What makes storms like hurricane harvey so strong?

What Makes Storms Like Hurricane Harvey So Strong?

Heat map of Hurricane Harvey, as seen from the Copernicus Sentinel-3A satellite on August 25, 2017. Photo: ESA

On Thursday, Harvey was a tropical storm. By the next day it was a Category 2 hurricane, and it strengthened to a Category 4 before hitting southeastern Texas on Friday night. That makes it the strongest tropical cyclone to strike the mainland United States in 12 years. What’s behind this storm’s sudden increase in power?

Harvey’s winds quickened from about 35 to 109 miles per hour between Thursday and Friday. That’s called “rapid intensification,” says Suzana Camargo, an ocean and climate scientist at the Earth Institute’s Lamont-Doherty Earth Observatory. She says the hurricane’s fast power-up was influenced by two factors.

The first is warm water. Warm water dumps heat energy into a developing storm.

More heat allows the low-pressure circulating system to draw in more air from its surroundings, which makes the storm spin faster and grow.

“A thick layer of warm water provides more fuel for the storm,” Camargo explains. The warm waters of the Gulf of Mexico, which Harvey is feeding off of, make it something of a breeding ground for hurricanes.

A satellite view of Hurricane Harvey as the storm approaches the Texas Coast, via Corpus Christi National Weather Service

But warm water isn’t enough to cause a rapid intensification; it also depends on wind speeds throughout the troposphere (the lowest region of the atmosphere).

If you think of the storm as a big tower, explains Camargo, you can’t have the winds blowing in one direction at the bottom of the storm but a different direction at the top—that would topple the column of air and the storm would be kaput.

The same thing happens if the winds have different strengths at different heights. Basically, having uniform winds from the bottom to the top of the storm allows it to grow in strength.

Hurricane Harvey: Why Is It So Extreme?

Hurricane Harvey is drowning southeastern Texas for the fourth day, putting a vast area under feet of water. Experts say Harvey has been stuck longer in one place than any tropical storm in memory. That is just one of the hurricane’s extremes; the storm is off the charts by many measures.

Scientific American wanted to learn why, and we asked meteorologist Jeff Masters for help. Masters is the co-founder of Weather Underground, a web site that meteorologists nationwide go to for their own inside information about severe weather.

Masters also wrote a fascinating article on why the jet stream is getting weird.

Why did Hurricane Harvey so quickly explode from a Category 1 hurricane to Category 4? Last Wednesday night, August 23, Harvey was a tropical depression, but after just eight overnight hours it was forming a hurricane eye wall. “That’s remarkably fast,” Masters says.

On Friday it rapidly ballooned from a Category 1 hurricane to Category 4. That is because it happened to pass over a region of extremely warm ocean water called an eddy.

This spot of hot water was 1 to 2 degrees Fahrenheit warmer than the Gulf of Mexico around it, which itself was already 1 to 2 degrees F higher than average, reaching 85 or 86 degrees F in places. The hotter the water, the more energy it drives into a storm.

Hurricane Katrina, which destroyed New Orleans in 2005, also mushroomed to Category 4 in a similar fashion because it, too, passed over a hot eddy in the Gulf.

Why is Harvey so stuck in place over Texas? Hurricanes are circular structures with winds that spiral counterclockwise, but they are steered by larger wind patterns in the greater atmosphere that push them in one direction.

In Harvey’s case, a big high-pressure system over the southeastern U.S. is trying to push the storm in one direction, but a big high pressure system over the southwestern U.S. is trying to push the storm in the opposite direction.

“The systems have equal strength and are cancelling each other out,” leaving Harvey stranded, Masters says. “It’s highly unusual to have two highs on either side of a hurricane of equal strength.

” The only other time Masters recalls that happening to a huge storm system was Hurricane Mitch in 1998, which struck Central America and killed an estimated 7,000 people in Honduras.

How can Harvey reverse direction, now, heading back out over the Gulf of Mexico from where it came? The high pressure system in the southeastern U.S. is also trying to push Harvey west, but now the storm has bumped into the high pressure system in the southwestern U.S., which is pushing it back to the east.

On any given day one of the systems might temporarily be winning this atmospheric ping-pong match. Masters says a low-pressure trough system has been setting up north of Harvey and might strengthen enough to start to pull the hurricane northward.

National weather forecasts released Monday morning indicate that might happen later this week.

What Makes Storms Like Hurricane Harvey So Strong? A member of the Texas Task Force 2 search and rescue team works through a destroyed apartment complex trying to find anyone that still may be in the apartment complex after Hurricane Harvey passed through on August 27, 2017 in Rockport, Texas.  Credit: Joe Raedle Getty Images

How can Harvey produce such extreme rainfall even though it is no longer over the ocean?

Hurricane Harvey

Category 4 Atlantic hurricane in 2017
For other storms of the same name, see Tropical Storm Harvey.

Hurricane HarveyCategory 4 major hurricane (SSHWS/NWS)Hurricane Harvey near peak intensity prior to landfall in southern Texas on August 25FormedAugust 17, 2017 (2017-08-17)DissipatedSeptember 2, 2017 (2017-09-02)(Extratropical after September 1)
Highest winds1-minute sustained: 130 mph (215 km/h) Lowest pressure937 mbar (hPa); 27.67 inHg
Fatalities68 direct, 39 indirectDamage$125 billion (2017 USD)(Tied as costliest tropical cyclone on record)Areas affectedWindward Islands, Suriname, Guyana, Nicaragua, Honduras, Belize, Cayman Islands, Yucatán Peninsula, Southern and Eastern United States (especially Texas, Louisiana)Part of the 2017 Atlantic hurricane season

  • Meteorological history


  • Texas

Other wikis

  • Commons: Harvey images

Hurricane Harvey was a devastating Category 4 hurricane that made landfall on Texas and Louisiana in August 2017, causing catastrophic flooding and many deaths.

It is tied with 2005's Hurricane Katrina as the costliest tropical cyclone on record,[nb 1] inflicting $125 billion (2017 USD) in damage, primarily from catastrophic rainfall-triggered flooding in the Houston metropolitan area and Southeast Texas.

[1][2] It was the first major hurricane[nb 2] to make landfall in the United States since Wilma in 2005, ending a record 12-year span in which no hurricanes made landfall at the intensity of a major hurricane throughout the country.

[3] In a four-day period, many areas received more than 40 inches (1,000 mm) of rain as the system slowly meandered over eastern Texas and adjacent waters, causing unprecedented flooding. With peak accumulations of 60.58 in (1,539 mm), in Nederland, Texas, Harvey was the wettest tropical cyclone on record in the United States. The resulting floods inundated hundreds of thousands of homes, which displaced more than 30,000 people and prompted more than 17,000 rescues.

The eighth named storm, third hurricane, and first major hurricane of the extremely active 2017 Atlantic hurricane season, Harvey developed from a tropical wave to the east of the Lesser Antilles, reaching tropical storm status on August 17.

[4] The storm crossed through the Windward Islands on the following day, making landfall on the southern end of Barbados and a second landfall on Saint Vincent.

Upon entering the Caribbean Sea, Harvey began to weaken due to moderate wind shear, and degenerated into a tropical wave north of Colombia, late on August 19.

[5] The remnants were monitored for regeneration as it continued west-northwestward across the Caribbean and the Yucatán Peninsula, before redeveloping over the Bay of Campeche on August 23.[6] Harvey then began to rapidly intensify on August 24, regaining tropical storm status and becoming a hurricane later that day.[7]

While the storm moved generally northwest, Harvey's intensification phase stalled slightly overnight from August 24–25; however, Harvey soon resumed strengthening and quickly became a major hurricane and attained Category 4 intensity later that day.

[8] Hours later, Harvey made landfall at San José Island, Texas, at peak intensity, followed by another landfall at Holiday Beach at Category 3 intensity.

Rapid weakening then ensued, and Harvey had downgraded to a tropical storm as it stalled near the coastline, dropping torrential and unprecedented amounts of rainfall over Texas.

[9] On August 28, it emerged back over the Gulf of Mexico, strengthening slightly before making a fifth and final landfall in Louisiana on August 29.[10] As Harvey drifted inland, it quickly weakened again as it became extratropical on September 1, before dissipating two days later.[11]

In addition to the huge cost and extent of the damage it caused, Harvey caused at least 107 confirmed deaths: 1 in Guyana and 106 in the United States, the first one in Rockport, Texas.[12] Due to the extensive damage, the name “Harvey” was retired in April 2018 and will not be used for another Atlantic tropical cyclone.[13][14]

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Meteorological history

Main article: Meteorological history of Hurricane Harvey
Map plotting the track and the intensity of the storm, according to the Saffir–Simpson scale

Hurricane Harvey originated from a westward-moving tropical wave that emerged from Africa over the eastern Atlantic Ocean, on August 12, 2017. A surface circulation slowly developed and convection consolidated around the low over the subsequent days; the system became a tropical depression on August 17, roughly 505 mi (815 km) east of Barbados.[4] Maintaining its brisk westward motion, the system strengthened slightly and became a tropical storm later that day, at which time it was assigned the name Harvey. With maximum sustained winds of 45 mph (75 km/h), Harvey made landfalls in Barbados and St. Vincent on August 18 before entering the Caribbean Sea. Hostile environmental conditions, namely wind shear, imparted weakening and caused Harvey to degenerate into a tropical wave by August 19.[5] Though it lacked an organized surface low, the remnants of Harvey continued to produce significant convection as it traversed the Caribbean Sea and Yucatán Peninsula. The system reached the Bay of Campeche in the Gulf of Mexico on August 23 and soon consolidated around a new surface low.[15]

What Makes Storms Like Hurricane Harvey So Strong?Play media Hurricane Harvey as seen by NASA aboard the International Space Station on August 25

Late on August 23, the remnants of Harvey regenerated into a tropical cyclone and reattained tropical storm intensity by 18:00 UTC.

[6] Initial reorganization was slow; however, within a highly favorable environment, the system soon underwent rapid intensification as an eye developed and its central pressure quickly fell.

After becoming a hurricane on August 24, Harvey continued to quickly strengthen over the next day, ultimately reaching peak intensity as a Category 4 hurricane.

[8] Around 03:00 UTC on August 26, the hurricane made landfall at peak intensity on San Jose Island, just east of Rockport, with winds of 130 mph (215 km/h) and an atmospheric pressure of 937 mbar (27.7 inHg). It made a second landfall on the Texas mainland, at Rockport, three hours later in a slightly weakened state. Harvey became the first major hurricane to make landfall in the United States since Wilma in 2005.[15]

After striking land, Harvey rapidly weakened as its speed slowed dramatically to a crawl, and Harvey weakened to a tropical storm on August 26. For about two days the storm stalled just inland, dropping very heavy rainfall and causing widespread flash flooding.

Harvey's center drifted back towards the southeast, ultimately re-emerging into the Gulf of Mexico on August 28. Once offshore, the poorly organized system struggled against strong wind shear. Deep convection persisted north of the cyclone's center near the Houston metropolitan area along a stationary front, resulting in several days of record-breaking rain.

Early on August 30, the former hurricane made its fifth and final landfall just west of Cameron, Louisiana with winds of 45 mph (75 km/h). Associated convection with Harvey became focused north of the center and along a warm front on September 1 as it moved further inland, indicating that the system transitioned into a post-tropical cyclone by 06:00 UTC that day.

The remnants continued northeastwards, before being absorbed into another extratropical system on September 3.[15]


Caribbean and Latin America

Tropical Storm Harvey in the Eastern Caribbean on August 18

Tropical cyclone warnings and watches for the Windward Islands were issued starting at 15:00 UTC on August 17, about six hours before Harvey developed. At that time, a tropical storm watch was posted for Dominica, while a tropical storm warning became in effect in Barbados, Martinique, Saint Lucia, and Saint Vincent and the Grenadines.[16] All watches and warnings were discontinued by late on August 18, as the storm continued westward into the Caribbean.[17]

In Honduras, a green alert was issued for the Atlántida, Islas de la Bahía, Colón, Cortés, Gracias a Dios, Olancho, and Yoro departments. About 8 inches (200 mm) of precipitation was expected along the coast, while inland areas were forecast to receive 2.76 to 3.15 in (70 to 80 mm) of rain.

[18] As the remnants of Harvey approached Mexico, the Civil Protection Secretary of the state of Campeche issued a blue alert, indicating minimal danger.[19] When Harvey redeveloped at 15:00 UTC on August 23, the Government of Mexico issued a tropical storm watch in Tamaulipas from Boca De Catan to the mouth of the Rio Grande.

[20] The watch remained in effect until 21:00 UTC on August 25, after it became evident that the storm no longer posed a significant threat to that area.[21]

United States

FEMA worked with the Coast Guard, Customs and Border Protection, and Immigration and Customs Enforcement to prepare for the storm and its aftermath. The agency placed disaster response teams on standby at emergency posts in Austin, Texas, and Baton Rouge, Louisiana.[22]


Upon the NHC resuming advisories for Harvey at 15:00 UTC on August 23, a hurricane watch was issued in Texas from Port Mansfield to San Luis Pass, while a tropical storm watch was posted from Port Mansfield south to the mouth of the Rio Grande and from San Luis Pass to High Island.

Additionally, a storm surge watch became in effect from Port Mansfield to High Island.

Additional watches and warnings were posted in these areas at 09:00 UTC on August 24, with a hurricane warning from Port Mansfield to Matagorda; a tropical storm warning from Matagorda to High Island; a hurricane watch and tropical storm warning from Port Mansfield to the Rio Grande; a storm surge warning from Port Mansfield to San Luis Pass; and a storm surge from Port Mansfield to the Rio Grande.[15] As the hurricane neared landfall on August 24, an extreme wind warning—indicating an immediate threat of 115–145 mph (185–235 km/h) winds—was issued for areas expected to be impacted by the eyewall; this included parts of Aransas, Calhoun, Nueces, Refugio, and San Patricio counties.[23] The watches and warnings were adjusted accordingly after Harvey moved inland and began weakening, with the warning discontinued at 15:00 UTC on August 26. By 09:00 UTC on the following day, only a tropical storm warning and a storm surge warning remained in effect from Port O'Connor to Sargent. However, watches and warnings were re-issued as Harvey began to re-emerge into the Gulf of Mexico, and beginning at 15:00 UTC on August 28, a tropical storm warning was in effect for the entire Gulf Coast of Texas from High Island northward.[15]

Governor Greg Abbott declared a state of emergency for 30 counties on August 23, while mandatory evacuations were issued for Brazoria, Calhoun, Jackson, Refugio, San Patricio, and Victoria counties, as well as parts of Matagorda County.

[24] On August 26, Governor Abbott added an additional 20 counties to the state of emergency declaration.

[25] Furthermore, the International Charter on Space and Major Disasters was activated by the USGS on behalf of the Governor's Texas Emergency Management Council, including the Texas Division of Emergency Management, thus providing for humanitarian satellite coverage.[26]


Natural Hazards Center || Hurricane Harvey News Articles

What Makes Storms Like Hurricane Harvey So Strong?

NOAA's GOES-East satellite shows Hurricane Harvey on August 24 while still in tropical storm status. Credit: NOAA/NASA GOES Project, 2017.

Ever since Hurricane Harvey barreled toward Texas, we've been gathering resources that could be helpful to those seeking further information on hurricanes and other extreme coastal weather events. The following is a collection of select new sources. Please also see our listings for websites and reports and local academic expertise.

Last updated October 30, 3:30 p.m.

Topic Listings

Harvey in Louisiana Harvey in Texas
Lori Peek on Hurricane Harvey
Impacts on the Oil Industry
Vulnerable Populations
Communication/Social Media
State and Federal Response and Recovery
Volunteer, Humantarian, and Business Response Insurance and Disaster Assistance Claims Evacuations Storm Dynamics
Economic and Infrastructure Impacts
Environmental Impacts
Public Health
Displacement, Migration, and Immigration
Planning and the Social Dimensions of Disaster
Hurricane Harvey and Climate Change
Prediction Scenarios
Associated Flooding
Hurricane Harvey Makes Landfall
Animals in Disasters Hurricane Harvey: News Before Landfall
News Releases and Statements

Harvey in Louisiana

With Death Toll at 30, Storm Makes 2nd Landfall
New York Times, August 30.

Gulf Coast Braces for More Rain as Harvey Makes Second Landfall
Los Angeles Times, August 30.

Harvey in Texas

  • Coastal Vietnamese Community Leans On Faith, And Each Other, To Rebuild After Harvey
    NPR, September 9.
  • In Houston After the Storm, a City Split in Two
    The New York Times, September 8.

What made the rain in Hurricane Harvey so extreme?

Fifty inches of rain. Nine trillion gallons of water. The Gulf Coast of Texas, and especially the Houston metropolitan area, has been inundated by rain produced by Hurricane Harvey. And as of this writing, the rain continues along a broad swath of the Gulf Coast, with a flood threat extending all the way east through New Orleans to the Florida Panhandle.

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Even for one of the wettest and most flood-prone parts of the United States, the rainfall totals and flooding are breaking records. So, what has made Harvey such a prodigious rain producer?

Left panel: Rainfall accumulation for four days ending Tuesday, Aug. 29, 2017 at 9 a.m. CDT. Right panel: Rainfall forecast for the 24 hours from 9 a.m. Tuesday, Aug. 29 to 9 a.m. Wednesday, Aug. 30. The National Weather Service said forecasters needed to change their usual color scale to illustrate the extreme rainfall amounts in Texas. National Weather Service

A ‘train’ of rainstorms

The amount of rain that falls at a given location can be boiled down to a surprisingly simple equation: The total precipitation equals the average rainfall rate, multiplied by the rainfall duration. In other words, the most rain falls where it rains the hardest for the longest.

Tropical cyclones in general are very efficient rain producers, because they draw large quantities of water vapor into the atmosphere from a warm ocean.

That moist air rises and the water vapor condenses, and a large fraction of that water falls as rain.

Tropical cyclones can also last a long time; if their motion slows, then a particular region can experience that heavy rainfall for multiple days.

Why Hurricane Harvey May Be Deadlier Than Other Storms

Hurricane Harvey has become an emergency management director’s nightmare.

The hurricane, which is the most serious storm to make landfall in the U.S. since Hurricane Wilma in 2005, combined rapid intensification with a deluge of rainfall that is expected to make it a catastrophic event for Texas. Harvey’s eye came ashore late Friday near Rockport, Texas, about 35 miles northeast of Corpus Christi.

The storm began gathering strength as it approached the Texas coast Thursday and Friday. At 8 a.m. Eastern Daylight time Thursday, the hurricane’s top winds were 60 mph. By 8 a.m.

Friday, Harvey’s top winds had exploded to 110 mph. And by 2 p.m. Eastern time its top winds had reached 120 mph.

That threshold made Harvey a Category 3 major hurricane on the Saffir-Simpson scale, meaning that its winds can do devastating damage.

On Friday evening, the storm was upgraded to a Category 4, with winds that can exceed 130 mph. As predicted the storm made landfall at that strength. By Saturday morning it was downgraded to a Category 1 storm, although serious risk of flooding remains given heavy rains and storm surges.

Meteorologists are still trying to unlock the secrets that cause a hurricane to rapidly intensify, says meteorologist Jeff Masters, founder of the website Weather Underground. (Learn about recent advances in hurricane forecasting and science.

) Three of the most powerful hurricanes on record—Hurricane Charley in 2004, Andrew in 1992, and the Labor Day Hurricane of 1935—underwent similar rapid intensification as they were coming ashore.

All of these hurricanes destroyed or inflicted massive damage to everything in front of them.

Hurricanes draw their energy from seawater that has been heated to at least 80 degrees Fahrenheit. A hurricane’s development can be impeded by the presence of upper-level winds—known as wind shear—that disrupt the storm’s circulation and cause it to lose strength. (Learn more about how hurricanes form.)

Masters said in a blog post today that Hurricane Harvey had been over very warm water—at least 85 degrees Fahrenheit—for more than six hours earlier today. And the storm is was not bothered by wind shear. Masters said these factors fueled Harvey’s rapid intensification.

What Makes Storms Like Hurricane Harvey So Strong?

Houston, the fifth most populated city in the United States, and the surrounding areas of southeast Texas are currently facing down a historic storm known as Hurricane Harvey.

The National Weather Service has warned of “catastrophic flooding” and tweeted that the storm “is unprecedented and all impacts are unknown and beyond anything experienced.” More than 250 highways have been closed due to flooding and more than 2,000 calls for rescue have been made since the storm began. An estimated 76,000 people remain without power.

When asked if his relief agency was prepared to be in Houston dealing with the aftermath for months, Brock Long, the head of the Federal Emergency Management Agency (FEMA) responded, “FEMA is going to be there for years.”

What makes Hurricane Harvey so uniquely strong? Does the storm represent a new norm in extreme weather?

How are hurricanes classified?

Hurricane Harvey was classified as a Category 4 storm when it first made landfall just south of Corpus Christi, Texas.

According to the National Hurricane Center, a branch of the National Oceanic and Atmospheric Administration, these categories rank the hurricane’s sustained wind speed on the Saffir-Simpson Hurricane Wind Scale.

The scale of 1 to 5 also accounts for potential property damage and loss of life.

In a Category 4 storm, winds clock in at 130 to 156 miles per hour. Power outages are predicted to last weeks and “most of the area will be uninhabitable for weeks or months”. Even well-built houses are expected to sustain severe damage including the potential for the loss of its roof and exterior walls.

But the extreme nature of Hurricane Harvey, and the potential threat brought on by other intense storms like it, is due to more than wind speed.

Storm surge – how much ocean levels rise due to onshore winds – and total rainfall also contribute to a hurricane’s intensity.

Harvey offers up a particularly destructive combination: an already problematic, but not unheard of, storm surge of a few feet, extremely high levels of rainfall, and a stalling of the storm over a single area for several days.


Hurricane Harvey’s Impact — And How It Compares To Other Storms

Hurricane Harvey, which dumped an estimated 27 trillion gallons of water on Texas and Louisiana, looks to be one of the most damaging natural disasters in U.S. history. Flooding continues to affect large areas of Houston, Beaumont and other areas of Texas.

Tens of thousands have been forced to evacuate their homes, and rig shut downs and evacuations along the Gulf have curbed oil and gas production. The White House, meanwhile, is expected to ask Congress for $14.5 billion in relief funding.

While we don’t know Harvey’s ultimate toll on life and property — and won’t for some time — here are the best estimates of the hurricane’s impacts so far, and how they compare to the destruction wrought by other major storms.

Economic impact

Estimates of Harvey’s cost vary, with some predicting that the storm will be the most expensive in U.S. history at over $190 billion, surpassing Hurricane Katrina.

(The National Oceanic and Atmospheric Administration estimates Katrina to have cost around $160 billion.) If that ends up being the case, it would greatly increase the total cost of billion-dollar-plus events since 1980.

Others predict that the cost will be closer to that of Superstorm Sandy, at around $70-90 billion.

In general, hurricanes are a particularly devastating type of natural disaster.

Of the billion-dollar disasters shown in the chart above, the 10 most destructive hurricanes caused an estimated $442 billion in losses, over a third of the $1.2 trillion caused by all 212 events combined.

And while billion-dollar hurricanes haven’t been growing more frequent, Harvey and other super damaging weather and climate disasters are part of a continuing, costly trend.

Rain and flooding

One reason for Harvey’s estimated record cost is the sheer amount of rain and flooding brought on by the storm. Harvey set the record for tropical cyclone rainfall measured in any one place in the U.S. over at least the past 50 years.

Since its landfall on Aug. 25th, Harvey also brought extensive flooding in and around Houston and Beaumont before it dissipated and made its way inland.

Because of Harvey’s flood impacts, many have compared it to Hurricane Katrina.

Katrina’s devastation was a result of the failure of government flood protection systems, violent storm surges, a chaotic evacuation plan and an ill-prepared city government.

Harvey, on the other hand, has caused massive flooding at a slower pace, without Katrina’s deadly surge. In this way it resembles other costly and damaging tropical cyclones of the past 30 years.


1 Aug. 25, 2005 Hurricane Katrina $160.0b 1,833
2 Oct. 30, 2012 Hurricane Sandy 70.2 159
3 Sept. 20, 2005 Hurricane Rita 23.7 119
4 Sept. 12, 2008 Hurricane Ike 34.8 112
5 Sept. 21, 1989 Hurricane Hugo 18.2 86
6 Sept. 14, 1999 Hurricane Floyd 9.7 77
7 Oct. 27, 1985 Hurricane Juan 3.5 63
8 Aug. 23, 1992 Hurricane Andrew 47.8 61
9 Sept. 12, 2004 Hurricane Ivan 27.1 57
10 Sept. 18, 2003 Hurricane Isabel 7.4 55
11 Aug. 31, 2008 Hurricane Gustav 7.0 53
12 Oct. 8, 2016 Hurricane Matthew 10.3 49
13 Sept. 3, 2004 Hurricane Frances 12.9 48
14 Aug. 25, 2017 Hurricane Harvey* 81-108 47
15 Aug. 26, 2011 Hurricane Irene 15.0 45
16 June 5, 2001 Tropical Storm Allison 11.9 43
17 Sept. 5, 1996 Hurricane Fran 8.0 37
18 Oct. 24, 2005 Hurricane Wilma 24.3 35
19 Aug. 13, 2004 Hurricane Charley 21.1 35
20 July 7, 1994 Tropical Storm Alberto 1.7 32
21 Sept. 15, 2004 Hurricane Jeanne 9.9 28
22 Oct. 4, 1995 Hurricane Opal 7.6 27
23 Sept. 1, 2011 Tropical Storm Lee 2.8 21
24 Aug.17, 1983 Hurricane Alicia 7.5 21
25 Aug.18, 1991 Hurricane Bob 2.7 18
26 Sept. 20, 1998 Hurricane Georges 9.1 16
27 July 9, 2005 Hurricane Dennis 3.2 15
28 Sept. 15, 1995 Hurricane Marilyn 3.4 13
29 Aug. 7, 1980 Hurricane Allen 1.9 13
30 Sept. 26, 1985 Hurricane Gloria 2.0 11
31 Aug. 26, 2012 Hurricane Isaac 3.0 9
32 Sept. 11, 1992 Hurricane Iniki 5.5 7
33 Aug. 30, 1985 Hurricane Elena 3.0 4
34 July 23, 2008 Hurricane Dolly 1.5 3
35 Aug. 27, 1998 Hurricane Bonnie 1.5 3
36 Aug. 1, 2002 Hurricane Lili 1.5 2

*The full scope of Hurricane Harvey’s impact and cost are not yet known. The estimated cost range is from Moody’s Analytics. Texas officials estimated Harvey has caused at least 47 deaths, according to the New York Times. Both estimates are as of Sept. 1, 2017.

Sources: National Oceanic and Atmospheric Administration, Moody’s analytics, New YOrk Times

Other impacts to look out for

The immediate effects of Harvey were also felt by the oil and gas industries. Around 10% of manned oil platforms in the Gulf were evacuated, according to the Bureau of Safety and Environmental Enforcement. While the fallout is still being determined, gas prices have risen and oil and gas rig production has continued to be hampered.

There are many more consequences that residents and officials are only now sorting through. Harvey’s impact may be felt as residents seek claims from insurance companies, encounter environmental contaminants from debris and infrastructural damage and incur the economic effects of displacement. The cleanup has only just begun.

Why Are Hurricanes Like Dorian Stalling, and Is Global Warming Involved?

Hurricane Dorian's slow, destructive track through the Bahamas fits a pattern scientists have been seeing over recent decades, and one they expect to continue as the planet warms: hurricanes stalling over coastal areas and bringing extreme rainfall.

Dorian made landfall in the northern Bahamas on Sept.

1 as one of the strongest Atlantic hurricanes on record, then battered the islands for hours on end with heavy rain, a storm surge of up to 23 feet and sustained wind speeds reaching 185 miles per hour.

The storm's slow forward motion—at times only 1 mile per hour—is one of the reasons forecasters were having a hard time pinpointing its exact future path toward the U.S. coast.

With the storm still over the islands on Sept. 2, the magnitude of the devastation and death toll was only beginning to become clear. “We are in the midst of a historic tragedy in parts of our northern Bahamas,” Prime Minister Hubert Minnis told reporters.

Recent research shows that more North Atlantic hurricanes have been stalling as Dorian did, leading to more extreme rainfall. Their average forward speed has also decreased by 17 percent—from 11.5 mph, to 9.6 mph—from 1944 to 2017, according to a study published in June by federal scientists at NASA and NOAA.

The researchers don't understand exactly why tropical storms are stalling more, but they think it's caused by a general slowdown of atmospheric circulation (global winds), both in the tropics, where the systems form, and in the mid-latitudes, where they hit land and cause damage.

Hurricanes are steered and carried by large-scale wind flows, “like a cork in a stream,” said Tim Hall, a hurricane researcher with NASA's Goddard Institute for Space Studies and author of the study. So, if those winds slow down or shift direction, it affects how fast hurricanes move forward and where they end up.

How that slowing is connected to global warming is still an area of debate. There are different mechanisms at work in the tropics and mid-latitudes, but, “in the broadest sense, global warming makes the global atmospheric circulation slow down,” said NOAA hurricane expert Jim Kossin, co-author of the June study.

He said scientists suspect the overall slowing of winds is at least partly due to rapid warming of the Arctic. The temperature contrast between the Arctic and the equator is a main driver of wind. Since the Arctic is warming faster than lower latitudes, the contrast is decreasing, and so are wind speeds.

“There is a lot of evidence to suggest this is more than just natural variability,” Kossin said.

In a 2018 paper, Kossin showed that the increase in tropical cyclones stalling is a global trend. The magnitude varies by region but is “generally consistent with expected changes in atmospheric circulation forced by anthropogenic emissions,” he wrote.

The Fifth Category 5 Hurricane in Four years

Rising global temperatures also influence storms in other ways: A warmer atmosphere holds more moisture, which means hurricanes can bring more rain, and warmer oceans provide additional energy that can make them stronger.

Hurricane Harvey dumped 60 inches of rain on parts of Texas in 2017 and stalled over the Houston area for days. Hurricane Florence stalled in 2018, flooding parts of coastal North Carolina.

Kossin said Hurricane Sandy, in 2012, also took an unusual path that may have been affected by shifting global wind patterns, turning west and slamming into New Jersey instead of being carried eastward, out to sea and away from land, by prevailing westerly winds.

“Stalling hurricanes wreak much more havoc than those that blow through quickly,” said Hall. “Dorian definitely fits the pattern that we found in our paper.”

Dorian is the fifth Category 5 hurricane in just four years in the Atlantic, and only the 35th on record going back nearly a century.

Scientists have seen a trend toward stronger hurricanes in the Atlantic, but not an increase in the total number of storms, said Kevin Trenberth, a climate scientist with the National Center for Atmospheric Research.

“The environment for all such storms has changed because of climate change. The oceans are warmer, especially in the upper 100 meters, which is most important for such storms,” Trenberth said. “This makes available more energy via water vapor for the storms and makes for more activity: more intensity, bigger and longer lasting storms, with heavier rainfalls.”

“The case can readily be made that all storms are affected but each responds differently. For example, Michael (2018) was a very intense Category 5 but moved fast. The slower storms can become large,” he said.

Leading Edge of the Science

Scientists are still working to understand the ways that global warming affects hurricanes and tropical storms, including its influence on wind patterns.

Karsten Haustein, a climate researcher with World Weather Attribution and Oxford University's Climate Research Lab, said there might be other dynamic factors at play, such as changing land-ocean temperature contrasts, but since models don't show such things, it is hard to know for sure.

“What we do know is that warmer ocean waters intensify storms if all other conditions remain constant,” Haustein said.

“In that sense, the simplest attribution experiment would be one in which ocean and atmosphere have warmed as observed.

In the case of Dorian, this would probably translate into an increased rainfall amount of at least 5 percent over affected areas. We found up to a 14 percent increase in case of Harvey.”

  • Penn State University climate scientist Michael Mann said that while there are uncertainties about what causes hurricanes to stall, some trends are becoming more clear.
  • “We are definitely seeing a trend toward stalling of these systems after they make landfall, and there may be a climate change connection, though this is really at the leading edge of the science and is still being debated,” Mann said.
  • Climate models can't precisely identify the atmospheric changes that cause stalling, he said, “so it is possible that those same models are not capturing how climate change in influencing this particular aspect of hurricane behavior.”
  • Published Sept. 3, 2019

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