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Meteorological history of Hurricane Katrina

2007 Schools Wikipedia Selection. Related subjects: Natural Disasters

   The path of Hurricane Katrina.
   Enlarge
   The path of Hurricane Katrina.
            Hurricane Katrina

   2005 Atlantic hurricane season

   General
     * Timeline
     * Meteorological history
     * Preparations
          + New Orleans preparedness

   Impact
     * Economic effects
     * Political effects
     * Criticism of gov't response
     * Social effects
     * Effects by region
          + Effects on Mississippi
          + Effects on New Orleans
               o Levee failures
               o Infrastructure repairs
               o Reconstruction

   Relief
     * Disaster relief
     * International response

   Analysis
     * Alternative theories
     * Historical context
     * Media involvement

   Other wikis
     * Commons: Katrina images
     * Wikinews: Katrina stories
     * Wikisource: Katrina sources

   The meteorological history of Hurricane Katrina, an extremely
   destructive Category 5 hurricane, began on August 23, 2005 when it
   originated as Tropical Depression Twelve near the Bahamas. The next
   day, the tropical depression strengthened to a tropical storm,
   receiving the name Katrina; then, it proceeded to make landfall on
   southern Florida as a minimal hurricane.

   After passing through Florida, Katrina weakened back to a tropical
   storm; however, the warm waters of the Gulf of Mexico allowed it to
   rapidly intensify to the sixth strongest Atlantic hurricane in history.
   Afterwards, Katrina made landfall as a Category 3 storm near
   Buras-Triumph, Louisiana, and once more near the Mississippi/ Louisiana
   border.

   Following its landfall, Katrina progressed up through the central
   United States and finally dissipated near the Great Lakes, when it was
   absorbed by a cold front.

Formation

   Tropical Depression Twelve formed over the southeastern Bahamas at 5:00
   p.m. EDT (2100 UTC) on August 23, 2005, partially from the remains of
   Tropical Depression Ten, which had dissipated due to the effects of a
   nearby upper tropospheric trough. While the normal standards for
   numbering tropical depressions in the Atlantic indicate that the old
   name/number is retained when a depression dissipates and regenerates,
   satellite data indicated that a second tropical wave combined with
   Tropical Depression Ten north of Puerto Rico to form a new system,
   which was then designated as Tropical Depression Twelve.
   Simultaneously, the trough in the upper troposphere weakened, causing
   the wind shear in the area to relax, thereby allowing the new tropical
   depression to develop. In a later re-analysis, it was determined that
   the low-level circulation of Ten had completely detached and
   dissipated, with only the remnant mid-level circulation moving on and
   merging with the aforementioned second tropical wave. As a result, the
   criteria for keeping the same name and identity were not met.

First landfall

   Katrina just before its first landfall
   Enlarge
   Katrina just before its first landfall

   As the atmospheric conditions surrounding Tropical Depression Twelve
   were favorable for tropical development, the system began to intensify
   and was upgraded to Tropical Storm Katrina on the morning of August 24.
   A burst of convection allowed Katrina to become the fourth hurricane of
   the 2005 season on August 25, only two hours before it made landfall
   around 6:30 p.m. EST (2230 UTC) between Hallandale Beach and Aventura,
   Florida. Katrina struck the peninsula with 80  mph (130  km/h) winds,
   and had a well-defined eye on Doppler radar, which remained intact
   throughout its passage over Florida. The storm weakened over land on
   August 26 to a tropical storm, but regained strength to hurricane
   status at 2:00 a.m. EDT (0600 UTC), approximately one hour after ending
   its passage through Florida and entering the Gulf of Mexico. Parts of
   the Florida Keys experienced tropical storm winds throughout August 26,
   with the Dry Tortugas briefly experiencing hurricane-force winds.

Gulf of Mexico

   The initial National Hurricane Centre forecasts predicted that Katrina
   would begin turning northward after landfall, eventually to hit the
   Florida Panhandle approximately three to four days later. Katrina,
   however, continued a westerly and west-southwesterly track, which
   eventually shifted the forecast track westward to New Orleans.
   Hurricane Katrina encountering the Gulf Loop Current.
   Enlarge
   Hurricane Katrina encountering the Gulf Loop Current.

   Immediately after the storm entered the Gulf of Mexico, the low wind
   shear, good upper-level outflow, and the warm sea surface temperatures
   of the Gulf Loop Current caused Katrina to intensify rapidly. On August
   27, the storm was upgraded to Category 3 intensity, becoming the third
   major hurricane of the season. An eyewall replacement cycle disrupted
   the intensification of maximum winds for about 18 hours, but almost
   doubled the radius of the storm. A second period of rapid
   intensification started by 7:00 p.m. CDT on August 27, and by 12:40
   a.m. CDT on August 28, Katrina was upgraded to a Category 4 hurricane
   with maximum sustained winds of 145 mph (233 km/h). It became a
   Category 5 storm by 7:00 a.m. CDT, twelve hours after the beginning of
   the second round of rapid intensification, and reached its peak
   intensity at 1:00 p.m. CDT with maximum sustained winds of 175 mph
   (280 km/h), gusts of 215 mph (344 km/h) and a central pressure of 902
   mbar (26.64  inHg). The minimum pressure made Katrina, at the time, the
   fourth most intense Atlantic hurricane on record (Hurricanes Rita and
   Wilma would later surpass Katrina that same year).

   By the afternoon of August 28, the storm was large enough that some
   areas of the Gulf Coast were already experiencing tropical storm-force
   winds. The centre of Katrina was about 180  statute miles (290 km) from
   the mouth of the Mississippi River, but tropical storm-force winds
   extended 230 mi (370 km) from the centre of the storm, and
   hurricane-force winds extended about 105 miles (170 km) away. Overnight
   on August 29, and into the morning of the next day, Katrina quickly
   weakened (in terms of maximum sustained winds) as it began to enter
   another eyewall replacement cycle. The inner eyewall deteriorated
   before an outer eyewall had fully formed, playing an important role in
   the weakening. In 18 hours, the hurricane's maximum sustained winds
   decreased from 170 mph (280 km/h) to 125 mph (205 km/h). However, storm
   surge remained high at landfall because large waves greater than 30 ft
   (9.1 m) in height were generated beforehand (with a buoy recording a
   55 ft/16.7 m wave at sea), when Katrina was at Categories 4 and 5 in
   the Saffir-Simpson Hurricane Scale. The waves then combined with the
   storm surge of the large Category 3 hurricane.

Second and third landfalls

   Hurricane Katrina on August 28 at 1:00 p.m. EDT.
   Enlarge
   Hurricane Katrina on August 28 at 1:00 p.m. EDT.

   Katrina made its second landfall at 6:10 a.m. CDT on August 29 as a
   Category 3 hurricane with sustained winds of 125 mph (205 km/h) near
   Buras-Triumph, Louisiana. At landfall, hurricane-force winds extended
   120 miles (190 km) and the storm's central pressure was 920 mbar
   (27.17 inHg). Because Katrina had just weakened from Category 4 and due
   to the shape of the coastline, sustained Category 4 winds likely
   existed on land while the eye was over water. At landfall,
   hurricane-force winds extended 120 miles (190 km) from the centre, the
   storm's pressure was 920 mbar (27.17 inHg), and its forward speed was
   15 mph (10 km/h). Making its way up the eastern Louisiana coastline,
   most communities in Plaquemines, St. Bernard Parish, and Slidell in St.
   Tammany Parish were severely damaged by storm surge and the strong
   winds of the eyewall, which also grazed eastern New Orleans.

   Original estimates indicated that Katrina had made this landfall as a
   Category 4 hurricane, with 135 mph (220 km/h) winds; however, as
   indicated above, the storm weakened just before landfall to Category 3
   intensity. The reasons behind this weakening are not completely known
   yet; while the eyewall replacement cycle played a part,
   slightly-increasing shear, dropping sea surface temperatures, dry air
   on the western semicircle of the storm and interaction with the
   continental landmass also may have played a role in weakening the
   cyclone. This follows the trend of previous strong cyclones in the Gulf
   of Mexico: all cyclones with minimum central pressures of 973 mbar
   (28.73 inHg) or less have weakened in the last 12 hours before making
   landfall in the Gulf Coast of the United States.

   A few hours later, after weakening slightly, Katrina made its third
   landfall near the Louisiana/Mississippi border with 120 mph (195 km/h)
   sustained winds and 928 mbar (27.37 inHg) pressure, still at Category 3
   intensity. Its minimum pressures at its second landfall was 920 mbar
   (27.17 inHg), making Katrina the third strongest hurricane on record to
   make landfall on the United States, behind Hurricane Camille's 909 mbar
   (26.85 inHg) reading in 1969, and the 1935 Labor Day Hurricane's
   892 mbar (26.35 inHg) record.
   Radar image of Hurricane Katrina making its second and third landfalls.
   Enlarge
   Radar image of Hurricane Katrina making its second and third landfalls.

   Because the storm was so large, extremely-damaging eyewall winds and
   the strong northeastern quadrant of the storm pushed record storm
   surges onshore, smashing the entire Mississippi Gulf Coast, including
   towns in Mississippi such as Waveland, Bay St. Louis, Pass Christian,
   Long Beach, Gulfport, Biloxi, Ocean Springs, Gautier and Pascagoula,
   and, in Alabama, Bayou La Batre. The surges peaked at 28 ft (8.5 m) in
   Bay St. Louis, Mississippi, and at 13 ft (4.0 m) as far away as Mobile,
   Alabama, which saw its highest storm surge since 1917. Storm surge was
   particularly high due to the hydrology of the region, the hurricane's
   extreme size, and the fact that it weakened only shortly before
   landfall. As Katrina moved inland diagonally over Mississippi, high
   winds cut a swath of damage that affected almost the entire state.

Demise

   Hurricane Katrina following its third landfall, but still at hurricane
   strength, over southern Mississippi
   Enlarge
   Hurricane Katrina following its third landfall, but still at hurricane
   strength, over southern Mississippi

   Katrina maintained hurricane strength well into Mississippi, but
   weakened thereafter, losing hurricane strength more than 150 mi
   (240 km) inland, near Meridian, Mississippi. It was downgraded to a
   tropical depression near Clarksville, Tennessee and broke in half. One
   half continued to race northward, affecting the Central United States
   along its path, and was last distinguishable in the eastern Great Lakes
   region on August 31. On August 31, Katrina was absorbed by a frontal
   boundary and became a powerful extratropical low, causing 1.97-6.69 in
   (50-170 mm) of rain in 12 hours, as well as gale-force wind gusts from
   31 to 61 mph (50 to 98 km/h) in southeastern Quebec and northern New
   Brunswick. In the region of Saguenay and Cote-Nord, rain caused
   breakdowns and failure in roads. The Cote-Nord region was isolated from
   rest of Quebec for at least 1 week. The other half of Katrina broke off
   in the eastern part of the Appalachians, primarily leading to a
   significant tornado outbreak in the area from central Georgia to
   central Pennsylvania, killing two people and causing millions of
   dollars in additional damage.

   At 11:00 p.m. EDT on August 31, the centre of the remnant low of what
   was Katrina had been completely absorbed by a frontal boundary in
   southeastern Canada, with no discernible circulation.

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