Minor C8.4 solar flare erupts at 12:03 UTC on October 16, 2025

A minor C8.4 solar flare erupted at 12:03 UTC on October 16, 2025.

Today’s flares include an M1.1 event from 00:17 to 00:24 UTC from region 4246, as well as several C-class events: C5.2 at 04:46 UTC from region 4246, C5.5 at 06:43 UTC from region 4246, C5.1 at 08:01 UTC from region 4246, C4.6 at 07:31 UTC, C3.5 at 09:49 UTC, and C3.3 at 08:49 UTC. Additional B-class and lower C-class flares also occurred.

In 24 hours to 12:30 UTC on October 16, solar activity remained at moderate levels due to M-class flare activity, most notably a long-duration M1.1, M2.7, and M2.4 flare, along with multiple C-class flares from several active regions.

Minor to moderate (R1-R2) radio blackouts are likely through October 18, with a slight chance for a strong (R3) event due to enhanced flare activity.

Active sunspot regions presently observed on the Earth-facing solar disk include AR 4246 (N22W56 – Beta-Gamma-Delta), AR 4248 (N07W27 – Beta-Gamma-Delta), AR 4250 (N07W21 – Alpha), AR 4252 (S13E28 – Beta), and AR 4254 (N10E60 – Alpha).

Over the past 24 hours, the greater than 2 MeV electron flux reached high levels, peaking at 2 850 pfu, while the greater than 10 MeV proton flux remained at background values. Electron flux is expected to decrease to normal to moderate levels on October 16 with CME arrivals, and rebound to moderate to high levels on October 17–18. There is a slight chance for a solar radiation storm above S1 – Minor levels through October 18.

Solar wind parameters were slowly returning to nominal levels as the negative CH HSS influence waned, with total interplanetary magnetic field at or below 6 nT, Bz between +3 and -4 nT, and solar wind speed decreasing from 520 km/s to 450 km/s. Solar wind conditions are expected to gradually wane over October 16, with disturbed periods likely late on October 16 through October 18 due to CME arrivals.

Geomagnetic field activity was mostly quiet. Geomagnetic field conditions are likely to reach G2 – Moderate storm levels late on October 16 following recent CME arrivals, with G1 – Minor storm levels possible through October 18 as additional CME influences persist.