Puerto Rica hurricane damage
© Joe Raedle/Getty ImagesPuerto Rico's governor said about 95% of Puerto Rico's power could be restored by mid-December.
It has been 36 days since Category 4 Hurricane Maria made landfall on Puerto Rico with maximum sustained winds of 155 mph, and about 75 percent of the island's 3.4 million residents are still without electricity, with tens of thousands more still in the dark in the U.S. Virgin Islands.

Based on the duration and the number of people affected, this is the largest blackout in U.S. history, the economic research firm Rhodium Group (RHG) reported Thursday.

Maria was the strongest Puerto Rico hurricane landfall since the Category 5 September 1928 San Felipe/Lake Okeechobee hurricane.

A wind gust to 137 mph was measured in Isla Culebrita, Puerto Rico, while San Juan clocked a 95-mph gust at Luis Muñoz Marin International Airport.

Prior to both Irma and Maria, only four other Category 4 hurricanes tracked within 75 miles of central Puerto Rico in historical records dating to the late 19th century. Hurricane Hugo in 1989 was the last to do that prior to 2017, though it had weakened to a Category 3 hurricane as it clipped the northeastern tip of Puerto Rico, according to the NOAA best tracks database.

There were already 61,000 customers without power in Puerto Rico due to Irma the day before Maria made landfall on Sept. 20, according to RHG. A customer is defined as a household or business, not an individual.

The day after Maria hit, the entire island of Puerto Rico was in the dark, with 1.6 million customers left without electricity. Now, 1.2 million customers (75 percent of the total) remain without power over a month later, RHG reported. This means Maria has disrupted 1.25 billion hours (and counting) of electricity supply for U.S. citizens, the report added.

For comparison, 681 million customer hours were disrupted by Hurricane Katrina in 2005, followed by an additional 203 million customer hours due to Hurricane Rita a few weeks later.

RHG sifted through data from all 20th- and 21st-century hurricanes, the 2000-01 California electricity crisis, the big Northeast blackouts in 2003 and 1965 and the 2014 polar vortex event. The company found no event in recorded U.S. history that featured as many people without power for as long as the residents of Puerto Rico and the U.S. Virgin Islands have been in the dark due to Hurricane Maria.

Irma, a few weeks before Maria, was estimated as the fourth-largest blackout on record, RHG added.

Six million Florida customers lost power as a result of Irma, plus 1 million Georgia customers and 180,000 South Carolina customers. The main difference: electricity was quickly restored in those areas, holding disruptions at 753 million customer hours, just shy of Superstorm Sandy's 775 million customer hours in late October 2012.