Some predictions have the Kp as high as 8, which is getting up there, but these assume a negative Bz magnetic polarity. Right now, following a negative swing, it has gone strongly positive again. This possibly explains the drop to 5 in the last Kp index.
(Keep in mind that K is a quasi-logarithmic range index of magnetic fluctuation, always expressed in whole integers between 0 and 9. A condition measuring at K=9, as high as it can go, makes for interesting, if unpredictable, conditions on the radio bands. Here, it's usually first noted as severe auroral flutter on WWV, with Doppler shift, even though this is a relatively low-latitude path. )
From SWPC:
:Product: 3-Day Forecast
:Issued: 2014 Sep 12 1230 UTC
# Prepared by the U.S. Dept. of Commerce, NOAA,
Space Weather Prediction Center
#
A. NOAA Geomagnetic Activity Observation and Forecast
The greatest observed 3 hr Kp over the past 24
hours was 5 (NOAA Scale G1).
The greatest expected 3 hr Kp for Sep 12-Sep 14
2014 is 7 (NOAA Scale G3).
NOAA Kp index breakdown Sep 12-Sep 14 2014
Sep 12 Sep 13 Sep 14
00-03UT 5 (G1) 6 (G2) 4
03-06UT 5 (G1) 7 (G3) 5 (G1)
06-09UT 2 6 (G2) 5 (G1)
09-12UT 3 5 (G1) 4
12-15UT 3 5 (G1) 3
15-18UT 3 4 3
18-21UT 3 5 (G1) 3
21-00UT 6 (G2) 5 (G1) 4
Rationale: G2 (Moderate) geomagnetic storms are
expected by late on day one (12 Sep) due to continued
effects from the 09 Sep CME along with the arrival
of the 10 Sep CME. G3 (Strong) geomagnetic storms are
expected on day two (13 Sep) with continued CME effects.
Unsettled to G1 (Minor) storm levels are expected for
day three (14 Sep) as CME influence begins to subside.
Source Link: http://www.swpc.noaa.gov/ftpdir/latest/three_day_forecast.txt
