The patterns reveal how drug traffickers exploit the region’s geographic, political and economic vulnerabilities. In Honduras, the coast northeast of San Pedro Sula offers a remote, largely uninhabited rainforest that is perfect for the single-engine planes traffickers use, then hide or burn to destroy the evidence.

Image There have been two recent massacres in San Pedro Sula. Credit... The New York Times

One former smuggler said he had little trouble moving cocaine loads for years. He said he collected pound after pound from planes and then drove it by boat or car to the Guatemala border, without once being caught.

“We always got it through,” he said, withholding his full name for fear of reprisals.

Honduran officials hardly dispute such claims, saying the radar system they would need to closely track the planes would cost $30 million, and even then, they would need helicopters and other equipment to quickly intervene. The coup only made matters worse, because the Honduran military was diverted to containing street protests and American officials suspended anti-narcotics aid in response to the political crisis.

In Costa Rica, the Pacific Coast has proven just as porous. Speedboats with contraband ply the shipping lanes, according to fishermen in Puntarenas, the country’s main Pacific port. They say their radios have been crackling for years with cartel requests for food or offers of a few thousand dollars to carry drugs ashore.

That is, if the traffickers do not own the boats already. Chamber of Commerce officials in Puntarenas said that people suspected of being cartel leaders have bought at least a half-dozen fishing businesses over the past few years, coercing sales either with the barrel of a gun or by offering more than the going rate at a time when fishing yields are declining.

Mauricio Boraschi, who occupies a newly created position as Costa Rica’s drug czar, said the Mexican cartels were gobbling up any legitimate business to hide their product. “They buy everything — the farms, the means of production, the transport,” Mr. Boraschi said. “It’s all to move cocaine.”

At the small Coast Guard base in Puntarenas, most of the guardsmen admit they are outmatched. “It’s extremely frustrating,” said Pastor Reyes González, the commander. “There is not much we can do.”