2011 Pacific hurricane season

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The 2011 Pacific hurricane season was a down season in the annual cycle of tropical cyclone formation. The season officially began on May 15 in the northeastern Pacific and June 1 in the central Pacific, ending on November 30, 2011 in both areas. These conventional dates delimit the period each year when most tropical cyclones form in the Pacific Ocean. However, the formation of these phenomena is possible at any time.

The first cyclone of the season was Hurricane Adrian, a rapidly intensifying and dissipating system that formed on June 7 off the coast of Mexico. Adrian reached category 4 on the Saffir-Simpson scale but did not cause any damage as it did not make landfall. Hurricanes Beatriz and Calvin were systems that barely reached hurricane status and also did not make landfall. In mid-July, the more intense Hurricane Dora also failed to threaten the coast of Mexico.

Forecasts

On May 19, the Climate Prediction Center released its pre-season outlook. 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. Climatologists expected 9-15 named storms, with 5-8 becoming hurricanes, and 1-3 becoming major hurricanes. Cumulative cyclone energy was expected to be 45-105% of the median.
The below-normal activity forecast was due to an increase in wind shear and a high expectation of neutral El Niño-Southern Oscillation conditions with the formation of La Niña throughout July, August and September; La Niña conditions initiate the season.

Season summary

The Cumulative Cyclone Energy Index (ACE) for the 2011 Pacific hurricane season totals 120 units (118 units in the Eastern Pacific and 1.23 units in the Central Pacific).

The season got off to an active start with the first storm, Adrian, becoming one of the tropical cyclones to reach Category 4 in June. Four other storms, Dora, Eugene, Hilary and Kenneth reached Category 4 status. Dora was the strongest storm of the year, peaking at 155 mph (250 km/h), just shy of the category 5 scale. August was about average in terms of the number of storms, being the strongest of that month. However, the first half of September had very little activity, due to the return of an event called La Niña.
Hilary became the second storm to form in September, becoming the fourth Category 4 hurricane (and the fourth major hurricane of the season), and became the second Category 4 hurricane in the first half of September, during the afternoon hours of September 22. After Hilary, Jova unexpectedly became the fifth 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 November 19, Kenneth formed as a tropical depression and quickly strengthened into a hurricane on November 21. Kenneth became the first major hurricane in November and last hurricane in the Northeast Pacific basin to be surpassed by Hurricane Sandra in 2015; the last to do so was Winnie in 1983, which only reached Category 1 status.

Tropical Cyclones

On June 3, the CNH began tracking a tropical disturbance associated with a semi-stationary low pressure area located off the coast of Mexico. In the following days, the system began to show increasing organization in an environment favorable for its development. On the afternoon of June 5, with the system located south of Acapulco, a definite cyclonic circulation was evident and the CNH assigned a 90% probability that the disturbance would develop to tropical cyclone intensity. On the morning of June 7, the formation of Tropical Depression Uno-E, the first of the season, was announced. Hours later, it was announced that the system had intensified, naming it Adrian. At 5:00 p.m. PDT on June 8, Adrian was announced. PDT on June 8, Adrian was designated a hurricane. As forecast, the system reached major hurricane category 3 on the Saffir-Simpson Scale (EHSS) on Thursday, June 9. The following day, the hurricane intensified its winds and reached category 4 on the EHSS. Adrian reached a peak intensity in the early morning hours of June 10 but remained far from the Mexican coast. But the cyclone began a progressive weakening as it entered cooler waters in the afternoon of that same day and by the morning of June 11 was tropical storm strength. The cyclone continued a rapid weakening process as it was affected by vertical wind shear and sea surface temperatures below 26.5°Celsius. On June 12, the CNH issued the final warning for Adrian, as it had lost its tropical characteristics.

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On June 19, satellite imagery indicated that a low pressure center that had been monitored off the coast of Mexico had gained enough intensity to be classified as the second depression of the season. On the morning of that day, the CNH issued tropical storm warnings and hurricane watches for sectors of the coast of the states of Guerrero and Michoacán. On June 20, the depression intensified and was named Beatriz and by the evening of the same day, it became the second hurricane of the season. The following day, Beatriz skimmed the coast of Mexico and then quickly dissipated. The storm was blamed for the deaths of three people and the disappearance of another.

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On July 5, an area of thunderstorms formed south of the Gulf of Tehuantepec associated with an area of low pressure. The system slowly organized and the CNH designated it as the third tropical depression of the season on July 7. That same night, the depression intensified and was named Tropical Storm Calvin. Calvin reached Category 1 hurricane intensity on July 8 but dissipated quickly the next day due to its transit over cold waters south of the California peninsula.



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On July 16, an area of low pressure moved from Costa Rica into the Pacific, albeit amidst strong shear conditions, unfavorable for further development. The following day conditions began to improve and on July 18 the system quickly organized itself over waters adjacent to Guatemala. The CNH began issuing warnings for Tropical Depression Four-E, which quickly intensified and was named Dora while located 425 km from San Salvador. On the night of June 19, Dora became a hurricane 390 km south of Acapulco and the following day became a Category 3 major hurricane on the EHSS. But it was on July 21 that the hurricane reached its peak intensity with winds of 250 km/h and gusts of 305 km/h, or 135 kn and 165 kn respectively, brushing category 5 and respectively moving to category 5 (If you don’t believe this consult the Saffir-Simpson Hurricane Scale). Immediately the system began a rapid weakening, and by July 23 Dora was again a tropical storm having encountered shear and being over cooler waters. Dora dissipated on July 24.

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On July 31, a tropical wave formed Tropical Depression Five-E about 600 km south of Acapulco. Just a few hours later, the depression had intensified and transformed into Tropical Storm Eugene. Eugene began a strengthening process until it reached hurricane intensity, and on August 2 it became a major hurricane. Eugene’s path did not bring it close to land. The system briefly reached Category 4 and then weakened extremely rapidly.

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By mid-August, a low-pressure system located near the intertropical convergence zone, midway between the southern tip of the Baja California peninsula and the Hawaiian Islands, was producing a compact area of deep convection. The system was affected by vertical shear from the east, but on August 15, the shear inrush ceased and the system became organized enough to be designated as the sixth tropical depression of the season, while located more than 2. 600 km from land, west of 132° meridian. By the morning of the following day, the depression began to intensify into Tropical Storm Fernanda, the sixth named system of the season. Fernanda continued its westward path and by 12:00 a.m. UTC on August 18 crossed 140° meridian, entering the Central Pacific Hurricane Center’s area of responsibility from Honolulu, Hawaii.



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On August 16, an area of low pressure that had been showing increasing organization became Tropical Depression Seven-E about 345 km south of Acapulco, Mexico. Just twelve hours later, it was upgraded to a tropical storm and named Greg, the seventh tropical system of the season. Greg reached hurricane strength on August 17 and its peak intensity the following day as it crossed the Revillagigedo Archipelago, passing between the islands of Clarion and Socorro, where an automatic weather station recorded winds of 61 km/h, with a gust of 86 km/h. Its transit over cooler ocean waters began to weaken it hours later. Greg moved over cooler waters, where it began to weaken until its dissipation on August 21.

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On August 29, an area of low pressure formed off the coast of southern Mexico. Over the next few days, the system quickly organized, as it slowly moved southward toward southern Mexico. Ocho-E soon made landfall in southwestern Mexico, and moved northward toward the northwest as it quickly weakened. Ocho-E dissipated from a remnant several hours low later, early on September 1. However, the remnants of Tropical Depression Ocho-E survived, and as it began to move westward, the remnants impacted western Mexico. During the afternoon on September 1, El Remate de Ocho-E moved away from the west coast of southwestern Mexico. During the next day, El Remate strengthened slightly in intensity as it moved northwest toward the Baja California peninsula. But on the night of September 2, Tropical Depression Eight-E’s El Remate shot up completely, just southwest of Baja California.
On September 18, a broad area of low pressure associated with minimal thunderstorm activity began to show signs of organization when it was several hundred kilometers south-southeast of the Gulf of Tehuantepec.
To the west and west-northwest, the disturbance gained enough early organization on September 21 to be declared a tropical cyclone, the ninth of the season. Permanent of organization, the depression intensified into a tropical storm hours later. On September 22, forecasters declared Hilary a category one hurricane on the Saffir-Simpson Hurricane Scale, making it the seventh of the season. On September 22, Hilary quickly strengthened into a Category 4 small hurricane with a well-defined eye and deep convection.
At 00:00 UTC 23 September, Hilary upgraded to a major hurricane, the fourth of the season. Continuing to strengthen rapidly, Hilary became a Category 4 hurricane just a few hours later after becoming a Category 3, and reached a maximum intensity of 145 mph (235 km/h) at 0600 UTC 23 September (23:00 AST 22 September). However, the storm began to enter colder waters. On September 24, Hilary began to weaken. The hurricane weakened back to a category 3 hurricane early on September 25, but was later briefly upgraded to category 4 again the following afternoon.
Several hours later, the storm was once again downgraded to a Category 3 hurricane, and during the afternoon of September 27 Hilary was downgraded further, to a Category 2 hurricane. Early the next morning, Hilary weakened to a Category 1 hurricane, and weakened to a tropical storm on September 28.
Losing much of its convection on September 30, the National Hurricane Center noted that Hilary had weakened to a tropical depression. Several hours later, after suffering no deep convection over its center, Hilary was declared a remnant low, which was several hundred miles away from land. However, over the next several days, the remnants of Hilary continued to move northwestward as a vortex of minor convection. By the afternoon of October 2, the minor convective eddy had dissipated over Baja California.

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