Solar activity was at low levels this past week. Low-level C-class
flaring was observed from Regions AR4216 and AR4217, as well as from
Region AR4213 just beyond the Southwest limb. Slight growth was
observed in all spotted regions. No Earth-directed CMEs were
observed. Solar activity is expected to be low, with a chance for an
isolated M-flare (R1-R2/minor-moderate), through September 20.
 
Solar wind parameters were indicative of coronal hole high speed
stream (CH HSS) influences. Solar wind speed increased to near 760
km/s early on September 15 before subsiding to between 600-700 km/s.
Solar wind parameters are expected to continue under the influence
of a negative polarity Coronal Hole High Speed Stream.  Solar wind
speed is likely to gradually diminish on September 20.  The
geomagnetic field is expected to be at quiet levels on September 20,
and quiet to active on September 21.

Spaceweather.com for September 19 reports that a co-rotating
interaction region, or CIR, could hit Earth on September 22.
 
Weekly Commentary on the Sun, the Magnetosphere, and the Earth's
Ionosphere, September 18, 2025, by F. K. Janda, OK1HH:

"The development of phenomena on the Sun and subsequently in the
Earth's magnetosphere and ionosphere during the second decade of
October was interesting and exciting. First, solar activity passed
through a 27-day minimum on October 10-13, and the subsequent
increase is likely to continue for most of the month. Above all,
however, we observed a large butterfly-shaped coronal hole on the
Sun. Predictions of when the intensified solar wind from its edges
would reach Earth rarely coincided on Sunday, September 14.

"And so, it happened after 1600 UTC. The CME of September 11 (1030
UTC) contributed to the intensification of the solar wind, while the
'Russell-McPherron effect,' which connects the Sun's magnetic field
with the Earth's magnetic field during the weeks around the equinox,
contributed to the impact. During the evening, the positive phase of
the disturbance continued with an increase in the MUF of the F2
ionospheric layer.

"The geomagnetic disturbance intensified to G3 on September 15,
while on September 15-16, we experienced its negative phase with a
significant decrease in MUF in the middle and higher latitudes of
the globe. And, of course, the overall deterioration in shortwave
propagation conditions was unmistakable. The improvement began
slowly on September 17 and will continue, as we expect further
growth in solar activity for most of September. As usual, the fact
that we are in the period around the Autumnal Equinox will also
contribute to the improvement.

"We could also tell that Summer in the ionosphere was over by the
significant decrease in the activity of the sporadic-E layer, which
was still quite frequent in mid-latitudes in the first half of
September."

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

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.

The Predicted Planetary A Index for September 20 to 26 is 5, 5, 5,
5, 5, 5, and 5, with a mean of 5.  Predicted Planetary K Index is 2,
2, 2, 2, 2, 2, and 2, with a mean of 2.  10.7 centimeter flux 135,
135, 135, 130, 125, 130, and 125, with a mean of 130.7.