After becoming a tropical storm, Greta intensified slowly due to a strong trough to the northwest, and with the South American coastline located to the south, the southerly inflow was disrupted. With a ridge to the north along the 30th parallel, the storm moved quickly west-northwestward across the Caribbean. On September 16, Greta intensified into a hurricane about south of Jamaica. Shortly thereafter, the trough to the northwest weakened, which had been preventing the storm's intensification. An increasingly well-defined eye developed while approaching the coast of Honduras as the barometric pressure quickly dropped. Early on September 18, the eyewall passed just offshore Cabo Gracias a Dios, the sparsely populated border between Honduras and Nicaragua The NHC described the eye as having "literally ricocheted off of the protruding northeast coast of Honduras", thus sparing much of the country from the strongest winds. At 0710 UTC on September 18, the Hurricane hunters observed a minimum pressure of just off the northern Honduras coast, which was the basis for the estimated peak intensity of . This made it a Category 4 hurricane on the Saffir–Simpson scale.
