Steady strengthening and organization took place initially, until favorable conditions enabled it to undergo explosive intensification on the afternoon of September 18, achieving Category 5 strength just before making landfall on the island of Dominica that night.

Passing north of The Bahamas, Maria remained a powerful hurricane over the following week as it slowly paralleled the East Coast of the United States, gradually weakening over time as conditions became less favorable.

[5] Favorable conditions along the system's path consisting of warm sea surface temperatures of 29 °C (84 °F), low wind shear, and abundant moisture aloft allowed the disturbance to consolidate and become Tropical Storm Maria 6 hours later, after satellite images had indicated that the low-level circulation of the wave had become well-defined.

[5] An eyewall replacement cycle caused Maria weaken to Category 4 strength before it made landfall near Yabucoa, Puerto Rico at 10:15 UTC (6:15 am local time) that day with winds of 155 mph (250 km/h)—the most intense to strike on the island since the 1928 San Felipe Segundo hurricane.

[15] Maria weakened significantly while traversing Puerto Rico, but was able to restrengthen to a major hurricane once it emerged over the Atlantic later that afternoon, eventually attaining a secondary peak intensity with winds of 125 mph (201 km/h) on September 22, while north of Hispaniola.

[16] Maria then began fluctuating in intensity for the next few days as the eye periodically appeared and disappeared, while slowly nearing the East Coast of the United States, although southwesterly wind shear gradually weakened the hurricane.

[5] Periodic bursts of convection near the center managed to maintain Maria's intensity as it accelerated east-northeast across the northern Atlantic Ocean, but interaction with an encroaching frontal zone ultimately resulted in the storm becoming an extratropical cyclone on September 30,[18] which continued east-northeastward, before dissipating on October 2.

[23] Prior to both Hurricanes Irma and Maria, the Puerto Rico Electric Power Authority (PREPA), already struggling with increasing debt, had seen budget cuts imposed by PROMESA as well as the loss of 30 percent of its work force since 2012.

[68] Initial ham radio reports from the capital of Roseau on September 19 indicated "total devastation," with half the city flooded, cars stranded, and stretches of residential area "flattened".

[71] Maria left the mountainous country blanketed in a field of debris: Rows of houses along the entirety of the coastline were rendered uninhabitable, as widespread floods and landslides littered neighborhoods with the structural remnants.

[61] The Basse-Terre region suffered severe damage to nearly 100% of its banana crops, comprising a total area of more than 5,000 acres (2,000 hectares); farmers described the destruction to their plantations as "complete annihilation".

[92] The storm made landfall on Puerto Rico on Wednesday, September 20, near the Yabucoa municipality at 10:15 UTC (6:15 a.m. local time) as a high-end Category 4 hurricane with winds of 155 mph (249 km/h).

[98] Extensive damage occurred to hundreds of thousands of buildings throughout Puerto Rico due to high winds, heavy rainfall, storm surge, wave action and landslides.

[107] Only twelve radio stations, namely WAPA 680 AM, WPAB 550 AM & WISO 1260 AM of Ponce, WKJB 710 AM, WPRA 990 AM & WTIL 1300 AM of Mayaguez, WMIA 1070 AM of Arecibo, WVOZ 1580 AM of Morovis, WXRF 1590 AM of Guayama, WALO 1240 AM of Humacao and WOIZ 1130 AM of Guayanilla, remained on the air during the storm.

[112] The remaining structures on the island of Culebra were extremely vulnerable to Maria's powerful winds after having recently experienced major damage due to Hurricane Irma, causing the complete destruction of many wooden houses, along with blown off roofs and sunken boats.

[113] Maria's Category 4 winds broke a 96-foot (29 m) line feed antenna of the Arecibo Observatory, causing it to fall 500 feet (150 m) and puncturing the dish below, greatly reducing its ability to function until repairs could be made.

[127] The prime minister urged churches to encourage their membership to provide housing for senior citizens and disabled, many of whom remained in damaged structures despite tarpaulin donations from Venezuela, Israel, Cuba, Jamaica, and other countries.

As schools began to reopen on October 16, the United Nations Children's Fund reported that the entire child population of Dominica—23,000 children—remained vulnerable due to restricted access to clean drinking water.

[157][158] The United States Transportation Command moved additional personnel and eight U.S. Army UH-60 Black Hawk helicopters from Fort Campbell, Kentucky to Luis Muñoz Marín International Airport to increase distribution capacity.

[159] National Guard troops were activated and deployed to Puerto Rico from Connecticut, Georgia, Iowa, Illinois, Kentucky, Missouri, New York, Rhode Island, and Wisconsin.

[167] By September 28, 44 percent of the population remained without drinking water and the U.S. military was shifting from "a short term, sea-based response to a predominantly land-based effort designed to provide robust, longer-term support" with fuel delivery a top priority.

[201] On February 11, an explosion and fire damaged a power substation in Monacillo,[202] causing a large blackout in northern parts of the island, including Caguas, Carolina, Guaynabo, Juncos, San Juan, and Trujillo Alto.

[220] FEMA attempted to bypass Puerto Rico's lack of capital by offering to disburse grant money up front rather than reimbursing already-spent funds, but the newness of this system caused delays.

[223][224]' In 2019 and 2020, the Trump Administration added layers of federal review for HUD CDBG money not required for U.S. states, citing the possibility of corruption and mismanagement and delaying the release of funds.

[226] The Washington Post reported that President Trump, contrary to the law he had signed, wanted to stop all aid to Puerto Rico and redirect it to Texas and Florida, and that (despite her citation of personal reasons) HUD Deputy Secretary Pam Patenaude resigned in part because of frustration over distribution efforts.

[265] General Joseph L. Lengyel, Chief of the National Guard Bureau, defended the Trump Administration's response, and reiterated that relief efforts were hampered by Puerto Rico being an island rather than on the mainland.

"[187] In response to a request for clarification on the tweet from Governor Rosselló, John F. Kelly assured that no resources were being pulled and replied: "Our country will stand with those American citizens in Puerto Rico until the job is done".

[279] After visiting Puerto Rico about two months after the hurricane, Refugees International issued a report that severely criticized the slow response of the federal authorities, noted poor coordination and logistics, and indicated the island was still in an emergency mode and in need of more help.

On April 19, 2018 (Thursday), Puerto Rico's power company said that it had restored electricity to all customers affected by an island-wide blackout that was caused by an excavator hitting a transmission line, but tens of thousands of families still remained without normal service seven months after Hurricanes Maria and Irma.

[289] San Juan Mayor Carmen Yulín Cruz said one week before the blackout that about 700,000 Americans in Puerto Rico did not have power after a line repaired by Montana contracting firm Whitefish Energy had failed.