Katrina the Storm

Satellite animation of Katrina as it travels into New Orleans from the Gulf of Mexico

Katrina was a category 5 hurricane that made landfall in Louisiana as a category 3 in August of 2005. It was one of the strongest and most damaging hurricanes in the world. The storm formed near the Bahamas, later making landfall in Florida. When it exited Florida, the storm rapidly picked up strength and peaked with winds of 175 mph. One day later, it made landfall in New Orleans as a category 3 with 125 mph winds, causing major flooding and $125 billion in damage. The system later weakened and became post-tropical along the Appalachian Mountains, bringing local rainfall and downed trees.

Timeline of the storm:

Track of Hurricane Katrina and it's intensity positions. Source: https://www.weather.gov/mob/katrina

Storm Path and how it affected the intensity:
When Katrina formed, it went in a general westward path towards Miami. Later, the storm made landfall there as a Cat. 1, and went into the Gulf of Mexico thereafter. Once it left Florida, the storm was moving southwest over the very warm Gulf waters of >86F. When this happened, it went from a strong tropical storm near Florida to a Cat. 5 in the Gulf of Mexico in a 42 hour-period ending on August 28 at noon. By this time, the storm was heading in a northwest direction towards the Louisiana Coast. One day later, it made landfall in New Orleans at a Cat. 3. When the storm exited into the Gulf of Mexico, it went over an area called the Loop Current. This is a current of warm water that travels through the Gulf of Mexico. Katrina went over it around the time it rapidly strengthened. On average, the water is around 85F, but factors related to global warming made the waters warmer, at 87-90F. The small change in temperature, depending on the local conditions around the storm, can be enough
to make an already intense storm like Katrina even stronger.

Katrina's size, along with the track, over it's lifespan as a tropical cyclone

Timeline:

August 24: Tropical Depression 12 develops, and later became Tropical Storm Katrina. Forecasters said the storm could strengthen to a hurricane in the Gulf of Mexico. A hurricane warning is issued for the Miami area as the system strengthens into a strong tropical storm fairly quickly.
August 25: Katrina becomes a category 1 with 75 mph winds and hits the Miami area, killing 4 and leaving millions without electricity. Forecast models begin predicting that the storm will turn northward in the Gulf of Mexico and strike the northern Gulf coast around the Florida Panhandle.
August 26: Katrina exits into the Gulf of Mexico and begins to rapidly pick up strength as it moved over waters that were already above their average temperature. Because of the warm water and very favorable environment, it became a category 2 by 11 A.M., with winds of 100 mph. Forecast models shift west in their predictions a day earlier and now forecast that it will hit Western Florida/Southern Alabama. The U.S. Federal Emergency Management Agency (FEMA) issues a statement about the storm and it’s possible effects on the coast. The agency is also concerned about New Orleans and Katrina's possible impacts since it’s below sea level.

Above: Evolution of forecasters' predictions for Hurricane Katrina on August 25, 26, and 27th. Notice the big change in the predictions over the course of 3 days and the differences between each prediction shown before August 27th. However, as the storm got closer to making landfall, virtually all forecasts agreed that the storm would hit some part of the Louisiana coast and affect New Orleans to some extent by August 27th. This is a classic example of spaghetti weather models and what they mean, which are essentially several predictions that typically disagree with each other in track and intensity on a single map. Sources:
https://929thelake.com/no-irma-is-not-following-the-same-path-as-katrina/(for 8/25 run), https://www.researchgate.net/figure/Track-forecasts-for-Hurricane-Katrina-from-a-number-of-models-initialized-at-0000-UTC-on_fig5_26438414(for 8/26 and 8/27 runs)

August 27: Katrina strengthens into a category 3 major hurricane with winds of 115 mph. Forecast models shift westward once again, this time predicting that the storm will hit Louisiana/New Orleans area. These models also predict that the storm will make landfall as a major hurricane with winds of at least 115 mph and flood the New Orleans area when it hits. By this time, evacuations begin in southern Louisiana and a hurricane warning is issued for the area.
August 28: Katrina further strengthens into a category 5 with winds of 175 mph. This was the storm’s peak intensity. By this time, it was 150-200 miles south of Louisiana and virtually all forecast models agree it will strike the New Orleans area as a devastating category 4 or 5 hurricane. They also predict that storm surge will be at least 20 feet. Government officials warn as a result, the area will be uninhabitable for weeks after landfall and that there will be a lot of damage to buildings. Mandatory evacuations are issued for New Orleans and the Superdome is opened for people who couldn't evacuate the city.
August 29: Katrina makes landfall in the Buras-Triumph area of Louisiana as a category 3 with 125 mph winds. Although it was weaker than what people expected at landfall, it still caused levees in the area to fail as some predicted and caused major flooding in New Orleans from the levee failures. As a result of these failures, most of New Orleans is underwater and over 1,800 people die. President Bush declares the New Orleans area a federal disaster area.
August 30-afterward: Katrina weakens to a post-tropical cyclone over the mid-eastern U.S. The effects in states along the western side of the Appalachian Mountains are mostly rainfall and some downed trees. The damage and flooding some forecasters correctly predicted in New Orleans has occurred and millions are without power or water after the storm and resulting damage.

Climate Change

Climate change impacted Katrina in a way where the waters in the Gulf of Mexico were above their average temperature, right before Katrina hit. This was because of the increased CO2 levels. When these levels go up, it causes thermal expansion, which is water expanding when it takes heat. When that happens, it makes the waters warmer. During the time Katrina passed over the Loop Current in the Gulf, the waters there were over 88F. The environment was also good for intense storms (e.g. moist atmosphere, high level of heat energy from warm water). These factors caused the storm to rapidly gain size and strength after it’s Florida landfall, and this is what resulted in a category 5 hurricane that made landfall one day later. On the right pictures, one can see the storm grow in size as it traveled over the warm Gulf waters. At it's peak size, the diameter of 40 mph winds was over 400 miles. Even though the storm lost some strength prior to hitting the coast, the storm continued growing in size right up to landfall because of the warm waters fueling the storm.

In addition, the 2005 Atlantic season was affected by all these factors, too. There were 28 storms and 15 hurricanes, surpassing 1933 in terms of storms. Also, there were 4 hurricanes that reached category 5 intensity (Emily, Katrina, Rita, and Wilma), a record for a single season. Climate change had so much of an effect on this season that there were tropical storms and hurricanes in December and January, during a time when environmental factors like drier air and cooler waters typically preclude the development of these storms. When the final storm dissipated in January, the season's storms caused $160 billion in property damages, mostly from intense and large storms like Katrina.

Extent of Tropical Storm and Hurricane force winds during Katrina's lifetime. Source: https://www.weather.gov/mob/katrina#

Katrina's track and the SST's along the storm. The warmest temps came right before the storm made landfall. Source: http://www.personal.psu.edu/rxc328/blogs/richard_cappellino/unique_8_lg.png

So as our climate continues to get warmer, we’ll be seeing an increase in the intensity we see in hurricanes and tropical storms. This has been shown in data collected; the data shows intensity and the amount of hurricanes per-year. It has been proven that our climate is getting warmer, which is leading to a rising sea level (ice caps melting). As the sea level rises and more intense storms roll in, storm surge will continuously get worse and worse. As for increased storm intensity, warmer water can cause stronger winds that are produced in hurricanes, and colder water weakens the storm. Also, intense storms like Katrina can get very large, because of these favorable factors around them. This can affect the storm as it could produce high storm surge and strong winds over a wide swath of land, contributing to worse impacts for more people. The only problem we have right now is how long we’ve been collecting data (a few decades), which isn't enough to say with 100% confidence that climate change is affecting the amount of future storms. However, we do know that the oceans will continue to get warmer, and hurricanes thrive in warmer water. This will cause hurricanes to do more damage on landfall. It will also bring storms, particularly intense ones, to new areas that have never seen these storms before.

The above factors are all evidence that storms like Katrina are being affected by climate change. These factors are including, but not limited to, thermal expansion(which gives off heat energy for storms and makes waters warm), sea level rise(which can worsen storm surge), and the way the storm moves, which can determine if the storm stays weak or becomes intense.