The 2017 Pacific hurricane season was an above average Pacific hurricane season in terms of named storms, though less active than the previous three, featuring eighteen named storms, nine hurricanes, and four major hurricanes. Despite the considerable amount of activity, most of the storms were weak and short-lived. The season officially started on May 15 in the eastern Pacific Ocean, and on June 1 in the central Pacific; they both ended on November 30. These dates conventionally delimit the period of each year when most tropical cyclones form in the respective regions. However, the formation of tropical cyclones is possible at any time of the year, as illustrated in 2017 by the formation of the season's first named storm, Tropical Storm Adrian, on May 9. At the time, this was the earliest formation of a tropical storm on record in the eastern Pacific basin proper (east of 140°W). The season saw near-average activity in terms of accumulated cyclone energy (ACE), in stark contrast to the extremely active seasons in 2014, 2015, and 2016; and for the first time since 2012, no tropical cyclones formed in the Central Pacific basin. However, for the third year in a row, the season featured above-average activity in July, with the ACE value being the fifth highest for the month. Damage across the basin reached $375.28 million (2017 USD), while 45 people were killed by the various storms.
Prior to the start of this season, the National Hurricane Center (NHC) changed its policy to permit issuance of advisories on disturbances that were not yet tropical cyclones but had a high chance to become one, and were expected to bring tropical storm or hurricane conditions to landmasses within 48 hours. As a result of this change, watches and warnings could be issued by local authorities. Such systems would be termed as "Potential Tropical Cyclones". The first system to receive this designation was Potential Tropical Cyclone Fourteen-E, which developed into Tropical Storm Lidia south-southeast of the Baja California Peninsula on August 30.
Seasonal forecasts
Forecasts include weekly and monthly changes in important factors that help determine the number of tropical storms, hurricanes, and major hurricanes within a particular year. According to the National Oceanic and Atmospheric Administration (NOAA), the average hurricane season in the Eastern and Central Pacific between 1981 and 2010 contained approximately 15 tropical storms, 7 hurricanes, and 3 major hurricanes. The NOAA generally classifies a season as above average, average, or below average based on the cumulative ACE index, but occasionally the number of tropical storms, hurricanes, and major hurricanes within a hurricane season is also considered.
On May 25, 2017, the National Oceanic and Atmospheric Administration released its annual forecast, predicting an 80% chance of a near- to above-average season in both the Eastern and Central Pacific basins, with a total of 14–20 named storms, 6–11 hurricanes, and 3–7 major hurricanes. During May 28, the Servicio Meteorológico Nacional (SMN) issued its first forecast for the season, predicting a total of 16 named storms, 10 hurricanes, and 6 major hurricanes to develop.
Seasonal summary
Although hurricane season in the eastern Pacific does not officially begin until May 15, and on June 1 in the central Pacific, activity began several days prior with the formation of a tropical depression in the eastern region on May 9. This was the earliest formation of a tropical cyclone on record in the eastern Pacific basin proper, until broken by Tropical Depression One-E in 2020. When it intensified into Tropical Storm Adrian a few hours later, the system became the earliest named storm on record in the region, a record that stood until broken by Tropical Storm Andres in 2021. Near normal activity occurred in June, with Tropical Storm Calvin formed on June 11, and Hurricane Dora on June 25. For the third year in a row, July featured above average activity, with the fifth highest ACE value for that month on record. This total was due to long-lived hurricanes Eugene, Fernanda, Hilary, and Irwin. August saw significantly less activity, with only three storms forming in the month; however it featured Hurricane Kenneth, the third major hurricane of the season. September featured four storms, including Hurricane Otis, which became the fourth major hurricane of the season. Only two storms formed after October 1, Ramon and Selma. Both did not attain hurricane status, though Selma became the first and last storm to make landfall in El Salvador. No systems were active in November for the first time since the 2010 season. The Accumulated Cyclone Energy index for the 2017 Pacific hurricane season as calculated by Colorado State University using data from the National Hurricane Center was approximately 100.7 units, about 20 percent near average.
Systems
Tropical Storm Adrian
Between May 5–6, a tehuantepecer occurred over the East Pacific, enhancing cyclonic spin over the eastern reaches of the basin. A tropical wave was first identified over Panama around the same time, and it interacted with the gap wind event on its westward trek. The disturbance gradually organized, becoming the season's first tropical depression around 18:00 UTC on May 9 while located about 275 nmi (315 mi; 510 km) south-southwest of the El Salvador–Guatemala border. At the time, it was the earliest tropical cyclone on record in the East Pacific. Six hours later, it intensified into Tropical Storm Adrian. Satellite imagery depicted a well-organized tropical storm with a mid-level eye feature, and Adrian attained peak winds of 40 kn (45 mph; 75 km/h) early on May 10. Although forecasters initially expected Adrian to become a hurricane, the influence of mid-level southeasterly wind shear was poorly modeled. Thunderstorm activity became increasingly displaced from the cyclone's center, and it weakened. By 00:00 UTC on May 11, Adrian degenerated to a remnant low. It moved northwestward and dissipated offshore the Mexico coastline the next day.
Tropical Storm Beatriz
A tropical wave emerged off the western coast of Africa on May 18 and entered the East Pacific about a week later, where steady organization led to the formation of a tropical depression around 12:00 UTC on May 31. Embedded within southwesterly flow around a large upper-level trough across northern Mexico, the depression moved steadily northeast in a favorable environment, and it intensified into Tropical Storm Beatriz by 06:00 UTC on June 1. After attaining peak winds of 45 mph (70 km/h), the system made landfall around 00:00 UTC on June 2 about 25 miles (40 km) west of Puerto Ángel before the mountainous terrain of Mexico quickly made Beatriz dissipate inland twelve hours later.
In the state of Oaxaca, flights out of Bahías de Huatulco International Airport were cancelled and schools were closed until June 3. Dozens of roads were impassable due to mudslides and flooding; numerous locales received over 4 in (100 mm) of rain, with rainfall at a maximum of 19.07 in (484 mm) in Huatulco. Numerous landslides caused significant disruption across the state; the storm blocked large areas of Federal Highway 200 in Oaxaca. A landslide in San Marcial Ozolotepec killed two girls and buried several houses, while another in San Carlos Yautepec killed a woman. As of June 4, a total of six people have been killed—five in Oaxaca and two in Tehuantepec. Damage in Oaxaca reached MXN$3.2 billion (US$172 million).
Tropical Storm Calvin
In the second week of June, the NHC forecast the development of a broad area of low pressure a few hundred miles south of Mexico over the next several days. This prediction came to fruition on June 9, and the fledgling disturbance steadily organized into a tropical depression by 12:00 UTC on June 11 while located about 150 mi (240 km) south-southeast of Salina Cruz. It was slow to organize initially due to moderate easterly wind shear as it drifted northwestwards; by 18:00 UTC on June 12, however, the tropical depression intensified into Tropical Storm Calvin. Intensifying slightly to reach winds of 45 mph (70 km/h), Calvin made landfall halfway between Salina Cruz and Puerto Ángel, near Paja Blanca, around 00:00 UTC on June 13. Just 12 hours later, Calvin dissipated into a remnant low. The remnants of the storm caused heavy rainfall and some flooding in the area, however no fatalities were reported. Calvin affected proximate areas of Mexico as Tropical Storm Beatriz less than two weeks earlier, causing at least 70 million pesos (US$3.88 million) additional damage in Oaxaca.
Hurricane Dora
A large gyre developed over Central America around June 15. A trough detached from the gyre and drifted across just south of the Gulf of Tehuantepec between June 21 and June 23. By June 23, a tropical wave associated with the remnants of Tropical Storm Bret in the Atlantic began merging with the trough. A surface low formed early on the next day, followed by the development of a tropical depression at 18:00 UTC. Initially located about 230 mi (370 km) south-southeast of Acapulco, the depression moved west-northwestward due to a mid-tropospheric ridge, which stretched from northern Mexico westward into nearby Pacific waters. At 06:00 UTC on June 25, the depression intensified into Tropical Storm Dora. Thereafter, favorable conditions including low wind shear and warm sea surface temperatures allowed Dora to undergo rapid intensification, becoming a hurricane at 06:00 UTC on June 26 and a Category 2 hurricane about six hours later.
With impressive outflow and an eye apparent on satellite imagery, the storm peaked with maximum sustained winds of 105 mph (170 km/h) and a minimum barometric pressure of 974 mbar (28.8 inHg) by 18:00 UTC June 26. Dora remained a Category 2 hurricane for about 12 more hours before beginning to rapidly weaken over cooler sea surface temperatures and in an environment of drier air, falling to Category 1 intensity at 06:00 UTC on June 27 and deteriorating to a tropical storm around 18:00 UTC. The storm later degenerated into a remnant low near Socorro Island early on June 28, after all of the storm's convection had been diminished. The remnant low moved slowly over the eastern Pacific before dissipating early on July 1. The outer bands of Dora brought heavy rains to Guerrero, resulting in flash floods that inundated 20 homes. Overall damage was minor, however.
Hurricane Eugene
A tropical wave emerged from Africa on June 25 and moved across the Atlantic before reaching the East Pacific on July 2. Shower and thunderstorm activity, previously lacking, began to gradually increase as the disturbance interacted with a convectively-coupled kelvin wave. Around 12:00 UTC on July 7, it organized into a tropical depression while located about 700 nmi (805 mi; 1,295 km) south of the southern tip of the Baja California peninsula. The cyclone intensified into Tropical Storm Eugene six hours later. A stout ridge over the Southwestern United States directed the storm toward the northwest, and a favorable combination of warm waters, low wind shear, and adequate moisture facilitated its rapid intensification. In the 42 hours between 00:00 UTC July 8 and 18:00 UTC July 9, Eugene strengthened from a 35 kn (40 mph; 65 km/h) tropical storm to a 100 kn (115 mph; 185 km/h) Category 3 hurricane. It exhibited a clear eye surrounded by very deep convection around this time. However, the steering ridge quickly directed the hurricane into colder waters on July 10, and within a 30-hour period, Eugene weakened from a major hurricane back to a tropical storm. It degenerated to a remnant low around 18:00 UTC on July 12. The circulation dissipated well west of Baja California two days later.
Dangerous rip currents combined with swells of 4 to 8 ft (1.2 to 2.4 m) across southern California resulted in hundreds of rescues. On July 10 alone, lifeguards in Huntington Beach made 200 rescues while 600 were made in Los Angeles County; lifeguards also responded to 700 medical emergencies.
Hurricane Fernanda
A tropical wave moved offshore Africa on June 26 and remained disorganized as it entered the East Pacific on July 5. There, a broad area of low pressure formed well south of Mexico, and associated shower and thunderstorm activity began to increase as the disturbance continued westward. This resulted in the formation of a tropical depression around 18:00 UTC on July 11 while located about 650 nmi (750 mi; 1,205 km) south of the southern tip of the Baja California peninsula. Its formation was unexpected by forecasters because of poor performance from reliable computer models; it was only given a low chance of development 18 hours before genesis. A day later, the system intensified into Tropical Storm Fernanda. A potent mid-level ridge over western North America caused the newly formed storm to lose latitude, while a very favorable environment triggered its prolonged rapid intensification. In 54 hours, Fernanda intensified from a 35 kn (40 mph; 65 km/h) tropical storm to a 125 kn (145 mph; 230 km/h) Category 4 hurricane. The system exhibited a clear eye surrounded by −70 °C (−95 °F) cloud tops and plentiful spiral banding around this time. The powerful hurricane maintained a protracted peak intensity even while undergoing an eyewall replacement cycle. However, Fernanda eventually shifted to the northwest, bringing it into colder waters that triggered weakening beginning on July 18. The increasingly disheveled storm, feeling the effects of increased wind shear, crossed into the Central Pacific on July 20–21. Fernanda degenerated to a remnant low around 18:00 UTC on July 22 while it was positioned about 430 nmi (495 mi; 795 km) east of the Big Island. The low dissipated several hours later.