ALERT: Geomagnetic K-index of 4 Alert issued on September 11

A Geomagnetic K-index of 4 Alert was issued on September 11, 2025, at 02:51 UTC by the NOAA Space Weather Prediction Center. The alert indicates that geomagnetic activity reached the K-index threshold of 4 at 02:44 UTC, with the active warning in effect during the synoptic period from 00:00 to 03:00 UTC.

During this period, regions poleward of 65 degrees geomagnetic latitude may experience weak power grid fluctuations due to induced currents. Additionally, aurora may be visible at high latitudes, such as in Canada and Alaska. These impacts are typical for elevated geomagnetic activity reported at this level.

According to the latest forecast discussion issued at 00:30 UTC on September 11, 2025, the geomagnetic activity was triggered by prolonged periods of southward interplanetary magnetic field orientation under the influence of a positive polarity coronal hole high speed stream. Solar wind speeds were observed between 500-550 km/s, with waning influence from the coronal hole expected after September 11. No Earth-directed coronal mass ejections were observed at this time.