A large filament eruption was observed at 19:45 UTC on September 4, 2025, followed by at least three CMEs. Model runs suggest a likely arrival early on September 7. In addition, a recurrent positive polarity coronal hole high-speed stream (CH HSS) activity is expected to enhance solar wind parameters beginning early September 6, with G1 – Minor to G2 – Moderate geomagnetic storm conditions likely through September 8.
An approximate 7 degree filament eruption centered near N12W04 was observed at 19:45 UTC on September 4, as detected in GONG H-alpha imagery. This eruption was followed by the appearance of multiple coronal mass ejections (CMEs), as seen in coronagraph data from CCOR and LASCO.
The first CME, narrow and directed toward the south-southwest, appeared in CCOR imagery around 18:30 UTC on September 4. A second CME, a faint full halo, was observed around 20:15 UTC the same day. Later, LASCO C2 recorded a third CME directed toward the north-northwest at 01:36 UTC on September 5.
Multiple ensemble model outputs suggest a likely arrival early on September 7.
In advance of the CME arrival, enhancements in solar wind speed and interplanetary magnetic field are anticipated by early September 6 due to a recurrent positive polarity coronal hole high speed stream (CH HSS). Combined influences from the CH HSS and CME arrival are expected to result in elevated geomagnetic activity.
The NOAA Space Weather Prediction Center (SWPC) forecasts G1 – Minor geomagnetic storm conditions early on September 6, increasing to possible G2 – Moderate levels on September 7.
CH HSS effects are expected to persist into September 8, maintaining unsettled to active conditions.
Solar activity is likely to remain at moderate levels through September 6, with isolated M-class flares possible due to flare-capable Active Regions 4197 and 4207. M-class flare probabilities decrease on September 7 and 8 as Region 4197 rotates off the visible disk.
References:
1 Forecast Discussion – NOAA/SWPC – Issued at 00:30 UTC on September 6, 2025