Hurricane Neki
Encyclopedia
Hurricane Neki was the final tropical cyclone
of the 2009 Pacific hurricane season
. It developed on October 18 as an unusually large disturbance from a trough
south of Hawaii
. Moving northwestward, it slowly organized at first due to its large size. After reaching hurricane status on October 21, Neki intensified at a much faster rate and peaked with winds of 125 mph (205 km/h). It later turned to the north and north-northeast and weakened due to hostile conditions. While passing through the Papahānaumokuākea Marine National Monument, Neki was downgraded to a tropical storm after the center became exposed from the deepest convection. It caused little impact in the island chain. After stalling and executing a small loop, Neki resumed its northward track and dissipated on October 27.
that persisted near the equator in the central Pacific Ocean in the middle of October 2009. A weak tropical disturbance became evident in the trough on October 15, and three days later the system began developing curved bands of convection on its northern and southern periphery. This created an unusually large gyre for the region. Following the formation of a well-defined circulation
, it is estimated the system developed into Tropical Depression Three-C late on October 18, about 730 mi (1175 km) south of Ka Lae
, Hawaii
.
Upon developing into a tropical cyclone, the storm was moving west-northwestward, influenced by a ridge
to its north. It was located over an area of warm sea surface temperature
s and moderate wind shear
, which favored gradual intensification. The convection diminished during a diurnal cycle before redeveloping the next day. Maintaining an unusually large size, the depression slowly organized, gradually separating from the trough from which it developed. On October 19, the CPHC upgraded it to Tropical Storm Neki, and shortly thereafter the storm turned toward the northwest. By the next day, the cyclone resembled the structure of a monsoon depression typically found in the western Pacific Ocean. However, the structure began to more resemble a tropical cyclone after the outermost convection diminished and the thunderstorms around the center increased. Following the development of a banding-eye feature
, Neki intensified into a hurricane early on October 21 about 625 mi (1010 km) southwest of Honolulu, Hawaii
, or about 335 mi (535 km) east-southeast of Johnston Atoll
.
After reaching hurricane status, Neki began rapidly intensifying
as it turned northward, due to an approaching upper-level trough to its north. An anticyclone
aloft provided favorable outflow
, which contributed in the strengthening. Early on October 22, Neki reached its peak winds of 125 mph (205 km/h) about 215 mi (345 km) northeast of Johnston Atoll, based on estimates from satellite imagery using the Dvorak technique
. Afterward, the trough that influenced the hurricane's track also began restricting westerly outflow and increasing wind shear, which caused a steady weakening trend. It maintained major hurricane status – a Category 3 on the Saffir-Simpson Hurricane Scale
– for about 24 hours, during which the track turned toward the north-northeast. The weakening and deterioration of the storm's structure became more marked on October 23 after the thunderstorms failed to persist over the center.
While approaching the Papahānaumokuākea Marine National Monument, Neki weakened to tropical storm status. Continued wind shear exposed the circulation from the convection, although further weakening was slow to occur. On October 24, Neki made its closest approach to land after passing within 13 mi (21 km) of the uninhabited Necker Island. Its forward motion slowed due to a building ridge to the north, causing the storm to execute a small loop. Despite the shear, Neki was initially able to continue developing thunderstorms, although cooler water temperatures resulted in further weakening. The storm resumed its northward motion after the ridge receded to the east, and on October 26 Neki weakened to a tropical depression once the circulation decoupled from the thunderstorms. The next day it dissipated as the center became elongated ahead of an approaching cold front.
for Johnston Island on the afternoon of October 19. The following day, the hurricane watch was replaced by a tropical storm watch as Neki was no longer forecast to pass close enough to the island to produce hurricane-force winds. Later that day, a hurricane watch was issued for the Papahānaumokuākea Marine National Monument for areas between the French Frigate Shoals
and Lisianski Island
. The following morning, a supplementary hurricane warning was issued for the monument for areas between the French Frigate Shoals and Nihoa
. Additionally, the tropical storm watch for Johnston Island was discontinued. Early on October 22, the hurricane watch for Lisianski Island to Marco Reef was replaced by a tropical storm watch. Several hours later, the CPHC discontinued this watch. Early on October 23, as Neki weakened to a tropical storm, the hurricane warning for areas between the French Frigate Shoals and Nihoa was replaced by a tropical storm warning. The tropical storm warning remained in effect for more than a day before being canceled during the afternoon of October 24.
As the hurricane turned northward and was seen as a threat to the Hawaiian Islands, officials in the Papahanaumokuakea requested that all 17 personnel in the region be evacuated. Several days before the storm passed through the islands, an AC-130 aircraft was flown to the area and evacuated the people stationed on Tern Island, while a National Oceanic and Atmospheric Administration
vessel evacuated the temporary residents on Laysan Island. Hurricane Neki caused relatively little damage in the Papahanaumokuakea Marine National Monument. All of the structures were undamaged; however, two small natural habitat islands, Round and Disappearing Islands, were affected substantially. The former lost some land area and the latter was completely washed away. Neki did not affect the state of Hawaii, other than producing high clouds across the region.
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...
of the 2009 Pacific hurricane season
2009 Pacific hurricane season
The 2009 Pacific hurricane season was an active event in the annual cycle of tropical cyclone formation, due to a moderate El Niño, unlike the 2009 Atlantic hurricane season, which was relatively quiet. The season officially started on May 15 in the eastern Pacific, and on June 1 for the central...
. It developed on October 18 as an unusually large disturbance from a trough
Trough (meteorology)
A trough is an elongated region of relatively low atmospheric pressure, often associated with fronts.Unlike fronts, there is not a universal symbol for a trough on a weather chart. The weather charts in some countries or regions mark troughs by a line. In the United States, a trough may be marked...
south 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...
. Moving northwestward, it slowly organized at first due to its large size. After reaching hurricane status on October 21, Neki intensified at a much faster rate and peaked with winds of 125 mph (205 km/h). It later turned to the north and north-northeast and weakened due to hostile conditions. While passing through the Papahānaumokuākea Marine National Monument, Neki was downgraded to a tropical storm after the center became exposed from the deepest convection. It caused little impact in the island chain. After stalling and executing a small loop, Neki resumed its northward track and dissipated on October 27.
Meteorological history
The origins of Hurricane Neki were from a surface troughTrough (meteorology)
A trough is an elongated region of relatively low atmospheric pressure, often associated with fronts.Unlike fronts, there is not a universal symbol for a trough on a weather chart. The weather charts in some countries or regions mark troughs by a line. In the United States, a trough may be marked...
that persisted near the equator in the central Pacific Ocean in the middle of October 2009. A weak tropical disturbance became evident in the trough on October 15, and three days later the system began developing curved bands of convection on its northern and southern periphery. This created an unusually large gyre for the region. Following the formation of a well-defined circulation
Atmospheric circulation
Atmospheric circulation is the large-scale movement of air, and the means by which thermal energy is distributed on the surface of the Earth....
, it is estimated the system developed into Tropical Depression Three-C late on October 18, about 730 mi (1175 km) south of Ka Lae
Ka Lae
Ka Lae , also known as South Point, is the southernmost point of the Big Island of Hawaii and of the 50 United States. The Ka Lae area is registered as a National Historic Landmark District under the name South Point Complex...
, 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...
.
Upon developing into a tropical cyclone, the storm was moving west-northwestward, influenced by a ridge
Ridge (meteorology)
A ridge is an elongated region of relatively high atmospheric pressure, the opposite of a trough....
to its north. It was located over an area of warm sea surface temperature
Sea surface temperature
Sea surface temperature is the water temperature close to the oceans surface. The exact meaning of surface varies according to the measurement method used, but it is between and below the sea surface. Air masses in the Earth's atmosphere are highly modified by sea surface temperatures within a...
s and moderate wind shear
Wind shear
Wind shear, sometimes referred to as windshear or wind gradient, is a difference in wind speed and direction over a relatively short distance in the atmosphere...
, which favored gradual intensification. The convection diminished during a diurnal cycle before redeveloping the next day. Maintaining an unusually large size, the depression slowly organized, gradually separating from the trough from which it developed. On October 19, the CPHC upgraded it to Tropical Storm Neki, and shortly thereafter the storm turned toward the northwest. By the next day, the cyclone resembled the structure of a monsoon depression typically found in the western Pacific Ocean. However, the structure began to more resemble a tropical cyclone after the outermost convection diminished and the thunderstorms around the center increased. Following the development of a banding-eye feature
Eye (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...
, Neki intensified into a hurricane early on October 21 about 625 mi (1010 km) southwest of Honolulu, Hawaii
Honolulu, Hawaii
Honolulu is the capital and the most populous city of the U.S. state of Hawaii. Honolulu is the southernmost major U.S. city. Although the name "Honolulu" refers to the urban area on the southeastern shore of the island of Oahu, the city and county government are consolidated as the City and...
, or about 335 mi (535 km) east-southeast of Johnston Atoll
Johnston Atoll
Johnston Atoll is a atoll in the North Pacific Ocean about west of Hawaii. There are four islands located on the coral reef platform, two natural islands, Johnston Island and Sand Island, which have been expanded by coral dredging, as well as North Island and East Island , an additional two...
.
After reaching hurricane status, Neki began rapidly intensifying
Rapid deepening
Rapid deepening, also known as rapid intensification, is a meteorological condition that occurs when the minimum sea-level atmospheric pressure of a tropical cyclone decreases drastically in a short period of time. The National Weather Service describes rapid deepening as a decrease of...
as it turned northward, due to an approaching upper-level trough to its north. An anticyclone
Anticyclone
An anticyclone is a weather phenomenon defined by the United States' National Weather Service's glossary as "[a] large-scale circulation of winds around a central region of high atmospheric pressure, clockwise in the Northern Hemisphere, counterclockwise in the Southern Hemisphere"...
aloft provided favorable outflow
Outflow (meteorology)
Outflow, in meteorology, is air that flows outwards from a storm system. It is associated with ridging, or anticyclonic flow. In the low levels of the troposphere, outflow radiates from thunderstorms in the form of a wedge of rain-cooled air, which is visible as a thin rope-like cloud on weather...
, which contributed in the strengthening. Early on October 22, Neki reached its peak winds of 125 mph (205 km/h) about 215 mi (345 km) northeast of Johnston Atoll, based on estimates from satellite imagery using the Dvorak technique
Dvorak technique
The Dvorak technique is a widely used system to subjectively estimate tropical cyclone intensity based solely on visible and infrared satellite images. Several agencies issue Dvorak intensity numbers for cyclones of sufficient intensity...
. Afterward, the trough that influenced the hurricane's track also began restricting westerly outflow and increasing wind shear, which caused a steady weakening trend. It maintained major hurricane status – a Category 3 on the Saffir-Simpson Hurricane Scale
Saffir-Simpson Hurricane Scale
The Saffir–Simpson Hurricane Scale , or the Saffir–Simpson Hurricane Wind Scale , classifies hurricanes — Western Hemisphere tropical cyclones that exceed the intensities of tropical depressions and tropical storms — into five categories distinguished by the intensities of their sustained winds...
– for about 24 hours, during which the track turned toward the north-northeast. The weakening and deterioration of the storm's structure became more marked on October 23 after the thunderstorms failed to persist over the center.
While approaching the Papahānaumokuākea Marine National Monument, Neki weakened to tropical storm status. Continued wind shear exposed the circulation from the convection, although further weakening was slow to occur. On October 24, Neki made its closest approach to land after passing within 13 mi (21 km) of the uninhabited Necker Island. Its forward motion slowed due to a building ridge to the north, causing the storm to execute a small loop. Despite the shear, Neki was initially able to continue developing thunderstorms, although cooler water temperatures resulted in further weakening. The storm resumed its northward motion after the ridge receded to the east, and on October 26 Neki weakened to a tropical depression once the circulation decoupled from the thunderstorms. The next day it dissipated as the center became elongated ahead of an approaching cold front.
Preparations and impact
Although still a minimal tropical storm at the time, the CPHC anticipated Neki to become a hurricane as it tracked northwestward. As such, they issued a hurricane watchTropical cyclone warnings and watches
Warnings and watches are two levels of alert issued by national weather forecasting bodies to coastal areas threatened by the imminent approach of a tropical cyclone of tropical storm or hurricane intensity. They are notices to the local population and civil authorities to make appropriate...
for Johnston Island on the afternoon of October 19. The following day, the hurricane watch was replaced by a tropical storm watch as Neki was no longer forecast to pass close enough to the island to produce hurricane-force winds. Later that day, a hurricane watch was issued for the Papahānaumokuākea Marine National Monument for areas between the French Frigate Shoals
French Frigate Shoals
The French Frigate Shoals is the largest atoll in the Northwestern Hawaiian Islands. Its name commemorates French explorer Jean-François de La Pérouse, who nearly lost two frigates when attempting to navigate the shoals...
and Lisianski Island
Lisianski Island
Lisianski Island is one of the Northwestern Hawaiian Islands, with a land area of and a maximum elevation of above sea level. Honolulu is away, to the southeast. Linked to Lisianski are the extensive Neva Shoals...
. The following morning, a supplementary hurricane warning was issued for the monument for areas between the French Frigate Shoals and Nihoa
Nihoa
Nihoa , also known as Bird Island or Moku Manu, is the largest and tallest of ten islands and atolls in the uninhabited Northwestern Hawaiian Islands . The island is located at the southern end of the NWHI chain, southeast of Necker Island...
. Additionally, the tropical storm watch for Johnston Island was discontinued. Early on October 22, the hurricane watch for Lisianski Island to Marco Reef was replaced by a tropical storm watch. Several hours later, the CPHC discontinued this watch. Early on October 23, as Neki weakened to a tropical storm, the hurricane warning for areas between the French Frigate Shoals and Nihoa was replaced by a tropical storm warning. The tropical storm warning remained in effect for more than a day before being canceled during the afternoon of October 24.
As the hurricane turned northward and was seen as a threat to the Hawaiian Islands, officials in the Papahanaumokuakea requested that all 17 personnel in the region be evacuated. Several days before the storm passed through the islands, an AC-130 aircraft was flown to the area and evacuated the people stationed on Tern Island, while a National Oceanic and Atmospheric Administration
National Oceanic and Atmospheric Administration
The National Oceanic and Atmospheric Administration , pronounced , like "noah", is a scientific agency within the United States Department of Commerce focused on the conditions of the oceans and the atmosphere...
vessel evacuated the temporary residents on Laysan Island. Hurricane Neki caused relatively little damage in the Papahanaumokuakea Marine National Monument. All of the structures were undamaged; however, two small natural habitat islands, Round and Disappearing Islands, were affected substantially. The former lost some land area and the latter was completely washed away. Neki did not affect the state of Hawaii, other than producing high clouds across the region.