Why Hurricane Maria Was Such a Catastrophe in Puerto Rico

At a Glance

• Hurricane Maria was a catastrophe for Puerto Rico and parts of the Virgin Islands for several reasons.
• Maria's intense eyewall raked the entire island of Puerto Rico with destructive winds.
• Torrential rain over mountainous terrain washed homes down hillsides, and washed out roads and bridges.
• Stifling heat and humidity lingered well after Maria was gone.

One month after Hurricane Maria pummeled Puerto Rico and the Virgin Islands, the U.S. territories continue to struggle to restore basic services, clear roads and provide shelter and medical care for those affected.

(MORE: By the Numbers, One Month Later | Photos One Month Later | Hurricane Central)

As of Oct. 18, barely 10 percent of customers in Puerto Rico, 16 percent in St. Thomas and 1.6 percent in St. Croix had electricity restored, according to reports from FEMA and the Puerto Rican government. More than half of all cell towers in Puerto Rico were still down, and about 1 million residents don't have drinking water. Nearly 100 shelters were still open on the island, housing some 4,300 evacuees.

Here are the meteorological factors that made Maria such a catastrophe.

First, There was Irma

Two weeks before Maria, Irma dealt its own devastating strike as a Category 5 hurricane in the Leeward and Virgin islands.

Packing 185 mph winds, Irma was the strongest hurricane to strike the Leeward Islands, and tied for the longest time spent as a Category 5 hurricane on record (37 hours), according to Dr. Phil Klotzbach, a tropical scientist at Colorado State University.

Irma raked through Antigua and Barbuda, St. Martin, St. Barthelemy, Anguilla, then the British and U.S. Virgin Islands, including St. John and St. Thomas. As of mid-October, St. John was still 100 percent without power, over 40 days after Irma.

(FULL RECAP: Hurricane Irma)

Puerto Rico was spared the worst of Irma by mere miles, as its eyewall tracked just north of the north coast. 

Despite that, up to 1.5 million customers were without power from Irma's graze of Puerto Rico.

Just two days before Maria, roughly 70,000 were still without power in Puerto Rico, the Miami Herald reported.

Maria's Intense Eyewall Rakes Puerto Rico

After pummeling the island of Dominica, then hammering the U.S. Virgin Island of St. Croix, the eye of Hurricane Maria came ashore near the town of Yabucoa, Puerto Rico, on Sept. 20, as a Category 4 hurricane with maximum sustained winds of 155 mph.

(FULL RECAP: Hurricane Maria)

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

Hurricane-force winds raked the entire 100-mile long by 35-mile wide island. Wind gusts of 100 mph or more were recorded at Isla Culebrita (137 mph), Gurabo (120 mph), Yabucoa (116 mph), and Fajardo (100 mph). 

Power Knocked Out to Millions, Extensive Damage

An intense hurricane eyewall tracking over a mountainous island with areas of extensive tree cover and a fragile electrical infrastructure is just about the worst-case scenario for wind damage.

Countless trees were downed, blocking roads, falling on homes and power lines, knocking out power to the entire island.

(WATCH: El Yunque Rainforest Devastated)

Given winds in a hurricane's eyewall are typically strongest from 1,000 to about 2,500 feet above the ground, wind damage, including structural damage to homes and other buildings, was particularly intense in Puerto Rico's hills and mountains. 

One of the island's primary Doppler radars was also obliterated by Maria's winds, not simply blowing apart its spherical protective radome, but also the radar dish itself.

Roads, Bridges Washed Out; Landslides Swept Homes Down Hillsides

Rainfall flooding or storm surge flooding accounts for many of the highest death tolls in the deadliest hurricanes in the U.S., Caribbean Sea, Central America and Mexico.

(MORE: Water is the Deadliest Factor in U.S. Hurricanes and Tropical Storms)

In Maria's case, up to 35 inches of rain over mountainous Puerto Rico, with rainfall rates of up to 5 to 7 inches per hour triggered destructive flash flooding.

Roads and bridges were washed out, landslides triggered by the heavy rain dragged some homes down hillsides and left many other areas isolated. 

Even homes that weren't swept down hillsides were isolated by washed-out or tree-blocked roads.

River levels in the Rio de la Plata Basin rose at least 20 feet in a matter of hours on Sept. 20, near the town of Comerio.

The Rio Grande de Manati near Ciales shattered its previous record by over 17 feet, and the Rio Gurabo at Gurabo neared its record crest set in September 1960. 

In San Juan, streets remained flooded weeks after Maria left its mark.

Stifling Heat, Humidity After Maria, Without Air Conditioning

If all this wasn't enough, what brought some to their breaking point was the prospect of weeks of heat and humidity without air conditioning.

Four days after Maria, San Juan soared to a daily record high of 94 degrees. Dew points, a measure of the moisture in the air topped 80 degrees, at times.

Nighttime offered little relief. Daily low temperatures didn't cool below 81 degrees for six straight days after Maria, from Sept. 22-27. 

(MORE: One of the Most Active Hurricane Seasons on Record)

If you keep your thermostat set to 78 degrees in the summer to save energy, you can understand how uncomfortable this would be, especially if there is little wind.

As of this writing, San Juan had two other days in October (Oct. 3 and Oct. 14) in which the low didn't drop out of the 80s.

Now consider standing in long lines for water in that searing heat, or trying to get some sleep in a damaged home or shelter without air conditioning.

Areas ravaged by Hurricanes Maria, Irma, and Harvey from the Caribbean to Florida and Texas will take months to recover and desperately need your help. 

We have a list of some charities and non-governmental organizations that will accept your donations here.

Jonathan Erdman is a senior meteorologist at weather.com and has been an incurable weather geek since a tornado narrowly missed his childhood home in Wisconsin at age 7. Follow him on Facebook and Twitter.