Why does the Panama Canal's Atlantic end lie west of its Pacific end?

The isthmus does not run straight north to south. At the canal's location it bends eastward, so the Pacific coast lies south and east of the Caribbean coast. A canal cutting across the narrowest point therefore runs from northwest to southeast, and the Atlantic entrance at Colón ends up west of the Pacific entrance at Panama City. The sources describe the Atlantic and Pacific labels as misleading here, because the usual association of Atlantic with east and Pacific with west does not apply at this spot. [1] [2] [3]

A 1913 book on the canal by Willis J. Abbot notes that, from Colón, the canal runs about 10 miles due south and then generally eastward toward the Pacific. It calls this contrary to the popular conception of the canal's direction and attributes it to the isthmus bending eastward at the canal, so that the Pacific is south and east of the Atlantic. [3]

One travel site describes Panama City as sitting on a peninsula that juts southward, which places it east of Colón even though it is on the Pacific side. That site presents the isthmus as curving in an S-shaped path. [4]

Wikipedia gives the Atlantic entrance as about 79°55′W and the Pacific entrance as about 79°31′W. Another site gives 79°53′W for Colón and 79°30′W for Panama City, a difference of about 23 minutes of longitude. Cruise writer Howard Hillman puts the Atlantic side about 40 kilometers (25 miles) west of the Pacific side. The sources differ slightly in their exact coordinates, depending on which point is taken as the entrance, but they agree on the direction and rough size of the offset. [1] [4] [5]

Wikipedia also notes that the Bridge of the Americas on the Pacific side is about a third of a degree east of the Colón end. Because of this geometry, the canal's passage from Atlantic to Pacific is described as northwest to southeast, and formal nautical communications use the simplified terms southbound and northbound. [1]

A Japanese space agency (JAXA) description of satellite imagery says the canal extends in a northwest-to-southeast direction for over 78 km between marking buoys, from near Colón to near Panama City. It passes through artificial Gatun Lake and Miraflores Lake, with locks at Gatun, Pedro Miguel and Miraflores. The Culebra Cut crosses the continental divide along the way. [6] [1]

Hillman frames the question as a trick question, since many people assume the Pacific end must be farther west. He says the isthmus bends northeast rather than south and that the canal is built on a southeast-to-northwest orientation. [5]