Shortly after peaking in intensity, the hurricane again weakened as it underwent an eyewall replacement cycle. At 1415 UTC on September 12 Ivan passed 25 miles (40 km) south-southwest of George Town, Cayman Islands, with winds of 150 mph (240 km/h). After its eyewall became re-established Ivan attained Category 5 status for a third time early on September 13. Shortly thereafter, a trough created a weakness in the ridge to its north, causing the hurricane to turn to the northwest. The combination of the combination of enhanced outflow from the trough and very warm waters allowed Ivan to maintain Category 5 status for 30 hours. Early on September 14 the hurricane passed through the Yucatán Channel about 17 miles (28 km) southwest of Cabo San Antonio, Cuba, with the eastern portion of the eyewall crossing the western portion of the island.
After entering the southern Gulf of Mexico, Hurricane Ivan weakened to Category 4 status by 0600 UTC on September 14. As it slowly turned to the north, southwesterly flow from a large trough over the central United States increased wind shear over the hurricane. An eyewall replacement cycle, along with dry air and restricted outflow, contributed to the weakening. By late on September 14 the weakening trend ceased as the eyewall became better defined, and Ivan was expected to restrengthen a little bit over an area of warmer water temperatures. The eye diameter expanded to 60 miles (95 km/h), though concurrently westerly wind shear and dry continued to increase. As Ivan approached the Gulf Coast of the United States, Hurricane Hunters reported erosion of the southern portion of the eyewall, and cooler waters just offshore contributed to further weakening. At around 0650 UTC on September 16, Hurricane Ivan made landfall just west of Gulf Shores, Alabama, with winds of 120 mph (195 km/h); the strongest winds occurred over a narrow area near the southern Alabama and western Florida border.
Upon moving ashore, the National Hurricane Center expected the forward path of Ivan to be blocked, and accordingly forecasted the hurricane to stall in the southern Appalachian Mountains before dissipating. As the hurricane crossed Mobile Bay it turned to the north-northeast, and within twelve hours Ivan rapidly weakened to tropical storm status. The circulation became less-defined, and early on September 17 the cyclone weakened into a tropical depression over northeastern Alabama. Ivan accelerated to the northeast ahead of an approaching cold front, dropping heavy rainfall along its path. Late on September 18, the remnants of Ivan became an extratropical low as it merged with the cold front over the Delmarva Peninsula.
After becoming an extratropical low, the remnants of Ivan turned to the southeast and entered into the Atlantic Ocean, due to the building of an upper-level ridge to its east. As an extratropical cyclone, Ivan remained identifiable in both surface and upper-level data, and the system turned south and southwestward over the next few days. By September 20, the system was off the east coast of Florida, creating scattered thunderstorms; unfavorable wind shear stopped tropical redevelopment, though forecasters mentioned the possibility for more favorable conditions a few days later. On September 21 the low crossed southern Florida and emerged into the Gulf of Mexico, and as it moved across the warm waters of the region the low began to re-acquire tropical characteristics; the low-level circulation became increasingly better defined, and convection redeveloped over the center. Based on reports from Hurricane Hunters, it is estimated the low redeveloped into Tropical Depression Ivan late on September 22 while about 175 miles (280 km) south-southeast of the mouth of the Mississippi River.
In its first advisory on the re-developed cyclone, the National Hurricane Center classified the system Ivan "after considerable and sometimes animated in-house discussion of [its demise]... in the midst of a low-pressure and surface frontal system over the eastern United States... based primarily on the reasonable continuity observed in the analysis of the surface and low-level circulation." In spite of unfavorable wind shear and its disorganized cloud structure, the cyclone strengthened to tropical storm status early on September 23, based on Hurricane Hunter reports. As an area of deep convection developed over the center, Ivan reached winds of 60 mph (95 km/h), though the winds decreased as thunderstorm activity diminished. Ivan weakened to a tropical depression at 0000 UTC on September 24, and two hours later it moved ashore near Holly Beach, Louisiana.
At first, computer models forecasted the low-level circulation to turn southwestward and re-emerge into the Gulf of Mexico. However, the storm rapidly weakened over land, and by 1200 UTC on September 24 Ivan degenerated into a remnant low pressure area over southeastern Texas. The low turned to the south and the circulation dissipated early on September 25. The remnant trough reached the northwestern Gulf of Mexico later that day, producing scatter thunderstorms for a short time, before it diminished.
Ivan became the southernmost major hurricane on record after reaching Category 3 status on the Saffir-Simpson Hurricane Scale at 10.2° N. Additionally, the hurricane reached Category 4 and Category 5 status further south than any other Atlantic hurricane. At the time, Ivan was the sixth most intense Atlantic hurricane on record; but has now dropped to the tenth most intense Atlantic hurricane. Throughout its existence, Ivan kept winds of major hurricane status or greater for a total of 10 days, establishing an Atlantic hurricane record. Lasting as a tropical cyclone for a total of 450 hours, Ivan was the tenth longest tracked Atlantic hurricane on record. After making its first landfall in the United States, the hurricane spawned a total of 117 tornadoes, which is the largest tornado outbreak caused by a tropical cyclone; this broke the previous record of 115 set by Hurricane Beulah in 1967.
Tropical cyclone scales
Tropical cyclones are ranked according to their maximum winds using several scales. These scales are provided by several bodies, including the World Meteorological Organization, the National Hurricane Center, and the Bureau of Meteorology. The National Hurricane Center uses the Saffir-Simpson Hurricane Scale for hurricanes in the eastern Pacific and Atlantic basins. Australia uses a difference set of tropical cyclone categories for their region. Many basins have different names for storms of hurricane/typhoon/cyclone strength. The use of different definitions for maximum sustained wind creates additional confusion into the definitions of cyclone categories worldwide.
Gulf Shores, Alabama
Gulf Shores is a coastal city in Baldwin County, Alabama, United States. As of the 2000 census, the population was 5,044. However, since the year 2000, Baldwin County, Alabama as a whole, has experienced the second fastest rate of population growth in the state, behind only Shelby County, Alabama.
Hurricane Ivan
Hurricane Ivan was the strongest hurricane of the 2004 Atlantic hurricane season. The storm formed as a Cape Verde-type hurricane in early September, and became the ninth named storm, the sixth hurricane, and the fourth major hurricane of the year. Ivan reached Category 5 strength on the Saffir-Simpson Hurricane Scale, the highest possible category and the only one of the season. At the time it was sixth most intense Atlantic hurricane on record.