Lead: NOAA’s Space Weather Prediction Center posted geomagnetic storm watches for 11–13 November 2025 after multiple coronal mass ejections (CMEs) were observed on 9–10 November. The agency issued a G2 (Moderate) watch for 11 November, a G3 (Strong) watch for 12 November and a G1 (Minor) watch for 13 November. Forecasting remains cautious because a faster CME from 10 November may interact with a slower CME from 9 November, producing uncertain arrival timing. Potential impacts include brief HF radio degradation and intermittent low-frequency navigation disturbance on the sunlit side of Earth.
Key Takeaways
- Watches issued: G2 (Moderate) for 11 Nov, G3 (Strong) for 12 Nov, G1 (Minor) for 13 Nov, per NOAA SWPC notice published 13 Nov 2025 02:34 UTC.
- Cause: Multiple CMEs observed 9–10 Nov are expected to reach Earth between 11 and 13 Nov; interactions between CMEs drive forecast uncertainty.
- Forecast uncertainty: SWPC describes a “moderate level of uncertainty” about timing and interaction effects for the incoming CMEs.
- Operational impacts: HF radio communications may experience weak to minor degradation and occasional loss; low-frequency navigation signals can see short degradations.
- Modeling: SWPC will update forecasts when forecasters finalize the likely scenario and will publish the best WSA–Enlil model run.
- Timing consensus: There is reasonable agreement on the general arrival window for the 10 Nov CME, though sequencing with the 9 Nov CME remains unresolved.
Background
Coronal mass ejections are large expulsions of plasma and magnetic field from the Sun that can produce geomagnetic storms when they interact with Earth’s magnetosphere. The NOAA Space Weather Scales classify geomagnetic activity from G1 (Minor) to G5 (Extreme); G2 and G3 levels correspond to effects on power systems, spacecraft operations and radio communications at varying severity. In early November 2025, multiple CMEs were observed; cataloging and model runs (including ensemble WSA–Enlil simulations) are standard practice to estimate arrival times and likely intensity. When two CMEs are launched in close succession, the faster trailing CME can compress or overtake the earlier one, altering magnetic structure and storm strength on arrival at Earth.
SWPC routinely issues watches, warnings and alerts based on observational data from spacecraft and ground magnetometers combined with numerical models. Stakeholders that monitor these products include satellite operators, power-grid managers, aviation HF communications teams and navigation-service providers. Past events where CME interactions changed outcomes illustrate why forecasters emphasize uncertainty until model consensus emerges and new observations confirm propagation speeds and directions.
Main Event
On 9 and 10 November, coronagraph and heliospheric imagery recorded at least two CMEs leaving the Sun. SWPC analysis indicates the 9 Nov CME is progressing more slowly while the 10 Nov CME appears faster; both have potential Earth-directed components. Current projections place the most significant geomagnetic activity between 11 and 13 November 2025, with the highest watch level (G3) centered on 12 November.
Because the two CMEs differ in speed, forecasters are evaluating whether the faster 10 Nov eruption will overtake the earlier 9 Nov structure before any Earth-directed portion arrives. If they merge en route, the combined structure could alter the magnetic orientation experienced at Earth, which is a key determinant of storm strength. If they remain separate, the planet could see two closely spaced disturbance intervals with limited time between peaks.
SWPC’s public notice (published 13 Nov 2025 02:34 UTC) emphasizes that analyses are ongoing and that model updates, including the selected WSA–Enlil run, will be posted once forecasters determine the most likely scenario. Practical advisories focus on transient HF degradation and short-lived navigation signal impacts on the sunlit hemisphere while urging stakeholders to monitor official updates.
Analysis & Implications
Space weather at G2–G3 levels can affect a range of technological systems. For G2 (Moderate) activity, grid operators may see induced currents in long conductors, and some spacecraft systems require operational adjustments. At G3 (Strong), airline HF communications on transpolar routes can be disrupted and spacecraft charging risks rise, potentially requiring temporary changes in operations or communications scheduling.
The key uncertainty is the magnetic field orientation embedded in the CMEs’ plasma when they arrive. Southward-directed magnetic fields (relative to Earth’s magnetic field) typically drive the strongest geomagnetic responses. Because CME–CME interactions can rotate or enhance southward components, forecasting their combined magnetic structure from remote observations is inherently limited until in situ measurements are available near Earth.
Economically and operationally, operators facing possible G2–G3 conditions should review mitigation procedures: power utilities for transformer and line monitoring, satellite teams for safe-mode thresholds and satellite charging controls, and aviation HF operations for alternate routing or switching to satellite communications where feasible. The relatively brief G1 watch on 13 Nov suggests a trailing recovery or low residual disturbance, but contingency plans should remain in place until the event concludes.
Comparison & Data
| Date (UTC) | NOAA Watch Level | Likely Effects |
|---|---|---|
| 11 Nov 2025 | G2 (Moderate) | HF degradation, minor navigation impacts, transformer monitoring advised |
| 12 Nov 2025 | G3 (Strong) | Possible HF communications outages, increased spacecraft charging risk |
| 13 Nov 2025 | G1 (Minor) | Brief weak geomagnetic activity; routine monitoring |
The table summarizes SWPC’s watch levels and typical effects associated with each G-scale category. Historical comparisons show G3 conditions are notable but occur several times per solar cycle; the primary operational concern remains the magnetic-field orientation at impact, not only the scale label. SWPC’s planned posting of the WSA–Enlil run will provide a model-based comparison to past events and refine timing estimates.
Reactions & Quotes
“Analyses of these events continues due to the large range of potential outcomes … there is a moderate level of uncertainty regarding the forecast.”
NOAA Space Weather Prediction Center (official notice)
“Once SWPC forecasters have made a decision on the final, most likely outcome, the forecast will be updated accordingly and the best solution WSA–Enlil model run will be posted.”
NOAA SWPC (operational statement)
Unconfirmed
- Whether the faster 10 Nov CME will overtake the slower 9 Nov CME before any Earth-impacting portion arrives remains unresolved.
- Exact timing between possible multiple arrivals and the peak interval of geomagnetic activity is still subject to change pending additional data and model runs.
- Precise magnitude of ground-induced currents and sector-specific impacts (power grid regions, specific satellite systems) cannot be determined until near-Earth in situ measurements confirm the CME magnetic orientation.
Bottom Line
NOAA SWPC has issued G2–G3 watches covering 11–12 November 2025 with a trailing G1 watch on 13 November; these reflect the expected arrival of CMEs launched 9–10 November. The highest practical impacts are likely on HF radio and satellite operations, with possible short navigation signal degradation. Authorities and operators should monitor official SWPC updates and implement standard mitigation procedures appropriate to their systems.
Forecasts will be refined as new observations and model runs (including the selected WSA–Enlil output) become available; until then, stakeholders should treat the situation as active and time-sensitive but not necessarily catastrophic. Continued attention to official updates at spaceweather.gov is the best way to follow evolving timing and impact expectations.