Hurricane Helene was the ninth
tropical storm
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. Depend ...
, fourth hurricane, and strongest hurricane 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 Octobe ...
, tied with
Hurricane Gordon
Hurricane Gordon was a long-lived and catastrophic late-season hurricane of the 1994 Atlantic hurricane season. The twelfth and final tropical cyclone of the season, Gordon formed as a tropical depression in the southwestern Caribbean on Novem ...
.
Helene was a long-lived
Cape Verde hurricane that formed in the extreme southeastern part of the North
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...
, peaking as a Category 3 hurricane on the
Saffir-Simpson hurricane scale as it traversed the central Atlantic. It never affected land until the very end of its lifespan as a weak extratropical system, which had minor impact in the northern
British Isles
The British Isles are a group of islands in the North Atlantic Ocean off the north-western coast of continental Europe, consisting of the islands of Great Britain, Ireland, the Isle of Man, the Inner and Outer Hebrides, the Northern Isles, ...
.
Meteorological history
In the second week of September, a strong tropical wave began to emerge off the coast of
Africa
Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
. It was well-organized from the start, and on September 11, even before it emerged off the coast, 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 ...
predicted that it could quickly develop into a tropical depression. That is indeed what happened, and it became Tropical Depression Eight on the morning of September 12.
The enormous size of the depression made it fairly slow to develop, combined with some easterly
wind shear in the eastern Atlantic and influence of the
Saharan Air Layer
The Saharan Air Layer (SAL) is an extremely hot, dry and sometimes dust-laden layer of the atmosphere that often overlies the cooler, more-humid surface air of the Atlantic Ocean. It carries upwards of 60 million tonnes of dust annually over th ...
to the north as it tracked south of the
Cape Verde
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islands.
Convection was also slow to build in, with little banding at first. The initial strengthening was delayed as a result.
However, on September 13, the organization improved as banding became better defined, and that evening, the depression strengthened into Tropical Storm Helene.
The storm slowly strengthened over the warm waters of the eastern Atlantic thereafter as it tracked west-northwest. Some dry air from the Saharan Air Layer continued to slow development on September 14 as Helene remained a low-end tropical storm.
However, a bout of intensification took place on September 15 as shear diminished.
The storm became much better organized with well-defined banding, and leveled off that evening at just under hurricane intensity.
On the morning of September 16, the storm began to develop a ragged
eye
Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light and conv ...
, and the storm strengthened to hurricane status.
The intensity leveled off for a while as a marginal
Category 1 hurricane, as the intensification was slowed by the presence of moderate wind shear despite the absence of significant dry air.
Late that evening, the storm began to slowly intensify once again.
![Helene STS-115 90 kt](https://upload.wikimedia.org/wikipedia/commons/5/54/Helene_STS-115_90_kt.jpg)
On September 17, the intensification became more rapid and Helene quickly became a Category 2 hurricane that morning as the eye became clearer and surrounded by deep convection.
Helene also turned more northward and slowed in the central Atlantic, which was in response to a weakness in the
subtropical ridge
The horse latitudes are the latitudes about 30 degrees north and south of the Equator. They are characterized by sunny skies, calm winds, and very little precipitation. They are also known as Subtropics, subtropical ridges, or highs. It is a h ...
farther north created by Gordon to the north. The northward turn shifted the course away from any land areas.
The intensification continued through the afternoon, and that evening, Helene strengthened into a major hurricane with and a minimum central pressure of 962 mbar. As shear remained low and the oceans remained warm, Helene intensified slightly more, peaking as a solid Category 3 hurricane with winds early on September 18. At that time, Helene and Gordon were at roughly the same
longitude
Longitude (, ) is a geographic coordinate that specifies the east–west position of a point on the surface of the Earth, or another celestial body. It is an angular measurement, usually expressed in degrees and denoted by the Greek letter l ...
in the open ocean.
Operationally, Helene was estimated to have had winds, but the post-storm analysis downgraded it slightly.
As Gordon moved eastward on the afternoon of 18th, a narrow ridge built in, forcing Helene westward. The eyewall collapsed somewhat, and Helene weakened slightly to a Category 2 hurricane, where it leveled off for about 48 hours until September 20 due to a lengthy
eyewall replacement cycle
In meteorology, eyewall replacement cycles, also called concentric eyewall cycles, naturally occur in intense tropical cyclones, generally with winds greater than , or major hurricanes ( Category 3 or above). When tropical cyclones reach this int ...
and an elongated cloud pattern.
On the 20th, Helene turned back to the northwest and weakened slightly due to a slight increase in wind shear.
That afternoon, it was downgraded to a Category 1 hurricane, which Helene remained until becoming
extratropical.
Early on September 21, the motion shifted to the north as it moved along the northwest periphery of the subtropical ridge.
That general motion continued throughout the day, however, Helene began to turn more northeastward that evening along the edge of the subtropical ridge, east of
Bermuda
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.
A decrease in wind shear and relatively warm water around kept the intensity mostly stationary, keeping Helene as a Category 1 hurricane.
The intensity held around before strengthening slightly late on September 22, despite losing some tropical characteristics (it was operationally downgraded to a tropical storm for a brief period)
as it accelerated northeast in the north Atlantic. A
QuikSCAT analysis early on September 23 confirmed a high-end Category 1 hurricane with winds.
Helene transitioned into a "hybrid" storm with both tropical and extratropical characteristics that afternoon, with both a deep warm core and an asymmetric, frontal-like appearance.
After that, increased shear weakened Helene once again, although it remained a hurricane-strength storm until it was fully extratropical on the morning of September 24.
After becoming extratropical, the storm weakened as it tracked eastward, becoming a gale center west of
Ireland
Ireland ( ; ga, Éire ; Ulster Scots dialect, Ulster-Scots: ) is an island in the Atlantic Ocean, North Atlantic Ocean, in Northwestern Europe, north-western Europe. It is separated from Great Britain to its east by the North Channel (Grea ...
early on September 27. It eventually merged with a larger extratropical low near the northern end of the
British Isles
The British Isles are a group of islands in the North Atlantic Ocean off the north-western coast of continental Europe, consisting of the islands of Great Britain, Ireland, the Isle of Man, the Inner and Outer Hebrides, the Northern Isles, ...
late on the 27th.
Impact
![TS Helene 15 sept 2006 1610Z](https://upload.wikimedia.org/wikipedia/commons/1/1f/TS_Helene_15_sept_2006_1610Z.jpg)
While a tropical system, Helene never approached land. Three ships were caught in the outer bands of Helene; the strongest of which reported sustained winds early on September 23 in the north Atlantic.
Though it remained far away from the island, the hurricane produced rough waves in
Bermuda
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, song = " Hail to Bermuda"
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. The hurricane had a positive impact on surfing conditions on the East Coast of the United States.
As a weakened extratropical system, strong wind gusts were reported in
Ireland
Ireland ( ; ga, Éire ; Ulster Scots dialect, Ulster-Scots: ) is an island in the Atlantic Ocean, North Atlantic Ocean, in Northwestern Europe, north-western Europe. It is separated from Great Britain to its east by the North Channel (Grea ...
and northern
Scotland
Scotland (, ) is a country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a border with England to the southeast and is otherwise surrounded by the Atlantic Ocean to the ...
. The strongest reported wind gust in Ireland was at the
Valentia Observatory
Valentia Island () is one of Ireland's most westerly points. It lies off the Iveragh Peninsula in the southwest of County Kerry. It is linked to the mainland by the Maurice O'Neill Memorial Bridge at Portmagee. A car ferry also departs from R ...
, where gusts were reported. In Scotland, the strongest gust was on
South Uist Island in the
Outer Hebrides
The Outer Hebrides () or Western Isles ( gd, Na h-Eileanan Siar or or ("islands of the strangers"); sco, Waster Isles), sometimes known as the Long Isle/Long Island ( gd, An t-Eilean Fada, links=no), is an island chain off the west coast ...
, where gusts were reported. No damage or fatalities were reported as a result of Helene.
See also
*
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 Octobe ...
*
Timeline of the 2006 Atlantic hurricane season
The 2006 Atlantic hurricane season was a cycle of the annual tropical cyclone season in the Atlantic Ocean in the Northern Hemisphere. The season officially began on June 1, 2006, and ended on November 30, 2006. These dates, adopted by c ...
References
External links
*The NHC'
archiveon Hurricane Helene
{{DEFAULTSORT:Helene (2006)
2006 Atlantic hurricane season
Category 3 Atlantic hurricanes
Helene (2006)
Hurricanes in Europe
Helene
September 2006 events in Europe
Helene