People are keeping a close eye on Waffle House as Hurricane Ian makes landfall — and there's a weird reason why

In preparation for Hurricane Ian, which has strengthened to a Category 4 storm, Waffle House is closing 21 of its locations in Florida.

The Federal Emergency Management Agency uses it to track the severity of a natural disaster and an unofficial Waffle House index that monitors potentially dangerous events.

The chain's restaurants are open 24 hours a day, every day of the year. That suggests a bad event that is likely to have a devastating effect on the economy.

The index is green if a Waffle House is open and has a full menu. It's yellow if it's open but not serving a lot of food. The index is red when the location has been closed.

This shows FEMA how quickly a business can rebound and how the community is doing.

"The sooner restaurants, grocery and corner stores, or banks can re-open, the sooner local economies will start generating revenue again, signaling a stronger recovery for that community," FEMA wrote in 2011.

"If we are open quickly after the storm broke, that means the community is coming back and we are getting back to that sense of normality," Pat Warner, director of PR at Waffle House, said in an interview with CNN in 2018).

In the past, Waffle House has taken to social media to share information about natural disasters, such as announcing in September of last year that its "Storm Center" was monitoring Hurricane Florence. Twenty stores were closed by the company.

—Waffle House News (@WaffleHouseNews) September 11, 2018

Most of the Waffle House restaurants are in the south.

Waffle House prepares for a storm's aftermath by having resources like generators, food, and staff at the ready outside, so that it can reopen as quickly as possible.

As of 12 p.m., the eyewall of Ian was approaching shore. The National Hurricane Center expects winds of 155 mph and up to 24 inches of rain in Florida on Wednesday.