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A dramatic blast from the sun set off the highest level geomagnetic storm in Earth’s atmosphere on Friday that is expected to make the northern lights visible as far south as Florida and Southern California and could interfere with power grids, communications and navigations system.

Tonight’s storm is the strongest to reach Earth since Halloween of 2003. That storm was strong enough to create power outages in Sweden and damage transformers in South Africa.

The effects could continue through the weekend as a steady stream of emissions from the sun continues to bombard the planet’s magnetic field.

The solar activity is so powerful that the National Oceanic and Atmospheric Administration, which monitors space weather, issued an unusual storm watch on Thursday for the first time in 19 years, which was then upgraded to a warning on Friday. The agency began observing outbursts on the sun’s surface on Wednesday, with at least five heading in the direction of Earth, the first of which reached the planet’s atmosphere on Friday.

“What we’re expecting over the next couple of days should be more significant than what we’ve seen certainly so far,” Mike Bettwy, the operations chief at NOAA’s Space Weather Prediction Center, said at a news conference on Friday morning.

For people in many places, the most visible part of the storm will be the northern lights, known also as auroras. But authorities and companies will also be on the lookout for the event’s effects on infrastructure, like global positioning systems, radio communications and even electrical power.