The year 2005 witnessed an extraordinary hurricane season. As of December 31, 27 storms ranked from tropical depression to fullblown hurricanes (9 of those) had developed in the Atlantic and were given names (the male/female naming system has been exceeded, so that the secondary system of Greek letters is now in place). Here is a map showing the names and tracks (paths) of these storms. For comparison below it is a map for 2009 hurricanes - a more normal year:
For 2005, the devastation to Atlanic and Caribbean islands, the Atlantic Coast line, and states and countries in the Gulf of Mexico is greater than any past time for which records are kept. The cost in 2005 U.S. dollars far surpasses any previous year. By far the worst destroyer is Hurricane Katrina - now rated as the worst natural weather disaster to ever beset the United States.
Before you proceed, check out these two websites: Audio-Video review of the 2005 hurricane season, made by NASA (note: the musical sound track may sound loud) and National Geographic summary of Katrina.
On August 29, 2005 and for days before and after, meteorological remote sensing experienced one of its "finest hours" as a monitoring system when the southern U.S. was subjected to arguably the worst natural disaster in North America on record. Hurricane Katrina (the second time this name was use; one called Katrina struck Central America in 1999) slammed into the Gulf Coast as a Category 4 storm (but later analysis has determined it to be a high Category 3 at New Orleans) which caused extraordinary havoc in and around the Crescent City. The death toll in Louisiana exceeded 1700 - most at and near New Orleans. Damage greatly exceeds $100 billion dollars ($55 billion covered by insurance companies), making it even more costly than Hurricane Andrew. Most of New Orleans (around 75%) was underwater for nearly a month after storm surges from Lake Pontchartrain breached several dikes, and anarchy was unfettered for several days. The effects of this massive storm, whose large size (width) accounts for huge area of devastation, have already exceeded the Category 5 Hurricane Camille in August, 1969 - reputed then to be the worst storm catastrophe as judged by the material destruction to hit the U.S Gulf Coast. Towns including New Orleans, Biloxi, and Gulfport may require years to rebuild.
On this special add-on page we will review the story of this national tragedy. First, let's establish the setting through these two images. The top one is an astronaut photo of the Gulf Coast of Louisiana and Mississippi (New Orleans is just at top center edge. The one below is a MODIS image that shows most of the areas hardest hit by Katrina; New Orleans is just below Lake Ponchartrain:
By the end of August of 2005 three significant hurricanes - Dennis, Emily, and Katrina - had hit Florida and/or the Gulf Coast. Here is their tracking history
Katrina, by far the worst of the trio, began as Tropical Depression 10 by mid-August in the tropical zone within the south-central Atlantic. (Already, with the main hurricane season still ahead through October, there have been an abnormally high number of such tropical disturbances, some developing into hurricanes such as Emily and Dennis.) That depression apparently dissipated but may have re-emerged as Tropical Depression 12, located several hundred kilometers southeast of the Bahamas. The space image below shows this depression, now named Katrina, in this area just before it became a Category 1 hurricane:
The new hurricane side-swiped the Bahamas to slam into South Florida near Miami. As it passed the Bahamas, the Quickscat satellite obtained this picture of the increasing wind velocities:
At this stage, the hurricane had yet to develop a distinct eye:
Cloud height data from TRMM is shown in the next image:
This NOAA satellite image, colored to show general ranges of wind speeds, shows Katrina had developed an eye which passed just north of Miami on August 25. Wind damage was moderate but widespread flooding inundated whole towns. Damage costs amounted to less than $2 billion; 12 lives were lost mainly by drowning.
For a while Katrina looked poorly organized and weakened as it entered the Gulf of Mexico. At first it seemed headed westward towards open Gulf water.
However, Sea Surface Temperatures (SST) were quite warm in the Gulf and steering currents began to divert Katrina's path towards a northwest, then a north trajectory.
As it moved northward, Katrina quickly intensified into a Category 2, then 3, then 4 strength hurricane. When it hit the New Orleans area, it finally had diminished to strength 3. Rainfall seen by TRMM indicated that it would be a floodmaker when it struck land.
Residents from west of New Orleans and east through Biloxi and Gulfport in Mississippi, and further east through Mobile, Alabama and Pensacola, Florida were first warned to "batten down", and then urged to begin a mass evacuation. More than three hundred thousand escaped New Orleans, spreading out northwards.
Finally, nearing land, the size of Katrina expanded and its winds topped 170 mph, making it for a short time a Category 5 hurricane. At one stage, its internal pressure reached 902 millibars, 4th lowest recorded from Atlantic storms. Evacuation on Saturday and Sunday accelerated. Here is a NOAA image of the storm at this stage.
The clouds of Katrina were impressive. The top of the next pair shows Katrina's cloud deck near its eye. The bottom indicates the front of Katrina as it passed inland over sugar cane fields:
No series of still pictures can give a "you were there" idea of the storm's fury. Those who were there attest to its frightening destruction. Here is just two that show something of the wind and rain effects on a stretch of the Gulf Coast.
Hurricane-force winds can cause direct damage, knocking over trees, smashing windows, and ripping off roofs. But they also can whip up water, creating what is known as a storm surge. Surges from Katrina established records: in several places these reached 10 meters (34 ft) and averaged 5 meters (16 ft) over the affected parts of the Gulf Coast. This map shows the surge distribution, and a picture beneath it indicates how water is raised up into destructive waves:
The storm, as it passed onto the Mississippi Delta, diminished to a category 3 and steering currents moved it just east of New Orleans, where it made landfall in the morning hours of August 29. Thereafter, it moved inland, constantly weakening, into the Tennessee and Ohio Valleys, into western New York and then Canada. The high level of damage it inflicted on the southern coast covered 237000 square kilometers (90000 square miles).
Observations made by the AIRS instrument on Aqua (see Section 16) show the temperatures of the cloud deck above Katrina as it began to dissipate. The oranges in the images indicate still considerable moisture causing the heavy rains in the central U.S. The blue shows lower temperature that correlate with the "drying out" of the central storm, hence less rainfall.
The greatest urban calamity in American history resulted from the passage of Katrina on shore. Let us set the stage for what happened to New Orleans by first reminding you of how this city appears from space (also, refer to the write-up on page 4-2). Below the space image are three maps - one giving a regional geographic perspective; the second, the central parts of the city; then a map of the Parishes (Counties) around New Orleans.
Because much of New Orleans is just below sea level, over decades a system of levees had been built up. These levees appear as maroon lines in the map below:
The writer (NMS) remembers one special feature of New Orleans from his first visit in 1952: Because of its sea level relation, and the water table in the region being so near the surface, most of the graves in New Orleans cemeteries cannot be below ground; families owned small masoleums in which individual members were entombed:
At first, the remaining residents of New Orleans - called "The Big Easy" or the "Crescent City" by the tourist interests - believed they had "dodged the bullet". Word came soon that Gulfport, Biloxi, and other Gulf towns had experienced heavy wind and water damage. There the storm surge reached 8.7 meters (29 ft), largest on record from an American hurricane.
The storm surge also affected Lake Pontchartrain. The levees coming off the lake (actually a lowlands connected to, and drowned by, the Gulf waters) started to break, spilling the top 2/3rds of a meter (two feet) of its water into New Orleans (remember, much of the city is in a topographic "bowl" just below sealevel), and eventually submerging up to 80% of its area to depths of 1 to 6 meters (3 to perhaps as much as 19 feet). These pictures show some aspects of this levee collapse, which occurred in three ways: 1. topping the structure, 2. breaching it with breaks, and 3. undermining its base.
Hundreds of photos of flooding in and around New Orleans have been published:
This aerial photo indicates the extent of flooding near the center of the city; note roof partly off the Superdome.:
This satellite image indicates how widespread the flooding was. The red arrows points to areas especially hard hit.
This map shows the extent of maximum flooding and the dikes that were breached (largely a failure of inadequate levee construction which eroded away its material as storm surge effects pressed against the structures). Note that neither the dikes along Lake Pontchartrain or the Mississippi were breached directly, only those along the canal system within the city.
The next two higher resolution (10 meters) images were obtained from NASA's EO-1 satellite. In both, flooded areas are indicated by black tones in the streets. The first image shows that the somewhat higher land in central (downtown) New Orleans remained dry - never flooded. This includes the famed French Quarter, which can trace its origin to the founding of New Orleans in 1718 when French pioneers built the first settlement on the highest ground adjacent to the Mississippi River (even in its early decades, the citizens experienced enough flooding to erect protective earthen levees). The second shows how north-central New Orleans was flooded by failure of the east 17th Street Canal dike but the west dike held up keeping that part of New Orleans from flooding.
Experts had known for years that a powerful hurricane could breach one or more of the (obviously too low and outdated) levees raised against Lake Pontchartrain and the Mississippi River. Their recommendations to upgrade these levels were ignored (in part for unwillingness to commit funding). What happened in the case of Katrina was that counterclockwise winds on the west side of the hurricane's eye (which passed just to the east) pushed water from Lake Ponchartrain against the levees from the northeast as a storm surge that topped many of the levees. Water from Lake Borgne, which lies in a swampy area, was particularly effective in inundating the Lower 9th Ward.
The Lower 9th Ward suffered the greatest damage, as shown in this aerial view and a ground photo. The Lower 9th has only been partially reoccupied since Katrina.
This cross-section explains why the French Quarter (St. Louis Cathedral, on left) and adjacent areas did not flood - they were five feet or more above sealevel. The French Quarter is where it is because the original settlers chose the high ground :
After a "mandatory evacuation" order was given on Sunday, August 28, a quarter of a million people left town. But more than 130,000 citizens of New Orleans stayed behind, some choosing not to evacuate but most without the means (such as autos) to escape on short notice. As waters rose, most of these were driven from their homes, or had to be rescued by air, or drowned. Over much of the first week, the search and rescue operations proved woefully inadequate (the "blame game" fingers all levels - federal, state, and local - for poor execution of existing plans. At the federal level, FEMA (Federal Emergency Management Agency) shouldered much of the criticism, particularly against its top management which included key decision makers with little emergency handling experience.
The famed Superdome in New Orleans was opened to shelter about 15000 people. That dome had its outer cover pealed off and some panels broken, causing roof leaks. The Superdome soon became uninhabitable and its refugees (and many at the Convention Center) were moved from New Orleans by bus. For several days, before National Guard and federal troops arrived to support the beleagured town police, looting, shooting, and other forms of anarchy ruled the passable streets. Here is the Superdome as seen by the Quickbird satellite and from the ground.