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Hurricane Isaac (2006)
Encyclopedia
Hurricane Isaac was the final tropical cyclone
of the 2006 Atlantic hurricane season
. Isaac originated in a tropical wave
that entered the Atlantic Ocean on September 18. An associated area of disturbed weather eventually organized sufficiently to be declared a tropical depression on September 27, while located 930 mi (1,496.7 km) southeast of Bermuda. The depression was upgraded to a tropical storm just 12 hours later, though unfavorable atmospheric conditions, including high wind shear
and cool water temperatures, initially inhibited further intensification. Isaac ultimately peaked as a Category 1 hurricane on the Saffir-Simpson Hurricane Scale
, and brushed Newfoundland
as a tropical storm. Effects from the storm were minimal and limited to gusty winds, rough surf, and sporadic rainfall.
emerged from the western coast of Africa and entered the Atlantic Ocean on September 18, 2006. On September 23, an associated area of disturbed weather began to exhibit indications of organization; in response, Dvorak classifications
were initiated. Influenced by moderate to strong wind shear
, the system moved west-northwestward for several days. Once environmental conditions became more favorable for tropical cyclone development, the storm had sufficiently organized to be designated a tropical depression on September 27. At this time, the depression was located about 930 mi (1,496.7 km) southeast of Bermuda
. Despite being upgraded, deep convection had not wrapped around the entire center of circulation. Although the depression was approaching tropical storm status by later on September 27, wind shear continued to affect the cyclone. On September 28—about 12 hours after the storm's formation—it became the ninth tropical storm of the 2006 Atlantic hurricane season
, and received the name Isaac.
Initially, the storm was tracking towards the northwest, between another low pressure system to its west and a low- to mid-level ridge
to its east. Throughout the day, thunderstorm activity remained unstable, possibly as a result of cooler waters churned up by previous storms. In addition, mid- to upper-level dry air had become entrained into the circulation, and the storm contained some subtropical characteristics
with a baroclinic-type cloud pattern. By early September 29, Isaac had slowed and turned towards the west. Convection began to intensify and consolidate later that day; outflow
had also improved, and became more symmetric in nature. Moving into warmer waters, Isaac continued to strengthen, and attained hurricane status on September 30. However, this period of intensification was short-lived, and the cyclone reached its peak intensity with winds of 85 mph (140 km/h) at around 0000 UTC on October 1. Around that time, a ragged eye
feature appeared on satellite imagery.
"A fairly well-defined hurricane", Isaac began to recurve around the periphery of a subtropical ridge while accelerating in forward speed. While tracking towards the north-northeast, the storm began to gradually weaken as a result of increasing southwesterly wind shear and colder sea surface temperatures. At about 1200 UTC on September 2, Isaac was downgraded to a tropical storm. The storm passed about 40 mi (64.4 km) to the southeast of the Avalon Peninsula
on October 2, spawning tropical storm-force winds on land. After passing Newfoundland
Isaac transitioned into an extratropical storm, and subsequently merged with a larger storm on October 3.
and Bonavista
peninsulas, though it was quickly discontinued. By 2100 UTC on October 2, all tropical cyclone watches and warnings were lifted. Heavy rainfall and gusty winds were expected, prompting the issuance of rainfall warnings for parts of southeastern Newfoundland, while wind and gale advisories were declared offshore.
On October 2, the Elektra (call sign SIWB) reported winds of 52 mph (83.7 km/h) while located about 170 mi (273.6 km) to the east of the storm's center. Two other ships, several buoys, and several oil platforms also recorded tropical storm-force winds. Waves offshore reached 16 ft (4.9 m) in height.
Impacts on land were generally insignificant; no damages or fatalities were reported. However, parts of the Avalon Peninsula experienced tropical storm conditions. At Cape Race
, sustained winds peaked at 46 mph (74 km/h), with gusts of up to 60 mph (96.6 km/h). The most intense winds remained offshore. Due to the storm's rapid passage, rainfall was primarily light and amounted to less than 1 in (25.4 mm).
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 2006 Atlantic hurricane season
2006 Atlantic hurricane season
The 2006 Atlantic hurricane season was significantly less active than the record previous season. It marked the first since 2001 in which no hurricanes made landfall in the United States, and was the first since 1994 that no tropical cyclones formed during October. Following the intense activity of...
. Isaac originated in 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 entered the Atlantic Ocean on September 18. An associated area of disturbed weather eventually organized sufficiently to be declared a tropical depression on September 27, while located 930 mi (1,496.7 km) southeast of Bermuda. The depression was upgraded to a tropical storm just 12 hours later, though unfavorable atmospheric conditions, including high 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...
and cool water temperatures, initially inhibited further intensification. Isaac ultimately peaked as a Category 1 hurricane 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...
, and brushed Newfoundland
Newfoundland and Labrador
Newfoundland and Labrador is the easternmost province of Canada. Situated in the country's Atlantic region, it incorporates the island of Newfoundland and mainland Labrador with a combined area of . As of April 2011, the province's estimated population is 508,400...
as a tropical storm. Effects from the storm were minimal and limited to gusty winds, rough surf, and sporadic rainfall.
Meteorological history
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 western coast of Africa and entered the Atlantic Ocean on September 18, 2006. On September 23, an associated area of disturbed weather began to exhibit indications of organization; in response, 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...
were initiated. Influenced by moderate 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...
, the system moved west-northwestward for several days. Once environmental conditions became more favorable for tropical cyclone development, the storm had sufficiently organized to be designated a tropical depression on September 27. At this time, the depression was located about 930 mi (1,496.7 km) southeast of Bermuda
Bermuda
Bermuda is a British overseas territory in the North Atlantic Ocean. Located off the east coast of the United States, its nearest landmass is Cape Hatteras, North Carolina, about to the west-northwest. It is about south of Halifax, Nova Scotia, Canada, and northeast of Miami, Florida...
. Despite being upgraded, deep convection had not wrapped around the entire center of circulation. Although the depression was approaching tropical storm status by later on September 27, wind shear continued to affect the cyclone. On September 28—about 12 hours after the storm's formation—it became the ninth tropical storm of the 2006 Atlantic hurricane season
2006 Atlantic hurricane season
The 2006 Atlantic hurricane season was significantly less active than the record previous season. It marked the first since 2001 in which no hurricanes made landfall in the United States, and was the first since 1994 that no tropical cyclones formed during October. Following the intense activity of...
, and received the name Isaac.
Initially, the storm was tracking towards the northwest, between another low pressure system to its west and a low- to mid-level ridge
Ridge (meteorology)
A ridge is an elongated region of relatively high atmospheric pressure, the opposite of a trough....
to its east. Throughout the day, thunderstorm activity remained unstable, possibly as a result of cooler waters churned up by previous storms. In addition, mid- to upper-level dry air had become entrained into the circulation, and the storm contained some subtropical characteristics
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...
with a baroclinic-type cloud pattern. By early September 29, Isaac had slowed and turned towards the west. Convection began to intensify and consolidate later that day; 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...
had also improved, and became more symmetric in nature. Moving into warmer waters, Isaac continued to strengthen, and attained hurricane status on September 30. However, this period of intensification was short-lived, and the cyclone reached its peak intensity with winds of 85 mph (140 km/h) at around 0000 UTC on October 1. Around that time, a ragged 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...
feature appeared on satellite imagery.
"A fairly well-defined hurricane", Isaac began to recurve around the periphery of a subtropical ridge while accelerating in forward speed. While tracking towards the north-northeast, the storm began to gradually weaken as a result of increasing southwesterly wind shear and colder sea surface temperatures. At about 1200 UTC on September 2, Isaac was downgraded to a tropical storm. The storm passed about 40 mi (64.4 km) to the southeast of the Avalon Peninsula
Avalon Peninsula
The Avalon Peninsula is a large peninsula that makes up the southeast portion of the island of Newfoundland.The peninsula is home to 257,223 people, which is approximately 51% of Newfoundland's population in 2009, and is the location of the provincial capital, St. John's. It is connected to the...
on October 2, spawning tropical storm-force winds on land. After passing Newfoundland
Newfoundland and Labrador
Newfoundland and Labrador is the easternmost province of Canada. Situated in the country's Atlantic region, it incorporates the island of Newfoundland and mainland Labrador with a combined area of . As of April 2011, the province's estimated population is 508,400...
Isaac transitioned into an extratropical storm, and subsequently merged with a larger storm on October 3.
Preparations and impact
A tropical storm watch was issued in response to Isaac on October 1 for the Avalon Peninsula. The watch was upgraded to a tropical storm warning the next day, while a separate watch was posted for the BurinBurin Peninsula
The Burin Peninsula is a Canadian peninsula located on the south coast of the island of Newfoundland in the province of Newfoundland and Labrador....
and Bonavista
Bonavista Peninsula
The Bonavista Peninsula is a large peninsula on the east coast of the island of Newfoundland in the Canadian province of Newfoundland and Labrador....
peninsulas, though it was quickly discontinued. By 2100 UTC on October 2, all tropical cyclone watches and warnings were lifted. Heavy rainfall and gusty winds were expected, prompting the issuance of rainfall warnings for parts of southeastern Newfoundland, while wind and gale advisories were declared offshore.
On October 2, the Elektra (call sign SIWB) reported winds of 52 mph (83.7 km/h) while located about 170 mi (273.6 km) to the east of the storm's center. Two other ships, several buoys, and several oil platforms also recorded tropical storm-force winds. Waves offshore reached 16 ft (4.9 m) in height.
Impacts on land were generally insignificant; no damages or fatalities were reported. However, parts of the Avalon Peninsula experienced tropical storm conditions. At Cape Race
Cape Race
Cape Race is a point of land located at the southeastern tip of the Avalon Peninsula on the island of Newfoundland, Canada. Its name is thought to come from the original Portuguese name for this cape, "Raso", or "bare"...
, sustained winds peaked at 46 mph (74 km/h), with gusts of up to 60 mph (96.6 km/h). The most intense winds remained offshore. Due to the storm's rapid passage, rainfall was primarily light and amounted to less than 1 in (25.4 mm).
See also
- List of Atlantic hurricanes
- Timeline of the 2006 Atlantic hurricane seasonTimeline of the 2006 Atlantic hurricane seasonThe 2006 Atlantic hurricane season was the first since 2001 in which no hurricanes made landfall in the United States, and the first since 1994 that no tropical cyclones formed during October. This timeline documents all the storm formations, strengthening, weakening, landfalls, extratropical...
- List of storms in the 2006 Atlantic hurricane season
- List of Canada hurricanes
External links
- The NHC's archive on Hurricane Isaac
- The CHC's archive on Hurricane Isaac