The 1958 Atlantic hurricane season included every tropical cyclone either affecting or threatening land. There were ten named storms as well as one pre-season tropical storm. Seven of the storms became hurricanes, including five that were major hurricanes, or the equivalent of a Category 3 on the Saffir-Simpson scale. The strongest storm was Hurricane Helene, which became a strong Category 4 hurricane with winds and a barometric pressure of while just offshore the southeastern United States.
In May, a subtropical depression formed in the Caribbean and dropped heavy rainfall near Miami, Florida. The first named storm of the season was Alma, which killed three people and caused flooding in Texas. Hurricane Daisy in August was a major hurricane that paralleled the eastern coast of the United States, although due to its small size it did not cause much damage. Hurricane Ella affected much of the northern Caribbean and Texas, most significantly the Dominican Republic where 30 people died. Ella also killed six people in Cuba, where it made landfall as a major hurricane. A few weeks later, Tropical Storm Gerda also struck the Dominican Republic and killed three people. The costliest storm of the season was Helene, which caused $11.2 million in damage (1958 USD), mostly in North Carolina. Although it passed within of the state, its effects were mostly limited to the coast, and the hurricane killed one person. The last storm of the season, Janice, killed eight people in Jamaica when its precursor dropped of rainfall, and one person was killed in the Bahamas.
Season summary
The ten tropical storms during the season is comparable to the 20 year average of ten. In contrast to the previous season when most storms were in the Gulf of Mexico, most storms in 1958 occurred over the western Atlantic Ocean. The first storm, Alma, formed in the middle of June. Subsequently, a trough persisted along the eastern United States, which suppressed tropical cyclone formation. Conditions remained unfavorable in July due to a large ridge suppressing the westerlies. In August, a persistent trough caused three storms – Becky, Cleo, and Daisy – to recurve and remain over the ocean. Most storms formed from the middle of August through the middle of October, when polar air reached as far south as Florida due to a shift in the ridge.
Before the season started, the United States Weather Bureau office in Miami began setting up a teleprinter to distribute hourly advisories to newspapers and the American Red Cross. The hurricane season officially began on June 15, and lasted until November 15. When the season started, the Lakeland Frost Warning Service sent four employees to assist the Miami Weather Bureau. The Hurricane Hunters flew daily to investigate potential storms in the Atlantic Ocean and Gulf of Mexico. In addition, there was a set of radars from Texas to Maine to track storms. Beginning in 1958, the Weather Bureau predicted the change in tide due to a storm with the assistance of a tide specialist. During the season, a reporter – daughter of Weather Bureau director Gordon Dunn – flew into Hurricane Daisy, becoming the first woman to fly into a hurricane. Utilizing radars along the East Coast of the United States, the Weather Bureau tracked both Hurricanes Daisy and Helene for , which was the first such occurrence of that feat.
The season's activity was reflected with a cumulative accumulated cyclone energy (ACE) rating of 121. ACE, broadly speaking, is 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 values. ACE is only calculated for full advisories on tropical systems at or exceeding or tropical storm strength.
Systems
Unnamed May tropical storm
A small circulation crossed Panama from the Pacific Ocean on May 17, and by the following day it was a developing depression near San Andrés in the western Caribbean. The system gradually organized over warm waters while moving to the northwest, developing a well-defined low pressure area by May 23 as it approached western Cuba. Later that day, the depression crossed the western portion of the island before turning to the northeast. On May 24, the system passed southeast of Florida, dropping heavy rainfall that peaked at in Homestead. May 1958 was the second wettest May since 1911, of which half of the precipitation fell during the depression. Several other locations in the Miami area reported record or near-record rainfall for the month. The high rainfall disrupted planting of vegetables, and there was some crop damage. Flooding entered homes and businesses, forcing some evacuations. About 2,900 people lost telephone service, and there was a brief water outage on Key Biscayne. There were also hundreds of vehicle accidents related to the storm.
After affecting Florida, the depression continued to the northeast, and although it had a warm core, it was not able to develop significantly due to lack of temperature instability, as well as another low developing southwest of the circulation. The depression was briefly forecast to strike North Carolina, but instead an eastward moving ridge kept it offshore. In Hatteras, North Carolina, the depression dropped of rainfall. The influx of cold air transitioned the depression to an extratropical cyclone on May 28. An approaching cold front absorbed the depression and produced heavy rainfall in eastern Canada.
Tropical Storm Alma
A tropical wave was first observed in the central Caribbean Sea on June 9. By the following day, there was evidence of a weak closed circulation off the south coast of Jamaica. Moving generally westward, on June 12 it crossed the Yucatán Peninsula, and the system emerged into the Bay of Campeche the next day. On June 14, a tropical depression formed about halfway between the Yucatán Peninsula and Tamaulipas. Within six hours, the depression intensified into Tropical Storm Alma about east of Tampico. Later that day, a ship reported a pressure of and high seas, and early on June 15 a United States Coast Guard plane measured winds of near the northeast Mexican coast. That day, Alma made landfall about south of Brownsville, Texas, in northeastern Mexico. The storm moved ashore in northeastern Tamaulipas early on June 15 before crossing into southern Texas. After weakening to a tropical depression, Alma straddled the Rio Grande before dissipating in western Texas late on June 16.
The United States Coast Guard recommended people to evacuate in beach areas near Brownsville, Texas. As it moved ashore, Alma produced a high tide of along Padre Island, and one person drowned near Galveston due to heavy surf. The highest wind gust was at Port Isabel, causing minor damage. However, Alma dropped heavy rainfall further inland, reaching about near Medina. The rains caused floods that resulted in heavy damage to property and crops. Some rivers and streams rose above their banks due to floods, creating torrents of up to in some arroyos. The floods covered highways and forced about 100 people to evacuate near Sabinal. The rains also knocked out telephone lines in Uvalde County, and temporarily trapped hundreds of scouts. One person drowned along the Concho River, and three people overall died due to the system.
Tropical Storm Becky
Based on reports from the Cape Verde islands offshore Africa, it is estimated a tropical depression developed on August 8. It moved westward due to the subtropical ridge to its north, a motion the depression would continue for much of its duration. Nearby ship reports indicated gradual strengthening, and the depression became a tropical storm on August 11. At 0400 UTC on August 12, the San Juan Weather Bureau office initiated advisories on Tropical Storm Becky about halfway between the Lesser Antilles and Cape Verde. That day, the Hurricane Hunters flew into the storm, reporting a pressure of and flight level winds of ; its peak surface winds were estimated at . Also on August 12, a storm warning was issued for the northern Leeward Islands, and a storm watch was issued for the United States Virgin Islands and northern Puerto Rico.
After peaking in intensity, Becky continued quickly to the west-northwest, and its fast motion may have prevented further strengthening. On August 14, a flight reported hurricane-force wind gusts in rainbands east-northeast of the center. The next day, the circulation became poorly defined, and by August 16, Becky had become extratropical after it merged with an approaching cold front. The storm turned to the north and northeast, dissipating later on August 17. As Becky was transitioning into an extratropical storm, it produced high waves along the southeastern coast of the United States.
Hurricane Cleo
A well-developed tropical wave spawned a tropical storm on August 11 to the south of Cape Verde. It moved westward, and ships in the area indicated that it had a large circulation. The Hurricane Hunters flew into the system and observed a well-developed hurricane with winds of , which were the highest measured winds. As a result, the San Juan Weather Bureau Office initiated advisories on Hurricane Cleo and issued a hurricane watch for the Lesser Antilles. Subsequent analysis determined that Cleo became a hurricane on August 13. A weak trough near 50° W allowed the hurricane to turn to the north, and Cleo continued to intensify, based on improved definition of the eye on radar imagery. A flight into the storm late on August 16 indicated a pressure of with winds of early on August 16. Originally winds were thought to be higher in Cleo, at , which would make it a Category 5 hurricane, but reanalysis later on determined it to be weaker.
After maintaining peak winds for about six hours, Cleo began weakening. It turned more to the northwest due to a strengthening ridge to the northeast and the hurricane's outflow weakening the trough. An approaching cold front turned Cleo to the northeast on August 18 and caused it to accelerate. That day, it passed about east of Bermuda. On August 20, the hurricane became extratropical to the southeast of Newfoundland. In St. John's, the storm dropped about of rainfall. The remnants of Cleo turned to the east and east-southeast, dissipating on August 22 between the Azores and mainland Portugal.
Hurricane Daisy
A tropical wave moved through the Lesser Antilles on August 20 and gradually spread north. On August 24, a nearby ship reported a low pressure area and strong winds, indicating the formation of a small tropical cyclone near the Bahamas. After a Hurricane Hunters flight indicated winds of , the Weather Bureau initiated advisories on Tropical Storm Daisy early on August 25 to the north of the Bahamas. That day it became a hurricane, and initially it moved slowly to the northwest due to a ridge to the northeast. On August 26, a trough turned Daisy to the northeast, and the hurricane continued to intensify due to an anticyclone aloft. By early August 28, the hurricane reached peak winds of , and a minimum pressure of while offshore South Carolina. Daisy accelerated to the north, passing about east of Hatteras, North Carolina; there, gusts peaked at due to the storm's small size.