official data (NOAA/NWS SWPC + USGS NEIC) · monitor-desk window stamp
SWPC: G1 (Minor) storms likely Sep 16–17 from coronal-hole stream + glancing CMEs — flares still B-class; strongest USGS day pin M5.1 off Saipan
NOAA’s Space Weather Prediction Center 3-Day Forecast, issued 0030 UTC September 16, says G1 (Minor) geomagnetic storms are likely on September 16–17 from a coronal-hole high-speed stream and glancing CME effects — while GOES X-ray activity stays in the B-class and the strongest reviewed USGS quake of the past day is an M5.1 east-southeast of Saipan, well below the Desk’s ~M6.5 interrupt line.
Key facts
- SWPC 3-Day Forecast
- Issued 2026 Sep 16 0030 UTC
- Observed max Kp (past 24h)
- 3 (below NOAA Scale levels)
- Greatest expected 3-hr Kp Sep 16–18
- 4.67 (NOAA Scale G1)
- G1 windows in table
- Sep 16 21–00 UT · Sep 17 03–06 UT (Kp 4.67)
- Rationale (SWPC)
- G1 (Minor) geomagnetic storms are likely on 16-17 Sep due to the anticipated effect of -CH HSS and CMEs glancing blow.
- Solar radiation (S) / Radio (R)
- S below S-scale past 24h · S1+ forecast 1%/1%/1% · R none observed · R1–R2 5% · R3+ 1% each day
- GOES X-ray (primary latest)
- Peak B3.4 at 2026-09-16T11:53Z (begin B2.5 11:46Z · end B2.9 12:03Z) — no M/X interrupt
- SGARF companion (15 Sep 2200 UTC)
- Solar activity very low · M 05/05/05 · X 01/01/01 · Proton 01/01/01 · PCAF green · wind peak 814 km/s · IMF 17 nT · Bz south to −13 nT
- USGS strongest past-day pin
- us7000thsx · M5.1 mb · reviewed · 2026-09-16 08:37:00 UTC · 172 km ESE of Saipan · depth 10.0 km · tsunami 0 · alert none
- Awareness only (same day)
- M5.0 us7000ths9 Dunhuang China 05:52Z · M5.0 us7000thrz Ocós Guatemala 03:45Z — not separate notes
- Live
- Revisions / DYFI → live USGS HUD · Kp/R/S → live SWPC HUD
G1 (Minor) geomagnetic storms are likely on 16-17 Sep due to the anticipated effect of -CH HSS and CMEs glancing blow.
NOAA/NWS SWPC 3-Day Forecast, Issued 2026 Sep 16 0030 UTC
Note
SWPC’s September 16 0030 UTC 3-Day Forecast is the space-weather stamp for this 8-hour cycle: greatest expected Kp 4.67 — NOAA Scale G1 — with the table marking G1 on Sep 16’s 21–00 UT slot and Sep 17’s 03–06 UT slot. The written rationale is plain: coronal-hole high-speed stream plus glancing CME effects. Radiation and radio-blackout odds stay near floor (S1+ 1%, R1–R2 5%). GOES primary’s latest flare peak at Desk fetch was B3.4 at 11:53Z — still a quiet X-ray panel, no M/X interrupt.
The companion Solar-Geophysical Activity Report (15 Sep 2200Z) keeps solar activity “very low,” with only a chance of C-class flares and M/X probabilities in the low single digits, even after a solar-wind spike above 800 km/s and a southward Bz excursion the day prior. That is the monitor-desk texture: drivers on the wind side, not a flaring active region.
On the ground-shake board, USGS’s strongest reviewed event in the past-day 4.5+ feed is us7000thsx — M5.1 at 08:37 UTC, 172 km ESE of Saipan, depth 10 km, tsunami flag 0. Same-day M5.0s near Dunhuang and Ocós stay awareness-only. Desk’s interrupt line remains near M6.5; the boarded Java M6.5 is not re-shipped.
Attribution: NOAA SWPC 3-Day Forecast (16 Sep 0030Z) + SGARF (15 Sep 2200Z) + GOES X-ray latest; USGS us7000thsx / 4.5_day.geojson.
Why it matters
Empty cycles are a miss. When flares are B-class and quakes top out at M5.1, the honest official product is still SWPC’s G1 table — a minor-storm window you can check against the live HUD, not a silence gap on the Wire.
Sources
- NOAA/NWS Space Weather Prediction Center
- SWPC 3-Day Forecast product page
- SWPC Report of Solar-Geophysical Activity (SGARF)
- GOES primary X-ray flares latest JSON
- USGS NEIC us7000thsx
- USGS 4.5+ day GeoJSON
Official data. Live values go to the HUD / source product.