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Hurricane Hernan (2008)
Encyclopedia
Hurricane Hernan was the ninth tropical depression
, eighth named storm, fifth hurricane, and first major hurricane of the 2008 Pacific hurricane season
. Hernan developed out of a tropical wave
that formed off the east coast of Africa
on July 24. Over the next week, the wave traversed the Atlantic
without development and entered the Eastern Pacific basin
on August 2. The wave became better organized over the next several days and was declared Tropical Depression Nine-E on August 6. The depression quickly became Tropical Storm Hernan later that day. Hernan steadily intensified over the next two days and was upgraded to a hurricane on the morning of August 8. Hernan continued to intensify and became the first major hurricane—a storm with winds of 111 mph (178 km/h) or higher—of the season on August 9. After reaching major hurricane status, Hernan steadily weakened to a minimal hurricane. The weakening continued, and Hernan was further downgraded to a tropical storm on August 11. As Hernan moved over cold waters, the convection
associated with the storm dissipated, leaving only a swirl of clouds. By the morning of August 12, almost all of the convection associated with Hernan had dissipated and the system was declared a remnant low-pressure area
despite retaining tropical storm-force winds. The low moved towards the west-southwest over the next several days before dissipating 460 mi (740 km) southeast of the Island of Hawaii
. The remnants of the hurricane caused light rain to Hawaii
.
emerged from the east coast of Africa
, near the Cape Verde
Islands. The wave was disorganized and failed to develop convection
as it traversed the Atlantic
over the next several days. The wave eventually entered the Eastern Pacific basin
on August 2, and interacted with a broad area of cyclonic flow located a few hundred miles south of Mexico
. The wave became better organized throughout the day, and cyclonic turning
was noted. This was due to the interaction between the wave and the area of cyclonic turning, which had produced an area of low pressure
660 mi (1060 km) south of Manzanillo, Mexico on August 5. Strong convection began to develop and slow development was forecast over the next 36–49 hours. On August 5, a banding feature formed as convection continued to persist around the center of the wave. On the morning of August 6, a Tropical Cyclone Formation Alert
was issued, as development of the system was anticipated over the next several days. Later in the day, the National Hurricane Center determined that the system had developed sufficient convection to be declared Tropical Depression Nine-E while located 775 mi (1230 km) to the south-southwest of the southern tip of Baja California
. However, the storm was operationally believed to have become a depression several hours later.
Tropical Depression Nine-E was influenced by a high pressure area located over Mexico, causing it to move 16 mph (26 km/h) to the north-west. The depression was upgraded to Tropical Storm Hernan overnight as the storm became more organized. Although Hernan was located over warm waters, moderate wind shear prevented the storm from intensifying quickly, and the storm continued towards the west-northwest at a slower pace. Hernan continued to slowly become better organized throughout the night, but was still being impaired by northeasterly vertical wind shear during the morning on August 7. Wind shear continued to impair Hernan through the morning; as a result, none of the forecast models, excluding the GFDL, forecast Hernan to become a hurricane.
feature began to form, prompting the National Hurricane Center
to state that Hernan was nearing hurricane status. However, by the nighttime hours, a microwave satellite found that the center of Hernan was located to the west-southwest of the eye feature, and the intensification ceased for the rest of the day and into the morning of August 8. Later in the morning, the center of Hernan was determined to be located underneath the eye and was determined to have become a hurricane, the fifth of the season, at 8 a.m. (PST) on August 8. Throughout the day, the eye became better defined, indicating that Hernan was intensifying. The moderate northeasterly wind shear had already begun to diminish, leading forecasters to show Hernan peaking as a Category 2 hurricane overnight. That night, the eye was determined to be 30 mi (50 km), though cloud-filled. The convection surrounding the eye also became more intense.
Early on August 9, Hernan was upgraded to a Category 2 hurricane, with winds of 100 mph (155 km/h). Convection around the eye continued become more symmetrical, though the National Hurricane Center
had stated that Hernan had most likely reached its peak intensity or was very close to doing so. Hernan continued to become better organized throughout the morning, and the eye suddenly became better defined and deep convection formed around the eye. Due to the sudden increase in organization, Hernan was upgraded to a major hurricane. The intensity of Hernan was uncertain, as there was some difference between intensity estimates. Hernan maintained its appearance through the early afternoon, and it was stated that the peak intensity of the storm may have been 125 mph (205 km/h). However, this was not supported by the post-storm report on Hernan. In the late afternoon, Hernan moved over cooler waters and started to weaken. The eye contracted slightly to 25 miles (35 km). Although the eye remained well defined, outflow to all the southwestern semicircle became poor.
remained intact throughout the night. Later in the morning, weakening slowed, and Hernan was downgraded to a strong Category 1. The western portion of the eyewall had begun to erode due to the cooling waters. The erosion of the eyewall was later found to be caused by an eyewall replacement cycle
that rapidly completed itself during the afternoon. Continuing to slowly weaken, The newly formed eye began to shrink and deteriorate through the early afternoon, but Hernan briefly stopped weakening. The weakening trend continued again during the night of August 10 as the cloud tops warmed. Once more, the weakening stopped as a strong burst of convection around the center of the storm appeared. Hernan's strong circulation allowed it to maintain hurricane status over 24°C waters.
Early on August 11, Hernan was downgraded to a tropical storm. Slow weakening continued through the morning and afternoon as convection diminished around the center of the storm. By the early morning of August 12, almost all of the deep convection dissipated as Hernan continued to weaken. Convection continued to diminish as Hernan traveled over 23°C water and was barely holding on to tropical storm status. By the afternoon of August 12, only a small area of tropical storm force winds remained with Hernan. Only a swirl of clouds remained and the storm was barely a tropical system
. Later that night, Hernan had degenerated into a remnant low, and the final advisory was issued by the National Hurricane Center. The remnant low still retained tropical storm-force winds for a short while before weakening further by the next morning. The low moved towards the west-southwest over the next several days before dissipating 460 mi (740 km) southeast of the Island of Hawaii
on August 16. The remnant low-pressure area
of Hernan later brought moisture to the island of Hawaii
, causing cloud and shower activity. The associated rainfall was light and insignificant.
Tropical cyclone
A tropical cyclone is a storm system characterized by a large low-pressure center and numerous thunderstorms that produce strong winds and heavy rain. Tropical cyclones strengthen when water evaporated from the ocean is released as the saturated air rises, resulting in condensation of water vapor...
, eighth named storm, fifth hurricane, and first major hurricane of the 2008 Pacific hurricane season
2008 Pacific hurricane season
The 2008 Pacific hurricane season was an event in the annual cycle of tropical cyclone formation. It officially started May 15, 2008 in the eastern Pacific, started on June 1, 2008 in the central Pacific, and lasted until November 30, 2008....
. Hernan developed out of a tropical wave
Tropical wave
Tropical waves, easterly waves, or tropical easterly waves, also known as African easterly waves in the Atlantic region, are a type of atmospheric trough, an elongated area of relatively low air pressure, oriented north to south, which move from east to west across the tropics causing areas of...
that formed off the east coast of Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
on July 24. Over the next week, the wave traversed the Atlantic
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
without development and entered the Eastern Pacific basin
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
on August 2. The wave became better organized over the next several days and was declared Tropical Depression Nine-E on August 6. The depression quickly became Tropical Storm Hernan later that day. Hernan steadily intensified over the next two days and was upgraded to a hurricane on the morning of August 8. Hernan continued to intensify and became the first major hurricane—a storm with winds of 111 mph (178 km/h) or higher—of the season on August 9. After reaching major hurricane status, Hernan steadily weakened to a minimal hurricane. The weakening continued, and Hernan was further downgraded to a tropical storm on August 11. As Hernan moved over cold waters, the convection
Atmospheric convection
Atmospheric convection is the result of a parcel-environment instability, or temperature difference, layer in the atmosphere. Different lapse rates within dry and moist air lead to instability. Mixing of air during the day which expands the height of the planetary boundary layer leads to...
associated with the storm dissipated, leaving only a swirl of clouds. By the morning of August 12, almost all of the convection associated with Hernan had dissipated and the system was declared a remnant low-pressure area
Low pressure area
A low-pressure area, or "low", is a region where the atmospheric pressure at sea level is below that of surrounding locations. Low-pressure systems form under areas of wind divergence which occur in upper levels of the troposphere. The formation process of a low-pressure area is known as...
despite retaining tropical storm-force winds. The low moved towards the west-southwest over the next several days before dissipating 460 mi (740 km) southeast of the Island of Hawaii
Hawaii (island)
The Island of Hawaii, also called the Big Island or Hawaii Island , is a volcanic island in the North Pacific Ocean...
. The remnants of the hurricane caused light rain to Hawaii
Hawaii
Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...
.
Origins
On July 24, a tropical waveTropical wave
Tropical waves, easterly waves, or tropical easterly waves, also known as African easterly waves in the Atlantic region, are a type of atmospheric trough, an elongated area of relatively low air pressure, oriented north to south, which move from east to west across the tropics causing areas of...
emerged from the east coast of Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
, near the Cape Verde
Cape Verde
The Republic of Cape Verde is an island country, spanning an archipelago of 10 islands located in the central Atlantic Ocean, 570 kilometres off the coast of Western Africa...
Islands. The wave was disorganized and failed to develop convection
Atmospheric convection
Atmospheric convection is the result of a parcel-environment instability, or temperature difference, layer in the atmosphere. Different lapse rates within dry and moist air lead to instability. Mixing of air during the day which expands the height of the planetary boundary layer leads to...
as it traversed the Atlantic
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
over the next several days. The wave eventually entered the Eastern Pacific basin
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
on August 2, and interacted with a broad area of cyclonic flow located a few hundred miles south of Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
. The wave became better organized throughout the day, and cyclonic turning
Coriolis effect
In physics, the Coriolis effect is a deflection of moving objects when they are viewed in a rotating reference frame. In a reference frame with clockwise rotation, the deflection is to the left of the motion of the object; in one with counter-clockwise rotation, the deflection is to the right...
was noted. This was due to the interaction between the wave and the area of cyclonic turning, which had produced an area of low pressure
Low pressure area
A low-pressure area, or "low", is a region where the atmospheric pressure at sea level is below that of surrounding locations. Low-pressure systems form under areas of wind divergence which occur in upper levels of the troposphere. The formation process of a low-pressure area is known as...
660 mi (1060 km) south of Manzanillo, Mexico on August 5. Strong convection began to develop and slow development was forecast over the next 36–49 hours. On August 5, a banding feature formed as convection continued to persist around the center of the wave. On the morning of August 6, a Tropical Cyclone Formation Alert
Tropical Cyclone Formation Alert
A Tropical Cyclone Formation Alert is a bulletin released by the U.S. Navy-operated Joint Typhoon Warning Center in Honolulu, Hawaii or the Naval Maritime Forecast Center in Norfolk, Virginia, warning of the possibility of a tropical cyclone forming from a tropical disturbance that has been...
was issued, as development of the system was anticipated over the next several days. Later in the day, the National Hurricane Center determined that the system had developed sufficient convection to be declared Tropical Depression Nine-E while located 775 mi (1230 km) to the south-southwest of the southern tip of Baja California
Baja California Sur
Baja California Sur , is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico. Before becoming a state on October 8, 1974, the area was known as the South Territory of Baja California. It has an area of , or 3.57% of the land mass of Mexico and comprises...
. However, the storm was operationally believed to have become a depression several hours later.
Tropical Depression Nine-E was influenced by a high pressure area located over Mexico, causing it to move 16 mph (26 km/h) to the north-west. The depression was upgraded to Tropical Storm Hernan overnight as the storm became more organized. Although Hernan was located over warm waters, moderate wind shear prevented the storm from intensifying quickly, and the storm continued towards the west-northwest at a slower pace. Hernan continued to slowly become better organized throughout the night, but was still being impaired by northeasterly vertical wind shear during the morning on August 7. Wind shear continued to impair Hernan through the morning; as a result, none of the forecast models, excluding the GFDL, forecast Hernan to become a hurricane.
Intensification and peak strength
In the early afternoon, an eyeEye (cyclone)
The eye is a region of mostly calm weather found at the center of strong tropical cyclones. The eye of a storm is a roughly circular area and typically 30–65 km in diameter. It is surrounded by the eyewall, a ring of towering thunderstorms where the second most severe weather of a cyclone...
feature began to form, prompting the National Hurricane Center
National Hurricane Center
The National Hurricane Center , located at Florida International University in Miami, Florida, is the division of the National Weather Service responsible for tracking and predicting weather systems within the tropics between the Prime Meridian and the 140th meridian west poleward to the 30th...
to state that Hernan was nearing hurricane status. However, by the nighttime hours, a microwave satellite found that the center of Hernan was located to the west-southwest of the eye feature, and the intensification ceased for the rest of the day and into the morning of August 8. Later in the morning, the center of Hernan was determined to be located underneath the eye and was determined to have become a hurricane, the fifth of the season, at 8 a.m. (PST) on August 8. Throughout the day, the eye became better defined, indicating that Hernan was intensifying. The moderate northeasterly wind shear had already begun to diminish, leading forecasters to show Hernan peaking as a Category 2 hurricane overnight. That night, the eye was determined to be 30 mi (50 km), though cloud-filled. The convection surrounding the eye also became more intense.
Early on August 9, Hernan was upgraded to a Category 2 hurricane, with winds of 100 mph (155 km/h). Convection around the eye continued become more symmetrical, though the National Hurricane Center
National Hurricane Center
The National Hurricane Center , located at Florida International University in Miami, Florida, is the division of the National Weather Service responsible for tracking and predicting weather systems within the tropics between the Prime Meridian and the 140th meridian west poleward to the 30th...
had stated that Hernan had most likely reached its peak intensity or was very close to doing so. Hernan continued to become better organized throughout the morning, and the eye suddenly became better defined and deep convection formed around the eye. Due to the sudden increase in organization, Hernan was upgraded to a major hurricane. The intensity of Hernan was uncertain, as there was some difference between intensity estimates. Hernan maintained its appearance through the early afternoon, and it was stated that the peak intensity of the storm may have been 125 mph (205 km/h). However, this was not supported by the post-storm report on Hernan. In the late afternoon, Hernan moved over cooler waters and started to weaken. The eye contracted slightly to 25 miles (35 km). Although the eye remained well defined, outflow to all the southwestern semicircle became poor.
Weakening and dissipation
Hernan rapidly weakened overnight and was barely a Category 2 in the early hours of August 10 as it moved over cooler waters. However, the eyewallEye (cyclone)
The eye is a region of mostly calm weather found at the center of strong tropical cyclones. The eye of a storm is a roughly circular area and typically 30–65 km in diameter. It is surrounded by the eyewall, a ring of towering thunderstorms where the second most severe weather of a cyclone...
remained intact throughout the night. Later in the morning, weakening slowed, and Hernan was downgraded to a strong Category 1. The western portion of the eyewall had begun to erode due to the cooling waters. The erosion of the eyewall was later found to be caused by an eyewall replacement cycle
Eyewall replacement cycle
Eyewall replacement cycles, also called concentric eyewall cycles, naturally occur in intense tropical cyclones, generally with winds greater than 185 km/h , or major hurricanes...
that rapidly completed itself during the afternoon. Continuing to slowly weaken, The newly formed eye began to shrink and deteriorate through the early afternoon, but Hernan briefly stopped weakening. The weakening trend continued again during the night of August 10 as the cloud tops warmed. Once more, the weakening stopped as a strong burst of convection around the center of the storm appeared. Hernan's strong circulation allowed it to maintain hurricane status over 24°C waters.
Early on August 11, Hernan was downgraded to a tropical storm. Slow weakening continued through the morning and afternoon as convection diminished around the center of the storm. By the early morning of August 12, almost all of the deep convection dissipated as Hernan continued to weaken. Convection continued to diminish as Hernan traveled over 23°C water and was barely holding on to tropical storm status. By the afternoon of August 12, only a small area of tropical storm force winds remained with Hernan. Only a swirl of clouds remained and the storm was barely a tropical system
Tropical cyclone
A tropical cyclone is a storm system characterized by a large low-pressure center and numerous thunderstorms that produce strong winds and heavy rain. Tropical cyclones strengthen when water evaporated from the ocean is released as the saturated air rises, resulting in condensation of water vapor...
. Later that night, Hernan had degenerated into a remnant low, and the final advisory was issued by the National Hurricane Center. The remnant low still retained tropical storm-force winds for a short while before weakening further by the next morning. The low moved towards the west-southwest over the next several days before dissipating 460 mi (740 km) southeast of the Island of Hawaii
Hawaii (island)
The Island of Hawaii, also called the Big Island or Hawaii Island , is a volcanic island in the North Pacific Ocean...
on August 16. The remnant low-pressure area
Low pressure area
A low-pressure area, or "low", is a region where the atmospheric pressure at sea level is below that of surrounding locations. Low-pressure systems form under areas of wind divergence which occur in upper levels of the troposphere. The formation process of a low-pressure area is known as...
of Hernan later brought moisture to the island of Hawaii
Hawaii
Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...
, causing cloud and shower activity. The associated rainfall was light and insignificant.
See also
- 2008 Pacific hurricane season2008 Pacific hurricane seasonThe 2008 Pacific hurricane season was an event in the annual cycle of tropical cyclone formation. It officially started May 15, 2008 in the eastern Pacific, started on June 1, 2008 in the central Pacific, and lasted until November 30, 2008....
- List of Pacific hurricanes
- Timeline of the 2008 Pacific hurricane seasonTimeline of the 2008 Pacific hurricane seasonBelow is the Timeline of the 2008 Pacific hurricane season, documenting all the storm formations, strengthening, weakening, landfalls, extratropical transitions, as well as dissipation. The 2008 Pacific hurricane season officially began on May 15, 2008, and will last until November 30. For...