The loop current is an area of warm water that travels up from the Caribbean, past the Yucatan Peninsula, and into the Gulf of Mexico. The current is also known as the Florida current as it flows through the Florida Strait, into the Gulf Stream, and heads north up the eastern coast of the U.S.
From the south, the Gulf of Mexico is fed by a current of warm water from the Caribbean, which enters the Gulf between Mexico's Yucatan Peninsula and Cuba. This forms the Gulf Loop Current, which curves east and south along Florida's coast and exits through the Straits of Florida.
The Gulf Loop is variable. Sometimes, the current barely enters the Gulf of Mexico before heading towards the Atlantic. At other times, it may travel nearly to the coast of Louisiana before swinging back towards the Florida Strait.
For more information:
Center for Operational Oceanographic Products and Services
National Current Observation Program
Diving Deeper Podcast, Episode15 (August 12, 2009) - What are currents?
Currents Tutorial, NOS Education
Original article: What is the Loop Current?