NOAA Issues G3 Geomagnetic Storm Warning As 500,000 Kilometer Hole Sends Solar Wind At Earth

On Monday 15 September 2025, the National Oceanic and Atmospheric Administration (NOAA) Space Weather Prediction Center issued a G3 geomagnetic storm warning, the result of a large coronal hole sending increased solar winds at Earth.

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Over the weekend, the northern lights were visible as far south as Maine and Connecticut, USA, as a moderate geomagnetic storm hit the planet. The storm, the result of a coronal hole spanning 500,000 kilometers (310,000 miles) across the solar surface, has now reached G3 on the NOAA Space Weather Scale.

"Four sunspot regions are currently visible on the Earth-facing solar disc. The largest, in the northeast, features several large leading spots followed by a few smaller trailing ones," the UK's Met Office explains, adding that no coronal mass ejections heading at Earth have been noted over the last few days of monitoring.

"A region rotating into view from the southeast limb and may reveal greater complexity as it continues to emerge. An active region has already moved beyond the western limb, with the region in the southwest not far behind. A new region near the northwest limb appears small and relatively simple for the moment. No Earth-directed Coronal Mass Ejections (CMEs) were noted during the period."

At G3, the storm is classified as "strong". As well as potentially causing aurora which will be visible in the northern parts of the USA and the UK, storms of this strength can cause problems for Earth and its satellites.

"Surface charging may occur on satellite components, drag may increase on low-Earth-orbit satellites, and corrections may be needed for orientation problems," the NOAA explains of G3 storms, adding "Intermittent satellite navigation and low-frequency radio navigation problems may occur, HF radio may be intermittent, and aurora has been seen as low as Illinois and Oregon (typically 50° geomagnetic lat.)."

Sun activity increases and decreases in an 11-year cycle known as the Schwabe cycle. From 1826 to 1843, German amateur astronomer Heinrich Schwabe observed the Sun, discovering that it rotates on its axis once every 27 days. He noticed the Sun goes from quiet periods, where no sunspots can be seen, to the maximum phase where 20 or more groups of sunspots can be seen.

During the solar cycle, storms can reach up to level G5, classified as "extreme", around four times on average. While G3-strength storms are more common, with around 200 per solar cycle, they can still produce powerful aurora around the equinoxes due to something known as the "Russell-McPherron Effect".

"During the equinoxes, the orientation of the Earth's poles is (almost) perpendicular to that of the Sun," Dr Ciaran Beggan, a geophysicist at the British Geological Survey, explained to Newsweek. 

“This maximizes the 'coupling' between the solar wind and the Earth's magnetic field. In summer or winter, one of the Earth's poles is pointing at an angle from the solar wind so the coupling between them is lower and hence there are fewer storms on average.”

According to the NOAA, infrastructure operators have been informed of the storm, and notified to mitigate any possible impacts from it, including risks to the power grid and potential disruption to satellite operations. While space weather experts continue to monitor the storm, feel free to sit back and enjoy the aurora, which can potentially be seen in the northern parts of the US and the UK today.