10 Jaw-Dropping Findings from the NHC's Final Hurricane Maria Report

Jonathan Belles
Published: April 11, 2018

Hurricane Maria was one of the biggest to strike Dominica and Puerto Rico over the last century, and it came as the third part of a trio of Category 4 hurricane strikes on U.S. soil.   

(MORE: Our Hurricane Maria RecapHurricane Central)

The postseason report from the National Hurricane Center (NHC) on Hurricane Maria has revealed a few truly startling facts about what has become the third-costliest U.S. tropical cyclone.

Let's recap the 10 most incredible facts from this report.

1. Maria caused 18 times more damage in the U.S. territories than the second-costliest hurricane

The most recent NOAA estimate of Maria's damage in Puerto Rico is about $90 billion in 2017 U.S. dollars.

Previously, the most damaging cyclone to roll through the territories was Georges in 1998, which caused about $5 billion in damage when converted to 2017 dollars.

All islands in the U.S. territories suffered damage in Maria, some of which was enhanced by Hurricane Irma, which passed through the islands two weeks earlier. St. Thomas, St. John and Culebra, all located to the east of Puerto Rico, suffered major damage in Irma, and any remaining structures were weaker than they would have otherwise been.

Costliest hurricanes in 2017 U.S. dollars.
(National Hurricane Center)

Severe to catastrophic damage was reported in Vieques, St. Croix and Puerto Rico.

"On the island of Vieques, all wooden structures were either damaged or destroyed," said the NHC report.

Unprecedented river flooding, severe harbor and marina damage, significant or complete destruction of buildings and near-complete destruction of the electrical and cell-service grids resulted from Hurricane Maria. At least 4 percent of the territories remain without power as of April 10.

The population in Puerto Rico has decreased by about 360,000 people from when Georges struck in 1998 through 2016. Unlike in much of the mainland U.S., the rise in population cannot be blamed on this increase in damage toll.

2. The death toll in Puerto Rico is still unknown

The official death toll in Puerto Rico remains 65, while hundreds of indirect deaths "may eventually be attributed to Maria’s aftermath pending the results of an official government review," according to the report.

While uncertain death tolls are somewhat common in some parts of the world, especially in developing and vulnerable countries, death tolls on American soil and throughout much of the Caribbean are usually far more certain.

(MORE: 2018 Hurricane Season Expected to Be More Active Than Usual, CSU Forecasters Say)

Even in 2016's Hurricane Matthew strike on Haiti, which is commonly known as one of the most vulnerable countries in the Atlantic tropics, a finite death toll was provided within six months.

Uncertain and less finite death tolls used to be much more common in the United States before the age of the internet and before the modern age of emergency management and pre-storm weather outreach.

3. Maria’s explosive rapid intensification is tied for the sixth-fastest intensifying hurricane in the Atlantic

Maria underwent a period of explosive rapid intensification on Sept. 18 that took its maximum sustained winds from 85 mph to 165 mph in just 24 hours – a rate of increasing winds by 35 mph every 10 and a half hours.

Rapid intensification is defined as "an increase in the maximum sustained winds of a tropical cyclone of at least 35 mph in a 24-hour period" by the NHC.

Incredibly, Maria had one six-hour period – between 2 p.m. and 8 p.m. EDT on Sept. 18 – when the maximum sustained winds increased by 35 mph in just those six hours. That's four times the rate of rapid intensification.

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

The current record for the fastest period of rapid intensification in the Atlantic is Hurricane Wilma in 2005, which intensified by a rate of 105 mph in 24 hours, or a rate of increasing winds by 35 mph every eight hours.

This intensification was not well-forecast by the NHC, although periods of rapid intensification are the most difficult-to-forecast process that a hurricane can undergo.

Forecasters at the NHC noted that this period of intensification was possible on Sept. 17, and increased the forecast peak intensity with that note in mind, but the explosive rate of intensification was not expected by any computer models.

You can see how all of the models showed a far less-impressive intensification rate on Sept. 18 and 19 compared to what actually happened (in solid black).

This is why meteorologists will often tell you to prepare for a hurricane at least one category higher than currently forecast.

4. Nearly every NHC forecast indicated that Maria would become a major hurricane by the time it reached Puerto Rico

Only the first forecast cycle released by the NHC on what was then Tropical Storm Maria did not indicate that the cyclone would attain maximum sustained winds of at least 111 mph, or become a major hurricane, before reaching Puerto Rico.

Landfall intensity forecasts for Hurricane Maria's landfall on Puerto Rico.
(Data: NHC)

(MORE: Five-Day Hurricane Track Forecasts Are More Accurate Today Than Two-Day Forecasts 25 Years Ago)

5. Landfall in Puerto Rico was exceptionally well-forecast

Every forecast issued by the NHC from the time Maria formed until its landfall on U.S. soil indicated a direct landfall was likely on Puerto Rico.

Track forecasts issued by the NHC for Hurricane Maria from cyclone genesis to landfall on Puerto Rico.
(National Hurricane Center)

Track errors were about 50 percent smaller than the average for the previous five-year period at all forecast intervals. The average error for Maria was about 120 miles off at five days out, compared to the average error of 280 miles off during the previous five years of hurricane forecasts.

6. Maria is the strongest hurricane on record to make landfall on Dominica

Hurricane Maria made landfall with winds of 165 mph, or a low-end Category 5 hurricane, late Sept. 18 on the island of Dominica in the eastern Caribbean.

Dominica is no stranger to hurricanes, even though the island had been in a recent hurricane drought. In fact, the island averages a direct or near-direct hit about once per decade.

Tracks of hurricanes that have come close to Dominica over the last 100 years. Not an exhaustive list.

At least two hurricanes previously struck the island in recent history: David in 1979 and Marilyn in 1995. David brought widespread destruction to the islands as a Category 4 hurricane with sustained winds of 145 mph.

(MORE: Countries Hit Most by Tropical Cyclones)

7. Dominica 'was effectively reduced to an immense field of debris'

The damage toll in the island nation was absolutely staggering – about $1.31 billion U.S., or 216 percent of the country's Gross Domestic Product.

(MORE: Dominica, One Month After Maria)

"We've been set back 40 years and need to focus on the short-term for now," Richmond Valentine, superintendent of Dominica's Police Force, told IRIN News. "If this is a war, it's a war we have no idea how to fight."

The vast majority of homes were damaged on the island and everyone was affected by Maria. Thirty-one people were killed on the island.

People survey the damage in Roseau, Dominica, on Sept. 20, the day after Hurricane Maria passed over the island.
(AFP/Getty Images)

"The agricultural sector was essentially eliminated," according to the NHC. "Power, phone and internet service was cut off, leaving the country almost incommunicado with the outside world."

Most trees on the island were defoliated.

8. Maria broke a weeks-old pressure record set by Irma

Maria’s minimum central pressure of 908 millibars, recorded near St. Croix of the U.S. Virgin Islands, late Sept. 19 set a new record for the lowest pressure of any hurricane in the Atlantic Basin east of the Bahamas. This broke the record from just weeks earlier, set by Irma's 914 millibars.

This shows both strength and size of Hurricane Maria as it approached Puerto Rico.

(MORE: 15 Most Iconic Hurricane Images of All-Time)

The lower the pressure in a hurricane, the higher the winds usually are. When this new pressure record was set, winds had climbed to 175 mph in the eyewalls of Hurricane Maria.

Severe winds were spreading out at the time due to the process described below, and were battering St. Croix.

9. Puerto Rico was saved from a Category 5 landfall by an eyewall replacement cycle

Maria underwent a well-documented eyewall replacement cycle just before landfall in Puerto Rico. This cycle resulted in its eye diameter tripling in size, from 9 miles wide to about 28 miles wide.

An eyewall replacement cycle occurs in many strong tropical cyclones and is caused by a shift in moisture and energy outward from the center of the hurricane as an inner eyewall begins to weaken.

An annotated version of the radar on Sept. 19, 2017.
(National Hurricane Center)

This widening of Maria's eye:

  • Expanded the full extent of Maria's wrath across Puerto Rico and the Virgin Islands. The swath of hurricane-force winds was about 60 miles wide before the eyewall replacement cycle and expanded to 120 miles wide following the eyewall replacement.
  • Weakened winds in the hurricane prior to landfall.
  • Expanded the calm zone near the landfall area and to the northwest.

By definition, Maria made landfall as a Category 4 hurricane, but sustained winds in the higher elevations of Puerto Rico likely topped out well into the 160-plus-mph range with higher gusts because winds usually increase with elevation due to friction and drag on the winds near the surface.

10. The rainfall maximum on one island was 22.8 inches, but it was a foot higher on Puerto Rico

Maria directly hit both Dominica and Puerto Rico with catastrophic sustained winds, but in some spots, heavy rainfall caused just as much damage.

Dominica experienced torrential rains from Maria, with a maximum observed total of 22.8 inches. The rains caused serious flooding and mudslides across that island.

Even heavier rainfall occurred in Puerto Rico, where one location had a storm total of nearly 38 inches. The La Plata River on the island completely filled its watershed. River flooding was the worst on the northern side of the island. Flash flooding in the municipality of Toa Baja necessitated the rescue of hundreds of families from their rooftops.

Storm total rainfall, in inches, from Hurricane Maria in Puerto Rico and in the neighboring U.S. Virgin Islands.
(David Roth/Weather Prediction Center)

Combined with Hurricane Harvey's record-smashing tropical cyclone rainfall in Texas, 2017 was a very wet year for the tropics.


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