological Organization warning the phenomenon will reach “very strong” intensity and persist through February 2027.

The warming is already embedded in the data. Daytime highs in July ran 1.6 degrees above baseline; nighttime lows were 1.2 degrees higher. June showed similar patterns, roughly one degree above normal, while August continued the trajectory with warmer conditions at lower elevations, though cooler temperatures held in the highlands. These readings arrived during the austral winter, when temperatures typically moderate.

Laurent Labbe, director of the Climate Service at Meteo-France, attributed the warming to elevated ocean temperatures and weakened trade winds from the east-northeast. “We have already seen stagnation of warm waters in the southwestern Indian Ocean basin for several years, and with El Nino arriving in the coming months, this situation will not improve,” Labbe said. He added that “we should expect temperatures well above normal, particularly given that we are already in an abnormally warm context during July and August.”

El Nino originates as a Pacific phenomenon but radiates effects across the full tropical band, including the southwestern Indian Ocean and the Mascarene Islands. The mechanism is well understood. The consequences for Reunion, however, are still unfolding.

Precipitation presents the more complex operational challenge. Historical analysis of eight El Nino episodes since the 1980s shows variable outcomes. The onset of the rainy season, typically October through December, has generally been wetter than normal. The core of the season is less predictable. “Some years Reunion experiences above-normal rainfall, while others see deficits,” Labbe said. For the coming months, the entry into the rainy season is expected to be “normal to above normal,” though the remainder carries significant uncertainty.

Meanwhile, cyclonic activity adds a further layer of risk. The expected number of tropical systems across the broader basin should fall substantially below the normal average of ten per season, and cyclone risk over the African continent, Mozambique, and Madagascar is projected to decline. The Mascarene Islands, Reunion among them, face cyclone risk roughly equivalent to normal levels.

The distinction matters because El Nino does not simply suppress storms; it redirects them. Systems may follow predominantly north-south paths rather than typical patterns, a dynamic illustrated by Cyclone Belal during the 2023-2024 season, which developed under El Nino conditions. “The risk changes because the trajectories of these systems are likely to shift depending on El Nino conditions,” Labbe noted.

The five-month window through February 2027 combines sustained heat, uncertain rainfall, and altered storm paths into a period when standard seasonal planning assumptions may not hold. Whether operational responses across weather-dependent sectors keep pace with conditions as they develop is the question that will define the season.