page_title: Meteorological history of Hurricane Katrina
section_title: Formation
hierarchical_section_title: Meteorological history of Hurricane Katrina / Formation
context_page_description: Hurricane Katrina was an extremely destructive Category 5 hurricane that affected the majority of the Gulf Coast. Its damaging trek 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, and was named Katrina; it proceeded to make landfall on the southern tip of the U.S. state of Florida as a minimal hurricane.
  In passing across Florida, Katrina did not attain any more strength but did manage to maintain hurricane status. After passing over Florida, the warm waters of the Gulf of Mexico allowed it to rapidly intensify to the sixth-strongest Atlantic hurricane in recorded history. Afterward, Katrina made landfall as a Category 3 storm near Buras-Triumph, Louisiana, and once more near the Mississippi/Louisiana border. Katrina progressed northward through the central United States and finally dissipated near the Great Lakes on August 31, when it was absorbed by a cold front.
context_section_description: On August 19, a tropical wave merged with the remnants of Tropical Depression Ten, the surface low of which had dissipated earlier due to the effects of a nearby upper tropospheric trough. On August 23, 2005, at 5:00 p.m. EDT (2100 UTC), this system developed into Tropical Depression Twelve over the southeastern Bahamas. 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, much more advanced system, which was then designated as Tropical Depression Twelve. Simultaneously, the trough in the upper storm 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.
caption: Tropical Storm Katrina shortly after formation on August 24 over The Bahamas.
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