K-index of 4 – Geomagnetic Storm Alert issued on September 16

A Geomagnetic K-index of 4 Alert was issued by NOAA’s Space Weather Prediction Center on September 16, 2026. The alert was triggered at 00:30 UTC and covers the synoptic period from 00:00 to 03:00 UTC. According to the official notification, an active warning is in effect.

Potential impacts of this alert include weak power grid fluctuations and possible aurora visibility at high latitudes, in regions poleward of 65 degrees geomagnetic latitude, such as Canada and Alaska. The Alert advises that induced currents could cause minor electrical disturbances in power systems at these latitudes.

The alert was issued in response to enhanced solar wind conditions, likely associated with a negative polarity coronal hole high-speed stream (CH HSS). No Earth-directed coronal mass ejections (CMEs) were detected in coronagraph imagery, and solar activity remains at very low levels. Forecasts indicate that elevated geomagnetic conditions may persist through September 18, 2026, as CH HSS effects continue.