The 2011 Pacific hurricane season was a below average season in terms of named storms, although it had an above average number of hurricanes and major hurricanes. During the season, 13 tropical depressions formed along with 11 tropical storms, 10 hurricanes and 6 major hurricanes. The season officially began on May 15 in the East 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 Pacific basin. The season's first cyclone, Hurricane Adrian formed on June 7, and the last, Hurricane Kenneth, dissipated on November 25.
Despite the decrease in storms, there were several intense and destructive hurricanes this season. Hurricane Beatriz killed four people in Southwestern Mexico. Hurricane Jova killed eight and caused $203.67 million (2011 USD) in damage to Western Mexico. Tropical Depression Twelve-E killed 30 people in Central America. Meanwhile, Kenneth became the strongest November storm at the time. Hurricane Hilary killed three fishermen in Southwestern Mexico.
Seasonal forecasts
In advance of each Pacific hurricane season, forecasts of hurricane activity are issued by the United States National Oceanic and Atmospheric Administration (NOAA)'s Climate Prediction Center and Mexico's Servicio Meteorológico Nacional (SMN). These include weekly and monthly changes in significant factors that help determine the number of tropical storms, hurricanes, and major hurricanes within a particular year. According to NOAA, the average eastern Pacific hurricane season between 1981 and 2010 contained roughly 14 tropical storms, 7 hurricanes, 3 major hurricanes, with a near-normal accumulated cyclone energy (ACE) index of 113. Broadly speaking, ACE is a measure of the power of a tropical or subtropical storm multiplied by the length of time it existed. It is only calculated for full advisories on specific tropical and subtropical systems reaching or exceeding wind speeds of 39 mph (63 km/h). NOAA typically categorizes a season as above-average, average, or below-average based on the cumulative ACE index, but the number of tropical storms, hurricanes, and major hurricanes within a hurricane season is sometimes also considered.
On May 19, the Climate Prediction Center released its pre-season outlook. The scientists stated a 70% chance of a below-normal season, a 25% chance of a near-normal season and a 5% chance of an above-normal season. The climatologists expected 9–15 named storms, with 5–8 becoming hurricanes, and 1–3 becoming major hurricanes. The accumulated cyclone energy was expected to be 45 to 105% of the median. The below-normal activity forecast was because of increased wind shear and a high expectation of El Niño–Southern Oscillation (ENSO)-neutral conditions (no El Niño or La Niña) throughout the peak months of July, August and September, together with lingering La Niña conditions at the beginning of the season.
Seasonal summary
The season got off to an active start with first storm, Adrian, becoming one of only a handful of tropical cyclones to attain Category 4 status in June. Four other storms, Dora, Eugene, Hilary, and Kenneth attained Category 4 status. Dora was the strongest storm of the year, peaking at 155 mph, just short of Category 5 status. The month of August was about average in terms of the number of storms, with the strongest of the month being Eugene. However, the first half of September had very little activity, due to the return of a La Niña event. Tropical Depression Eight-E was the only storm in the first half of September, when it dissipated on September 1.
Hilary became the second storm to form in September, becoming the fourth major hurricane of the season, during the afternoon hours of September 22. After Hilary, Jova unexpectedly became the fifth major hurricane of the season during the early morning hours of October 10. Tropical Depression Twelve-E killed 30 people in Central America when it made landfall near El Salvador on October 12. On November 19, Kenneth formed as a tropical depression and quickly strengthened into a hurricane two days later. Kenneth became the first major hurricane in November and latest-forming major hurricane in the eastern north Pacific basin in the satellite era, until being surpassed by Hurricane Sandra in 2015; the last to do so was Winnie in 1983, which only peaked at Category 1 hurricane status. Hurricane Kenneth, however, intensified to attain Category 4 status on November 22, which broke the record at the time.
The accumulated cyclone energy (ACE) index for the 2011 Pacific hurricane season as calculated by Colorado State University using data from the National Hurricane Center was 120.9 units. Broadly speaking, ACE is a measure of the power of a tropical or subtropical storm multiplied by the length of time it existed. It is only calculated for full advisories on specific tropical and subtropical systems reaching or exceeding wind speeds of 39 mph (63 km/h).
Systems
Hurricane Adrian
On May 31, the Intertropical Convergence Zone produced an area of convection south of the Gulf of Tehuantepec. The system remained disorganized for several days, until the circulation became more defined on June 6. At 12:00 UTC on June 7, it developed into Tropical Depression One-E about 370 mi (600 km) south of Acapulco, Mexico. The depression strengthened into Tropical Storm Adrian 12 hours later. With light wind shear and ocean temperatures near 86 °F (30 °C), Adrian intensified further while moving northwestward. An eye-like feature developed in the center of the central dense overcast (CDO). At 00:00 UTC on June 9, Adrian attained hurricane status as it began a period of rapid deepening. The eye became well-defined, reaching a diameter of 23 to 29 mi (37 to 47 km), while surrounded by a ring of intense thunderstorms with symmetrical outflow. About 24 hours later on June 10, Adrian reached peak winds of 140 mph (220 km/h) about 320 mi (515 km) south-southwest of Manzanillo, and a minimum pressure of 944 mbar, as estimated from satellite imagery. This made it a Category 4 hurricane. Soon after peaking, Adrian encountered cooler waters and stronger wind shear, resulting in rapid weakening. Late on June 11, it dropped to tropical storm status, as the track shifted more to the west. After losing all of its convection, Adrian transitioned into a post-tropical cyclone on June 12, which dissipated two days later.
Across the southwestern Mexican coastline, Adrian sent waves up to 13 ft (4.0 m) high, generating swells and rough seas. The storm's outer rainbands produced rain in the states of Oaxaca, Guerrero and Michoacán, reaching 2.11 in (54 mm) at Lake Chapala in a 24-hour period.
Hurricane Beatriz
On June 14, the NHC noted a large area of scattered showers and thunderstorms associated with a monsoon trough over the east Pacific, several hundred miles from the coast of Acapulco, Mexico. A quasi-stationary surface low formed in association with the activity, and over the subsequent days convection consolidated in the vicinity of an anticyclone over the southwestern Caribbean. Curved rainbands began developing around the center, and on June 19 the system acquired sufficient organization to be classified as a tropical depression. Turning toward the northwest along a weakness in the subtropical ridge to its north, the depression further strengthened within a favorable environment and was upgraded to Tropical Storm Beatriz at 1800 UTC that day, with winds of 40 mph (65 km/h).
Late on June 20, Beatriz was upgraded to a hurricane, with winds of 75 mph (120 km/h) and a pressure of 985 mbar (29.1 inHg). Beatriz continued to strengthen and reached winds of 90 mph (145 km/h) and a pressure reading of 977 mbar (28.9 inHg) while it neared the coast of Mexico. After moving along the coast, it weakened to a tropical storm and dissipated the next day. But the NHC noted that Beatriz's remnants still had a near 0% chance of redeveloping, as they remained almost stationary. But on June 23, convection dissipated, and Beatriz's remnants slowly began to accelerate to the west, as the remnant low dissipated rapidly. Late on June 24, the remnants of Hurricane Beatriz dissipated completely, to the southwest of the Baja California Peninsula.
Several landslides blocked off roads and a 100 m (330 ft) section of a roundabout was destroyed. In the community of Amatillo, three people were killed after being washed away by flood waters. Heavy rains from Beatriz caused the Sabana River to overflow its banks, placing 150 homes across 14 colonias under water.
Hurricane Calvin
A tropical wave exited western Africa on June 24, which reached Central America on July 3. Two days later, the wave merged with a low-pressure area in the east Pacific Intertropical Convergence Zone (ITCZ) in the Gulf of Tehuantepec. Convection increased and organized as the system continued to the west-northwest. On July 7, it developed into Tropical Depression Three-E about 175 mi (280 km) southwest of Acapulco. While parallelling the Mexican coastline offshore, the depression continued to organize amid moderate wind shear. It strengthened into Tropical Storm Calvin at 00:00 UTC on July 8. Around that time, the wind shear dropped and the storm moved farther away from Mexicco. About 18 hours after becoming a tropical storm, Calvin attained hurricane status, as it developed a well-defined mid-level eye. At 00:00 UTC on July 9, Calvin reached peak winds of 80 mph (130 km/h), with a minimum pressure of 984 mbar (29.1 inHg). About 12 hours later, Calvin weakened back into a tropical storm due to cooler waters. On July 10, it degenerated into a remnant low after it lost its convection while still maintaining tropical storm-force winds. That day, the remnants of Calvin passed over Clarion Island, which recorded wind gusts of 45 mph (72 km/h). On July 11, the winds dropped below tropical-storm force. The remnants continued to the west-northwest before turning to the southwest on July 13. The circulation dissipated a day later while located about 775 mi (1,250 km) southwest of Cabo San Lucas.
Hurricane Dora
In the early morning hours of July 14, a tropical wave had moved off the Colombian coast. The wave gained convection as it moved into the southwestern Caribbean, and the National Hurricane Center (NHC) began to monitor the disturbance, giving it a 10% chance of development into a tropical cyclone. Over the rest of the day, the storm continued to move westward until it moved ashore on the Nicaragua/Costa Rica border the next day. On July 16, the National Hurricane Center began monitoring the area of low pressure off the coast of Guatemala. Slowly organizing, the low-pressure area had gained enough strength to be declared Tropical Depression Four-E during the morning hours of July 18. Just three hours later, the system was upgraded to Dora, the fourth tropical storm of the 2011 Pacific hurricane season. Continuing to organize, Dora reached hurricane strength late on July 20, before rapidly intensifying into a major hurricane later the next day. Strengthening further, Dora reached a peak of 155 mph (250 km/h) early on July 21, making it a Category 4 hurricane on the Saffir–Simpson hurricane scale. However, after entering cooler waters, Dora began to weaken the next day. On July 23, Dora was downgraded to a tropical storm, and the next day, Dora was no longer a tropical cyclone. As a remnant low, the circulation began to curve around the high-pressure area that had steered Dora for much of its existence on July 25. Early on July 26, the remnants of Hurricane Dora dissipated completely, over Central Baja California.