Subject: Weekly Highlights of Solar and Geomagnetic Activity, 31 August - 06 September 2026

:Product: Weekly Highlights and Forecasts
:Issued: 2026 Sep 07 0224 UTC
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# Weekly Highlights and Forecasts
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Highlights of Solar and Geomagnetic Activity
31 August - 06 September 2026

Solar activity was at moderate levels on 02 Sep and 04-05 Sep due to
three R1 (Minor) M-class flares, and low levels on the remaining
days. The largest flare of the period was an M3.0 at 02/1920 UTC
from Region 4524 (N12, L=224, class/area Cso/100 on 05 Sep), which
was also responsible for another M1.2/1n at 04/0753 UTC and 11
C-class flares throughout the period. The M3.0 was accompanied by
Type II (estimated velocity 1181 km/s) and IV radio sweeps and a CME
first observed in LASCO C2 at ~02/1936 UTC, which modeling indicated
would pass behind Earth orbit.

The last R1 was an M1.0/1f at 05/1518 UTC from Plage Region 4520
(S12, L=337, class/area Dai/40 on 01 Sep); this region had fully
decayed to plage on 03 Sep. An associated CME first became visible
in LASCO C2 at ~ 05/1800 and in STEREO coronagraph imagery at
~05/1608 UTC as a halo. Modeling indicated this eruption would pass
ahead of Earth orbit.

Notably, Plage Region 4518 (N07, L=354, class/area Cri/30 on 26
Aug), which had fully decayed to plage on 03 Sep as well, also
produced a C1.3 at 04/1527 UTC.

7 additional CMEs were observed this reporting period. Coronal
dimming seen in GOES/SUVI 195 starting ~02/0910 UTC was associated
with a CME first seen in STEREO coronagraph imagery at ~02/1108 UTC;
modeling indicated that the bulk of the material is likely to pass
ahead of Earth orbit but a glancing blow on 07 Sep was possible. A
C7.9/Sn at 03/1630 UTC from Region 4524 was accompanied by a Type II
radio sweep (estimated velocity 1359 km/s) and a CME first observed
in LASCO C2 at ~03/1636 UTC, which modeling indicated would not hit
Earth. A C6.7/Sf at 04/1930 UTC from Region 4524 was accompanied by
Type II (estimated velocity 698 km/s) and IV radio sweeps and a CME
first visible in LASCO C2 at ~04/1924 UTC and STEREO at ~ 04/2030
UTC; modeling indicates this eruption may swallow the 02 Sep
eruption and produce a glancing blow at Earth either late 07 Sep or
early 08 Sep. A north-south filament just SE of disk-center began
erupting at ~05/0530 UTC, and an associated CME was first observed
in STEREO coronagraph imagery at ~05/0638 UTC. A C6.4/1n at 05/1045
UTC from Region 4524 was associated with a CME first observed in
LASCO C2 at ~ 05/1112 UTC. A C8.5/2n at 05/1746 UTC from Region 4524
was associated with a CME first observed in LASCO C2 at ~05/1800.
Modeling indicates that these three CMEs may have a merged arrival
at Earth on 08 Sep. Finally, a C5.0/1n at 06/1042 UTC from Region
4524 was associated with a CME first observed in STEREO coronagraph
imagery at ~06/1053 UTC, which modeling indicates may produce an
arrival at Earth late 08 Sep or early 09 Sep.

Proton levels at geosynchronous orbit rapidly enhanced on 05 Sep in
response to the M1.0 from Plage Region 4520. The greater than 100
MeV proton flux crossed the 1 pfu threshold at 05/1545 UTC, peaked
at 05/1550 UTC at 1.16 pfu, and crossed back below the threshold at
05/1615 UTC. The greater than 10 MeV proton flux crossed the 10 pfu
threshold at 05/1615 UTC, peaked at 05/1645 UTC at 18 pfu, and
crossed back below the threshold at 05/2135 UTC.

The greater than 2 MeV electron flux at geosynchronous orbit was at
high levels from 31Aug - 04 Sep and on 06 Sep, returning to normal
to moderate levels on 05 Sep.

Geomagnetic field activity was at unsettled levels 31 Aug-01 Sep and
05 Sep, and was otherwise at quiet levels.

Forecast of Solar and Geomagnetic Activity
07 September - 03 October 2026

Solar activity is expected to be at low levels, with a chance for
moderate levels and a slight chance for high levels throughout the
forecast period.

No proton events are expected at geosynchronous orbit.

The greater than 2 MeV electron flux at geosynchronous orbit is
expected to be at high levels on 09-12 Sep, 16-23 Sep, and 27 Sep-03
Oct. Levels are expected to be at normal to moderate levels on 07-08
Sep, 13-15 Sep, and 24-26 Sep.

Geomagnetic field activity is expected reach active to G1 storming
levels on 07-08 Sep due to the anticipated arrivals of the CMEs
discussed above. G1 storming levels are again anticipated on 24-26
Sep due to a recurrent positive polarity coronal hole high speed
stream (CH HSS), with active levels anticipated on 27 Sep. Active
levels are also anticipated on 14-16 Sep due to a recurrent negative
polarity CH HSS. Largely quiet levels are anticipated for all
remaining dates in the forecast period.


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