New York's attorney general called Tuesday for a federal investigation into Puerto Rico energy provider LUMA and the U.S. territory's overall power situation after Hurricane Fiona caused an island-wide blackout nearly five years to the day of the Maria catastrophe -- and despite billions of U.S. dollars spent to strengthen its electrical grid.

More than 1.5 million lost power when Fiona slammed into Puerto Rico, near Ponce, as a category 1 storm Sunday. Most are still in the dark and grappling with rainfall of up to 35 inches in spots triggering life-threatening flash floods. The latest storm only exacerbated longstanding outrage and electric cost issues, Attorney General Letitia James said.

Her office sent a letter to the U.S. Department of Energy, Federal Emergency Management Agency and the Federal Energy Regulatory Commission raising concerns and urging an investigation.

"While I fully support relief efforts underway to help Puerto Rico, I am convinced that we need long-term structural support for the island, not just band-aids that take us from one crisis to the next," James said in a statement. "One of these structural challenges is the power grid and the electrical supply Puerto Ricans rely on for basic necessities."

"Puerto Ricans are rightly concerned about the failures of LUMA, the island's electric supplier. I am calling for a federal investigation into LUMA and for critical upgrades and system improvements so that Puerto Ricans are never again left in the dark," the attorney general added. "Together, we must continue to fight for long-term fixes to stabilize and strengthen Puerto Rico and stand in solitary with our brothers and sisters on the island."

James addressed the letter to U.S. Department of Energy Secretary Jennifer Granholm, FEMA Administrator Deanne Criswell, and FERC Chair Richard Glick. She asked them to review the situation and ensure LUMA Energy is held accountable for providing safe reliable, and affordable electric service to the people of Puerto Rico.

She also noted the cost of electricity per kilowatt-hour in Puerto Rico is roughly double the U.S. national average, which James said is a substantial burden for the average household in Puerto Rico, where more than 40% live in poverty.

According to James, LUMA Energy issues transcend how it handled Fiona. She provided the following examples, which her office called "especially disturbing" in light of recent federal investments:

For its part, LUMA said Sunday that bad weather had disrupted power transmission lines, causing the blackout.

The power outage was hardly the only issue in Puerto Rico during Fiona. Communities, southern areas especially, were inundated with torrential rain and wild winds, amounting to more than 2 feet of water. Lago Cerillos, not far from Ponce, where Fiona made landfall in Puerto Rico ahead of a second landfall in the Dominican Republic a day later, saw nearly 3 feet of fain. The National Hurricane Center says parts of Puerto Rico could see 35 inches, ultimately.

President Joe Biden declared a state of emergency for Puerto Rico ahead of the storm, while the governor of Puerto Rico, as the worst of it hit, described "catastrophic" damages as the island plunged into darkness.

While the rain has mostly ebbed, isolated flash floods are possible in southern parts Tuesday as heavy rainfall and life-threatening flash floods continue in the Dominican Republic Tuesday. Heavy rains around Fiona's center impact the Turks and Caicos through Tuesday afternoon with continued life-threatening flooding. Storm surge could raise water levels by as much as 8 feet above normal tide levels in parts of coastal Turks and Caicos, NHC says.