official data (NOAA / NWS Space Weather Prediction Center 3-Day Forecast)
SWPC: G1 geomagnetic storm likely Sep 24 as coronal-hole wind arrives
NOAA’s Space Weather Prediction Center 3-Day Forecast issued 1230 UTC on September 23 says the greatest expected three-hour Kp for Sep 23–25 is 5.33 — NOAA Scale G1 — with G1 (Minor) geomagnetic storm conditions likely on September 24 from coronal-hole high-speed-stream effects, after a quiet prior day that topped out at observed Kp 1.
Key facts
- Issued
- 2026 Sep 23 1230 UTC (Desk fetch HTTP 200, AM cycle) — supersedes overnight 0030 UTC card
- Observed Kp
- Greatest observed 3-hr Kp past 24h: 1 (below NOAA Scale levels)
- Expected Kp
- Greatest expected 3-hr Kp Sep 23–25: 5.33 (G1). G1 (Minor) likely on 24 Sep due to CH HSS effects
- Sep 24 G1 bins
- 03–06 UT 5.33 (G1); 06–09 UT 4.67 (G1)
- Solar radiation
- Below S-scale past 24h; S1 or greater forecast 1% / 1% / 1% — no S1 or greater expected
- Radio blackouts
- None observed past 24h; R1–R2 20% each day Sep 23–25; R3+ 1%
- Scope
- Official SWPC geomagnetic bin on the ECDO lane as monitor only. ECDO remains a labeled hypothesis — this card is not proof of ECDO.
- Live
- Live Kp / G-scale revisions → SWPC HUD / next 3-Day. No invented live Kp dial or aurora claim beyond the official G1 likely line.
G1 (Minor) geomagnetic storm conditions are likely on 24 Sep due to CH HSS effects.
NOAA/NWS SWPC 3-Day Forecast, Issued 2026 Sep 23 1230 UTC
Note
NOAA’s Space Weather Prediction Center reissued its three-day forecast at 1230 UTC on September 23. The past day stayed quiet — greatest observed three-hour Kp was 1. The outlook is not blank: the product stamps a greatest expected Kp of 5.33, NOAA Scale G1, and says G1 minor geomagnetic storm conditions are likely on September 24 from coronal-hole high-speed-stream effects.
Solar radiation stays off the S-scale in the forecast. Radio blackout odds are listed at 20 percent for R1–R2 and 1 percent for R3 or greater. Live Kp revisions belong on the SWPC HUD, not this note. ECDO stays a labeled hypothesis only — this card is an official geomagnetic bin.
Why it matters
The morning reissue keeps the same G1-tomorrow stamp from coronal-hole wind — not an X-flare spectacle. Observed Kp stayed quieter (1) while the Sep 24 early-UT bins still carry the G1 flags.
Sources
Primary + secondary attribution as listed. Live values go to the HUD / source product.