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 brought additional flooding to Southwestern Mexico.
Seasonal forecasts +Predictions of tropical activity in the 2011 seasonSourceDateNamedstormsHurricanesMajorhurricanesRefAverage (1981–2010) 15.6 8.6 4.1 Average (1995–2010) 14 7 3 Record high activity 27 16 (Tie) 11 Record low activity 8 (Tie) 3 0 (Tie) CPC May 19, 2011 9–15 5–8 1–3 Actual activity 11 10 6 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 . 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 .
Systems Hurricane Adrian
By June 3, a surface low formed off an area of disturbed weather that existed several hundred miles south-southeast of Acapulco, Mexico. Remaining nearly stationary, it produced a few disorganized showers and thunderstorms. Favorable environmental conditions allowed gradual organization, and convection became better defined on June 5. It subsequently acquired sufficiently organized structure to be recognized as a tropical cyclone and NHC initiated advisories on the newly formed tropical depression One-E at 1200 UTC, June 7 while it was located around 365 mi (590 km) south of Acapulco, Mexico. The depression was situated over warm sea surface temperatures of around . Upper-level wind shear in its vicinity were minimal, which was also conducive for intensification. As a result, the tropical depression continued to become better organized, with a large rainband flaring up to the west of the circulation. Based on the improved appearance on satellite imagery, it is estimated the depression intensified into Tropical Storm Adrian at 0000 UTC on June 8, twelve hours after formation. Briefly caught within light steering winds, Adrian tracked toward the north-northwest. Continuing to increase in deep convection, NHC re-assessed the intensity to 60 mph (95 km/h) at around 0900 UTC. By nightfall, the eye-like feature developed into a central dense overcast (CDO), and at around 0000 UTC on June 9, the NHC upgraded Adrian to a minimal hurricane as it attained sustained winds of 80 mph (130 km/h). Later that day, a well-defined eye formed beneath the CDO and the surrounding cloud tops reached below , indicating intensification is present. Adrian rapidly deepened, and over the following 24 hours, it is estimated by satellite observations that winds increased from 80 mph (120 km/h) to 140 mph (240 km/h) and its barometric pressure decreased by 43 mbar (hPa; 1.27 inHg), going from a category 1 to a category 4 hurricane on the Saffir–Simpson Hurricane Scale (SSHS). During that time, its eye became more distinct, and the upper-level outflow was symmetrical. Throughout most of June 9, Adrian began transitioning into an annular hurricane, displaying a large and circular eye around in diameter, devoid of any convective banding. Adrian reaching its peak intensity at around 0000 UTC on June 10, with maximum sustained winds of 140 mph (220 km/h) and a barometric pressure estimated at 944 mbar (hPa; 27.88 inHg). It was located about 320 mi (515 km) south-southwest of Manzanillo, Mexico.
After reaching peak intensity, the convection associated with the Adrian had lessened. By then, Adrian also began moving into a more stable environment with stronger westerly wind shear, which is highly unfavorable for the sustaining tropical cyclones. By June 11, Adrian's eye completely disappeared on satellite imagery, and it no longer maintained its symmetrical structure. Steered by a low-to-mid-level ridge over the northeastern Pacific, Adrian recurved to the west, traversing sea surface temperatures cooler than . Deteriorating faster due to an unexpected increase in wind shear, Adrian weakened back into a tropical storm around 1800 UTC on June 11. Soon enough, Adrian degenerated into a tight swirl of low-level clouds with very limited deep convection. Intermittent bursts of deep convection kept satellite intensity estimates at 45 mph (65 km/h), briefly halting the weakening process. Weakening resumed and Adrian degenerated into a tropical depression six hours later, and subsequently decaying into a remnant low-pressure area at around 1200 UTC on June 12 while located about 585 mi (940 km) southwest of the southernmost tip of Baja California peninsula. Devoid of any convection, the remnant low of Adrian continued to move west for roughly two days, until gradual dissipation, as the low-level circulation opened up into a surface though.
Across the southwestern Mexican coastline, Adrian sent waves up to high, generating swells and rough seas. Plumes of moisture from the outer rainbands of Adrian caused heavy rain in the Mexican states of Oaxaca, Guerrero and Michoacán. As much as of precipitation was recorded 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 .
Late on June 20, Beatriz was upgraded to a hurricane, with winds of and a pressure of . Beatriz continued to strengthen and reached winds of and a pressure reading of 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 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