:Product: 3-Day Forecast :Issued: 2026 Sep 09 0030 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 09-Sep 11 2026 is 5.67 (NOAA Scale G2). NOAA Kp index breakdown Sep 09-Sep 11 2026 Sep 09 Sep 10 Sep 11 00-03UT 5.00 (G1) 3.00 2.00 03-06UT 5.67 (G2) 2.67 2.33 06-09UT 4.00 2.67 2.00 09-12UT 3.33 2.33 2.00 12-15UT 2.67 1.33 2.33 15-18UT 3.00 2.00 2.67 18-21UT 3.00 2.00 2.67 21-00UT 3.33 2.33 3.00 Rationale: G1-G2 (Minor-Moderate) geomagnetic storms are likely on 09 Sep due to the combination of positive polarity coronal hole high speed stream effects and the anticipated arrival of CMEs that left the Sun 05-06 Sep. B. NOAA Solar Radiation Activity Observation and Forecast Solar radiation, as observed by NOAA GOES-18 over the past 24 hours, was below S-scale storm level thresholds. Solar Radiation Storm Forecast for Sep 09-Sep 11 2026 Sep 09 Sep 10 Sep 11 S1 or greater 1% 1% 1% Rationale: No S1 (Minor) or greater solar radiation storms are expected. No significant active region activity favorable for radiation storm production is forecast. C. NOAA Radio Blackout Activity and Forecast No radio blackouts were observed over the past 24 hours. Radio Blackout Forecast for Sep 09-Sep 11 2026 Sep 09 Sep 10 Sep 11 R1-R2 10% 10% 10% R3 or greater 1% 1% 1% Rationale: Solar activity is likely to be at low levels with occasional C-class flare activity and a slight chance for M-class flares (R1-R2/Minor-Moderate) through 11 Sep.