:Product: 3-Day Forecast :Issued: 2023 Sep 28 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 3 (below NOAA Scale levels). The greatest expected 3 hr Kp for Sep 28-Sep 30 2023 is 3.67 (below NOAA Scale levels). NOAA Kp index breakdown Sep 28-Sep 30 2023 Sep 28 Sep 29 Sep 30 00-03UT 1.67 1.67 2.67 03-06UT 3.00 2.33 2.67 06-09UT 0.67 2.00 2.33 09-12UT 1.67 1.67 2.67 12-15UT 1.33 2.33 3.67 15-18UT 1.33 2.33 2.00 18-21UT 1.67 2.67 2.67 21-00UT 1.33 2.33 2.33 Rationale: No G1 (Minor) or greater geomagnetic storms are expected. No significant transient or recurrent solar wind features are forecast. B. NOAA Solar Radiation Activity Observation and Forecast Solar radiation, as observed by NOAA GOES-16 over the past 24 hours, was below S-scale storm level thresholds. Solar Radiation Storm Forecast for Sep 28-Sep 30 2023 Sep 28 Sep 29 Sep 30 S1 or greater 10% 5% 5% Rationale: There is a slight chance for S1 (Minor) solar radiation storms on 28 Sep. C. NOAA Radio Blackout Activity and Forecast Radio blackouts reaching the R1 levels were observed over the past 24 hours. The largest was at Sep 28 2023 0907 UTC. Radio Blackout Forecast for Sep 28-Sep 30 2023 Sep 28 Sep 29 Sep 30 R1-R2 35% 30% 30% R3 or greater 10% 5% 5% Rationale: There is a chance for isolated R1 (Minor) radio blackouts through 30 Sep primarily due to ARs 3435 and 3445.