NOAA’s Space Weather Prediction Center has posted a G1 (minor) geomagnetic storm watch for October 31, 2026. The watch, serial number 1133, was issued at 16:38 UTC on October 28 and supersedes the center’s previous watch, number 1132, which covered only October 21. Nothing has been observed yet, and the watch is a forecast of storm conditions the center considers likely.
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The watch’s day-by-day line reads below G1 on October 29 and October 30, then G1 on October 31. The center’s comment says G1 minor storms are likely that day and ties them to a recurrent, positive-polarity coronal hole high-speed stream, meaning fast solar wind flowing from a coronal hole on the Sun. The forecast day is a UTC day, which runs from 8 p.m. Eastern time on October 30 to 8 p.m. Eastern time on October 31.
The watch itself: G1, serial 1133 and a single day
The center’s alerts feed carries the product as a WATA20 watch, with the issue time of 16:38 UTC on October 28 and the single G1 day of October 31. Its listed impacts are modest: effects mainly poleward of 60 degrees geomagnetic latitude, possible weak power grid fluctuations, a minor effect on satellite operations, and aurora visible at high latitudes such as northern Michigan and Maine. No cancellation or upgrade of watch 1133 appeared in the feed when it was read on October 29, so the G1 level and the October 31 date stood as issued.
Where Halloween falls on the forecast clock
The center’s three-day forecast, issued at 12:30 UTC on October 29, gives the finer timing. It puts the Kp index at 5.00 in the 00-03 UTC block on October 31 and 4.67 in the 03-06 UTC block, the two blocks it marks as G1. On American clocks those blocks are the evening and late night of Friday, October 30: 8 p.m. to 2 a.m. Eastern, or 5 to 11 p.m. Pacific. From 06 UTC onward the forecast eases to 4.33, 4.00, 3.00 and 3.00, then rises to 3.67 and 4.00 in the final two blocks, all below the Kp of 5 that defines G1.
The practical consequence is that the strongest forecast hours fall on the night before Halloween in the Americas. Saturday evening’s trick-or-treat hours sit in the 3.67 to 4.00 blocks, and anything after 8 p.m. Eastern on October 31 belongs to the next UTC day, which the watch does not cover. The center’s rationale in the three-day table repeats the coronal hole stream as the cause and says G1 or greater is expected on October 31.
Other time zones shift the picture. The two G1 blocks run from 7 p.m. to 1 a.m. Central and from 6 p.m. to midnight Mountain on Friday, October 30. In the United Kingdom, where clocks already matched UTC after October 25, they run from midnight to 6 a.m. on Saturday, October 31. The center’s earlier watch, number 1132, was issued October 20 at 19:12 UTC with G1 forecast for October 21 only, so the Prediction Center has now posted minor-storm watches for two separate dates within about ten days.
What G1 means for power, satellites and the sky
NOAA’s space weather scales define G1 as Kp 5. At that level weak power grid fluctuations can occur, a minor impact on satellite operations is possible, and aurora is commonly visible at high latitudes such as northern Michigan and Maine. The scale puts the frequency at about 1,700 G1 events per 11-year solar cycle, roughly 900 days, which makes G1 the lowest rung of the scale and a routine one.
Whether lights actually show over a given backyard is a question for a shorter-range product. The center’s aurora forecast uses the OVATION model with a lead time of 30 to 90 minutes, and the product page says aurora can often be seen from just after sunset to just before sunrise, and sometimes from up to 1,000 kilometers away when it is bright. The watch gives days of warning, while the 30-minute map is the one that responds to the solar wind actually arriving.
A forecast, not an observation
The center describes its alerts, watches and warnings as levels of severity of the solar activity that can be expected to affect Earth’s environment, with the current products published in the alerts feed. A watch looks ahead; an alert reports that a threshold has been crossed. Every number above is therefore a prediction as of October 29, and the 12:30 UTC three-day table is the version read for this article.
The open question is whether the 5.00 peak in the 00-03 UTC block on October 31 survives the next issuances of the three-day forecast, and whether a later watch moves the level or the date. With a single G1 day posted and Kp forecast at 4.00 or lower for Saturday evening in the Americas, the forecast leaves the night of October 30 as the more likely window for any storm-level conditions.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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