The storm’s energy, expressed in terajoules, is calculated based on its wind speed and its size.

30 mph

One-minute

sustained winds

110 mph

Hurricane-force

wind contour

MEXICO

NORTH

U.S.

2017

Texas

Harvey

28 terajoules

Gulf of Mexico

MEX.

2005

Katrina

116 terajoules

Carribean

Sea

1992

Andrew

Florida

15 terajoules

BAHAMAS

CUBA

Atlantic

Ocean

2017

Irma

112 terajoules

DOM.

REP.

300 MILES

Source: RMS HWind

The storm’s energy, expressed in terajoules, is calculated based on its wind speed and its size.

30 mph

Hurricane-force

wind contour

One-minute

sustained winds

110 mph

Atlantic Ocean

2017

2005

1992

2017

Harvey

Katrina

Andrew

Irma

116 terajoules

28 terajoules

15 terajoules

112 terajoules

Carribean

Sea

300 MILES

Source: RMS HWind

The storm’s energy, expressed in terajoules, is calculated based on its wind speed and its size.

30 mph

Hurricane-force

wind field

One-minute

sustained winds

110 mph

Atlantic Ocean

2017

2005

1992

2017

Harvey

Katrina

Andrew

Irma

116 terajoules

28 terajoules

15 terajoules

112 terajoules

Gulf of Mexico

300 MILES

Caribbean Sea

Source: RMS HWind

The most common metric for understanding the strength of a hurricane is the Saffir-Simpson scale, which is determined by maximum wind speed. Irma broke the record for consecutive hours at Category 5 on Sept. 7.

But hurricane strength is about more than just maximum wind speed. Energy is an important metric, because it can help determine the storm’s impact, how bad it will be and how far it will extend. A very large storm with moderate winds may have more total energy than an intense but small storm.

The map above, provided by RMS, a company specializing in risk assessment, compares the energy of Irma at its peak with other historic and recent hurricanes in the Atlantic basin. Irma’s wind speed combined with its size carried an energy value of 112 terajoules, which is similar to the energy of Katrina in 2005. Hurricane Sandy, not depicted in this map, was a Category 1, but according to RMS carried 330 terajoules of energy before its landfall in New Jersey because its wind field was so big. (These numbers represent energy in a thin slice of each storm measured about 10 meters off the ground. The energy of the entire height of the storm would be much, much greater.)

Atlantic

Ocean

Tampa

Detail below

Florida

Gulf of

Mexico

Miami

BAHAMAS

CUBA

Caribbean

Sea

JAMAICA

Ft. Myers

Florida

Fort Lauderdale

Naples

Miami

Gulf of

Mexico

Hurricane Irma

Atlantic

Ocean

Sunday 10 a.m. Eastern

Key West

Cudjoe Key

Landfall at 9:10 a.m. Eastern

Image source: GOES 16 satellite image via NOAA

Atlantic

Ocean

Tampa

Gulf of

Mexico

Detail below

Florida

Miami

BAHAMAS

CUBA

Caribbean

Sea

Ft. Myers

Naples

Fort Lauderdale

Florida

Miami

Gulf of

Mexico

Atlantic

Ocean

Hurricane Irma

Sunday 10 a.m. Eastern

Key West

Cudjoe Key

Landfall at 9:10 a.m. Eastern

Image source: GOES 16 satellite image via NOAA

Tampa

Gulf of

Mexico

Detail below

Florida

Miami

Atlantic

Ocean

BAHAMAS

CUBA

Ft. Myers

Naples

Fort Lauderdale

Florida

Miami

Gulf of

Mexico

Atlantic

Ocean

Hurricane Irma

Sunday 10 a.m. Eastern

Key West

Cudjoe Key

Landfall at 9:10 a.m. Eastern

Image source: GOES 16 satellite image via NOAA

Irma’s maximum sustained winds were measured at 185 mph. Only one Atlantic Ocean storm in recorded history has exceeded that level: Hurricane Allen, which slammed into Mexico and Texas in 1980, had top wind speeds of 190 mph.

Irma is an extremely

powerful hurricane

Strongest Atlantic hurricanes on record by max wind speed (mph)

Allen (1980)

190

Irma (2017)

185

Wilma (2005)

185

Gilbert (1988)

185

Fla. Keys (1935)

185

Rita (2005)

180

Mitch (1998)

180

Irma is an extremely powerful hurricane

Strongest Atlantic hurricanes on record by max wind speed

Allen (1980)

190 mph

Irma (2017)

185

Wilma (2005)

185

Gilbert (1988)

185

Florida Keys (1935)

185

Rita (2005)

180

Mitch (1998)

180

Irma is an extremely powerful hurricane

Strongest Atlantic hurricanes on record by max wind speed

Allen (1980)

190 mph

Irma (2017)

185

Wilma (2005)

185

Gilbert (1988)

185

Florida Keys (1935)

185

Rita (2005)

180

Mitch (1998)

180

About 425 miles wide, Irma is significantly larger than Hurricane Andrew, which devastated parts of South Florida in 1992. Andrew’s top sustained winds were 175 mph, as were Hurricane Katrina’s in 2005.

HURRICANE IRMA

 

Maximum sustained winds

185 mph

 

Maximum extent of hurricane-force winds

Sept. 5, 2017

HURRICANE KATRINA

 

Maximum sustained winds

175 mph

 

Aug. 28, 2005,

one day before Louisiana landfall

HURRICANE ANDREW

 

Maximum sustained winds

175 mph

 

Aug. 23, 1992,

one day before Florida landfall

HURRICANE KATRINA

 

HURRICANE IRMA

 

HURRICANE ANDREW

 

Max. sustained winds

Max. sustained winds

Max. sustained winds

185 mph

 

175 mph

 

175 mph

 

Maximum extent of hurricane-force winds

Sept. 5, 2017

Aug. 23, 1992,

one day before Florida landfall

Aug. 28, 2005,

one day before

Louisiana landfall

HURRICANE IRMA

 

HURRICANE ANDREW

 

HURRICANE KATRINA

 

Maximum sustained winds

Maximum sustained winds

Maximum sustained winds

185 mph

 

175 mph

 

175 mph

 

Maximum extent of hurricane-force winds

Sept. 5, 2017

Aug. 23, 1992,

one day before Florida landfall

Aug. 28, 2005,

one day before Louisiana landfall

But while Katrina had declined to a Category 3 storm by the time it struck the Gulf Coast, Andrew strengthened to a Category 5 just before it barreled into Florida. (Exact numbers for Andrew are sketchy because the storm destroyed much of the measuring equipment in its path.)

As of Sept. 6, Irma was smaller than Katrina at its peak but much larger than Andrew, and its hurricane-force winds stretched about 100 miles across — roughly the width of Florida in many places. By Sept. 11, the storm was much weaker but so spread out that its clouds covered parts of Florida and Canada simultaneously.

As Irma lumbered toward Florida, there were two other hurricanes in the Atlantic Ocean basin. This is the first time since 2010 there have been three active hurricanes. Hurricane Katia made landfall late Sept. 8 in Mexico with winds of 75 mph. Like Irma, Hurricane Jose formed in the far eastern Atlantic and traveled west. It peaked as a Category 4 hurricane with 155 mph winds as it spun in the Caribbean.

NORTH

MEXICO

Texas

Katia

Pacific

Ocean

Gulf of

Mexico

Fla.

CUBA

Caribbean

Sea

Irma

BAHAMAS

HAITI

DOM.

REP.

Atlantic

Ocean

500 MILES

Jose

Satellite image

as of Saturday

8:42 a.m. Eastern

 

Image source: GOES 16 satellite image via NOAA

Texas

Satellite image

as of Saturday

8:42 a.m. Eastern

 

Fla.

Gulf of

Mexico

BAHAMAS

Irma

Atlantic Ocean

DOM.

REP.

MEX.

CUBA

Jose

Katia

HAITI

Caribbean Sea

Pacific

Ocean

300 MILES

Image source: GOES 16 satellite image via NOAA

Texas

Atlantic Ocean

Fla.

Gulf of

Mexico

BAHAMAS

Satellite image

as of Saturday

8:42 a.m. Eastern

 

MEX.

Irma

DOM.

REP.

CUBA

Jose

Katia

HAITI

Caribbean Sea

Pacific

Ocean

300 MILES

Image source: GOES 16 satellite image via NOAA

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Sources: National Hurricane Center, Weather Underground and the National Weather Service. Originally published Sept. 6, 2017.

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