Alma developed on June 4 over Central America, and while moving through Honduras, it dropped heavy rainfall that killed at least 73 people in the city of San Rafael.

Alma dropped heavy rainfall and produced winds across most of Florida, which damaged crops and caused scattered power outages.

The storm re-intensified into a hurricane over the western Atlantic Ocean, and its outer rainbands dropped heavy rainfall in Wilmington, North Carolina.

During June 1966, low atmospheric pressure stretched across the western Caribbean and Gulf of Mexico—a pattern that is conducive for tropical cyclogenesis.

On June 5, the depression crossed Honduras and emerged into the western Caribbean, moving north-northeastward through an area of warm sea surface temperatures.

It had a good cyclonic circulation, convection, and moisture content, but most significantly, a passing trough to the north provided the depression with favorable outflow.

[4] The hurricane accelerated on June 8, quickly moving across Isla de la Juventud and later mainland Cuba with winds of around 100 mph (160 km/h).

Alma did not weaken over land and entered the Gulf of Mexico, where it turned northwestward and passed between Key West and the Dry Tortugas.

[2] Late on June 8, a station in the Dry Tortugas reported winds of 125 mph (201 km/h) and a minimum barometric pressure of 970 mbar (29 inHg).

However, a conflict in observations from Dry Tortugas and a reconnaissance aircraft flight, as well as the possibility that the former experienced a mesocyclone that did not represent the intensity of the storm, led to the maximum sustained winds being adjusted to 115 mph (185 km/h) in a 2022 renalysis.

While the hurricane moved northward through the Gulf of Mexico, it had a large, ragged eye that reached 75 mi (121 km) in diameter.

[6] Cool water temperatures contributed to weakening, and Alma made landfall near Apalachee Bay with winds of 85 mph (140 km/h) on June 9.

Afterward, Alma turned to the north into an area of drier air and colder waters, and again weakened to a tropical storm on June 12.

[7] President Fidel Castro declared a state of emergency in four western provinces due to the threat to the local sugar industry.

[12] Because Alma was initially forecast to cross the central portion of the state, residents along the Florida panhandle were not adequately prepared for the hurricane.

[6] One week before a scheduled hurricane preparedness drill at Kennedy Space Center, Alma presented the facility with an actual storm threat.

A full-scale version of a Saturn V rocket was rolled back to the Vehicle Assembly Building on June 8 in less than 11 hours, which was within the anticipated time for such a move and before the expected arrival of 60 mph (97 km/h) wind gusts.

[14] During its formative stages, Alma produced heavy rainfall for several days across Central America, primarily in Nicaragua and Honduras.

Overnight on June 5, the city of San Rafael, Honduras recorded about 30 in (760 mm) of precipitation, possibly in relation to a localized cloudburst.

[1][10] On Isla de la Juventud, the combination of high winds and rains destroyed dairy facilities, chicken farms, and large areas of fruit crops.

[4][17] When Alma struck Cuba, it produced high tides in southern La Habana Province that destroyed many fishing boats and wharves.

Many of them were poorly constructed due to lack of government funding to repair the gradually deteriorating structures in the tropical climate.

[12] There was heavy structural damage across western Cuba, including in Havana, Matanzas, Camagüey, Pinar del Río, and Las Villas.