Weekly Propagation Forecast Bulletins, September 28 2026

Highlights of Solar and Geomagnetic Activity -21 - 27 September 2026

Solar activity was at low levels throughout the summary period.

Region 4534 (N11, L=075, class/area=Dai/050 on 22 Sep) produced the

strongest flare of the period, an impulsive C3.1 flare at 26/1655

UTC. There were 13 other numbered active regions recorded on the

visible disk this week, but they all remained relatively simple and

absent of any significant activity. No Earth-directed CMEs were

observed in available coronagraph imagery. 

No proton events were observed at geosynchronous orbit.

The greater than 2 MeV electron flux at geosynchronous orbit reached

high levels on 23 Sep, and 26-27 Sep due to influence from a

positive polarity CH HSS. 

Geomagnetic field activity was at quiet levels from 21-23 Sep. A CIR

ahead of a positive-polarity CH HSS caused active levels over 24-27

Sep. Total magnetic field strength reached 15 nT during the CIR on

24 Sep, with the Bz component rotating as far south as -12 nT. Solar

wind speeds steadily increased from below 300 km/s on 23 Sep to a

peak of ~525 km/s by 25 Sep. Both total magnetic field strength and

solar wind speeds gradually declined during the waning phase of the

coronal hole HSS over 26-27 Sep. 

Forecast of Solar and Geomagnetic Activity - 28 September - 24 October 2026

Solar activity is likely to continue at very low to low levels

throughout the outlook 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 from 28 Sep-03 Oct, 05 Oct-11 Oct, and

23-24 Oct due to anticipated influence from multiple, recurrent, CH

HSSs. Moderate levels are likely over the remainder of the outlook

period. 

Geomagnetic field activity is likely to reach G1 (Minor) geomagnetic

storm levels on 22 Oct. Active conditions are likely over 04-06 Oct,

21 Oct, and 23-24 Oct. Unsettled conditions are likely over 07-08

Oct and 11-14 Oct. All increases in geomagnetic activity are

associated with anticipated influence from multiple, recurrent,

coronal hole HSSs. The remainder of the outlook period is likely to

be at mostly quiet levels. 

Product: 27-day Space Weather Outlook Table 27DO.txt

:Issued: 2026 Sep 28 0221 UTC

# Prepared by the US Dept. of Commerce, NOAA, Space Weather Prediction Center

# Product description and SWPC contact # https://www.swpc.noaa.gov/content/subscription-services

#

#      27-day Space Weather Outlook Table

#                Issued 2026-09-28

#

#   UTC      Radio Flux   Planetary   Largest

#  Date       10.7 cm      A Index    Kp Index

2026 Sep 28      98           5          2

2026 Sep 29     100           5          2

2026 Sep 30     105           5          2

2026 Oct 01     105           5          2

2026 Oct 02     100           5          2

2026 Oct 03      95           5          2

2026 Oct 04      90          12          4

2026 Oct 05      91          15          4

2026 Oct 06      91          12          4

2026 Oct 07      92          10          3

2026 Oct 08      93           8          3

2026 Oct 09      95           5          2

2026 Oct 10      98           5          2

2026 Oct 11     100           9          3

2026 Oct 12     102           8          3

2026 Oct 13     102           8          3

2026 Oct 14     100           8          3

2026 Oct 15     102           5          2

2026 Oct 16     102           5          2

2026 Oct 17     100           5          2

2026 Oct 18      98           5          2

2026 Oct 19      97           5          2

2026 Oct 20      96           5          2

2026 Oct 21      94          15          4

2026 Oct 22      92          20          5

2026 Oct 23      90          15          4

2026 Oct 24      88          12          4

(NOAA)