The 1970 Atlantic hurricane season officially began on May 17 and lasted until November 30. These dates conventionally delimit the period of each year when most tropical cyclones form in the Atlantic basin. The season was fairly average, with 14 named storms forming, of which seven were hurricanes. Two of those seven became major hurricanes, which are Category 3 or higher on the Saffir–Simpson scale. Also, this was the first season in which reconnaissance aircraft flew into all four quadrants of a tropical cyclone.
The first system, Hurricane Alma, developed on May 17. The storm killed eight people, seven from flooding in Cuba and one from a lightning strike in Florida. In July, Tropical Storm Becky brought minor flooding to Florida and other parts of the Southern United States, leaving one death and about $500,000 (1970 USD) in damage. The most significant storm of the season was Hurricane Celia, a Category 4 hurricane that slammed South Texas in early August. Celia resulted in about $930 million in damage and was the costliest hurricane in Texas until Alicia in 1983. There were 28 fatalities, with four in Cuba, eight in Florida, and sixteen in Texas. Later that month, Tropical Storm Dorothy caused severe flooding in Martinique, which left up to 51 deaths and $34 million in damage. One death occurred in Mexico as a result of Hurricane Ella after a house collapsed. In October, Tropical Depression Fifteen brought a devastating flood to Puerto Rico. At least 22 fatalities and $65.5 million in damage occurred. Collectively, the storms of this season left at least $1.03 billion in damage and 115 deaths.
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Season summary
The Atlantic hurricane season officially began on June 1, though activity began slightly earlier with Hurricane Alma forming on May 17. Although 21 tropical depressions developed, only fourteen of them reached tropical storm intensity. However, this was well-above the 1950–2000 average of 9.6 named storms per season. Seven of these reached hurricane status, slightly above the 1950–2000 average of 5.9. Furthermore, two storms reached major hurricane status, near the average 1950–2000 average of 2.3. Collectively, the cyclones of this season caused at least 115 deaths and over $1.03 billion in damage.
The Atlantic hurricane season officially ended on November 30, though the final tropical cyclone became extratropical on December 1.
Tropical cyclogenesis began in May, with Alma developing on May 17. No tropical cyclone activity occurred in June. Three systems originated in July, including Tropical Storm Becky and the depression that would eventually intensify into Hurricane Celia, as well as another tropical depression that remained below tropical storm intensity. Celia became the most intense tropical cyclone of the season on August 3, peaking as a Category 3 hurricane on the Saffir–Simpson scale with maximum sustained winds of 140 mph (220 km/h) and a minimum barometric pressure of . In August, four tropical systems developed, including two tropical depressions, an unnamed hurricane, and Dorothy. September eight featured tropical depressions, though only three became named storms – Ella, Felice, and Greta. October featured two unnamed hurricanes. Two more systems, a tropical depression and an unnamed tropical storm, developed in November, the latter of which transitioned into an extratropical cyclone on December 1, ending the season's activity.
The season's activity was reflected with an accumulated cyclone energy (ACE) rating of 67. ACE is a metric used to express the energy used by a tropical cyclone during its lifetime. Therefore, a storm with a longer duration will have high values of ACE. It is only calculated at six-hour increments in which specific tropical and subtropical systems are either at or above sustained wind speeds of 39 mph (63 km/h), which is the threshold for tropical storm intensity.
Systems
Hurricane Alma
An area of disturbed weather persisted over the southwestern Caribbean in the middle of May. It gradually organized, and a tropical depression formed on May 17. In response to low wind shear and warm sea surface temperatures, the depression rapidly strengthened to a tropical storm early on May 20 and to a hurricane that night. However, increasing upper-level wind shear caused Alma to deteriorate back into a tropical depression on May 22. The depression continued its general northward movement, with a brief jog to the west, and struck Cuba on May 24 with maximum winds of . As Alma crossed the eastern Gulf of Mexico, it retained a well-defined circulation with an eye feature evident on weather radar, but the persistent shear limited the system's intensity. Tropical Depression Alma made landfall near Cedar Key, Florida, on May 25 and became extratropical two days later over North Carolina.
Although Alma passed just offshore, impact in Central America, if any, is unknown. In the Cayman Islands, winds of 65 mph (105 km/h) were reported. Impact was most severe in Cuba, where flash flooding caused seven fatalities, destroyed several homes, forced the evacuation of 3,000 people in Oriente Province, and forced 16 sugar mills to suspend operations. The storm brought light rainfall to Florida, though precipitation peaked at near Miami. Thunderstorms caused one death in Miami and damaged some buildings in Fort Myers. In other states, impact came mostly in the form of rain, though a tornado near Columbia, South Carolina, unroofed one building.
Tropical Storm Becky
A large disturbance began to detach from the Intertropical Convergence Zone near Panama on July 16. By July 19, the disturbance developed into a tropical depression. After tracking through the Yucatán Channel, the depression became Tropical Storm Becky on July 20. Becky tracked northward to north-northeastward across the Gulf of Mexico and eventually strengthened to reach peak winds of 65 mph (100 km/h) late on July 20. Thereafter, upper-level winds began weakening the storm. By July 22, Becky made landfall near Port St. Joe, Florida, as a tropical depression. The storm weakened further over land, eventually dissipating over western Kentucky on the July 23.
Throughout Florida, Becky produced mostly light rainfall and gale-force winds. However, in Tallahassee, the storm dropped more than of rain, which caused flooding in and around the city. According to the Red Cross, 104 families in the Tallahassee region suffered flood-related losses. Additionally, two injuries were reported. Some houses near Tallahassee were flooded with of water, resulting in the evacuation of 15 households by rowboat. More than 100 cars in the area were also submerged. In nearby Wakulla County, knee-deep waters were reported at the county courthouse in Crawfordville. A tornado spawned near Panacea, destroyed a house and damaged two others. Light to moderate rain fell in neighboring states, and a tornado in Georgia caused one fatality and destroyed two homes.
Hurricane Celia
A tropical wave emerged into the Atlantic Ocean from the west coast of Africa on July 23. It moved rapidly westward and reached the western Caribbean Sea by July 30. On the following day, the system developed into a tropical depression near Grand Cayman. The depression tracked north-northwestward and intensified into a tropical storm just prior to crossing far western Cuba on August 1. Due to warm sea surface temperatures, Celia soon intensified into a hurricane late on August 1 over the Gulf of Mexico. However, the storm failed to strengthen beyond Category 1 status until reaching the northwest Gulf of Mexico on August 3. Celia then underwent rapid intensification and at 21:00 UTC, the storm peaked as a Category 4 hurricane with sustained winds of 140 mph (220 km/h) and a minimum pressure of as it made landfall near Corpus Christi, Texas. Celia weakened while moving inland and dissipated over New Mexico late on August 5.
In Cuba, heavy rains on the island caused severe flooding, leading to five fatalities. Storm surge and swells lashed the west coast of Florida, especially the Panhandle. Several life guard rescues occurred, while eight people drowned. In Louisiana, abnormally tides caused minor coastal flooding. The strongest sustained wind speeds in Texas were around , while winds gusts were estimated to have reached as high as in Nueces County. Much of the damage was caused by a series of microbursts and downbursts, most of which occurred in a 15-minute span. Severe damage was reported in Nueces County, with 85% of Celia's total property losses caused in Corpus Christi alone. Approximately 90% of downtown buildings were damaged or destroyed, while about one-third of homes in the city suffered severe impact or were demolished. Throughout the state, 8,950 homes were destroyed and about 55,650 others were damaged. About 252 small businesses, 331 boats, and 310 farm buildings were either damaged or destroyed. In Texas, Celia caused 15 deaths and $930 million in damage.
August hurricane
A tropical depression developed off the west coast of Africa on August 7, with organized convection and banding features. A day later, the depression passed south of Cabo Verde as it moved across the tropical Atlantic. On August 10, it intensified into a tropical storm, after the thunderstorms became more concentrated. However, a Hurricane Hunters flight two days later observed a weak system, suggesting the storm weakened back to a tropical depression. While approaching the Lesser Antilles, the depression turned to the northwest and re-intensified back into a tropical storm, with hurricane-force wind gusts north of the center. Late on August 14, the circulation opened into a trough. On August 15, a circulation reformed, and the system became a tropical depression again as it bypassed the eastern Bahamas. A day later, the system re-intensified into a compact tropical storm while turning northward. On August 17, the storm made landfalls along the Outer Banks of North Carolina, first on Atlantic Beach and later at Rodanthe. As the storm accelerated northeastward, it intensified into a hurricane, with peak winds of 80 mph (130 km/h), based on the well-defined eye and a report from a nearby ship. On August 18, the system became extratropical south of Newfoundland, and subsequently it slowed and shifted its track back to the south, only to resume an easterly track on August 21. Late on August 24, the former hurricane dissipated north of the Azores.
Along the coast of North Carolina, higher than normal tides capsized about 20 boats, including a yacht. At Salvo, where the tide may have reached above normal, boardwalks and camping equipment were damaged at the campgrounds. Heavy squalls produced winds as strong as 75 mph (120 km/h) in Atlantic Beach. Minor wind damage was reported in Atlantic Beach and Morehead City, primarily limited to some trees, power lines, roof shingles, television antennas, and signs. From North Carolina to Maryland, lifeguards made dozens of rescues. Four drowning deaths occurred, with two in North Carolina and two in Virginia.
Tropical Storm Dorothy
A tropical wave moved off the western coast of Africa on August 13. Moving westward, a tropical disturbance spawned by the wave led to the formation of a tropical depression beginning east of the Lesser Antilles on August 18. As it moved west-northwestward, it slowly intensified, and was upgraded to Tropical Storm Dorothy several hours later. Around 06:00 UTC on August 20, Dorothy attained its peak intensity with maximum sustained winds of , several hours before striking Martinique. After passing through the Lesser Antilles, Dorothy moved under an upper-level cold-core trough, which generated stronger wind shear and caused the storm to weaken. Early on August 22, Dorothy degenerated into a trough south of Puerto Rico.