A look at the meteorology behind Hurricane Katrina 20 years later

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What started arsenic Tropical Depression Twelve connected Aug. 23, 2005, implicit the Greater Antilles would soon go 1 of the deadliest hurricanes connected grounds to deed the United States.

Traveling through southeastern Florida, up into the Gulf Coast and yet disintegrating implicit the Ohio Valley, thing could hole those successful Katrina's way for what they are inactive reeling from to this day, 20 years later.

How Hurricane Katrina formed

A tropical question moved disconnected the seashore of Africa into the Atlantic Ocean connected Aug. 11, 2005, connected a westward path. As it crossed the Central Atlantic and yet reached the Leeward Islands, connected Aug. 19 it combined with the remnants of what was erstwhile Tropical Depression Ten.

The tropical question dominated the enactment and began to signifier a ample country of organized thunderstorms implicit parts of Puerto Rico.

At 2 p.m. ET connected Aug. 23, Tropical Depression Twelve formed arsenic a chiseled halfway of circulation and was strengthening astir 175 nautical miles southeast of Nassau, Bahamas.

As hurricane hunters investigated the tempest system, Katrina received its sanction erstwhile it strengthened into a tropical tempest with maximum sustained winds of 40 mph connected Aug. 24, 2005, astatine 8 a.m. ET, astir 65 nautical miles east-southeast of Nassau.

Tropical Storm Katrina continued connected a west-northwestward way toward Florida, arsenic residents had minimal clip to prepare. Katrina became a hurricane astatine 5 p.m. ET connected Aug. 25, 2005, with maximum sustained winds of 75 mph. A Category 1 hurricane has a sustained upwind speed of 74-95 mph.

Katrina became a hurricane little than 2 hours earlier it made landfall successful Southern Florida.

Katrina made landfall successful the U.S. 3 times

Also known arsenic "the forgotten landfall," the archetypal of 3 landfalls was made connected Aug. 25, 2005, astatine 6:30 p.m. ET successful Hollywood, Florida, arsenic a Category 1 hurricane with maximum sustained winds of 80 mph. It spent astir 6 hours overnight traveling done the authorities of Florida, mostly impacting the Florida Everglades. As it had nary substance root implicit land, it rapidly weakened backmost down to tropical tempest presumption overnight with 69 mph winds.

As Katrina continued connected its westward way and yet reached the Gulf, it rapidly regained strength. It became a Category 1 hurricane erstwhile again astatine 2 a.m. ET connected Aug. 26, 2005, implicit the Eastern Gulf. Not lone did it commencement to strengthen, but it besides underwent accelerated intensification doubly successful the adjacent 48 hours.

Rapid intensification occurs erstwhile the maximum sustained winds of a tropical cyclone summation by astatine slightest 35 mph successful a 24-hour period. Katrina jumped from 75 mph to 109 mph from Aug. 26 to the greeting of Aug. 27. It underwent accelerated intensification a 2nd time, from Aug. 27 to Aug. 28, erstwhile it jumped from 115 mph to 167 mph.

Katrina reached its highest strength with maximum sustained winds of 173 mph astatine 2 p.m. ET connected Aug. 28, astir 170 nautical miles southeast of the rima of the Mississippi River.

Katrina experienced an Eyewall Replacement Cycle

Katrina was truthful aggravated successful spot that it besides experienced what is known arsenic an Eyewall Replacement Cycle. This occurs erstwhile the eyewall, which is wherever the strongest winds of a tropical strategy are, reaches its maximum capacity, truthful overmuch truthful that different eyewall forms connected the extracurricular of it. This cuts disconnected substance to the archetypal eyewall and yet diminishes it, resulting successful the strategy weakening, arsenic well. This occurred with Katrina connected Aug. 28, starring to the accelerated weakening anterior to its 2nd landfall connected the Gulf Coast.

That 2nd landfall took spot connected Aug. 29, 2005, astatine 7:10 a.m. ET successful Buras, Louisiana, arsenic a Category 3 hurricane with maximum sustained winds of 127 mph. It rapidly made a method 3rd landfall connected the Louisiana-Mississippi borderline astatine 10:45 a.m. ET, arsenic a somewhat weaker Category 3 hurricane with maximum sustained winds of 121 mph.

If a tempest is simply a Category 3, 4 oregon 5, it is deemed a "major" hurricane owed to the imaginable for "significant nonaccomplishment of beingness and damage," the National Hurricane Center says.

As expected, the tempest mislaid its substance from the lukewarm waters of the Gulf arsenic it moved implicit land. Katrina rapidly weakened to a Category 1 hurricane by 2 p.m. ET and a tropical tempest lone 6 hours later, astatine midnight connected Aug. 30, 2005. It became a tropical slump implicit the Tennessee Valley by 8 a.m. ET connected Aug. 30, but afloat transitioned into a remnant low-pressure strategy by 8 p.m. ET that day.

Some facts and figures:

Numerous observations of precocious tempest surge were investigated by the Federal Emergency Management Agency, which determined that upwards of 24-to-28-foot tempest surge was observed on the Mississippi coast.
Storm surge was besides observed to transverse implicit Interstate 10 successful respective locations, with the highest eastbound of Katrina's oculus path.
Even aft the archetypal menace of Katrina had passed, the strength of the tempest surge enactment a strain connected the New Orleans levee system. Levees are either manmade oregon earthy embankments that assistance power the travel of h2o to support onshore and communities. Storm surge overtopped and broke done levees and floodwalls, which caused excessive flooding successful the New Orleans area.
About 80% of New Orleans flooded, with immoderate depths reaching up to 20 feet wrong the archetypal 24 hours of Katrina's landfall.

Katrina besides produced a full of 43 tornadoes successful the Florida Keys, Georgia, Alabama and Mississippi.

1,392 full fatalities were attributable to Katrina, according to a 2023 study from the National Hurricane Center. And according to the hurricane center, Louisiana reported that radical implicit the property of 60 made up the bulk of Katrina deaths successful that state.

Katrina stands arsenic the 3rd deadliest hurricane successful the mainland U.S. since 1900, according to the hurricane center.

Katrina contributed to astir $125 cardinal successful harm successful 2005, according to the hurricane halfway — the costliest successful U.S. history. Adjusting for inflation, that would beryllium astir $186.3 cardinal successful 2022 dollars.

The highest rainfall reports recorded from Katrina were up to 14.04 inches astatine Homestead Air Force Base successful Florida.

On Aug. 28, 2005, astatine 2 p.m. ET, Katrina's measured barometric unit fell to 902 millibars, which was the fourth-lowest connected grounds successful the Atlantic Ocean. However, it has since dropped to sixth-lowest, down Hurricane Rita and Hurricane Wilma, some of which occurred aboriginal successful 2005.

When Katrina made landfall successful Buras, Louisiana, the measured unit was astatine 920 millibars, which is the lowest connected grounds successful the Atlantic Ocean for a hurricane astatine an strength of 127 mph.

The 920 millibars astatine the Buras landfall is besides the third-lowest connected grounds for storms that made landfall successful the U.S.

The strongest sustained winds measured astatine a fixed determination connected onshore from Katrina were astatine 4:20 a.m. ET connected Aug. 29, 2005, astatine 88 mph.

Nikki Nolan

Nikki Nolan is simply a meteorologist for CBS News and Stations. She graduated from Metropolitan State University of Denver with a Bachelor of Science grade successful Meteorology and has worked successful nationalist upwind TV sum since 2019.

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