1947 Florida–Georgia hurricane

The 1947 Florida–Georgia hurricane (Air Weather Service designation: King ) was a moderate hurricane that caused catastrophic flooding in South Florida and the Everglades in mid-October 1947. The ninth tropical storm and fourth hurricane of the 1947 Atlantic hurricane season, it first developed on October 9 in the southern Caribbean Sea and hence moved north by west until a few days later it struck western Cuba. The cyclone then turned sharply to the northeast, accelerated, and strengthened to a hurricane, within 30 hours crossing the southern Florida peninsula. Across South Florida, the storm produced widespread rainfall of up to 15 in and severe flooding, among the worst ever recorded in the area, that led to efforts by the United States Congress to improve drainage in the region.

Once over the Atlantic Ocean on October 13, the storm made history when it was the first to be targeted for modification by government and private agencies; dry ice was spread by airplanes throughout the storm in an unsuccessful effort to weaken the hurricane, though changes in the track were initially blamed upon the experiment. On the same day as that of the seeding, the cyclone slowed dramatically and turned westward, making landfall on the morning of October 15 south of Savannah, Georgia. Across the U.S. states of Georgia and South Carolina, the small hurricane produced tides up to 12 ft and significant damage to 1,500 structures, but the death toll was limited to one person. The system dissipated the next day over Alabama, having caused $3.26 million in losses along its path.

Meteorological history
At 18:00 UTC on October 8, a tropical depression developed in the Intertropical Convergence Zone about 65 miles (105 km) west-northwest of Isla de Providencia, Colombia, near 13.5°N, -82.3°W. Moving generally west of due north, the depression gradually strengthened, becoming a tropical storm a day later. At 15:30 UTC on October 10, the Hurricane Hunters—reconnaissance aircraft—first intercepted the storm, registering a pressure of 1000 mb, which suggested maximum sustained winds of 54 mph (87 km/h). Afterward, the storm began curving east of due north, while nearing the island of Cuba. At 07:00 UTC October 11, the deepening tropical cyclone made landfall near La Coloma, Pinar del Río Province, with winds of 65 mph (100 km/h). After crossing the western portion of the island, the cyclone underwent robust intensification over the southeastern Gulf of Mexico, with most of its strengthening occurring in under four hours. At 17:16 UTC aircraft entered the eye of the storm and measured a pressure of 983 mb, which corresponded to winds of 85 mph (140 km/h), making the storm equivalent to a Category 1 hurricane on the present-day Saffir–Simpson scale. The cyclone then angled sharply northeastward, passing near the Dry Tortugas en route to peninsular Florida. At 02:00 UTC on October 12, the hurricane impacted Southwest Florida north of Cape Sable with a slightly stronger intensity of 975 mb, along with winds of 90 mph (150 km/h); the estimated pressure was based on a barometric measurement of 29.00 inHg taken at 07:00 UTC in Fort Lauderdale, on the edge of the eye, that was "'still falling'" at the time. Then a smaller-than-average storm, it crossed the mostly uninhabited Everglades and passed over the Miami metropolitan area between Fort Lauderdale and Pompano Beach.

Shortly before 08:00 UTC it entered the Atlantic Ocean near Hillsboro Inlet Light, which experienced the center of a hurricane for the second time in a month, with winds of 80 mph (130 km/h). After leaving South Florida, the hurricane passed north of the Bahamas while gradually weakening. By 00:00 UTC on October 13, the cyclone degenerated into a strong tropical storm, but regained hurricane status 12 hours later. Over the next day, the storm slowed substantially and began veering landward, executing a semicircular turn northward and westward, a trajectory that threatened the Southeastern United States. During the night of October 13–14 a dearth of in-situ observations prevented forecasters from appraising its exact location and movement. At this time reconnaissance aircraft penetrating the storm reported winds of up to 55 kn, and data from the aircraft suggested the ill-defined center "split in two". The secondary center meandered westward and became dominant on October 14, while slowly consolidating and intensifying. Late that day aircraft reported peak winds of 80 kn in the storm. At 00:00 UTC on October 15, the cyclone intensified into the equivalent of a low-end Category 2 hurricane, and began accelerating westward toward Georgia. Six hours later it attained its peak of 105 mph (165 km/h), which it maintained until landfall around 11:00 UTC near Ossabaw Island, approximately 15 mi south of Savannah. The lowest pressure in the eye at landfall was estimated to have been near 965 mb, based in part on a report from a ship just offshore more than eight hours earlier. At the time, the coverage of hurricane-force winds was small, extending about 20 mi in all directions from the eye. The storm weakened rapidly as it crossed inland over Georgia, and by 00:00 UTC on October 16 it weakened to a tropical storm, dissipating 18 hours later over Alabama.

Preparations
On October 10, watercraft in the Straits of Florida, the northwestern Caribbean, and the Yucatán Channel were advised to proceed cautiously. The steamship Florida, bound for Havana, was forced to discontinue its excursion. The next day tropical storm warnings were posted between Fort Myers and Miami, Florida. By 19:00 UTC, the United States Weather Bureau issued hurricane warnings between Punta Gorda and Key West. On October 12, warnings were extended from the Miami metropolitan area to Vero Beach. A pair of 75-car trains were dispatched to evacuate the Lake Okeechobee area. Airline traffic out of Jacksonville was halted, and several hundred vessels sought shelter in the Miami River. Owing to short notice of the storm, only an estimated 10% of businesses in Miami had erected shutters.

Cuba and Florida
In Cuba, the cyclone generated gust of up to 57 mph at Batista Field, near Havana.

Upon striking southernmost Florida, the cyclone only produced $75,000 in wind-related losses, largely due to its having struck an area hit by the more powerful September hurricane. Peak winds in Florida were unofficially estimated to have reached 95 mph around Cape Sable, the area where the storm made landfall. At the Dry Tortugas, wind instruments reported readings up to 84 mph before failing due to "'friction from lack of oil'"; higher winds, unofficially estimated to have reached 150 mi/h, were believed to have occurred thereafter. An elevated anemometer at the Dry Tortugas Light, on Loggerhead Key, measured gusts of 125 to 140 mi/h prior to its destruction. An observer at Fort Jefferson reported that the winds lofted small pine trees. Elsewhere in South Florida, the U.S. Weather Bureau Air Station at Miami International Airport reported sustained winds of 80 mph, while the Weather Bureau Office in downtown Miami recorded peak winds of 62 mph. In the 7 mi distance between the two stations, atmospheric pressure varied 3 mb, but the lowest pressure was not below 995.3 mb. Region-wide, the hurricane produced significant rainfall totals of 5 in to 12 in—and, in the interior, locally as high as 15 in—causing severe flooding. The highest measured rainfall total in 24 hours in South Florida was 14.2 in in northeastern Broward County. On the morning of October 12 the Weather Bureau office in Miami measured 3.77 in in just a few hours, most of which fell in 20 minutes, eclipsing the previous daily record of 1.18 in. The deluge submerged stores and flooded hundreds of vehicles in Downtown Miami, rendering streets "virtual canals". At a weather observation site in Hialeah, 1.32 in of rain fell in as little as 10 minutes. In all, as much as 6 in fell in just 1¼ hour in the city; due to saturated ground preceding the arrival of the storm, much of the area flooded easily, leaving parts of the city submerged under 6 ft of water. Similarly, "waist deep" depths were reported in nearby Miami Springs, Opa-locka, rural western sections of Pompano Beach, and many other cities of the Miami metropolitan area. In Boca Raton, homes in the historic Old Floresta district that housed Army Air Field soldiers were flooded in up to 8 in of water. In the wake of the flooding in his city, Hialeah City Mayor Henry Milander blocked access from surrounding cities. In the Miami area, the Little River and the Seybold Canal overflowed, as did the New River once again in Fort Lauderdale, which had previously done so during the September hurricane. During the storm, up to 11 in of rain in three hours were reported to have fallen on the city of Fort Lauderdale, and sections of Broward County were under 8 ft of water. Floodwaters inundated the Tamiami Trail between the Miami metropolitan area and Everglades City. Due to the floods, septic tanks overflowed, leaving canal banks and patches of ground isolated by floodwaters; reportedly, U.S. Route 1, locally called Federal Highway and built largely upon the Atlantic coastal ridge—the highest elevation in South Florida—was flooded out between Miami and Fort Lauderdale. Having been isolated by the floods, deer, rattlesnakes, and other wildlife, along with horses and cattle, sought shelter upon the remaining exposed ground, particularly levee banks.

The flooding that resulted from the storm and the earlier September hurricane was among the worst ever recorded in South Florida and became known as the "Flood of 1947" or, as the South Florida Sun-Sentinel newspaper in 1990 called it, "the Great South Florida Flood." The rains from the storms followed an abnormally wet rainy season in the spring of 1947 that raised the water table to dangerous levels and by July forced several emergency meetings by the Everglades Drainage District (EDD) to address widespread flooding. Despite the measures, which resulted in the opening of floodgates to relieve flooded farmlands by diverting water through back-pumping to Lake Okeechobee, lack of funding hampered efforts by EDD Chief Engineer Lamar Johnson to address the situation. After the October hurricane struck Florida, eleven counties extending south from Osceola County were at least 50% flooded —roughly 90% of the land mass from Orlando to the Florida Keys. South of Lake Okeechobee, a 20 to 40 mi, 1/2 to 10 ft sheet of standing water inundated much of the region, including the Everglades. In the region, 5,000,000 acre of land were flooded as abnormally high coastal tides prevented water from being released through canals to the Atlantic Ocean. The flooding divided many communities: near Fort Lauderdale, a temporary dam that had been erected by the U.S. Army Corps of Engineers to protect Davie—a town in which 90% of the homes by the end of October were at least partially submerged —lowered waters in some areas but merely diverted them to others, flooding a neighborhood and leading to angry complaints by residents; the situation worsened after the October hurricane produced even more rain over flooded South Florida.

The storm also generated many tornadoes in South Florida. One of the twisters downed trees and damaged a home at Redlands. Another, estimated to have been an F2, unroofed a pair of homes in Miami.

Georgia and South Carolina
Upon making landfall, the storm produced high tides of up to 12 ft at Parris Island, South Carolina, and 9 ft at Charleston, South Carolina. Up to 1,500 or more buildings were significantly damaged due to wind gusts that reached 95 mph at Savannah, Georgia. One person died due to high tides preceding the storm. Total property losses in Georgia and South Carolina reached $2,185,000 (1947 USD).

Aftermath
In South Florida, the flooding from the September and October hurricanes led to the creation in 1949 of what is now the South Florida Water Management District, which under a Congressional plan was entrusted with the task of preventing a recurrence of significant flooding by forming an improved flood-control system to modulate the water table and by providing suitable water levels with which to water crops, prevent saltwater intrusion, and support recreational opportunities as well as the growing South Florida communities. Large pumping systems were constructed, along with numerous new levees and canals, to mitigate the risk of large-scale flooding, yet population growth since the late 1940s is believed to have reduced the extent of vacant lands needed for effective drainage, thereby increasing the risk of damage during a flood similar to that of 1947. In his 1974 book Beyond the Fourth Generation, former EDD Chief Engineer Lamar Johnson voiced his concerns about large-scale development near the levees, which separate the Everglades water conservation areas from the Miami metropolitan area. Johnson wrote, "It is my opinion...that anytime that area gets a foot or more of rainfall overnight, the shades of 1947's flood will be with them again."

The cyclone was historically significant in that it was the first tropical cyclone to be modified as part of a multi-year operation called Project Cirrus. In July 1946, General Electric (GE) scientists concluded after experimentation that dry ice seeding could induce heavy rainfall and thus ultimately weaken storms by cooling temperatures in the eye. To undertake Project Cirrus, GE, the United States Army Signal Corps, the Office of Naval Research, and the U.S. Weather Bureau functioned jointly on research and planning. A pair of B-17s and a B-29 of the Hurricane Hunters were dispatched from MacDill Air Force Base. Early on October 13, 1947, 200 lb of dry ice were dropped throughout the storm, then located about 350 mi east of Jacksonville, Florida. While the appearance of the clouds changed, the initial results of the seeding were inconclusive. Shortly after the seeding took place, the hurricane turned sharply toward the Southeastern United States. While the move the leading GE scientist, Irving Langmuir, later blamed upon the seeding, subsequent examination of the environment surrounding the storm determined that a large upper-level ridge was in fact responsible for the abrupt turn, which imitated that of a hurricane in 1906.