Solar activity reached moderate levels this past week. An impulsive
M1.0 flare was observed on September 24 from Region AR4217. Slight
growth was observed in Region AR4226 with an increase in spots near
the leader. New Regions AR4229 and AR4230 were numbered this period.
All other regions were either stable or in decay. No Earth-directed
CMEs were observed. Solar activity is expected to return to low
activity.

Solar wind parameters were indicative of the arrival of a negative
polarity Coronal Hole High Speed Stream (CH HSS). Solar wind speed
increased from approximately 310 km/s to near 530 km/s. Total field
showed an increase beginning on September 22. The CH HSS influence
persisted through September 23 and diminished to background levels
on September 25. A trend towards nominal solar wind conditions is
expected through September 26 as Earth moves out of a geoeffective
position with the CH HSS.

Weekly Commentary on the Sun, the Magnetosphere, and the Earth's
Ionosphere, September 25, 2025, by F. K. Janda, OK1HH:

"A study published on September 8 in the Astrophysical Journal
Letters states that solar activity will increase after approximately
sixty years of decline (following the high Solar Cycle No. 19). The
next solar cycles should be even higher than the current one and, in
particular, higher than the previous one (i.e., than Solar Cycles 24
and 25).

"Short-term developments in the second half of September are in line
with forecasts. Overall solar activity has increased, although
eruptive activity is slightly lower than expected. In line with the
forecast, on September 21, the Earth's magnetic field entered the
common rotation interaction (CIR) region and the solar wind
intensified. After a two-day increase that began on September 24,
geomagnetic field activity declined again. Although the forecasts
are based primarily on the expected increase in the speed of the
solar wind flowing from the edges of coronal holes, while should
therefore be less accurate than forecasts based on observed
eruptions and CMEs, they are still relatively reliable.

"Most sunspot groups are now on the solar disk (the visible part of
the Sun), but they will gradually begin to set. Solar activity
should therefore decline by the end of September, with the decline
likely to stop in mid-October. In the Earth's ionosphere, the
decline in maximum usable frequencies (MUF) will begin with a slight
delay, similar to the expected rise in the second half of the
month."

There is a chance for isolated R1-R2 (Minor-Moderate) radio
blackouts until September 28. Unsettled to active levels are likely
on September 29 and 30, October 3 to 7, October 11 to 13, and on
October 18 due to recurrent CH HSS influences. Quiet to unsettled
levels are likely for the remaining days in this outlook period.

The geomagnetic field is expected to be quiet to unsettled levels on
September 27, and quiet to active levels on September 28.

The latest video report from Dr. Tamitha Skov, WX6SWW, can be found
on YouTube at, https://www.youtube.com/watch?v=xzoxXGTDLyM .

The Predicted Planetary A Index for September 27 to October 3 is 5,
5, 15, 8, 5, 5, 5, and 15, with a mean of 8.3.  Predicted Planetary
K Index is 2, 2, 5, 3, 2, 2, and 5, with a mean of 3.  10.7
centimeter flux is 175, 170, 170, 170, 160, 150, and 140, with a
mean of 162.1.

For more information concerning shortwave radio propagation, see
http://www.arrl.org/propagation and the ARRL Technical Information
Service web page at, http://arrl.org/propagation-of-rf-signals. For
an explanation of numbers used in this bulletin, see
http://arrl.org/the-sun-the-earth-the-ionosphere . Information and
tutorials on propagation can be found at, http://k9la.us/ .

Also, check this:

https://bit.ly/3Rc8Njt

"Understanding Solar Indices" from September 2002 QST.