Newsletter Issue 68 (June 2026)

The Weather of May 2026 – A cloudy and relatively hotter May

May 2026 was characterised by cloudier than usual weather with localised heavy rain. The mean amount of cloud in the month was 82 percent, 6 percent above the normal of 76 percent. The rainfall over the territory was highly uneven. The total rainfall recorded at the Hong Kong Observatory Headquarters in the month was 227.2 millimetres, about 78 percent of the normal of 290.6 millimetres, whereas rainfall exceeded 500 millimetres over the North District. There were 6 consecutive hot nights starting from 23 May, one of the highest on record for May.

Records fall as extreme heat grips Europe

WMO, its members and partners are mobilizing with coordinated heat-health action plans against a record-breaking late June heatwave, which is impacting millions of people in Europe, with knock-on impacts on economic activities, infrastructure, agriculture and ecosystems. The heatwave will spread over large parts of Western, Central, and Southern Europe within the next two weeks. Current forecasts predict that the focus of the heat is likely to shift more towards the Balkans.

Trends in Atmospheric Carbon Dioxide (CO2)

The monthly average Mauna Loa CO2 in May 2026 was 432.34 ppm. The red lines and symbols represent the monthly mean values, centered on the middle of each month. The black lines and symbols represent the same, after correction for the average seasonal cycle. The vertical bars on the black lines show the uncertainty of each monthly mean based on the observed variability of CO2 in different weather systems as they go past the top of Mauna Loa.

Global Seasonal Climate Update for July-August-September 2026

For the July–September 2026 (JAS 2026) season, the multi-model ensemble (MME) indicates a rapid development into a strong El Niño event. By JAS 2026, the MME is forecast to reach approximately 2.0°C for the seasonal average. The intensification trajectory maintains an upward trend throughout the boreal autumn. Spread among the individual forecast systems is generally narrow during JAS 2026, indicating high forecast confidence.

El Nino forms, expected to strengthen, say NOAA forecasters

NOAA’s National Weather Service announced that El Nino has developed in the tropical Pacific, and issued an El Nino Advisory. El Nino, the warm phase of the El Nino Southern Oscillation (ENSO), is predicted to intensify to a moderate or strong level this fall. Forecasters predict a 63% chance of sea surface temperatures exceeding 2.0°C in the Nino-monitored region of the Pacific. I f this threshold is surpassed, NOAA considers the event a “very strong” El Nino.

ArchesWeatherGen

A team proposes to leverage deterministic weather models in the design of probabilistic weather models, leading to improved performance and reduced computing costs. They design a probabilistic weather model “ArchesWeatherGen” based on flow matching, a modern variant of diffusion models, that is trained to project deterministic weather predictions to the distribution of ERA5 weather states, surpassing IFS ENS and NeuralGCM on almost all WeatherBench headline variables.

風雲氣象衞星主要奠基者 – 許健民院士獲“氣象界諾貝爾獎”

中國工程院院士許健民在瑞士日內瓦獲第70屆國際氣象組織獎。作為中國衛星氣象學的主要貢獻者，許健民推進並提升了衛星產品在數值預報與天氣分析中的應用能力，為“兩代四型”共23顆風雲氣象衛星的成功發射、運行和應用做出了突出貢獻，推動中國氣象衛星成為世界氣象組織全球綜合觀測系統的重要支柱。此次獲獎，不僅是國際社會對許健民個人在氣象衛星領域傑出貢獻的肯定，更是對中國氣象科技和航天科技整體實力的認可。

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