The 2006 Central Pacific cyclone, also known as Invest 91C or Storm 91C, was an unusual weather system that formed in 2006. Forming on October 30 from a

mid-latitude cyclone Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are low-pressure areas which, along with the anticyclones of high-pressure areas, drive the weather over much of the Earth. Extratropical cyclones are capable o ...

in the north Pacific mid-latitudes, it moved over waters warmer than normal. The system acquired some features more typical of subtropical and even

tropical cyclone A tropical cyclone is a rapidly rotating storm system characterized by a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls. Dep ...

s. However, as it neared the western coastline of North America, the system fell apart, dissipating soon after landfall, on November 4. Moisture from the storm's remnants caused substantial rainfall in

British Columbia British Columbia (commonly abbreviated as BC) is the westernmost Provinces and territories of Canada, province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include ...

and the

Pacific Northwest The Pacific Northwest (sometimes Cascadia, or simply abbreviated as PNW) is a geographic region in western North America bounded by its coastal waters of the Pacific Ocean to the west and, loosely, by the Rocky Mountains to the east. Though ...

. The exact status and nature of this weather event is unknown, with meteorologists and weather agencies having differing opinions.

Meteorological history

On October 28, 2006, a cut-off extratropical cyclone over the central north Pacific moved over an area of ocean with

sea surface temperature Sea surface temperature (SST), or ocean surface temperature, is the ocean temperature close to the surface. The exact meaning of ''surface'' varies according to the measurement method used, but it is between and below the sea surface. Air ma ...

s as high as 2

°C The degree Celsius is the unit of temperature on the Celsius scale (originally known as the centigrade scale outside Sweden), one of two temperature scales used in the International System of Units (SI), the other being the Kelvin scale. The d ...

above normal, at , and stalled there for two days. By October 31, the system had acquired

convection Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the c ...

, a warmer-than-normal core, and an eye-like feature. During this time, the storm had moved eastward, then northeastward, before turning northwestward. On November 1, the system reached its peak intensity, and had estimated 1-minute sustained winds of and its most developed convection. After that, the storm slowly weakened, looped counter-clockwise, and headed east towards the west coast of North America. This system's center of circulation passed south of observation buoy 46637 on November 1. The buoy's lowest pressure reading was . Other buoys indicated that a rather large area of low pressure was associated with the system. Buoy 46637 was not at the system's center of circulation, so it is possible that this system had a lower minimum pressure than was actually measured. On November 2,

wind shear Wind shear (or windshear), sometimes referred to as wind gradient, is a difference in wind speed and/or direction over a relatively short distance in the atmosphere. Atmospheric wind shear is normally described as either vertical or horizon ...

and cooler waters began to take their toll on 91C, and all convection was gone by the next day, when the storm was located roughly off the coast of

Oregon Oregon () is a state in the Pacific Northwest region of the Western United States. The Columbia River delineates much of Oregon's northern boundary with Washington, while the Snake River delineates much of its eastern boundary with Idah ...

. On November 3, the storm made landfall on the

Olympic Peninsula The Olympic Peninsula is a large arm of land in western Washington that lies across Puget Sound from Seattle, and contains Olympic National Park. It is bounded on the west by the Pacific Ocean, the north by the Strait of Juan de Fuca, an ...

in the

State of Washington Washington (), officially the State of Washington, is a state in the Pacific Northwest region of the Western United States. Named for George Washington—the first U.S. president—the state was formed from the western part of the Washingto ...

, bringing tropical storm-like conditions to the Pacific Northwest, including sustained winds at and wind gusts up to . Following its landfall, the storm rapidly weakened and dissipated on the next day.

Impact, preparation, and records

In response to the weather system, the American

National Weather Service The National Weather Service (NWS) is an agency of the United States federal government that is tasked with providing weather forecasts, warnings of hazardous weather, and other weather-related products to organizations and the public for the ...

issued wind watches for the Oregon Coast. The National Weather Service also issues a High Wind Warning for the southern Washington coast all the way south to

Tillamook Tillamook may refer to: Places: * Tillamook County, Oregon, United States * Tillamook, Oregon, a city, the seat of Tillamook County * Tillamook River, United States * Tillamook Bay, a bay in the northwestern part of Oregon * Tillamook Head, a natur ...

. The storm brought tropical storm-like conditions to the Pacific Northwest, including sustained winds at and wind gusts up to . The system also brought heavy rain to portions of

Vancouver Island Vancouver Island is an island in the northeastern Pacific Ocean and part of the Canadian province of British Columbia. The island is in length, in width at its widest point, and in total area, while are of land. The island is the largest by ...

. If Storm 91C is considered a tropical or subtropical cyclone, it holds several records. Since it formed at 36°N, this system formed at the northernmost latitude of any cyclone in the eastern north Pacific basin. The previous record-holder was Tropical Storm Wene, which formed at 32°N before crossing the dateline. In addition, this system's track data indicated that it crossed from the central to the east Pacific as it formed at longitude 149°W and dissipated at 135°W. Only two recorded other tropical cyclones had done this previously. However, since the storm was not officially classified, these records are not justified.

Nature of the system

This system has been considered a

tropical The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S. The tropics are also referred to ...

, subtropical, or extratropical cyclone. Mark Guishard, a meteorologist with

Bermuda Weather Service The Bermuda Weather Service is Bermuda's national meteorological service. It provides public, marine, tropical and aviation weather forecasts as well as warnings and climatolological services. The service began operations under contract from the De ...

, was of the opinion that the system had completed

tropical cyclogenesis Tropical cyclogenesis is 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 temperate cyclogenesis occurs. Tropi ...

and was a tropical cyclone. Meteorologist Mark Lander thought that cloud tops were similar to several

Atlantic hurricane An Atlantic hurricane, also known as tropical storm or simply hurricane, is a tropical cyclone that forms in the Atlantic Ocean, primarily between the months of June and November. A hurricane differs from a tropical cyclone, cyclone or typhoon on ...

s, Hurricane Vince in particular. James Franklin, a meteorologist at the

National Hurricane Center The National Hurricane Center (NHC) is the division of the United States' NOAA/ National Weather Service responsible for tracking and predicting tropical weather systems between the Prime Meridian and the 140th meridian west poleward to the 3 ...

, said:

The system was of frontal origin... the frontal structure was eventually lost.... The convective structure resembled a tropical, rather than subtropical cyclone, and the radius of maximum winds (based on QuikSCAT) was very close to the center, also more typical of tropical cyclones... on balance, it was more tropical than subtropical.

Clark Evans of Florida State University reported that forecasting tools showed that the system's structure was consistent with that of a subtropical or marginally tropical cyclone.

NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeedi ...

, a non-meteorological government agency, asserted that the system was a subtropical cyclone. In its review of the

2006 Atlantic hurricane season The 2006 Atlantic hurricane season was the least active since 1997 as well as the first season since 2001 in which no hurricanes made landfall in the United States, and was the first since 1994 in which no tropical cyclones formed during October ...

, the

Canadian Hurricane Centre The Canadian Hurricane Centre (CHC; french: Centre canadien de prévision des ouragans) is an organisation that monitors and warns of the threat of tropical cyclones such as hurricanes and tropical storms. CHC is a division of the Meteorological Se ...

considered this to be an extratropical cyclone. In 2016, a study by Alica Bently and Nicholas Metz found that this cyclone underwent tropical transition, confirming its status as a tropical cyclone. Since this system had one-minute sustained winds of 100 km/h (65 mi/h), which are above the 60 km/h (39 mi/h) boundary between a depression and a storm, it would qualify as a named storm if it was a tropical or subtropical cyclone. However, neither of the official

Regional Specialized Meteorological Center A Regional Specialized Meteorological Centre (RSMC) is responsible for the distribution of information, advisories, and warnings regarding the specific program they have a part of, agreed by consensus at the World Meteorological Organization as p ...

s for the eastern north Pacific, the

and the

Central Pacific Hurricane Center The Central Pacific Hurricane Center (CPHC) of the United States National Weather Service is the official body responsible for tracking and issuing tropical cyclone warnings, watches, advisories, discussions, and statements for the Central Pacifi ...

, include this system in their annual archives, nor is it included in the official "best track" file. Hence, this system is not an official tropical or subtropical cyclone of the

2006 Pacific hurricane season The 2006 Pacific hurricane season was the first above-average season since 1994 which produced twenty-five tropical cyclones, with nineteen named storms, though most were rather weak and short-lived. Only eleven hurricanes formed and six major hu ...

References

External links

Unofficial track data
{{2006 Pacific hurricane season buttons Central Pacific Cyclone, 2006 Central Pacific Cyclone, 2006 Pacific Northwest storms Eastern Pacific tropical storms Subtropical cyclones 2006 Central Pacific cyclone

Meteorological history

Impact, preparation, and records

Nature of the system

See also

References

External links