By Scott DiSavino

(Reuters) – Hurricane Irma poses a bigger menace to power supplies in Florida than Hurricane Harvey did in Texas because Irma is packing near 200 mile-per-hour winds (320 km/h) that could down power lines, close nuclear plants and threats to leave millions of homes and businesses in the dark for weeks.

Irma’s winds rival the strongest for any hurricane in history in the Atlantic, whereas Harvey’s damage came from record rainfall. Even as Houston flooded, the power stayed on for most, allowing citizens to use TV and radio to stay apprised of danger, or social media to call for help.

“When Harvey made landfall in Texas it made it fully inland and weakened pretty quickly. Irma, however, could retain much of its strength,” said Jason Setree, a meteorologist at Commodity Weather Group.

Irma has killed several people and devastated islands in the Caribbean.

Current forecasts put almost the entirety of the Florida peninsula in the path of the storm, which made landfall in the Caribbean with wind speeds of 185 mph (295 km/h).

The threat of the Category 5 storm, at the top of the Saffir-Simpson Hurricane Wind Scale, is grave enough that electricity generator Florida Power & Light (FPL) plans to shut its two nuclear power plants in the state, and officials warned that it may have to rebuild parts of its power system, which could take weeks.

Most Florida residents have not experienced a major storm since 2005, when total outages peaked around 3.6 million during Hurricane Wilma. Some of those outages lasted for weeks.

Setree compared the projected path of Irma to Hurricane Matthew in 2016, which knocked out power to about 1.2 million FPL customers in October.

FPL, a unit of Florida energy company NextEra Energy Inc, restored service to most customers affected by Matthew in just two days. But FPL spokesman Chris McGrath said: “With a storm as powerful as Irma, we want customers to prepare for damage to our infrastructure and potentially prolonged power outages.”

He said it was too soon to speculate on the number and location of customers Irma could affect.

In a statement this week, FPL estimated about half of its near five million customers – particularly in the trio of populous southeast counties Miami-Dade, Palm Beach and Broward – had not experienced a major hurricane since 2005.

“Should Irma’s worst fears be realized, our crews will likely have to completely rebuild parts of our electric system. Restoring power through repairs is measured in days; rebuilding our electric system could be measured in weeks,” FPL Chief Executive Eric Silagy said.

FPL, Florida’s biggest power provider, said it had invested nearly $3 billion since 2006 to strengthen its grid, including placing 60 main power lines underground and installing nearly five million smart meters and other devices.

Other publicly traded utilities in the Sunshine State, including units of Duke Energy Corp, Southern Co and Emera Inc, said in statements that they had also invested in intelligent, self-healing devices.

Smart meters allow utilities to see outages as they occur, rather than waiting on customer calls, and utilities also use automated devices that can reenergize lines without damage that were taken offline because of contact with trees or other objects, said Jay Apt, director of the Carnegie Mellon Electricity Industry Center in Pittsburgh.

Olivia Ross, a spokeswoman for CenterPoint Energy, which serves the greater Houston area, said these devices helped the utility keep the lights on for more people in the aftermath of Harvey as some issues were resolved remotely.

But such devices can only do so much. Harvey’s outages were limited to 312,000 customers, of which CenterPoint was responsible for about 109,000, as it quickly lost force after landfall and turned into a tropical storm. By contrast, Ross noted, Hurricane Ike in 2008 caused 2.1 million of CenterPoint’s customers to lose power when it hit the Texas coast near Houston.

(Reporting by Scott DiSavino; Editing by Richard Chang)