2017 Atlantic hurricane season (Jarrell)

The 2017 Atlantic hurricane season was an above average hurricane season that, with a damage total of at least $175.2 billion (USD), was the costliest tropical cyclone season on record for the Atlantic basin. With at least 690 deaths, 2017 was also the deadliest season since 2008 and also featured both the highest total accumulated cyclone energy (ACE) and the highest number of major hurricanes since 2010. Most of the season's damage was due to three of the season's major hurricanes – Angelo, Craig, and Heidi. Two other notable storms that caused significant impacts were Hurricanes Garrett and Kenny.

The season officially began on June 1, and ended on November 30, 2017. These dates historically describe the period of year when most tropical cyclones form in the Atlantic basin and are adopted by convention. Breaking the trend that had been seen in the previous two seasons, there was no formation of a tropical cyclone before the official start of the season. The first storm, Hurricane Angelo, formed in early June and became the second-earliest, as well as most recent June major hurricane, to develop in a season behind only Hurricane Alma of 1966 when it reached Category 3 intensity on June 11. It struck Galveston Island and Houston, Texas directly, causing 37 deaths and $16.8 billion in damage--as well as becoming the first major hurricane to make landfall in the United States since Wilma in 2005, as well as the first June major hurricane to make landfall in the basin. In mid-August, Hurricane Craig became the first Category 5 hurricane to make landfall in the United States since Andrew in 1992, and became the fifth-costliest tropical cyclone on record in the North Atlantic when it struck the Florida Keys. In September, Hurricane Garrett tracked through the Caribbean Sea as a tropical storm, dropping copious amounts of rainfall that triggered mudslides across Venezuela and Colombia. After being steered south by a ridge of high pressure, it later struck Belize as a Category 2 hurricane. Later that month, Hurricane Heidi developed in the western Atlantic. The storm became one of the largest Atlantic hurricanes on record as it briefly reached major hurricane status while it paralleled the U.S. Eastern Seaboard. Heidi's most significant impacts were felt when it moved ashore on the southern coastline of New Jersey as a very large and intense post-tropical cyclone. The storm left 273 dead and $79 billion dollars of damage in its wake, making it the second-costliest Atlantic hurricane on record. In late October, Hurricane Kenny developed in the Gulf of Mexico and made landfall in Alabama before stalling around the border with Florida for three days, dumping torrential rainfall in the area; the Mobile area was particularly hard hit. Kenny resulted in $28 billion in damage as well as 47 fatalities. A very unusual aspect of the season was that every named storm had some degree of impact on land throughout the basin. This peculiarity of the season's storms led to the most destructive and one of the deadliest seasons in the history of the Atlantic basin. Only the season's two depressions that never attained tropical storm strength caused no damage in any way.

Initial predictions for the season anticipated that an El Niño would develop, lowering tropical cyclone activity. However, the predicted El Niño failed to develop, with cool-neutral conditions developing instead, later progressing to a La Niña – the second one in a row. This led forecasters to raise their predicted totals, with some later anticipating that the season could be the most active since 2010.

Pre-season forecasts
Ahead of and during the season, several national meteorological services and scientific agencies forecast how many named storms, hurricanes and major (Category 3 or higher on the Saffir–Simpson scale) hurricanes will form during a season and/or how many tropical cyclones will affect a particular country. These agencies include the Tropical Storm Risk (TSR) Consortium of the University College London, the National Oceanic and Atmospheric Administration (NOAA) and Colorado State University (CSU). The forecasts include weekly and monthly changes in significant factors that help determine the number of tropical storms, hurricanes, and major hurricanes within a particular year. Some of these forecasts also take into consideration what happened in previous seasons and the dissipation of the 2014–16 El Niño event. On average, an Atlantic hurricane season between 1981 and 2010 contained twelve tropical storms, six hurricanes, and two major hurricanes, with an Accumulated Cyclone Energy (ACE) index of between 66 and 103 units.

Pre-season outlooks
The first forecast for the year was issued by TSR on December 13, 2016. They anticipated that the 2017 season would be a near-average season, with a prediction of 14 named storms, 6 hurricanes, and 3 major hurricanes. They also predicted an ACE index of around 101 units. On December 14, CSU released a qualitative discussion detailing five possible scenarios for the 2017 season, taking into account the state of the Atlantic Multidecadal Oscillation and the possibility of El Niño developing during the season. On December 30, the JMC released its official forecast of the year, expecting 12 named storms, 5 hurricanes, and 2 major hurricanes. TSR lowered their forecast numbers on April 5, 2017 to 11 named storms, 4 hurricanes, and 2 major hurricanes, based on recent trends favoring the development of El Niño. The next day, CSU released their prediction, also predicting a total of 11 named storms, 4 hurricanes, and 2 major hurricanes. On April 17, The Weather Company released their forecasts, calling for 2017 to be a near-average season, with a total of 12 named storms, 6 hurricanes, and 2 major hurricanes. The next day, on April 18, North Carolina State University released their prediction, also predicting a near-average season, with a total of 11–15 named storms, 4–6 hurricanes, and 1–3 major hurricanes. On May 25, NOAA released their prediction, citing a 70% chance of an above average season due to "a weak or nonexistent El Niño", calling for 11–17 named storms, 5–9 hurricanes, and 2–4 major hurricanes. On May 26, TSR updated its prediction to around the same numbers as its December 2016 prediction, with only a minor change in the expected ACE index amount to 98 units.

Mid-season outlooks
The JMC released their updated forecast on June 1 with 15 named storms, 6 hurricanes, and 4 major hurricanes. It was based on the current status of the North Atlantic Oscillation, which was showing signs of leaning towards a negative phase, favoring a warmer tropical Atlantic; and the chances of El Niño forming were significantly lower. However, they stressed on the uncertainty that the El Niño–Southern Oscillation could be in a warm-neutral phase or weak El Niño conditions by the peak of the season. On the same day, the United Kingdom Met Office (UKMO) released its forecast of a very slightly above-average season. It predicted 13 named storms, with a 70% chance that the number would be in the range between 10 and 16, and 8 hurricanes, with a 70% chance that the number would be in the range between 6 and 10. It also predicted an ACE index of 145, with a 70% chance that the index would be between 92 and 198. On July 4, TSR released their fourth forecast for the season, increasing their predicted numbers to 17 named storms, 7 hurricanes, and 3 major hurricanes, due to the fact that El Niño conditions would no longer develop by the peak of the season and the warming of sea-surface temperatures across the basin. Additionally, they predicted a revised ACE index of 116 units. During August 9, NOAA released their final outlook for the season, raising their predictions to 14–19 named storms, though retaining 5–9 hurricanes and 2–5 major hurricanes. They also stated that the season had the potential to be extremely active, possibly the most active since 2010.

Seasonal summary
The 2017 Atlantic hurricane season officially began on June 1, 2016. It was an above average season and the most active since 2012, producing a total of 14 named storms, 8 hurricanes, and 5 major hurricanes. The first storm, Hurricane Angelo, developed on June 8, while the final system, Tropical Storm Natalie, was absorbed by a low pressure system on November 23. The higher-than-normal activity was attributed to many factors. Pre-season projections noted the potential for a weak to moderate El Niño event to evolve through the summer and fall on the basis of statistical model guidance; these forecasts were proven to be over-amplified as a result of a phenomenon known as the spring predictability barrier. Instead, equatorial Pacific Ocean temperatures began cooling throughout the summer, reaching La Niña threshold in November and curtailing the negative effects on Atlantic hurricane activity originally expected. This led to warmer than normal sea surface temperatures across the Atlantic, though many other environmental factors were similar to 2016: the subtropical regions were slightly cooler than normal; slightly lower than normal sea level pressures; and reduced wind shear, especially in the Caribbean Sea, which had experienced record values of wind shear in the past recent years. Moisture levels, however, were anomalously dry, which likely prevented some of the storms from becoming significant hurricanes. Steering currents had also been different from past years, which had previously had a trough of low pressure dominating the East Coast of the United States. The tropical cyclones of this season caused about $175.2 billion in damage and at least 687 deaths, solidifying the 2017 season as the costliest in recorded history and the deadliest season since 2008. The Atlantic hurricane season officially ended on November 30, 2016.

The season's first storm, Angelo, made landfall near Galveston Island, Texas shortly after reaching its peak strength as a low-end Category 3 hurricane, becoming the first major hurricane to make landfall in the United States since Hurricane Wilma in 2005. July saw the formation of Tropical Storm Belle, which resulted in minimal impact through the Lesser Antilles. In August, two systems – Craig and Edmond – became major hurricanes. Hurricane Craig became the first hurricane to make landfall at Category 5 strength in the United States since Hurricane Andrew in 1992. With damage estimates up to $41 billion, Craig was established as the fifth-costliest natural disaster on record in the United States. Tropical Storm Denise followed on the heels of Craig's path, but soon dissipated due to the environmental changes caused by the preceding storm. Hurricane Edmond brushed by Bermuda later in the month as a minimal Category 4 hurricane, with no significant damage reported on the island. September saw the formation of four storms: Flo, an unnamed tropical depression, Garrett, and Heidi. Hurricane Heidi became one of the largest tropical cyclones observed in the Atlantic, reaching a diameter of 815 mi (1,310 km) while centered off the coastline of the Carolinas. Heidi would transition into a potent extratropical system and undergo bombogenesis to reach winds of 100 mph (161 km/h) prior to crossing the New Jersey coastline, inflicting damages estimated to be around $90 billion. Hurricane Garrett caused hundreds of fatalities as it tracked through South and Central America; most of its life was spent as a tropical storm.

October featured five storms, another unnamed depression, Ilias, Joy, Kenny and Lisa. Kenny was the cause of a catastrophic flooding event in late October when it moved ashore in Alabama and stalled around the border with Florida, dumping several feet of rain as the system meandered over the area for nearly four days, becoming one of the wettest tropical cyclones in the United States. In the late days of that month, Lisa passed to the south and east of the Azores as a Category 1 hurricane. Two storms developed in November, Mason and Natalie; the latter of which became the third-most intense hurricane observed in the month of November.

The season's activity was reflected with an accumulated cyclone energy (ACE) rating of 144.8. 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. ACE is only calculated for full advisories on tropical systems at or exceeding 34 knots (39 mph, 63 km/h) or tropical storm strength. This does not include subtropical systems.

Hurricane Angelo
An area of thunderstorm activity from the remnants of a frontal trough in the Straits of Florida organized into the first tropical depression of the season on June 8, which was upgraded to Tropical Storm Angelo the following morning. A high-pressure area strengthened to Angelo's north, causing a west-northwestern movement as the storm curved around the high's periphery. During the period of June 9 to June 11, an anticyclone had formed over Angelo and along with slow movement over warm waters, caused the storm to intensify rapidly. A compact system, Angelo reached its peak intensity with sustained winds of 115 mph (185 km/h) and 964 millibars (28.40 inHg) in pressure on June 13. Shortly after attaining its peak strength, Angelo made landfall at the same intensity near Galveston Island, Texas. The storm weakened quickly over land and accelerated over the Midwest, before dissipating over southern Missouri on June 15. Angelo was one of few June major hurricanes, and the earliest major hurricane to make landfall in the United States.

Angelo caused tremendous damage in Texas, largely from its impacts from Galveston. The storm made landfall in the central span of Galveston Island, with its western eyewall passing directly over the city. Traveling northwest, Angelo rapidly weakened as it moved inland, passing west of Texas City as a Category 1 hurricane. The weakening storm then meandered over the western side of the Houston Metropolitan Area before accelerating northeast. The storm surge produced by Angelo failed to top the 17-foot Galveston Seawall, thus sparing the city from significant flooding. However, high winds and heavy rainfall swept through the area for several hours, resulting in heavy damage. Further north, impacts from wind were generally lighter, but heavy rainfall fell across much of the areas adjacent to Galveston, with peak accumulations of 19 inches (483 mm) observed around Pearland, Texas. Overall impacts from the storm amounted to $16.8 billion in damage, along with 37 deaths.

Tropical Storm Belle
A tropical wave east of the Windward Islands developed into Tropical Depression Two on the afternoon of July 19. The depression slowly intensified, and was eventually upgraded to Tropical Storm Belle by noon on the next day. The storm continued to gradually organize as it curved northwest towards the Lesser Antilles. Late on July 22, Belle attained its peak strength of 65 mph (100 km/h). Around this time, building high pressures to the system's north caused a shift to the south in its track before resuming its northwesterly course. Tropical Storm Belle crossed the Windward Islands chain, and it was noted that the storm made landfall on Saint Vincent. Belle emerged into the Caribbean Sea as a weakened depression and continued to move west. Wind shear began increasing over the storm as it tracked further into the Caribbean Sea. By noon on July 25, Air Force reconnaissance and satellite imagery did not show a low-level circulation, indicating that Belle had degenerated into open tropical wave 270 mi (435 km) south of the U.S. Virgin Islands.

Shortly before Belle was upgraded to a tropical storm, a tropical storm warning was issued for Martinique, Saint Lucia, Saint Vincent, and the Grenadines on July 21. About 48 hours later, all of the warnings were discontinued. As Belle headed further into the Caribbean Sea, tropical storm watches were issued for Hispaniola and Puerto Rico on July 22, as the system was initially expected to strengthen. All of the tropical storm watches and later warnings were discontinued after Belle failed to redevelop. After Belle made landfall on Saint Vincent, several landslides occurred, and electrical and water services were significantly disrupted. Bill caused damage to two factories, a church, and hundreds of houses. Damage was also reported on Saint Lucia, where hundreds of buildings were damaged, electricity and telephone service was disrupted, and crops were affected as well. Wind gusts on the island of Saint Lucia reportedly reached 35 mph (56 km/h).

Hurricane Craig
A westward moving tropical wave developed into a tropical depression on August 11 while located roughly halfway between the Lesser Antilles and Cape Verde. Initially steered to the southwest, the system became the third named storm of the season, Craig, before taking on a steady track to the west-northwest. Entering increasingly favorable environmental conditions, Craig reached an initial peak strength as a major hurricane with sustained winds of 125 mph (201 km/h) on August 16. The storm briefly weakened to Category 2 strength before it regained major hurricane status and intensified further in a environment of light wind shear and warm waters. Craig passed through the Bahamas throughout August 20-21 as a fluctuating Category 4 hurricane. Passing over the warm waters of the Gulf Stream thereafter, Craig reached Category 5 intensity on August 22. Later that day, Craig made landfall in Key West, Florida at its peak strength with 175 mph sustained winds and a central pressure of 910 millibars, making it the fourth-most intense hurricane to strike the United States. Entering the Gulf of Mexico, Craig's intensity slowly leveled off as it curved to the north, making landfall in Vermilion Parish, Louisiana as a Category 2 hurricane late on August 27. Rapid weakening ensued, and Craig degenerated to a remnant low early on August 29. The low eventually dissipated over the Appalachian Mountains on September 1.

Despite Craig's long path across the Atlantic, the most devastating impacts were confined to several islands within the Bahamas and South Florida due to the compact nature of the storm. In the former, high tides and hurricane-force winds caused extensive damage across much of the nation. A total of over 1,500 homes were damaged or destroyed across the Bahamas while the transport, communications, water, sanitation, agriculture, and fishing sectors experienced prolonged disruption. Damages in the nation amounted to $750 million and 21 people were killed. High winds caused catastrophic damage in South Florida, especially in Monroe County, where approximately 50,000 homes were severely damaged or destroyed. Most of the storm's monetary damage occurred here, as losses in the Florida Keys amounted to $50 billion. 51 fatalities were also recorded in the Keys. In Louisiana, impacts from the storm were widespread, but less substantial than anticipated. Craig made landfall in a scarcely populated area, and quickly weakened upon moving inland. Damages in the state totaled to $1.5 billion, with three fatalities reported.

Tropical Storm Denise
On August 14, a well-defined tropical wave exited the coast of Africa. The next day, it had rapidly organized into a tropical depression. That afternoon, the depression attained tropical storm strength, and it was given the name Denise. Denise turned to the northwest, and passed very near Cape Verde. 19 people were killed as the storm passed by the country. Denise continued to the northwest and it continued to organize throughout October 18. During this period satellite imagery indicated that the system peaked with winds of 60 mph (95 km/h) and a minimum surface pressure of 996 mbar (29.36 inHg). As the storm passed the Cape Verde islands weather stations reported 35 miles per hour (56 km/h) winds, equivalent to that of a tropical depression. Late that day, Juan turned towards westward and began to encounter a less favorable environment in response to the passage of Hurricane Craig, which caused it to rapidly weaken and dissipate by August 18.

Hurricane Edmond
A tropical wave developed into Tropical Depression Five on August 25 while situated several hundred miles west of Cape Verde. Moving on a northwesterly path, the depression intensified into a tropical storm early the next day, receiving the name Edmond upon doing so. Edmond steadily intensified after being named, eventually reaching major hurricane status late on August 28. This status lasted only for a little over twelve hours before dropping back down to Category 2 strength due to internal fluctuations. Under the influence of a subtropical ridge to its east and a building upper-level low over the Southeastern U.S., Edmond curved to the north, with a trajectory aimed at Bermuda. Against predictions of a weakening trend, Edmond began to quickly re-intensify through August 31, regaining major hurricane status that evening. On September 1, the hurricane reached its peak intensity as a Category 4 hurricane with sustained winds of 140 mph (220 km/h), and a minimum barometric pressure of 942 mbar. Shortly after the time of its peak intensity and subsequent weakening, the eyewall made a direct hit on Bermuda. The hurricane rapidly lost strength soon after it passed the island nation, owing to an environment of colder waters and increasing wind shear. By the early hours of September 2, Edmond had fallen below hurricane status and began to undergo extratropical transition, a process it completed later that same day. Edmond's remnants eventually impacted Nova Scotia and later crossed over the far North Atlantic, before being absorbed into another extratropical cyclone on September 5.

As Edmond's eyewall passed over Bermuda, an elevated observing station at Southampton Parish reported sustained winds of 124 mph (200 km/h), while wind gusts reached 130 mph (215 km/h); L.F. Wade International Airport recorded sustained winds of 93 mph (150 km/h) and gusts up to 113 mph (181 km/h). At the height of the storm about 90% of electricity customers on the island lost power. Hundreds of buildings suffered partial or total roof destruction, and downed trees and power lines prevented travel across the island. On Bermuda alone, the storm left at least $200 million in damage and five dead. After transitioning into an extratropical cyclone, Edmond delivered tropical storm force winds to Newfoundland, with gusts peaking at 53 mph (85 km/h) at Burgeo; though damage in the region was minimal.

Tropical Storm Flo
On August 31, a mid-level circulation area formed over Nicaragua and slowly drifted northeastward into the Gulf of Mexico. As it entered the Gulf, the system developed thunderstorm activity and an area of low pressure, and as a result the JMC began initiating advisories on a newly formed tropical depression by 1800 UTC on September 4. The depression gradually intensified and attained tropical storm strength late the next day. The newly-named Flo intensified to reach peak winds of 70 mph (115 km/h) on September 6, and held that intensity before making landfall near Marsh Island in southeastern Louisiana that same morning. At the time of landfall, the system had a minimum pressure of 998 mbar (hPa; 29.45 inHg), as reported by a hurricane reconnaissance flight; this would be the lowest measured pressure associated with Flo. The storm weakened over land and was eventually absorbed by a extratropical system over the Great Lakes by 0600 UTC on September 10.

In Louisiana, Flo produced sustained winds of 70 mph (89 km/h) and gusts up to 90 mph (145 km/h), as observed near Morgan City. Gusty winds resulted in 132,000 customers losing electricity. A maximum of 13.4 in (340 mm) of precipitation was recorded near Biloxi, Mississippi. Damage became less severe as the storm moved inland and weakened, with moderate winds and rainfall produced over a large area as Flo transitioned to a extratropical cyclone over the Midwestern United States. Across this region, the system resulted in over 150,000 power outages and 7.5 in (190 mm) of precipitation was recorded of in Greensburg, Kentucky. Overall, Flo was responsible for $650 million in damage and 7 fatalities.

Tropical Depression Seven
On September 5, a tropical wave exited Africa and quickly developed a low pressure area. Following a convective increase and better-defined outflow, it developed into Tropical Depression Seven about 280 miles (450 km) west-southwest of the southernmost Cape Verde Islands early on September 7. Because the depression was isolated from the subtropical ridge, it drifted west-northwestward. Westerly wind shear prevented significant development, and its peak winds were only 35 mph (56 km/h); operationally, satellite imagery suggested the storm may have reached 40 mph (64 km/h), the bare minimum for a tropical storm. By September 10, the shear and cooler waters weakened the tropical depression, which now contained a poorly defined surface center. The system lost its deep convection and by that afternoon, the depression degenerated into a remnant low. It continued west-northwestward, producing intermittent convection, until dissipating entirely east of the Lesser Antilles without redevelopment on September 15. There were no reports of damage or casualties.

Hurricane Garrett
On September 12, the eighth tropical depression of the season organized from a tropical wave in the Caribbean Sea. The system organized gradually, and was named Tropical Storm Garrett early on September 14. The storm continued to strengthen as it moved west-northwest, attaining winds of 65 mph (105 km/h) before a building ridge to its north pushed the storm into the southwestern Caribbean Sea, an area unaccustomed to tropical cyclones. Fluctuation in strength occurred as Garrett slowly drifted south. Rounding the periphery of the ridge, the storm encountered very favorable conditions and began to reorganize as it resumed its northwestern movement once again. Garrett reached hurricane status late on September 17, and continued to strengthen to reach its peak intensity as a Category 2 hurricane with peak winds of 105 mph (165 km/h) before making its final landfall north of Bluefields, Nicaragua on September 19. The storm gradually spun down inland, becoming a depression by the following afternoon. The depression remained over Central America until the evening of September 21, when it dissipated completely over the region's mountainous terrain.

Rainfall in Venezuela reached 13.3 in (340 mm) in some areas. As a result, widespread mudslides were reported, which in turn damaged or destroyed hundreds of houses and caused 34 deaths. Twenty fatalities were reported in neighboring Colombia. In Nicaragua, where Garrett made landfall at peak intensity, 134 deaths were reported. The storm destroyed 1,500 houses and damaged another 3,000; an estimated 38,000 people were left homeless in that country. Overall, Hurricane Garrett caused 188 deaths and about $44 million in damage.

Hurricane Heidi
A tropical wave developed into Tropical Depression Nine at 00:00 UTC on September 25, while located about 304 mi (489 km) east of Guadeloupe. Over a day following its formation, the depression intensified into Tropical Storm Heidi. It gradually organized over the Gulf Stream, and based on reports from the Hurricane Hunters, Heidi attained hurricane status late on September 27. The storm continued to deepen, eventually becoming a Category 2 hurricane at 1200 UTC the next day. Although it soon weakened back to a Category 1 hurricane, the barometric pressure decreased to 967 mbar (28.5 inHg). The large storm paralleled the Bahamas and eventually regained its Category 2 strength by 0600 UTC on September 30. The hurricane began to turn towards the north-northeast in response to a subtropical ridge over the Atlantic and a trough over the southeastern United States. After further intensification off the Carolinas, Heidi reached peak winds of 120 mph (195 km/h) to the east North Carolina on October 2, making it a major hurricane, while growing larger in diameter. Upwelled waters and a eyewall replacement cycle greatly weakened the hurricane, and by the following morning, Heidi transitioned from a Category 1 hurricane to an extratropical cyclone by 0900 UTC.

Around the same time that Heidi entered the vicinity of the Eastern seaboard, a separate extratropical cyclone was established in the area, which had entered a period of explosive deepening. The large circulation of Heidi, which was now about 815 mi (1,310 km) across, absorbed the deepening low to its north and caused a period of extreme intensification, which was further enhanced by a strong jet stream and sufficient sea surface temperatures ideal for cyclogenesis. With these factors at hand as well as the aiding of baroclinic processes, the post-tropical Heidi began to explosively intensify. By 1800 UTC on October 3, the cyclone reached a minimum barometric pressure of 973 mbar and sustained winds of 100 mph (155 km/h). The center of the massive extratropical Heidi then moved inland at Wildwood, New Jersey shortly after reaching this intensity. The system slowly continued to the northwest before dissipating around the Great Lakes region on October 6.

In the United States, damage was most severe in New Jersey and New York, mostly due to the storm's 18-foot (5 m) surge. Within the former, 285,000 houses were damaged or destroyed, while nearly 15,000 businesses suffered severe losses. In New York, an estimated 305,000 homes were destroyed. Severe coastal flooding occurred in New York City, with the hardest hit areas being New Dorp Beach, Red Hook, and the Rockaways; eight tunnels of the subway system were inundated. Heavy snowfall was also reported, peaking at 27 inches (686 mm) in West Virginia. Additionally, the remnants of Heidi left $500 million in damage in Canada, with Ontario and Quebec being the worst impacted. Overall, 263 fatalities were attributed to Heidi. Damages totaled $77 billion in the United States and $79 billion overall, making Heidi the second-costliest Atlantic hurricane in recorded history, second only to Hurricane Katrina in 2005.

Tropical Depression Ten
A tropical depression developed in the southwestern Caribbean Sea on October 4. Designated as Tropical Depression Ten, it headed west-southwestward toward Panama with little change in strength due to a generally hostile environment primarily caused by upwelling from Hurricane Garrett, which passed through the area days prior. At 0600 UTC on October 5, the depression dissipated about 40 mi (64 km) northeast of Bastimento, Panama. No known damage resulted from the storm.

Tropical Storm Ilias
A unusually well-organized disturbance moved off the African coast on October 9 and rapidly developed into Tropical Depression Sixteen. The JMC began issuing advisories while it was 450 mi (724 km) southeast of Cape Verde. Twelve hours after the depression formed, it was named Tropical Storm Ilias. For two days a large trough of low pressure northwest of Ilias steered it north-northwest towards cooler waters. Winds in the system peaked at 60 mph (95 km/h), while moderate to heavy rain was reported along the west coast of Africa; but no damage was reported. Ilias eventually weakened and merged with the low pressure trough 450 miles (724 km) southwest of the Canary Islands late on October 12.

Tropical Storm Joy
A tropical wave spawned a tropical depression about 270 miles (442 km) east-southeast of the Lesser Antilles on October 17, which quickly became Tropical Storm Joy. It initially headed westward, before re-curving west-northwestward early on the following day. Shortly thereafter, the storm passed through the Windward Islands between Martinique and Dominica. The storm peaked with winds of 60 mph (95 km/h) while moving northwestward across the Caribbean Sea. Joy weakened to a tropical depression before making landfall near Guayama, Puerto Rico on October 20. The system emerged in the Atlantic that evening and turned north, losing its tropical characteristics the following morning. The extratropical remnant subsequently dissipated on October 22.

There was considerable damage in the Lesser Antilles. On Martinique where the storm made its closest pass, up to 4 inches (100 mm) of rain washed out roads and caused several landslides. Homes across the island experienced moderate damage from Joy's winds, mainly from debris impacts and falling trees. Many banana and sugar cane fields were also ruined, which accounted for most of the financial cost of the storm. In Dominica, light winds and precipitation up to 5.91 inches (150 mm) yielded damages reaching $65,000, entirely to roads and communications. There were also strong gales reported in Puerto Rico prior to the storm's arrival. There, heavy rainfall exceeding 10 inches (250 mm) in some areas of the nation led to widespread agricultural damage, flooded homes and streets. Four fatalities occurred when a bridge collapsed under a vehicle as the occupants were attempting to drive through the stormy conditions. Overall, Joy was responsible for $2.5 million in damages and 7 fatalities

Hurricane Kenny
A tropical wave emerged into the Atlantic from the west coast of Africa between October 8 and October 9. The wave failed to develop for several days due to its quick movement and dry air. Deep convection eventually consolidated and a circulation finally developed by October 20, with a tropical depression developing at 18:00 UTC, about 70 mi (112 km) south-southeast of Key West, Florida. The depression took a northwesterly course throughout its trek across the Gulf of Mexico, eventually intensifying into Tropical Storm Kenny. The storm steadily intensified further into a 80 mph (130 km/h) Category 1 hurricane by early on October 23. Kenny later made landfall west of Gulf Shores, Alabama at 10:30 UTC. The storm spun down, becoming a tropical storm by 12:00 UTC, as it meandered across the Florida-Alabama state border. A light steering pattern caused the storm to emerge into the Gulf of Mexico early on October 26, but a turn toward the north-northeast brought it ashore at Miramar Beach, Florida, as a weak tropical storm around 21:00 UTC. The system weakened to a tropical depression over central Georgia on the afternoon of October 28 before losing tropical characteristics after emerging into the Atlantic the following day.

Winds primarily left power outages and downed trees, some of which fell onto buildings and vehicles. However, the most significant damage resulted from the freshwater flooding due to the storm's slow movement across the Alabama-Florida border. Dire predictions of potentially catastrophic flooding came to fruition in Mobile and nearby locales, where floodwaters inundated major highways, forced residents to their attics and roofs, and overwhelmed emergency lines. In addition to the flooding, Kenny spawned several tornadoes around the city. Estimates placed the damage caused by Kenny at $28 billion, which ranks it as the seventh-costliest tropical cyclone on record. Overall, Kenny killed 67 people across the Southeastern United States, 48 of which were in Mobile.

Hurricane Lisa
A tropical wave moved off the coast of Africa on October 16. The wave tracked westward and later northeastward across the Atlantic until it reached an area of relaxed wind shear and its associated low-pressure area organized into a tropical depression. It moved almost due east and was upgraded to Tropical Storm Lisa on October 28, while located 585 mi (981 km) southwest of the Azores. Although located in an unfavorable environment, Lisa steadily intensified and was upgraded to a Category 1 hurricane at 00:00 UTC on November 30 despite a partially exposed circulation and disorganized cloud pattern. As the hurricane turned east-northeastward the following day, its cloud pattern became much more symmetric and an eye became evident, yielding peak winds of 80 mph (130 km/h). Tracking to the northeast, it began to weaken and lose tropical characteristics. A frontal boundary wrapped around the storm's circulation, transitioning the system into an extratropical cyclone by 18:00 UTC on November 1. The post-tropical low eventually regained hurricane-force winds while accelerating towards Britain.

Lisa's extratropical remnant impacted Britain with high winds and heavy rain, which shut down roads and prompted evacuations. During its passage through the nation, 80,000 homes were left without power after winds of 80 mph (130 km/h) affected the country.

Tropical Storm Mason
A broad area of low pressure associated with remnants of a cold front developed into Tropical Depression Fifteen in the southwestern Caribbean Sea on November 7. Eighteen hours later, it strengthened into Tropical Storm Mason. Moving on a westward trajectory, Mason continued to intensify until peaking with winds of 50 mph (80 km/h) and a minimum barometric pressure of 1,001 mbar (29.4 inHg) early on November 8. Later that day, Mason weakened to a minimal tropical storm as it neared the Nicaraguan coast. At 1800 UTC, the storm made landfall north Greytown, Nicaragua and weakened to a tropical depression; rapid dissipation ensued as it moved inland. Greytown reported only light winds and minimal rainfall, the latter peaking at 4.46 inches (113 mm) within a 20‑hour period.

Hurricane Natalie
An area of low pressure developed in the Caribbean Sea on November 14 and was monitored for development by the JMC. There, an increase in convection led to the formation of a tropical depression around 06:00 UTC on November 17; it intensified into Tropical Storm Natalie twenty four hours later. A broad, deep upper-level trough to the cyclone's northwest caused it to conduct a counter-clockwise turn and accelerate northeast while also aiding in the onset of an extended period of rapid intensification. Natalie attained hurricane strength around 18:00 UTC on November 19 before ultimately reaching winds of 100 mph (161 km/h) by 06:00 UTC the next day. Shortly thereafter, the hurricane made landfall in the Dominican Republic. The storm quickly tracked across the nation, having emerged in the Atlantic as a Category 1 storm twelve hours later. Natalie then resumed strengthening over an unusually favorable environment in the open waters of the Atlantic ocean, rapidly deepening to reach its peak strength of 150 mph (241 km/h) on November 21. As the storm continued to accelerate into the colder waters of the central Atlantic, it quickly lost its strength at a faster rate than it had intensified, weakening to a tropical storm around 15:00 UTC on November 22 and degenerating to a remnant low twelve hours later. The low was absorbed by a passing extratropical cyclone later the next day.

Storm names
The following names were used for storms that formed in the north Atlantic in 2017. Names that were not assigned are marked in. This particular list had not been used in any previous season, as it was drafted by the Jarrell Meteorological Center (JMC); a independent branch of atmospheric observation and research stationed in Central Texas. It was the first of six new naming lists introduced by the agency and used for public information, following the disenfranchisement of the National Hurricane Center (NHC) in the 2016 government budget. All of the storms in this season were used in the Atlantic for the first time except for Belle and Lisa, which had been previously used in 1976 and 2016, respectively.

Retirement
On April 11, 2018, at the 40th session of the RA IV hurricane committee, the World Meteorological Organization retired five names: Angelo, Craig, Garrett, Heidi, and Kenny from its rotating name lists due to the amount of damage and deaths they caused, and they will not be used again for another Atlantic hurricane. They will be replaced with Andreas, Carlos, Gage, Harper, and Kody, respectively, for the 2023 season. This season is tied with the 2005 season for the second-highest number of names retired after a single season in the Atlantic basin, surpassed only by the 2018 season, which had seven names retired.

Seasonal effects
This is a table of all the storms that formed in the 2017 and their landfall(s), if any. It includes their duration, names, landfall(s), denoted in parentheses, damages, and death totals. Deaths in parentheses are additional and indirect (an example of an indirect death would be a traffic accident), but were still related to that storm. Damage and deaths include totals while the storm was extratropical, a wave, or a low, and all the damage figures are in 2017 USD.