Meteorological History of Hurricane Katrina - Gulf of Mexico

Gulf of Mexico

The initial National Hurricane Center 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.

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 (the first in the Gulf of Mexico since Hurricane Allen 25 years prior) 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). As the hurricane approached New Orleans, the Weather Forecast Office in Slidell, Louisiana issued two strongly worded warnings of the storm's danger.

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 center 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 center 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 feet (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 on the Saffir-Simpson Hurricane Scale. The waves then combined with the storm surge of the large Category 3 hurricane.