The storm, considered the strongest since 2005, has caused minor disruptions for U.S. airlines, and Delta said it altered routes for "a handful" of flights, and that the changes were adding about 15 minutes to travel times.

"We are undergoing a series of solar bursts in the sky that are impacting the northern side of the world," Delta spokesman Anthony Black said.

"It can impact your ability to communicate," he said. "So, basically, the polar routes are being flown further south than normal."

United Airlines spokesman Mike Trevino said the carrier diverted one flight on Monday because of the storm, but none on Tuesday.

American Airlines reported no operational impact due to solar flares but that it is monitoring the atmosphere, spokesman Ed Martelle said.

The National Oceanic and Atmospheric Administration said in a press release on Monday that it had issued a watch on Sunday for "a geomagnetic storm associated with a bright flare on the sun."

NOAA said it also issued a warning for solar radiation storming, which can affect communication systems at high latitudes, satellites in space and rocket launches. NOAA said it was the strongest solar radiation storm since 2005.

(Reporting By Kyle Peterson; Editing by Phil Berlowitz)

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