The Atlantic hurricane season officially began on June 1, though activity began slightly earlier with Hurricane Alma forming on May 17. Although 23 tropical depressions developed, only ten of them reached tropical storm intensity; this was normal compared to the 1950–2000 average of 9.6 named storms. Five of these reached hurricane status, slightly under 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 October 28.
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, the depression that would eventually intensify into Hurricane Celia, and 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 125 mph (205 km/h) and a minimum barometric pressure of 945 mbar (27.9 inHg). In August, four tropical systems developed, including an unnamed tropical storm, Dorothy, and three other tropical depressions. September eight featured tropical depressions, though only three became named storms – Ella, Felice, and Greta. Two unnamed hurricanes developed in October, the second of which became an extratropical cyclone on October 28.
The season's activity was reflected with an accumulated cyclone energy (ACE) rating of 40. ACE is, broadly speaking, a measure of the power of the hurricane multiplied by the length of time it existed, so storms that last a long time, as well as particularly strong hurricanes, have high ACEs. It is only calculated for full advisories on tropical systems at or exceeding 39 mph (63 km/h), which is tropical storm strength.
An area of disturbed weather persisted over the southwestern Caribbean Sea in the middle of May. It gradually organized, and a tropical depression formed on May 17. In response to low shear aloft and warm water temperatures, the depression rapidly strengthened on May 20, becoming a storm early in the day and a hurricane by night. However, Alma quickly weakened back to a tropical storm on May 21. Furthermore, it weakened to a tropical depression on the following day, mostly due to upper-level shear. The depression continued its general northward movement, with a brief jog to the west, and hit Cuba on May 24 as a 30 mph (48 km/h) tropical depression. As Alma crossed the eastern Gulf of Mexico, it retained a very well defined circulation with an eye appearing on radar, but shear limited convection and strength.
Alma made landfall near Cedar Key, Florida, on May 25 as a tropical depression 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) was reported. Impact was severest in Cuba, where flash flooding caused seven fatalities, destroyed several homes, forced the evacuation of 3,000 people in Oriente Province, and resulted in a shutdown of 16 sugar mills. The storm brought light rainfall to Florida, peaking at 6.66 in (169 mm) near Miami. Hazardous thunderstorms caused one death in Miami and damaged some roofs and building in Fort Myers. In other states, impact was mostly in the form of rain, though a tornado near Columbia, South Carolina, destroyed a roof.
A large disturbance began to detach from the Intertropical Convergence Zone near Panama on July 16. It is possible that the disturbance interacted with a low-level vortex over the northwest Caribbean Sea. By July 19, the disturbance developed into a tropical depression. After tracking through the Yucatan 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 (105 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 the state of Florida, Becky produced mostly light rainfall and gale-force winds. However, in Tallahassee, the storm dropped more than 8 in (200 mm) of rain, which caused flooding in and round 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 4 ft (1.2 m) of water, resulting in the evacuation of 15 households by rowboat. More than 100 cars in the area were also flooded. In nearby Wakulla County, knee-deep waters were reported at the county courthouse at Crawfordville. Additionally, a tornado spawned near Panacea, destroyed a house and damaged two others. Outside of Florida, effects were mainly limited to light to moderate rainfall, though a tornado in Georgia caused one fatality and destroyed two homes.
A tropical wave emerged into the Atlantic Ocean from the west coast of Africa on July 23. It moved rapidly western 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 without significantly strengthening and struck crossed western Cuba on August 1. Heavy rains on the island caused severe flooding, leading to five fatalities. The depression entered the Gulf of Mexico and was upgraded to Tropical Storm Celia later on August 1. Due to warm sea surface temperatures, Celia rapidly intensified into a Category 3 hurricane on August 1. Storm surge and swells lashed the west coast of Florida, especially the Panhandle. Several life guard rescues occurred, while eight people drowned.
Early on August 2, Celia began to weaken and fell to Category 2 intensity. The storm weakened further to a Category 1 hurricane on August 3. However, while approaching the Texas coastline later that day, Celia began to rapidly intensify again. At 1800 UTC on August 3, Celia attained its peak intensity with maximum sustained winds of 125 mph (205 km/h) and a minimum barometric pressure of 945 mbar (27.9 inHg). In Louisiana, tides caused minor coastal flooding. Late on August 3, Celia made landfall near Corpus Christi, Texas. In Nueces County, wind gusts as high as 180 mph (290 km/h) were observed. Severe damage occurred in the 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 damaged about 55,650 others. About 252 small businesses, 331 boats, and 310 farm buildings were either damaged or destroyed. In Texas alone, Celia caused 15 deaths and $930 million in damage. Celia weakened while moving further inland and dissipated over New Mexico on August 6.
A tropical depression developed about 95 mi (155 km) east-northeast of the Abaco Islands in the Bahamas at 12:00 UTC on August 15. Initially, the depression continued moving west-northwestward, before turning northward early the following day. Around 06:00 UTC on August 16, the system made landfall near Beaufort, North Carolina, with winds of 35 mph (55 km/h). After re-emerging into the Atlantic early on August 18, the depression moved northeastward and intensified into a tropical storm. The ship Hotel observed sustained winds of 65 mph (100 km/h) around that time. At 18:00 UTC, the storm peaked with winds of 70 mph (110 km/h) and a minimum pressure of 992 mbar (29.3 inHg). Shortly thereafter, the cyclone became extratropical about 180 mi (290 km) east of Sable Island.
Along the coast of North Carolina, higher than normal tides capsized about 20 boats, including a 68 ft (21 m) yacht. At Salvo, where the tide may have reached 4 ft (1.2 m) 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.
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 500 mi (800 km) east of the Lesser Antilles on August 17. As it moved west-northwestward, it slowly intensified, and was upgraded to Tropical Storm Dorothy on August 19. By the following day, Dorothy attained its peak intensity with maximum sustained winds of 70 mph (110 km/h). Around that time, Dorothy crossed the island of Martinique. After passing through the Lesser Antilles, Dorothy moved under an upper-level cold-core trough, which caused the storm to weaken. On August 23, Dorothy dissipated south of the Tiburon Peninsula of Haiti.
Throughout the Lesser Antilles, Dorothy produced high winds and heavy rainfall. On Martinique, large amounts of precipitation resulted in flooding and mudslides, which in turn, caused bridge collapses and damage to homes. In addition, strong tropical storm force winds were also reported on the island. The storm destroyed 186 homes and left 700 people homeless. Severe crop damage also occurred, especially to bananas and sugar cane. Flooding also occurred on Dominica and Guadeloupe, although effects were less severe. The exact death toll of Dorothy is unknown, although some sources claim that as many as 51 fatalities occurred. Dorothy also caused $34 million in damage.
A surface trough spawned a tropical depression near Cabo Gracias a Dios, Honduras, on September 8. The depression moved northwestward without intensifying before striking Tulum, Quintana Roo, on September 10. Hours later, the system emerged into the Gulf of Mexico and soon strengthened into Tropical Storm Ella. A ridge to the north caused it to curve in a general westward direction. Just six hours after becoming a tropical storm, Ella intensified into a hurricane early on September 11. While approaching the Gulf Coast of Mexico, the cyclone deepened significantly, peaking as a Category 3 hurricane on September 12 with winds of 125 mph (205 km/h) and a minimum pressure of 967 mbar (28.6 inHg). Shortly thereafter, Ella made landfall near La Pesca, Tamaulipas, at the same intensity. The hurricane rapidly weakened inland, falling to tropical storm intensity on September 13 and dissipating several hours later.
In the Yucatan Peninsula, wind gusts of 55 mph (90 km/h) were observed. Ella brought heavy rainfall to portions of northeastern Mexico. Several homes were destroyed and villages along the San Marcos River were inundated by water. One girl died after her house collapsed. Flooding and persist precipitation prevented the transportation of relief items, including food and medicine, by helicopters. In Texas, tides peaked at 7 ft (2.1 m) normal, but no coastal flooding damage was reported.
On September 12, a tropical depression developed from an upper-level trough just south of Abaco Islands. Without significant intensification, the system crossed the Florida Keys and entered the Gulf of Mexico. Felice remained a disorganized storm for its entire duration, plagued by dry air, a lack of deep thunderstorm activity, and an ill-defined center of circulation. However, early on September 16, the cyclone peaked with maximum sustained winds of 70 mph (110 km/h) and a minimum barometric pressure of 997 mbar (29.4 inHg). Felice tracked northwestward and brushed southern Louisiana on September 15, before making landfall near Galveston, Texas, later that day. Once ashore, Felice quickly deteriorated as it recurved into the central United States, dissipating on September 17. While over southeastern Oklahoma, however, its remnants still closely resembled a formidable tropical cyclone.
In advance of the cyclone, officials advised residents in vulnerable communities to evacuate their homes, and temporary storm shelters were established. However, the effects from Felice were generally light. Beneficial rains fell over parts of southern Florida, while sections of coastal Louisiana experienced minimal gale-force winds and above-normal tides. In Texas, winds gusting to 55 mph (89 km/h) at Galveston—and estimated near 70 mph (110 km/h) elsewhere—caused scattered power outages and minor tree damage, while heavy rainfall totaling over 6 in (150 mm) triggered some street flooding. Felice delayed the local rice harvest and damaged some hay that had been cut before the storm. Significant precipitation and gusty winds accompanied the system into northern Texas and Oklahoma.
The long-lived depression formed on September 24 just off the west coast of Africa, and for several days maintained a general westward track. It passed through the Lesser Antilles on October 1, and later stalled in the eastern Caribbean Sea. On October 8, the depression crossed over the eastern portion of the Dominican Republic, and subsequently it accelerated to the northeast. It was declassified as a tropical cyclone on October 12, although its remnants persisted for another week before dissipating in the westerlies near the Azores.
The depression produced heavy rainfall in the Lesser Antilles, reaching 12 in (300 mm) on Barbados; it left three deaths and moderate damage on the island. Another death was reported in the United States Virgin Islands. Torrential rainfall in Puerto Rico inflicted heavy damage, totaling $65 million. The highest precipitation total was 41.68 in (1,059 mm) in Jayuya, of which 17 in (430 mm) fell in a 24‑hour period. Most of the damage can be attributed to damaged sugar cane and coffee crops. At least 18 people were killed on the island, and the system was considered one of the worst disasters in Puerto Rican history.
A tropical wave exited western Africa and emerged into the Atlantic Ocean on September 15. Initially, it moved slowly westward, until September 22, when a high-pressure area caused it to accelerate west-northwestward towards the Leeward Islands. By the next day, the wave interacted with a cold-core low, producing an area of convection. As the system moved over warmer waters, gale-force winds were measured. Because a surface low formed on September 26, the system was then designated as Tropical Storm Greta. However, the storm did not strengthen, despite favorable conditions, and as a result, it was described as a "bomb that did not explode".
While approaching the Florida Keys, Greta abruptly weakened to a tropical depression, coinciding with deterioration of the cloud pattern. In addition, Hurricane Hunters reported rising pressures and lower winds. On the evening of September 27, Greta made landfall in Key West, Florida with sustained winds of 26 mph (42 km/h). Once in the Gulf of Mexico, Greta did not re-intensify, though it retained a closed circulation while moving around a high-pressure area. It moved across the northern Yucatán Peninsula, though it quickly re-emerged into the Gulf of Mexico. Eventually, Greta made landfall near Tampico, Mexico on October 5, and dissipated shortly thereafter. Due to the weak nature of the storm, minimal impact was reported. In Florida, tides were generally minor, and were no more than 3 and 4 feet (0.91 and 1.22 m) in height, as reported in the Florida Keys. Rainfall was mostly light, peaking at 8.94 in (227 mm) in Fort Pierce.
On October 12, a subtropical depression developed while located northeast of the Bahamas. It steadily intensified and became a subtropical storm by the following day. After tracking east-northeastward, the storm made a sharp westward turned, followed by a curved to the north-northeast. After fully acquiring tropical characteristics, the subtropical storm transitioned into a tropical cyclone early on October 16. Twelve hours later, the storm strengthened into a hurricane, shortly before passing near Bermuda. It continued to intensify and briefly became a Category 2 hurricane on October 17. The hurricane then accelerated rapidly northeastward, and made landfall on the Avalon Peninsula of Newfoundland as a Category 1 hurricane. Shortly thereafter, the hurricane transitioned into an extratropical cyclone on October 17.
The hurricane produced high winds on Bermuda, causing suspension schools, transportation, and interrupted businesses, though minimal damage occurred. In addition, light rainfall fell on the island. Throughout Newfoundland, hurricane-force winds were reported, which caused damage to structures, though mostly limited to broken windows. Rough seas along the Atlantic coast of the island damaged fishing dories and a fishing ramp. Heavy rainfall was also reported in the region, reaching nearly 5 in (130 mm) in Quebec. Damage on the Burin Peninsula was in the thousands, although the specific figure is unknown. On the French Territory of Saint Pierre and Miquelon, several buildings lost their roof due to high winds.
A subtropical depression developed about 970 mi (1,560 km) east-northeast of Bermuda at 12:00 UTC on October 20. After intensifying into a subtropical storm early the following day, further strengthening was slow. Initially, the system northeastward, but curved southeastward on October 24. During that time, it began acquiring characteristics of a tropical cyclone, transitioning into a tropical storm at 12:00 UTC. The storm resumed its northeastward motion and continued to intensify. Early on October 27, the storm strengthened into a hurricane,. based on a report of winds of 75 mph (120 km/h) from the Pretoria several hours later. At the time of hurricane intensity, it is likely that the hurricane-force wind field was only 6 mi (9.7 km) in diameter and its tropical storm force wind field was only 69 mi (111 km) in diameter. By 12:00 UTC on October 27, the cyclone weakened to a tropical storm and began accelerating. About 24 hours later, the system transitioned into an extratropical cyclone while situated approximately 500 mi (800 km) north-northeast of Graciosa in the Azores..
In addition to the ten named storms of 1970 and the notable Tropical Depression Fifteen, there were several minor systems that were also classified as depressions by the National Hurricane Center. A tropical depression developed offshore of North Carolina on July 27. Initially, the depression tracked toward the Outer Banks, but veered east-southeastward and avoided landfall. While nearing Bermuda on July 30, the depression slowly curved north-northeastward. By late on August 1, the depression dissipated while located east of Cape Race, Newfoundland. Tropical Depression Five developed on August 2 in the vicinity of Cape Verde. It moved west-northwestward across the eastern-North Atlantic Ocean and eventually curved nearly due eastward. The depression dissipated about halfway between Puerto Rico and the west coast of Africa on August 6. While Tropical Depression Nine was dissipating in the open Atlantic on August 5, Tropical Depression Ten developed near the Bahamas. By the following day, the depression made landfall near Palm Bay, Florida, and dissipated early on August 7.
On August 7, Tropical Storm Seven developed over the eastern Atlantic. It moved westward toward the Lesser Antilles, before dissipating northeast of the islands on August 12. The next depression originated about halfway between the Lesser Antilles and Cape Verde on September 3. The system moved west-southwestward for much of its duration and dissipated by September 9. Another tropical depression began just offshore Dakar, Senegal, on September 5. It crossed through Cape Verde before dissipating on September 7. Later that month, the next system formed just east of Cape Verde on September 22. The depression dissipated on September 25, after moving northwestward across the far eastern Atlantic. On September 29, a system developed about 400 mi (640 km) southeast of Bermuda. The depression moved rapidly north-northeastward and dissipated about 280 mi (450 km) south of Cape Race, Newfoundland, on October 1.
The following names were used for named storms (tropical storms and hurricanes) that formed in the North Atlantic in 1970. A storm was named Felice for the first time in 1970. Names that were not assigned are marked in gray. The name Celia was later retired and replaced by Carmen in the 1974 Atlantic hurricane season.
This is a table of the storms in 1970 and their landfall(s), if any. Deaths in parentheses are additional and indirect (an example of an indirect death would be a traffic accident), but are still storm-related. Damage and deaths include totals while the storm was extratropical or a wave or low.