A G3 – Strong geomagnetic storm watch means strong disturbances in Earth’s magnetic field are forecast, but not yet observed. The highest predicted storm level is G3 – Strong for both June 4 and June 5, followed by a drop below G1 – Minor on June 6 if no more Earth-directed CMEs take place today or tomorrow.
The forecast follows a sharp increase in solar activity from Region 4455, which produced an M9.3 flare at 01:36 UTC, an M7.7 flare at 07:00 UTC, and an X1.0 flare at 11:28 UTC on June 3.
The M9.3 flare was associated with a CME that became visible in LASCO C2 coronagraph imagery at about 02:13 UTC. Forecasters at the Space Weather Prediction Center (SWPC) said the structure was very faint, but GOES/SUVI imagery suggested a partial to full halo, while STEREO triangulation indicated an Earth-directed component. Modeling was still ongoing in the latest SWPC Forecast Discussion issued at 12:30 UTC today.
The M7.7 flare also produced a CME, first seen in LASCO C2 imagery at about 07:48 UTC. Coronagraph and GOES/SUVI imagery suggested that the bulk of that eruption may have been deflected northward by a nearby coronal hole, but STEREO triangulation suggested an Earth-directed component.
SWPC ENLIL model shows two Earth-directed CMEs interacting en route to Earth, with the later, faster CME catching up to the earlier structure and producing a combined solar-wind enhancement near Earth late on June 4.
This type of CME interaction can compress plasma ahead of the arrival and increase storm potential, although the final geomagnetic response will still depend on the magnetic orientation of the incoming solar wind.
The later X1.0 flare produced the strongest radio blackout classification of the three events, reaching R3 – Strong.
If a CME was associated with the X1.0 flare, it should become visible in coronagraph imagery within a few hours, SWPC forecasters said at 12:30 UTC today.
G3 – Strong geomagnetic storm conditions can affect power systems, spacecraft operations, satellite navigation, radio communications, and aurora visibility. At this level, power systems may require voltage corrections, spacecraft operators may see increased surface charging and drag effects, and intermittent problems may occur with HF radio and satellite navigation, especially at higher latitudes.
The geomagnetic response will depend on the arrival time, speed, density, and magnetic orientation of the incoming CME material. Southward magnetic field orientation in the solar wind couples more efficiently with Earth’s magnetic field and can produce stronger geomagnetic storming than a northward orientation.
Under G3 – Strong conditions, auroras may be seen at lower-than-usual latitudes, including across parts of the northern United States, when viewing conditions are favorable.
Region 4455 remains magnetically complex with an anti-Hale configuration, continuous flux emergence, mixed polarities, and substantial shear, conditions that supported the high-level M-class flaring from the region.
Solar activity is expected to remain at moderate levels through June 5, with M-class flaring likely and a slight chance for additional X-class activity, mainly from Regions 4455, 4458, 4461, and 4462. Further updates are expected as CME modeling is refined and as solar wind conditions upstream of Earth begin to reflect the incoming disturbances.
References:
1 Forecast Discussion – NOAA/SWPC – June 3, 2026