on october 20, a tropical depression formed in the caribbean sea, 170 miles (270 km) northwest of cartagena, colombia. fox is believed to have developed from a low pressure area in the intertropical convergence zone, though it was not operationally detected until october 21. the system steadily advanced northwest and it gradually intensified. on october 21, a reconnaissance mission flew into the system, reporting sustained winds in excess of 40 mph (65 km/h). at the time, the system is estimated to have strengthened to tropical storm fox. the cyclone continued to deepen, and it reached the equivalent of a category 1 hurricane on the saffir-simpson hurricane scale, 120 miles (200 km) southeast of the swan islands, honduras. the hurricane rapidly intensified and turned north on october 23, strengthening to attain winds which correspond to a modern-day major hurricane, a storm of category 3 status or higher on the saffir-simpson hurricane scale. late on october 24, the cyclone struck the small island of cayo guano del estes in the archipelago de los canarreos, south of cienfuegos. maximum sustained winds were near 150 mph (240 km/h), and the island's weather station recorded a minimum pressure of 934 mbar (27.59 inhg). the cyclone crossed the mainland coast of cuba west of cienfuegos, and it weakened as it crossed the island.