Early tropical storm cuts solar in Philippines, while East Asia sees La Niña gains

Most of East Asia recorded normal to above‑normal solar irradiance in January, as weak La Niña conditions continued to influence regional weather patterns. The largest gains were observed across southeastern China, where suppressed cloud formation and reduced aerosol-effects delivered a strong start to the year for solar operators, while unusual early tropical storm activity brought significant rainfall and irradiance losses to parts of the Philippines. With two days left in January at time of publishing, this data uses live data from 1-29 January, and forecasts for 30-31 Jan from the Solcast API.

Irradiance in southeastern China surged well above historical averages in January, with Hong Kong exceeding 25% above average. A dominant Siberian high pressure system, with temperatures in parts of Siberia more than 10 C below normal, extended into western China. The resulting northerly flow delivered drier air into southeastern China, reducing both precipitation and cloud formation. This irradiance pattern aligns with typical La Niña effects, even though the La Niña signal was weak and fading toward neutral by late January. Additionally, lower than normal aerosol levels contributed to above average irradiance in coastal parts of China.

In a continuation of the irradiance and aerosol pattern seen in 2025, many parts of China, in particular low-lying industrial areas saw significant drops in aerosol load and a corresponding increase in available irradiance. Both Hong Kong and Shanghai regions saw significantly lower winter average aerosol loads, than the historical average for winter months from 2007-2026. Whilst this supported the exceptionally high irradiance in Hong Kong through January, Shanghai recorded slightly above-average irradiance, despite experiencing a rare snowfall late in the month. By contrast, Beijing has historically lower aerosol loads, however still saw slightly below-average irradiance due to prevailing cloud levels.

Elsewhere in East Asia, irradiance levels were generally normal to above normal for this month. Seoul and Tokyo recorded irradiance 5–10% above January averages and Taipei saw gains exceeding 10%. Across the maritime continent, irradiance and precipitation anomalies were near normal.

The most significant negative irradiance anomaly in the region was associated with Tropical Storm Nokaen (Ada), which marked an unusually early start to the 2026 Pacific typhoon season. Making landfall in January—the first such occurrence since 2019— Nokaen delivered intense rainfall and heavy cloud cover to the central and northern Philippines. Daily rainfall totals reached up to 200 mm, triggering mudslides and widespread disruption. Irradiance across the northern Philippines dropped by as much as 10% below average, while the southern parts of the archipelago, spared from the worst of the storm, saw irradiance climb to 10% above average.

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