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Why does the Gulf Stream follow the eastern coast of the United States?

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Map of the North Atlantic Ocean showing major ocean currents, with warm currents like the Gulf Stream and North Atlantic Drift highlighted in pink and cold currents in blue. Arrows indicate current directions and relative speeds, connecting the eastern coasts of North America, the western coasts of Europe and Africa, and the Arctic region. — Gulf Stream Major warm and cold currents of the North Atlantic Ocean.

The Gulf Stream follows the eastern coast of the United States as part of a large-scale, clockwise-rotating subtropical gyre in the North Atlantic ocean.12

Its position along the North American continental margin is primarily due to a phenomenon known as westward intensification. This occurs because the Coriolis force—the force resulting from Earth's rotation—increases with latitude. As the oceanographer Henry M. Stommel explained, this variation in the Coriolis force causes the poleward-flowing western boundary currents of subtropical gyres to become narrow, intense, and jetlike.3

Additionally, the formation of a deep "lens" of warm, saline North Atlantic Central Water creates a horizontal pressure gradient. The interaction between this pressure gradient and the Coriolis force results in a geostrophic current that flows along the continental slope of North America. The current maintains this path until it reaches Cape Hatteras, where it separates from the continental margin and turns northeastward into the open ocean.13