GISTDA detects moderate G3 geomagnetic storm over Thailand

The Geo-Informatics and Space Technology Development Agency (Public Organisation), or GISTDA, reported that its sensors have detected a moderate geomagnetic storm (G3 level) over Thailand. The disturbance was caused by a Coronal Mass Ejection (CME) emitted from sunspot AR4100 on May 31, 2025.

According to local measurements using the Local K index, Thailand recorded a reading of K=7, on a scale where the maximum level is 9. This indicates moderate to strong geomagnetic activity, which may affect the following:

Temporary disruptions in the accuracy of Global Navigation Satellite Systems (GNSS)

High-frequency (HF) radio interference

Potential operational anomalies in satellite systems

The event comes as part of the solar maximum of Solar Cycle 25, during which solar activity such as sunspots, solar flares, and CMEs occurs more frequently and with higher intensity.

GISTDA stated that it is closely monitoring the space weather situation and will issue updates or warnings if future solar activity poses potential risks to Thailand.

Previously, GISTDA noted that the solar eruption on May 30–31, 2025, from the same sunspot (AR4100), emitted both a significant solar flare and a large CME directed toward Earth. This CME was expected to reach the planet on June 1, 2025, potentially triggering a strong geomagnetic storm (G4 level on the NOAA scale), which could disrupt navigation systems, communication signals, and satellite operations.

Additionally, the current geomagnetic storm may produce widespread colourful auroras in high-latitude and polar regions. However, Thailand is not expected to experience direct visual or operational impacts from this auroral activity.

According to Assoc Prof Jessada Denduangboripant, a science communicator and biology lecturer at Chulalongkorn University, Thailand, will not experience direct effects from this geomagnetic storm. While colourful auroras may be visible in polar and high-latitude regions, there is no need for concern within Thailand.

The Thai Astronomical Society reported that the US National Oceanic and Atmospheric Administration (NOAA) classifies geomagnetic storms on a five-level scale (G1–G5), similar in principle to the Richter scale for earthquakes or the Fujita scale for tornadoes, to help communicate the severity of space weather events to the public.

Geomagnetic Storm Impact Levels (NOAA Scale):
G5 (Extreme):

Widespread voltage control failures; possible power grid collapse; damage to transformers; satellite anomalies; HF radio blackout; visible auroras at 40° magnetic latitude.

G4 (Severe):

Possible large-scale voltage issues; satellite surface charging; disruption in satellite orientation and communication; auroras visible down to 45° magnetic latitude; induced currents in pipelines.

G3 (Moderate):

Voltage fluctuations in power systems, minor satellite control errors, intermittent HF radio issues, and auroras down to 50°.

G2 (Moderate):

Transformer strain at high latitudes; potential satellite orientation drift; signal fading in high-latitude HF radio; auroras down to 55°.

G1 (Minor):

Small power system variations, migratory animal disorientation, and auroras at polar regions.