Tropical Cyclone Helen
Encyclopedia
Tropical Cyclone Helen was the first tropical cyclone
to bring gale
-force winds to Darwin, Australia
since 1985. The fourth named storm
of the 2007–08 Australian region cyclone season, Helen developed out of a weak area of low pressure
in late December over the Top End
region of Australia. Generally tracking westward, the system eventually intensified into a tropical cyclone and was given the name Helen on 2 January. By this time, it was situated over the Joseph Bonaparte Gulf
and was beginning to retrograde eastward. Late on 4 January, the storm made landfall
near Channel Point
with winds of 95 km/h (60 mph) though rapidly weakened to a tropical low within 12 hours. Gradually accelerating, the remnants of Helen moved over the Gulf of Carpentaria
before striking land again on 6 January. The system was last noted over the Cape York Peninsula
on 7 January.
From late December through 6 January, Helen and its precursor low produced significant rainfall
over the Northern Territory, generally amounting between 100 millimetre. One person drowned in the Victoria River
after his car was swept away in a flood. As a tropical cyclone, Helen produced significant wind gusts across the Top End, peaking at 120 km/h (75 mph), downing thousands of trees. In Darwin, roughly 15,000 people were without power due to the storm, more than 100 of which remained so four days after the storm. Overall losses from the storm reached A$1.3 million (US$1.1 million) with an additional A$1 million (US$882,000) in cleanup costs.
indicated that a La Niña
would develop by December of that year. In general, this event results in increased sea surface temperature
s near Australia
. Following this, a strong Madden–Julian oscillation phase took shape, leading to the development of Tropical Cyclone Melanie off the coast of Western Australia
and an area of low pressure
over the Top End
by 28 December. Situated over land, the system initially embedded within a disorganised trough
and to intensify as it slowly tracked eastward. By 30 December, it separated itself from the trough and travelled towards the west. The following day, the interaction between the two systems allowed the low to significantly deepen, attaining a barometric pressure of 993 mbar
(hPa
; 29.32 inHg). This strengthening was short-lived as wind shear
over the low increased, displacing convection from its centre.
By 2 January, the weak low moved over the Joseph Bonaparte Gulf
where it slowly developed over the following day. Once over water, the Joint Typhoon Warning Center
(JTWC) designated the system as Tropical Depression 09S. As organisation improved, a mid-level subtropical ridge
over Western Australia pushed the system westward, away from the Kimberley coast. Steadily strengthening, the low attained gale-force winds near its centre during the morning of 4 January and was subsequently named Helen by the Bureau of Meteorology. Shortly thereafter, a strong westerly monsoon flow
to the north caused Helen to turn eastward, back towards land. Intensification continued up until landfall
, by which time Helen had attained Category 2 status on the Australian tropical cyclone intensity scale. Maximum ten-minute sustained wind
s reached 95 km/h (60 mph) and the storm's barometric pressure decreased to 975 mbar
(hPa
; 28.79 inHg). The JTWC assessed Helen to have been slightly weaker, with peak winds estimated at 85 km/h (50 mph).
Around 10:00 pm local time on 4 January, the centre of Tropical Cyclone Helen made landfall near Channel Point. As it moved ashore, the storm developed an eye
; however, this feature began breaking apart once overland and the eyewall merged into the system's feeder bands. Roughly 12 hours after landfall, Helen weakened to a tropical low before moving over the Gulf of Carpentaria
late on 5 January. Due to an increase in forward motion, the system was unable to regenerate sufficient convection to be reclassified a tropical cyclone before making a second landfall along the Cape York Peninsula. Once overland again, the remnants of Helen abruptly slowed and were last noted on 7 January in the same region.
for areas between the Mitchell Plateau, in Western Australia, to Cape Hotham
in the Northern Territory. According to local officials, flooding was the greatest concern from the storm rather than wind damage. The warning area was later condensed to encompass areas from Wadeye
to Cape Hotham, including Darwin and the Tiwi Islands
. By 6 January, warnings were issued for the western coast of the Cape York Peninsula between Karumba
and Weipa
as the remnants of Helen were forecast to regain storm intensity.
In light of Helen's approach in the Top End region, the Compass Resources
mining company suspended construction of a new mine in Batchelor
. Mining at the Ranger Uranium Mine
maintained by Energy Resources of Australia
was also suspended until the storm passed. The George Brown Darwin Botanic Gardens
and Territory Wildlife Park were also closed for the duration of the storm. Residents in the Aboriginal community of Wadeye were strongly advised to take precautions for the storm. Following the issuance of a cyclone warning in Darwin, local shelters were opened to the public. At the Darwin International Airport
, all incoming and outgoing flights through Jetstar Airways
were cancelled while Tiger Airways
rescheduled their flights and no changes were made by Qantas
. Darwin Harbour was mostly shut down as seas became too rough to sail in. Schools and day cares within a 50 km (31.1 mi) radius of the city were closed on 4 January.
to swell over its banks and flood nearby areas. On 4 January, a car with three people was swept away by the river; two of the passengers managed to escape and swim to shore, but the third person remained trapped. Aerial searches were made later that day for him, though he was later declared dead. After becoming a tropical cyclone, the storm produced additional moderate to heavy rainfall, generally totaling between 100 and 200 mm (3.9 and 7.9 in). Between 1 and 6 January, a total of 174.6 mm (6.9 in) of rain fell in Darwin. These rains affected two additional major rivers in the area: the Adelaide
and Katherine
rivers. Near where the storm made landfall, wind gusts up to 120 km/h (75 mph) were recorded; Darwin recorded a maximum wind gust of 102 km/h (63.4 mph) as Helen moved by the city.
Near Channel Point, the cyclone brought a storm surge
of 2 to 3 m (6.6 to 9.8 ft), barely surpassing the highest astronomical tide in a few areas. In some cases, waves over topped sand dunes but no damage took place. Roughly 10-15% of trees in open areas were snapped or uprooted by high winds. Only two structures sustained direct wind damage while several others were struck by downed trees. Damage was more widespread in Darwin where roughly 15,000 homes, 60% of the city's residences, were left without power. Approximately 1,500 trees were downed in the city, falling on roads, homes and power lines. In the days following the storm's passage, the Adelaide and Katherine rivers continued to rise, of which the former exceeded minor flood levels. In the harbour, seven vessels washed ashore, each sustaining minor damage. Losses caused by the storm was placed at A$1.3 million (US$1.1 million).
The day after Helen passed through, cleanup efforts began as power crews had to remove downed trees before fixing power lines. The main power lines in the city were restored within 24 hours and rural areas were stated to have their power back within a day or two. Two days after the storm, 500 homes remained without electricity and frustrated residents were further angered after discovering that the Power and Water agency was in control of tree removal and not emergency services. With the power company in charge of clearing downed trees, they stated that their crews would only be dealing with cases involved power lines. Residents with trees in their yards or even on their homes were told to contact private contractors to remove them. By 9 January, more than 100 homes were still without power in northern Darwin, resulting in angry outcries from those still left in the dark. Cleanup efforts dragged on for more than two months as debris was still present in Darwin in March. Removal of tree stumps took through at least mid-April as the cost to remove downed trees exceeded A$1 million (US$882,000). Due to the damage wrought by Helen, its name was retired following its usage. However, it was not replaced by any particular name as a new naming scheme was implemented the following season.
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...
to bring gale
Gale
A gale is a very strong wind. There are conflicting definitions of how strong a wind must be to be considered a gale. The U.S. government's National Weather Service defines a gale as 34–47 knots of sustained surface winds. Forecasters typically issue gale warnings when winds of this strength are...
-force winds to Darwin, Australia
Darwin, Northern Territory
Darwin is the capital city of the Northern Territory, Australia. Situated on the Timor Sea, Darwin has a population of 127,500, making it by far the largest and most populated city in the sparsely populated Northern Territory, but the least populous of all Australia's capital cities...
since 1985. The fourth named storm
Tropical cyclone naming
Tropical cyclones have officially been named since 1945 and are named for a variety of reasons, which include to facilitate communications between forecasters and the public when forecasts, watches, and warnings are issued. Names also reduce confusion about what storm is being described, as more...
of the 2007–08 Australian region cyclone season, Helen developed out of a weak area of low pressure
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...
in late December over the Top End
Top End
The Top End of northern Australia is the second northernmost point on the continent. It covers a rather vaguely-defined area of perhaps 400,000 square kilometres behind the northern coast from the Northern Territory capital of Darwin across to Arnhem Land with the Indian Ocean on the west, the...
region of Australia. Generally tracking westward, the system eventually intensified into a tropical cyclone and was given the name Helen on 2 January. By this time, it was situated over the Joseph Bonaparte Gulf
Joseph Bonaparte Gulf
Joseph Bonaparte Gulf is a large body of water off the coast of the Northern Territory, Australia and Western Australia. It was named after Joseph Bonaparte, brother of Napoleon and King of Naples and then Spain by French explorer and naturalist Nicholas Baudin in 1803...
and was beginning to retrograde eastward. Late on 4 January, the storm made landfall
Landfall (meteorology)
Landfall is the event of a tropical cyclone or a waterspout coming onto land after being over water. When a waterspout makes landfall it is reclassified as a tornado, which can then cause damage inland...
near Channel Point
Northern Territory
The Northern Territory is a federal territory of Australia, occupying much of the centre of the mainland continent, as well as the central northern regions...
with winds of 95 km/h (60 mph) though rapidly weakened to a tropical low within 12 hours. Gradually accelerating, the remnants of Helen moved over the Gulf of Carpentaria
Gulf of Carpentaria
The Gulf of Carpentaria is a large, shallow sea enclosed on three sides by northern Australia and bounded on the north by the Arafura Sea...
before striking land again on 6 January. The system was last noted over the Cape York Peninsula
Cape York Peninsula
Cape York Peninsula is a large remote peninsula located in Far North Queensland at the tip of the state of Queensland, Australia, the largest unspoilt wilderness in northern Australia and one of the last remaining wilderness areas on Earth...
on 7 January.
From late December through 6 January, Helen and its precursor low produced significant rainfall
Rain
Rain is liquid precipitation, as opposed to non-liquid kinds of precipitation such as snow, hail and sleet. Rain requires the presence of a thick layer of the atmosphere to have temperatures above the melting point of water near and above the Earth's surface...
over the Northern Territory, generally amounting between 100 millimetre. One person drowned in the Victoria River
Victoria River
Victoria River may refer to:*Victoria River , the longest river in the Northern Territory of Australia*Victoria River, New Zealand in New Zealand*Victoria River in Newfoundland and Labrador...
after his car was swept away in a flood. As a tropical cyclone, Helen produced significant wind gusts across the Top End, peaking at 120 km/h (75 mph), downing thousands of trees. In Darwin, roughly 15,000 people were without power due to the storm, more than 100 of which remained so four days after the storm. Overall losses from the storm reached A$1.3 million (US$1.1 million) with an additional A$1 million (US$882,000) in cleanup costs.
Meteorological history
As early as autumn 2007, long-rage forecast modelsNumerical weather prediction
Numerical weather prediction uses mathematical models of the atmosphere and oceans to predict the weather based on current weather conditions. Though first attempted in the 1920s, it was not until the advent of computer simulation in the 1950s that numerical weather predictions produced realistic...
indicated that a La Niña
La Niña
La Niña is a coupled ocean-atmosphere phenomenon that is the counterpart of El Niño as part of the broader El Niño-Southern Oscillation climate pattern. During a period of La Niña, the sea surface temperature across the equatorial Eastern Central Pacific Ocean will be lower than normal by 3–5 °C...
would develop by December of that year. In general, this event results in increased 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 near Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
. Following this, a strong Madden–Julian oscillation phase took shape, leading to the development of Tropical Cyclone Melanie off the coast of Western Australia
Western Australia
Western Australia is a state of Australia, occupying the entire western third of the Australian continent. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Indian Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east...
and an area of low pressure
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...
over the Top End
Top End
The Top End of northern Australia is the second northernmost point on the continent. It covers a rather vaguely-defined area of perhaps 400,000 square kilometres behind the northern coast from the Northern Territory capital of Darwin across to Arnhem Land with the Indian Ocean on the west, the...
by 28 December. Situated over land, the system initially embedded within a disorganised 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...
and to intensify as it slowly tracked eastward. By 30 December, it separated itself from the trough and travelled towards the west. The following day, the interaction between the two systems allowed the low to significantly deepen, attaining a barometric pressure of 993 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...
(hPa
Pascal (unit)
The pascal is the SI derived unit of pressure, internal pressure, stress, Young's modulus and tensile strength, named after the French mathematician, physicist, inventor, writer, and philosopher Blaise Pascal. It is a measure of force per unit area, defined as one newton per square metre...
; 29.32 inHg). This strengthening was short-lived as 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...
over the low increased, displacing convection from its centre.
By 2 January, the weak low moved over the Joseph Bonaparte Gulf
Joseph Bonaparte Gulf
Joseph Bonaparte Gulf is a large body of water off the coast of the Northern Territory, Australia and Western Australia. It was named after Joseph Bonaparte, brother of Napoleon and King of Naples and then Spain by French explorer and naturalist Nicholas Baudin in 1803...
where it slowly developed over the following day. Once over water, the Joint Typhoon Warning Center
Joint Typhoon Warning Center
The Joint Typhoon Warning Center is a joint United States Navy – United States Air Force task force located at the Naval Maritime Forecast Center in Pearl Harbor, Hawaii...
(JTWC) designated the system as Tropical Depression 09S. As organisation improved, a mid-level subtropical ridge
Subtropical ridge
The subtropical ridge is a significant belt of high pressure situated around the latitudes of 30°N in the Northern Hemisphere and 30°S in the Southern Hemisphere. It is characterized by mostly calm winds, which acts to reduce air quality under its axis by causing fog overnight, and haze during...
over Western Australia pushed the system westward, away from the Kimberley coast. Steadily strengthening, the low attained gale-force winds near its centre during the morning of 4 January and was subsequently named Helen by the Bureau of Meteorology. Shortly thereafter, a strong westerly monsoon flow
Monsoon trough
The monsoon trough is that portion of the Intertropical Convergence Zone which extends into or through a monsoon circulation, as depicted by a line on a weather map showing the locations of minimum sea level pressure, and as such, is a convergence zone between the wind patterns of the southern and...
to the north caused Helen to turn eastward, back towards land. Intensification continued up until landfall
Landfall (meteorology)
Landfall is the event of a tropical cyclone or a waterspout coming onto land after being over water. When a waterspout makes landfall it is reclassified as a tornado, which can then cause damage inland...
, by which time Helen had attained Category 2 status on the Australian tropical cyclone intensity scale. Maximum ten-minute sustained wind
Maximum sustained wind
The maximum sustained winds associated with a tropical cyclone are a common indicator of the intensity of the storm. Within a mature tropical cyclone, they are found within the eyewall at a distance defined as the radius of maximum wind, or RMW. Unlike gusts, the value of these winds are...
s reached 95 km/h (60 mph) and the storm's barometric pressure decreased to 975 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...
(hPa
Pascal (unit)
The pascal is the SI derived unit of pressure, internal pressure, stress, Young's modulus and tensile strength, named after the French mathematician, physicist, inventor, writer, and philosopher Blaise Pascal. It is a measure of force per unit area, defined as one newton per square metre...
; 28.79 inHg). The JTWC assessed Helen to have been slightly weaker, with peak winds estimated at 85 km/h (50 mph).
Around 10:00 pm local time on 4 January, the centre of Tropical Cyclone Helen made landfall near Channel Point. As it moved ashore, the storm developed 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...
; however, this feature began breaking apart once overland and the eyewall merged into the system's feeder bands. Roughly 12 hours after landfall, Helen weakened to a tropical low before moving over the Gulf of Carpentaria
Gulf of Carpentaria
The Gulf of Carpentaria is a large, shallow sea enclosed on three sides by northern Australia and bounded on the north by the Arafura Sea...
late on 5 January. Due to an increase in forward motion, the system was unable to regenerate sufficient convection to be reclassified a tropical cyclone before making a second landfall along the Cape York Peninsula. Once overland again, the remnants of Helen abruptly slowed and were last noted on 7 January in the same region.
Preparations
Starting in late December, widespread rains produced by the precursor to Helen prompted the issuance of flood warnings throughout the Top End region. Prior to the arrival of Cyclone Helen on 4 January, the Bureau of Meteorology issued cyclone warningsTropical 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 areas between the Mitchell Plateau, in Western Australia, to Cape Hotham
Cape Hotham Light
Cape Hotham Light is an active lighthouse located on Cape Hotham, which is on a the shore of the Timor Sea on a long unnamed peninsula about northeast of Darwin, Northern Territory, Australia...
in the Northern Territory. According to local officials, flooding was the greatest concern from the storm rather than wind damage. The warning area was later condensed to encompass areas from Wadeye
Wadeye, Northern Territory
Wadeye is a town in Australia's Northern Territory.Wadeye was formerly known as Port Keats. The town is remote, situated on the western edge of the Daly River Reserve more than 200 km south west of Darwin, with road access being cut off by flooding during the wet season. Year round access is via...
to Cape Hotham, including Darwin and the Tiwi Islands
Tiwi Islands
The Tiwi Islands are part of Australia's Northern Territory, north of Darwin where the Arafura Sea joins the Timor Sea. They comprise Melville Island and Bathurst Island, with a combined area of ....
. By 6 January, warnings were issued for the western coast of the Cape York Peninsula between Karumba
Karumba, Queensland
Karumba is a town in the Gulf Country region of Queensland, Australia, 71 km by road from Normanton and 2159 km from the state capital, Brisbane. The settlement was previously known as Norman Mouth and Kimberely. Karumba was used by the local aborigines to describe the place...
and Weipa
Weipa, Queensland
Weipa is the largest town on the Gulf of Carpentaria coast of the Cape York Peninsula in Queensland, Australia. At the 2006 census, Weipa had a population of 2,830; the largest community on Cape York Peninsula. It exists because of the enormous bauxite deposits along the coast...
as the remnants of Helen were forecast to regain storm intensity.
In light of Helen's approach in the Top End region, the Compass Resources
Compass Resources
Compass Resources NL is an Australian mining and mineral exploration company listed on the Australian Stock Exchange and currently in voluntary administration since 29 January 2009....
mining company suspended construction of a new mine in Batchelor
Batchelor, Northern Territory
Batchelor is a town in the Northern Territory of Australia. The town is located in the Coomalie Shire Local Government Area, 98 kilometres south of the territory capital, Darwin...
. Mining at the Ranger Uranium Mine
Ranger Uranium Mine
The Ranger uranium mine is surrounded by Kakadu National Park, in the Northern Territory of Australia, 230 km east of Darwin. The orebody was discovered in 1969, and the mine commenced operation in 1980, reaching full production of uranium oxide in 1981...
maintained by Energy Resources of Australia
Energy Resources of Australia
Energy Resources of Australia Ltd is a public company based in Australia. It is a subsidiary of the Rio Tinto Group which owns 68.4% of the company. The chairman is David Klingner and chief executive officer is Harry Kenyon-Slaney....
was also suspended until the storm passed. The George Brown Darwin Botanic Gardens
George Brown Darwin Botanic Gardens
The George Brown Darwin Botanic Gardens are botanical gardens located 2 km North of the CBD of Darwin, Northern Territory, Australia. The gardens cover 42 hectares and are noted for their collections of north Australian and other tropical species....
and Territory Wildlife Park were also closed for the duration of the storm. Residents in the Aboriginal community of Wadeye were strongly advised to take precautions for the storm. Following the issuance of a cyclone warning in Darwin, local shelters were opened to the public. At the Darwin International Airport
Darwin International Airport
Darwin International Airport is the busiest airport serving the Northern Territory and the tenth busiest airport in Australia. It is the only airport serving Darwin....
, all incoming and outgoing flights through Jetstar Airways
Jetstar Airways
Jetstar Airways is an Australian low-cost airline headquartered in Melbourne, Australia. It is a subsidiary of Qantas, created in response to the threat posed by low-cost airline Virgin Blue...
were cancelled while Tiger Airways
Tiger Airways
Tiger Airways Singapore Pte Ltd, operating as Tiger Airways Singapore, is a low cost airline which commenced services on 25 March 2005. It is a subsidiary of Tiger Airways Holdings, a Singapore-based company, which is owned partially by Singapore Airlines...
rescheduled their flights and no changes were made by Qantas
Qantas
Qantas Airways Limited is the flag carrier of Australia. The name was originally "QANTAS", an initialism for "Queensland and Northern Territory Aerial Services". Nicknamed "The Flying Kangaroo", the airline is based in Sydney, with its main hub at Sydney Airport...
. Darwin Harbour was mostly shut down as seas became too rough to sail in. Schools and day cares within a 50 km (31.1 mi) radius of the city were closed on 4 January.
Impact and aftermath
Throughout the Top End region, the precursor to Helen resulted in a prolonged period of moderate rains over a relatively large area. These rains caused the Victoria RiverVictoria River
Victoria River may refer to:*Victoria River , the longest river in the Northern Territory of Australia*Victoria River, New Zealand in New Zealand*Victoria River in Newfoundland and Labrador...
to swell over its banks and flood nearby areas. On 4 January, a car with three people was swept away by the river; two of the passengers managed to escape and swim to shore, but the third person remained trapped. Aerial searches were made later that day for him, though he was later declared dead. After becoming a tropical cyclone, the storm produced additional moderate to heavy rainfall, generally totaling between 100 and 200 mm (3.9 and 7.9 in). Between 1 and 6 January, a total of 174.6 mm (6.9 in) of rain fell in Darwin. These rains affected two additional major rivers in the area: the Adelaide
Adelaide River
Adelaide River is a river in the Northern Territory of Australia. It starts in Litchfield National Park and flows generally northwards to Clarence Strait, being crossed by both the Stuart Highway and the Arnhem Highway...
and Katherine
Katherine River
Katherine River is located in the Northern Territory, Australia. Its headwaters are in Nitmiluk National Park, it flows through the town of Katherine, and is a major tributary of the Daly River....
rivers. Near where the storm made landfall, wind gusts up to 120 km/h (75 mph) were recorded; Darwin recorded a maximum wind gust of 102 km/h (63.4 mph) as Helen moved by the city.
Near Channel Point, the cyclone brought a storm surge
Storm surge
A storm surge is an offshore rise of water associated with a low pressure weather system, typically tropical cyclones and strong extratropical cyclones. Storm surges are caused primarily by high winds pushing on the ocean's surface. The wind causes the water to pile up higher than the ordinary sea...
of 2 to 3 m (6.6 to 9.8 ft), barely surpassing the highest astronomical tide in a few areas. In some cases, waves over topped sand dunes but no damage took place. Roughly 10-15% of trees in open areas were snapped or uprooted by high winds. Only two structures sustained direct wind damage while several others were struck by downed trees. Damage was more widespread in Darwin where roughly 15,000 homes, 60% of the city's residences, were left without power. Approximately 1,500 trees were downed in the city, falling on roads, homes and power lines. In the days following the storm's passage, the Adelaide and Katherine rivers continued to rise, of which the former exceeded minor flood levels. In the harbour, seven vessels washed ashore, each sustaining minor damage. Losses caused by the storm was placed at A$1.3 million (US$1.1 million).
The day after Helen passed through, cleanup efforts began as power crews had to remove downed trees before fixing power lines. The main power lines in the city were restored within 24 hours and rural areas were stated to have their power back within a day or two. Two days after the storm, 500 homes remained without electricity and frustrated residents were further angered after discovering that the Power and Water agency was in control of tree removal and not emergency services. With the power company in charge of clearing downed trees, they stated that their crews would only be dealing with cases involved power lines. Residents with trees in their yards or even on their homes were told to contact private contractors to remove them. By 9 January, more than 100 homes were still without power in northern Darwin, resulting in angry outcries from those still left in the dark. Cleanup efforts dragged on for more than two months as debris was still present in Darwin in March. Removal of tree stumps took through at least mid-April as the cost to remove downed trees exceeded A$1 million (US$882,000). Due to the damage wrought by Helen, its name was retired following its usage. However, it was not replaced by any particular name as a new naming scheme was implemented the following season.
See also
- 2007–08 Australian region cyclone season
- Timeline of the 2007–08 Australian region cyclone season
- Tropical Cyclone Gretel - The last storm to bring gale-force winds to DarwinDarwin, Northern TerritoryDarwin is the capital city of the Northern Territory, Australia. Situated on the Timor Sea, Darwin has a population of 127,500, making it by far the largest and most populated city in the sparsely populated Northern Territory, but the least populous of all Australia's capital cities...
prior to Helen