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Unnamed Hurricane (1975)
Encyclopedia
The 1975 Pacific Northwest hurricane was an unusual Pacific
tropical cyclone
that attained hurricane status farther north than any other Pacific hurricane. It was officially unnamed, with the cargo ship
providing vital meteorological data in assessing the storm. The twelfth tropical cyclone of the 1975 Pacific hurricane season
, it developed from a cold-core upper-level low merging with the remnants of a tropical cyclone on August 31, well to the northeast of Hawaii
. Convection increased as the circulation became better defined, and by early on September 2 it became a tropical storm. Turning to the northeast through an area of warm water temperatures, the storm quickly strengthened, and, after developing an eye
, it attained hurricane status late on September 3, while located about 1,200 miles (1,950 km) south of Alaska
. After maintaining peak winds for about 18 hours, the storm rapidly weakened, as it interacted with an approaching cold front
. Early on September 5, it lost its identity near the coast of Alaska.
that was once Hurricane Ilsa degenerated into a remnant low pressure area
about 1,200 miles (1,950 km) west of the southern tip of the Baja California Peninsula
. The remnants of Ilsa drifted northwestward through the Stratocumulus cloud
field of the eastern north Pacific Ocean
. At the same time, a mid-tropospheric trough
slowly intensified while gradually undergoing cyclogenesis to develop into a cold-core upper-level low. Early on August 31, a low-level circulation formed within the upper-level low about 930 miles (1,500 km) northeast of Hawaii
; at that time, the circulation and the remnants of Ilsa were located within 370 miles (600 km) of each other. The cold-core low rapidly intensified as convection increased, and late on August 31 it absorbed the remnants of Ilsa, which influenced the development of the system. Convection steadily organized as it tracked westward, and it is estimated it transitioned into a subtropical depression
by 18:00 UTC on September 1.
With warm water temperatures, the system strengthened and began to develop tropical characteristics
. Subsequent to the development of banding features
, convection contracted and deepened over the increasingly well-defined center, and is estimated it became a tropical storm by early on September 2 while located about 685 miles (1,100 km) north of the Hawaiian island of Kauai
. The storm quickly developed a central dense overcast, and by 00:00 UTC on September 3 Dvorak classifications
began on the cyclone. With water temperatures of over 82 °F (28 °C), it strengthened rapidly as an approaching cold front
caused it to accelerate to the northeast. An eye
became apparent on satellite imagery, and the storm intensified into a hurricane at 18:00 UTC on September 3, while located about 1,170 miles (1,885 km) south of Aniakchak National Monument and Preserve
in Alaska
. Upon becoming a hurricane, the cyclone was small, measuring about 85 miles (140 km) in diameter.
Operationally, the hurricane was not classified due to lack of ship confirmation; by the time it became a hurricane, the strongest winds reported by a ship was 40 mph (65 km/h) about 80 miles (130 km) southeast of the center. Additionally, upon developing a closed eyewall, the cyclone was beginning to interact with the frontal system to its west. However, late on September 3, a ship reported a pressure of 1003 mbar
with a 3-hour tendency increase of 13.5 mb, suggesting a minimum pressure of under 990 mbar. At the time, the storm maintained a T-number of 4.0, resulting in estimated winds of 75 mph (120 km/h) and an estimated pressure of 987 mbar. Maintaining hurricane status for about 18 hours, the storm continued rapidly northeastward and weakened due to strong wind shear
from the approaching cold front. Early on September 5, it is estimated the cyclone became extratropical
in the Gulf of Alaska
while located about 315 miles (510 km) southwest of Juneau, Alaska. The circulation was rapidly absorbed by the front, and the remnants quickly reached the coast of British Columbia
. The remnants of the storm turned southeastward, and was last tracked definitively to a point north of Montana
.
recorded winds of 65 mph (100 km/h) about 120 miles (200 km), the strongest reported winds in association with the tropical cyclone; the ship also reported 27 foot (8.5 m) swells. No significant land impact occurred in association with the cyclone, and no fatalities were reported.
Forming at 31° N
, the storm formed farther north than any other Pacific
tropical cyclone at the time, though, in 2000, Tropical Storm Wene formed farther to the north. The cyclone marked the first known occurrence of a mid-Pacific upper tropospheric low developing into a tropical cyclone, though Tropical Storm Fausto
in 2002 redeveloped in a similar occurrence to the hurricane. The cyclone attained hurricane status at 40° N, a record for a Pacific hurricane. Only Tropical Storm Dot in 1970, Hurricane John
in 1994, Tropical Depression Guillermo
in 1997, and Tropical Storm Wene in 2000 were tropical cyclones north of the latitude, of which only John was a hurricane; none maintained tropical cyclone status further north than the cyclone.
Pacific hurricane
A Pacific hurricane or tropical storm is a tropical cyclone that develops in the northeastern part of the Pacific Ocean. For organizational purposes, the northern Pacific Ocean is divided into three regions: the eastern, , central , and western...
tropical cyclone
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...
that attained hurricane status farther north than any other Pacific hurricane. It was officially unnamed, with the cargo ship
Cargo ship
A cargo ship or freighter is any sort of ship or vessel that carries cargo, goods, and materials from one port to another. Thousands of cargo carriers ply the world's seas and oceans each year; they handle the bulk of international trade...
providing vital meteorological data in assessing the storm. The twelfth tropical cyclone of the 1975 Pacific hurricane season
1975 Pacific hurricane season
The 1975 Pacific hurricane season officially started May 15, 1975 in the eastern Pacific, and June 1, 1975 in the central Pacific, and lasted until November 30, 1975. These dates conventionally delimit the period of each year when most tropical cyclones form in the northeast Pacific Ocean.The 1975...
, it developed from a cold-core upper-level low merging with the remnants of a tropical cyclone on August 31, well to the northeast 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...
. Convection increased as the circulation became better defined, and by early on September 2 it became a tropical storm. Turning to the northeast through an area of warm water temperatures, the storm quickly strengthened, and, after developing an eye
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...
, it attained hurricane status late on September 3, while located about 1,200 miles (1,950 km) south of Alaska
Alaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...
. After maintaining peak winds for about 18 hours, the storm rapidly weakened, as it interacted with an approaching cold front
Cold front
A cold front is defined as the leading edge of a cooler mass of air, replacing a warmer mass of air.-Development of cold front:The cooler and denser air wedges under the less-dense warmer air, lifting it...
. Early on September 5, it lost its identity near the coast of Alaska.
Meteorological history
On August 26, the tropical cycloneTropical 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...
that was once Hurricane Ilsa degenerated into 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...
about 1,200 miles (1,950 km) west of the southern tip of the Baja California Peninsula
Baja California Peninsula
The Baja California peninsula , is a peninsula in northwestern Mexico. Its land mass separates the Pacific Ocean from the Gulf of California. The Peninsula extends from Mexicali, Baja California in the north to Cabo San Lucas, Baja California Sur in the south.The total area of the Baja California...
. The remnants of Ilsa drifted northwestward through the Stratocumulus cloud
Stratocumulus cloud
A Stratocumulus cloud belongs to a class of clouds characterized by large dark, rounded masses, usually in groups, lines, or waves, the individual elements being larger than those in altocumuli, and the whole being at a lower altitude, usually below 2,400 m...
field of the eastern north Pacific Ocean
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...
. At the same time, a mid-tropospheric 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...
slowly intensified while gradually undergoing cyclogenesis to develop into a cold-core upper-level low. Early on August 31, a low-level circulation formed within the upper-level low about 930 miles (1,500 km) northeast 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...
; at that time, the circulation and the remnants of Ilsa were located within 370 miles (600 km) of each other. The cold-core low rapidly intensified as convection increased, and late on August 31 it absorbed the remnants of Ilsa, which influenced the development of the system. Convection steadily organized as it tracked westward, and it is estimated it transitioned into a subtropical depression
Subtropical cyclone
A subtropical cyclone is a weather system that has some characteristics of a tropical and an extratropical cyclone. As early as the 1950s, meteorologists were unclear whether they should be characterized as tropical or extratropical cyclones. They were officially recognized by the National...
by 18:00 UTC on September 1.
With warm water temperatures, the system strengthened and began to develop tropical characteristics
Tropical cyclogenesis
Tropical cyclogenesis is the term that describes the development and strengthening of a tropical cyclone in the atmosphere. The mechanisms through which tropical cyclogenesis occurs are distinctly different from those through which mid-latitude cyclogenesis occurs...
. Subsequent to the development of banding features
Squall
A squall is a sudden, sharp increase in wind speed which is usually associated with active weather, such as rain showers, thunderstorms, or heavy snow. Squalls refer to an increase in the sustained winds over a short time interval, as there may be higher gusts during a squall event...
, convection contracted and deepened over the increasingly well-defined center, and is estimated it became a tropical storm by early on September 2 while located about 685 miles (1,100 km) north of the Hawaiian island of Kauai
Kauai
Kauai or Kauai, known as Tauai in the ancient Kaua'i dialect, is geologically the oldest of the main Hawaiian Islands. With an area of , it is the fourth largest of the main islands in the Hawaiian archipelago, and the 21st largest island in the United States. Known also as the "Garden Isle",...
. The storm quickly developed a central dense overcast, and by 00:00 UTC on September 3 Dvorak classifications
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...
began on the cyclone. With water temperatures of over 82 °F (28 °C), it strengthened rapidly as an approaching cold front
Cold front
A cold front is defined as the leading edge of a cooler mass of air, replacing a warmer mass of air.-Development of cold front:The cooler and denser air wedges under the less-dense warmer air, lifting it...
caused it to accelerate to the northeast. An eye
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...
became apparent on satellite imagery, and the storm intensified into a hurricane at 18:00 UTC on September 3, while located about 1,170 miles (1,885 km) south of Aniakchak National Monument and Preserve
Aniakchak National Monument and Preserve
Aniakchak National Monument and Preserve is a U.S. National Monument and National Preserve, consisting of the region around the Aniakchak volcano on the Aleutian Range of south-western Alaska....
in Alaska
Alaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...
. Upon becoming a hurricane, the cyclone was small, measuring about 85 miles (140 km) in diameter.
Operationally, the hurricane was not classified due to lack of ship confirmation; by the time it became a hurricane, the strongest winds reported by a ship was 40 mph (65 km/h) about 80 miles (130 km) southeast of the center. Additionally, upon developing a closed eyewall, the cyclone was beginning to interact with the frontal system to its west. However, late on September 3, a ship reported a pressure of 1003 mbar
Bar (unit)
The bar is a unit of pressure equal to 100 kilopascals, and roughly equal to the atmospheric pressure on Earth at sea level. Other units derived from the bar are the megabar , kilobar , decibar , centibar , and millibar...
with a 3-hour tendency increase of 13.5 mb, suggesting a minimum pressure of under 990 mbar. At the time, the storm maintained a T-number of 4.0, resulting in estimated winds of 75 mph (120 km/h) and an estimated pressure of 987 mbar. Maintaining hurricane status for about 18 hours, the storm continued rapidly northeastward and weakened due to strong 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...
from the approaching cold front. Early on September 5, it is estimated the cyclone became extratropical
Extratropical cyclone
Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are a group of cyclones defined as synoptic scale low pressure weather systems that occur in the middle latitudes of the Earth having neither tropical nor polar characteristics, and are connected with fronts and...
in the Gulf of Alaska
Gulf of Alaska
The Gulf of Alaska is an arm of the Pacific Ocean defined by the curve of the southern coast of Alaska, stretching from the Alaska Peninsula and Kodiak Island in the west to the Alexander Archipelago in the east, where Glacier Bay and the Inside Passage are found.The entire shoreline of the Gulf is...
while located about 315 miles (510 km) southwest of Juneau, Alaska. The circulation was rapidly absorbed by the front, and the remnants quickly reached the coast of British Columbia
British Columbia
British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...
. The remnants of the storm turned southeastward, and was last tracked definitively to a point north of Montana
Montana
Montana is a state in the Western United States. The western third of Montana contains numerous mountain ranges. Smaller, "island ranges" are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...
.
Impact and records
At 18:00 UTC on September 3, a ship named Pluvius recorded 50 mph (85 km/h) winds near the center of the storm. At 06:00 UTC on September 4, the U.S. Navy-chartered cargo shipCargo ship
A cargo ship or freighter is any sort of ship or vessel that carries cargo, goods, and materials from one port to another. Thousands of cargo carriers ply the world's seas and oceans each year; they handle the bulk of international trade...
recorded winds of 65 mph (100 km/h) about 120 miles (200 km), the strongest reported winds in association with the tropical cyclone; the ship also reported 27 foot (8.5 m) swells. No significant land impact occurred in association with the cyclone, and no fatalities were reported.
Forming at 31° N
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...
, the storm formed farther north than any other Pacific
Pacific hurricane
A Pacific hurricane or tropical storm is a tropical cyclone that develops in the northeastern part of the Pacific Ocean. For organizational purposes, the northern Pacific Ocean is divided into three regions: the eastern, , central , and western...
tropical cyclone at the time, though, in 2000, Tropical Storm Wene formed farther to the north. The cyclone marked the first known occurrence of a mid-Pacific upper tropospheric low developing into a tropical cyclone, though Tropical Storm Fausto
Hurricane Fausto (2002)
Hurricane Fausto was a long-lived tropical cyclone that formed during the 2002 Pacific hurricane season. The eighth tropical cyclone and fifth named storm of the season, Fausto developed on August 21 from a tropical wave that had crossed the Atlantic, and entered the Pacific on August 17...
in 2002 redeveloped in a similar occurrence to the hurricane. The cyclone attained hurricane status at 40° N, a record for a Pacific hurricane. Only Tropical Storm Dot in 1970, Hurricane John
Hurricane John (1994)
Hurricane John formed during the 1994 Pacific hurricane season and became both the longest-lasting and the farthest-traveling tropical cyclone ever observed...
in 1994, Tropical Depression Guillermo
Hurricane Guillermo (1997)
Hurricane Guillermo was the sixth strongest Pacific hurricane on record, attaining peak winds of 160 mph and a barometric pressure of 919 mbar . Forming out of a tropical wave on July 30, 1997, roughly 345 mi south of Salina Cruz, Mexico, Guillermo tracked in a steady...
in 1997, and Tropical Storm Wene in 2000 were tropical cyclones north of the latitude, of which only John was a hurricane; none maintained tropical cyclone status further north than the cyclone.
See also
- List of Pacific hurricanes
- 2006 Central Pacific cyclone2006 Central Pacific cycloneThe 2006 Central Pacific cyclone, also called 91C.INVEST or Storm 91C, was an unusual weather event of 2006. Forming on October 30 from a mid-latitude cyclone in the north Pacific mid-latitudes, it moved over waters warmer-than-normal. It acquired some features more typical of subtropical or even...