Benjamin Franklin was the first scientist to study and map the Gulf Stream, measuring wind speeds and current depths, speeds, and temperatures during four crossings of the Atlantic in the late 18th century. More than 300 years later, scientists are still probing the secrets of that "river" of warm water flowing north from the West Indies, along the East Coast of North America, and east across the Atlantic to Europe.
The US Minerals Management Service recently released a study of the Loop Current (LC) and Loop Current Eddies (LCEs) in the eastern gulf aimed at better forecasting the effect on hurricanes and oil and gas activity in deep waters.
The LC and hurricanes
Part of the Gulf Stream, the horseshoe-shaped LC flows clockwise, transferring warm subtropical waters from the Caribbean through the Yucatan Straits into the Gulf of Mexico. It then loops west and south before exiting to the east through the Florida Straits. The deepest levels of warm water in the gulf are associated with the LC. The current meanders in its journey, sometimes penetrating deeper into the gulf, sometimes less, and the temperature of its waters is sometimes higher than at other times.
Random eddies or LC "rings" occasionally separate from the LC and slowly drift west to splash upon the shores of Texas or Mexico. The current and its eddies can be determined by measuring the level of the sea's surface. The flow is somewhat higher than the surrounding ocean waters because of the warm water it carries. On Sept. 21, 2005, the surface level of the LC and eddies was 24 in. above surrounding waters when Hurricane Rita intensified to Category 5 strength as it passed over those warmer waters.
The LC apparently has stimulated some of the biggest storms ever to blow through the gulf. In 1969, Camille was already a Category 3 hurricane when it rounded the western tip of Cuba and charged north directly over the LC, rapidly intensifying into the top Category 5 on the Saffir-Simpson Hurricane Scale before smashing into Mississippi. Hurricane Allen ramped up to Category 5 over the current but weakened over cooler waters before it hit Texas in 1980. Hurricane Andrew crossed the LC and grew into a Category 5 storm before it smashed into Florida in 1992.
In 1995, Hurricane Opal escalated from Category 1 to Category 4 in 14 hr after encountering a warm-water eddy. That's when meteorologists first recognized the pivotal role of warm water in strengthening hurricane intensity, according to an Oct. 4, 2005, online article in Science Daily.
Hurricane Ivan—the 10th most intense Atlantic hurricane ever recorded—twice crossed the LC in 2004, growing to the size of Texas over those warm waters. In 2005 when the LC extended deep into the gulf, it boosted Hurricanes Katrina and Rita, respectively, to the sixth and fourth-strongest storms ever, and it jacked up the weaker Hurricane Wilma to a Category 3 before it blew into Florida that same year.
In 2008, Hurricane Gustav encountered the current, but the LC was shorter and cooler that year with cooler gulf waters between it and Louisiana, so the storm remained Category 3.
After Hurricane Katrina and a week before Hurricane Rita, scientists deployed various technologies in the gulf to measure salinity, currents, and water temperature to 3,300 ft in another study aimed at determining the paths and intensity changes of hurricanes in their last hours over open water.
Latest study
The latest 2-year study by MMS in conjunction with Louisiana State University's Coastal Marine Institute involved deployment in the eastern gulf of an 11,800-ft deepwater mooring cable to supplement information gathered from a previous 3-year deployment. The mooring data suggest the LC and LCEs that dominate upper-layer circulation in the eastern gulf also influence the deeper currents in those water.
Alexis Lugo-Fernandez, the MMS physical oceanographer responsible for the study, noted that a method to transmit significant energy in the form of heat to deep water in the gulf during the 2005 hurricane season was observed during this study.
As sea levels rise near the center of tropical storms, the resulting higher pressure causes a small but measurable increase in temperature at all water depths. Lugo-Fernandez said, "Simply due to the large number of storm occurrences within the [gulf], these findings represent an important process for transmitting energy to the deep water."
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