Cyclone Emma
Encyclopedia
Tropical Cyclone Emma was a weak but unusually large tropical cyclone
that affected a substantial portion of Western Australia
during the 2005–06 Australian region cyclone season. Forming out of an area of low pressure on 25 February, the precursor to Emma slowly tracked southward. Although classified tropical, the structure of the system represented that of a monsoon
al storm. However, low wind shear
and well-developed outflow
gradually allowed convection
to develop near the centre of circulation
. As the system approached the Pilbara coastline of Western Australia on 27 February, it intensified into a Category 1 cyclone and attained peak 10-minute sustained winds of 75 km/h (45 mph). After moving inland near Mardie, Emma weakened to a tropical low but became exceedingly large; its cloud cover obscured most of Western Australia. The remnants of the weak storm persisted until 1 March, at which time they dissipated over the Great Australian Bight
.
Although a weak storm, rainfall from Emma caused flooding in numerous parts of Western Australia. In Karratha
, six people required rescue after their cars became stranded in flood waters. The most significant damage took place along the Murchison River
which swelled to roughly 20 km (12.4 mi) in width. Although only one town was threatened by the river, large areas of farmland were inundated by the expanding river, leading to substantial agricultural losses. Despite the extensive flooding, no fatalities were reported as a result of Emma.
on 22 February 2006. Over the following few days, a monsoon
al trough
developed over the Timor Sea
, leading to an increased likelihood of tropical cyclone
formation from the initial low within several days. On 25 February, the Australian Bureau of Meteorology began monitoring the system as a tropical low. The low tracked slowly towards the south throughout the day and the centre of circulation
relocated farther south late on 26 February. By this time, the Bureau of Meteorology anticipated the low to develop into a tropical cyclone and attain winds of 95 km/h (60 mph 10-minute sustained) before moving over land in Western Australia
.
Early on 27 February, the Joint Typhoon Warning Center
(JTWC) classified the system as a tropical depression. During the day, a QuikSCAT
pass revealed a broad low-level circulation with the highest winds located around the periphery of the storm, a characteristic of monsoonal systems. Although it was situated within a region of low wind shear
and underneath an anticyclone
, convective activity
was mostly present in the system's large outer bands
. Later that day, the Bureau of Meteorology upgraded the system to a Category 1 cyclone on the Australian intensity scale and named it Emma. At this time, Emma was located roughly 305 km (190 mi) north of Onslow, Western Australia
. Several hours later, the JTWC classified Emma as Tropical Storm 15S following the development of convection near the centre of circulation.
The storm continued to track southward in response to a strong mid to upper-level ridge
situated over central Australia. Emma attained its peak wind speed of 75 km/h (45 mph 10-minute sustained) late on 27 February as it neared landfall
. However, the JTWC assessed Emma to have been slightly weaker, peaking with winds of 65 km/h (40 mph 1-minute sustained). The storm maintained this intensity through its landfall early on 28 February near Mardie
along the Pilbara coastline. Shortly after moving over land, the JTWC declared Emma extratropical
and issued their final advisory on the storm. The Bureau of Meteorology, however, continued to monitor the cyclone as it rapidly tracked over Western Australia. Over land, the storm became unusually large, with outer bands from the storm covering most of Western Australia. Late on 28 February, the lowest barometric pressure in relation to Emma, 988 mbar
(hPa
; 29.18 inHg
), was recorded. The remnants of Emma persisted through most of 1 March before the system moved over the Great Australian Bight
and dissipated.
The Australian Bureau of Meteorology uses 10-minute sustained winds
, while the Joint Typhoon Warning Center uses one-minute sustained winds. The Bureau of Meteorology's peak intensity for Emma was 75 km/h (45 mph) 10-minute sustained, or 85 km/h (50 mph) one-minute sustained. The JTWC's peak intensity for Emma was 65 km/h (40 mph) one-minute sustained, or 55 km/h (35 mph) 10-minute sustained.
and Daryl, residents were warned about the likelihood of flooding due to the already saturated grounds. The Bureau of Meteorology also issued tropical cyclone warnings
for most of the Pilbara coastline on 28 February. The same day, the Fire and Emergency Services of Australia issued a Yellow Alert for Point Samson
, Roebourne
, Wickham
, Dampier
, Karratha
, and Mardie. Residents in these areas were advised to evacuate if necessary and ensure that all cyclone preparations had been completed. Shelters were also opened for residents who sought need for one. Schools throughout the Pilbara region were also closed for several days as a result of the storm.
Due to the low intensity of the storm at landfall, little or no wind damage took place from Emma. On land, sustained winds were recorded up to 78 km/h (48.5 mph) and gusts up to 95 km/h (59 mph). A storm surge
of 0.8 m (2.6 ft) was recorded at Dampier but, no damage resulted from it. Heavy rains produced by the storm caused moderate to severe flooding in Western Australia. In Karratha, six people were rescued from two cars after they became stranded on a flooded road. Total rainfall from the storm was recorded at 308 mm (12.1 in) in the city. Localised flooding was reported in Pannawonica
. Some buildings reported minor flooding but overall structural damage was minimal. The 190 mm (7.5 in) of rain that fell in a 24-hour span in Karratha pushed the city above its annual average rainfall totals in the first two months of the year. Near the Yarraloola Station, the Robe River
overflowed its banks, inundating the area and forcing the evacuation of everyone in the homestead. In the Gascoyne region 30 cattle drowned after flood waters rapidly overtook a pasture.
In the Murchison region, rainfall exceeding 100 mm (3.9 in) brought the worst floods in decades, inundating numerous farms and causing substantial agricultural losses. Two weeks after the storm passed, the mouth of the Murchison River
was closed after a ship became stranded in the swollen river. By 14 March, the river had broadened to roughly 20 km (12.4 mi) in places normally 500 m (1,640.4 ft) in width. These values marked the largest flood ever recorded in the river's history. Officials distributed sandbags to build temporary levee
to protect low-lying areas. The largest operation took place at Kalbarri
, near the mouth of the river, where 60 firefighters and 18 volunteers worked to put up 9,000 sandbags. The Billabalong and Twinpeaks stations were also isolated from surrounding areas after the Murchison River inundated the area. Several stations in the area remained under water for over a month and farmers requested urgent assistance from the government to help alleviate losses. Initial damage from the storm was placed at A$
1 million ($706,580 USD
).
Flood waters from the Murchison River finally began to recede on 17 March; however, it took several weeks for the river to return to its normal level. Although Emma had only minor effects in Carnarvon
, the town enacted a A$14 million ($10 million USD) flood protection plan in the wake of the storm. The plan would lead to the construction of new levees in areas surrounding the town and keep flood waters within Nicol Bay Flats. Additionally, four sections of the North West Coastal Highway
were set to be upgraded for similar reasons. Due to the combined effects of Cyclones Clare, Darryl, Jim, Emma, Kate and Glenda, gold production in Australia fell by 8 percent, resulting in earnings losses of A$130 million.
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 affected a substantial portion 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...
during the 2005–06 Australian region cyclone season. Forming out of an area of low pressure on 25 February, the precursor to Emma slowly tracked southward. Although classified tropical, the structure of the system represented that of a monsoon
Monsoon
Monsoon is traditionally defined as a seasonal reversing wind accompanied by corresponding changes in precipitation, but is now used to describe seasonal changes in atmospheric circulation and precipitation associated with the asymmetric heating of land and sea...
al storm. However, low 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 well-developed 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...
gradually allowed convection
Atmospheric convection
Atmospheric convection is the result of a parcel-environment instability, or temperature difference, layer in the atmosphere. Different lapse rates within dry and moist air lead to instability. Mixing of air during the day which expands the height of the planetary boundary layer leads to...
to develop near the centre of circulation
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...
. As the system approached the Pilbara coastline of Western Australia on 27 February, it intensified into a Category 1 cyclone and attained peak 10-minute sustained winds of 75 km/h (45 mph). After moving inland near Mardie, Emma weakened to a tropical low but became exceedingly large; its cloud cover obscured most of Western Australia. The remnants of the weak storm persisted until 1 March, at which time they dissipated over the Great Australian Bight
Great Australian Bight
The Great Australian Bight is a large bight, or open bay, off the central and western portions of the southern coastline of mainland Australia.-Extent:...
.
Although a weak storm, rainfall from Emma caused flooding in numerous parts of Western Australia. In Karratha
Karratha, Western Australia
-Facilities:A range of hotel, motel, B&B and caravan/RV accommodation is available for visitors. However, as the town is booming, accommodation is often hard to come by.The town has restaurants, a tavern, two hotels and two night clubs...
, six people required rescue after their cars became stranded in flood waters. The most significant damage took place along the Murchison River
Murchison River (Western Australia)
The Murchison River is the second longest river in Western Australia. It flows for about from the southern edge of the Robinson Ranges to the Indian Ocean at Kalbarri. It has a mean annual flow of about 200 million cubic metres.-Course:...
which swelled to roughly 20 km (12.4 mi) in width. Although only one town was threatened by the river, large areas of farmland were inundated by the expanding river, leading to substantial agricultural losses. Despite the extensive flooding, no fatalities were reported as a result of Emma.
Meteorological history
Tropical Cyclone Emma originated from an area of low pressure that formed to the southeast of JavaJava
Java is an island of Indonesia. With a population of 135 million , it is the world's most populous island, and one of the most densely populated regions in the world. It is home to 60% of Indonesia's population. The Indonesian capital city, Jakarta, is in west Java...
on 22 February 2006. Over the following few days, a monsoon
Monsoon
Monsoon is traditionally defined as a seasonal reversing wind accompanied by corresponding changes in precipitation, but is now used to describe seasonal changes in atmospheric circulation and precipitation associated with the asymmetric heating of land and sea...
al 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...
developed over the Timor Sea
Timor Sea
The Timor Sea is a relatively shallow sea bounded to the north by the island of Timor, to the east by the Arafura Sea, to the south by Australia and to the west by the Indian Ocean....
, leading to an increased likelihood of 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...
formation from the initial low within several days. On 25 February, the Australian Bureau of Meteorology began monitoring the system as a tropical low. The low tracked slowly towards the south throughout the day and the centre of circulation
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...
relocated farther south late on 26 February. By this time, the Bureau of Meteorology anticipated the low to develop into a tropical cyclone and attain winds of 95 km/h (60 mph 10-minute sustained) before moving over land in 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...
.
Early on 27 February, 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) classified the system as a tropical depression. During the day, a QuikSCAT
QuikSCAT
The QuikSCAT is an earth-observing satellite that provided estimates of wind speed and direction over the oceans to National Oceanic and Atmospheric Administration and others. This "quick recovery" mission intended to replace the NASA Scatterometer , which failed in June 1997...
pass revealed a broad low-level circulation with the highest winds located around the periphery of the storm, a characteristic of monsoonal systems. Although it was situated within a region of low 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 underneath an anticyclone
Anticyclone
An anticyclone is a weather phenomenon defined by the United States' National Weather Service's glossary as "[a] large-scale circulation of winds around a central region of high atmospheric pressure, clockwise in the Northern Hemisphere, counterclockwise in the Southern Hemisphere"...
, convective activity
Atmospheric convection
Atmospheric convection is the result of a parcel-environment instability, or temperature difference, layer in the atmosphere. Different lapse rates within dry and moist air lead to instability. Mixing of air during the day which expands the height of the planetary boundary layer leads to...
was mostly present in the system's large outer bands
Rainband
A rainband is a cloud and precipitation structure associated with an area of rainfall which is significantly elongated. Rainbands can be stratiform or convective, and are generated by differences in temperature. When noted on weather radar imagery, this precipitation elongation is referred to as...
. Later that day, the Bureau of Meteorology upgraded the system to a Category 1 cyclone on the Australian intensity scale and named it Emma. At this time, Emma was located roughly 305 km (190 mi) north of Onslow, Western Australia
Onslow, Western Australia
Onslow is a coastal town in the Pilbara region of Western Australia, north of Perth. It currently has a population of around 573 people and is in the Shire of Ashburton Local Government Area....
. Several hours later, the JTWC classified Emma as Tropical Storm 15S following the development of convection near the centre of circulation.
The storm continued to track southward in response to a strong mid to upper-level ridge
Ridge (meteorology)
A ridge is an elongated region of relatively high atmospheric pressure, the opposite of a trough....
situated over central Australia. Emma attained its peak wind speed of 75 km/h (45 mph 10-minute sustained) late on 27 February as it neared 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...
. However, the JTWC assessed Emma to have been slightly weaker, peaking with winds of 65 km/h (40 mph 1-minute sustained). The storm maintained this intensity through its landfall early on 28 February near Mardie
Mardié
Mardié is a commune in the Loiret department in north-central France.-See also:*Communes of the Loiret department...
along the Pilbara coastline. Shortly after moving over land, the JTWC declared Emma 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...
and issued their final advisory on the storm. The Bureau of Meteorology, however, continued to monitor the cyclone as it rapidly tracked over Western Australia. Over land, the storm became unusually large, with outer bands from the storm covering most of Western Australia. Late on 28 February, the lowest barometric pressure in relation to Emma, 988 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...
; 29.18 inHg
Inch of mercury
Inches of mercury, ' is a unit of measurement for pressure. It is still widely used for barometric pressure in weather reports, refrigeration and aviation in the United States, but is seldom used elsewhere....
), was recorded. The remnants of Emma persisted through most of 1 March before the system moved over the Great Australian Bight
Great Australian Bight
The Great Australian Bight is a large bight, or open bay, off the central and western portions of the southern coastline of mainland Australia.-Extent:...
and dissipated.
The Australian Bureau of Meteorology uses 10-minute sustained winds
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...
, while the Joint Typhoon Warning Center uses one-minute sustained winds. The Bureau of Meteorology's peak intensity for Emma was 75 km/h (45 mph) 10-minute sustained, or 85 km/h (50 mph) one-minute sustained. The JTWC's peak intensity for Emma was 65 km/h (40 mph) one-minute sustained, or 55 km/h (35 mph) 10-minute sustained.
Preparations and impact
Ahead of the storm, oil and mining operations in threatened regions were temporarily shut down. Already suffering from the impacts of Cyclones ClareCyclone Clare
Severe Tropical Cyclone Clare was a moderately strong cyclone that struck Western Australia in January 2006. The storm formed as an area of low pressure in the Arafura Sea, and moved westward. After receiving the name Clare on 7 January, the system ultimately peaked at Category 3 intensity on the...
and Daryl, residents were warned about the likelihood of flooding due to the already saturated grounds. The Bureau of Meteorology also issued tropical cyclone warnings
Tropical 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 most of the Pilbara coastline on 28 February. The same day, the Fire and Emergency Services of Australia issued a Yellow Alert for Point Samson
Point Samson, Western Australia
,Point Samson is a small coastal hamlet 1,579 km north of Perth and 18 km north of Roebourne in the Pilbara region of Western Australia. The town is a popular holiday location for the nearby mining towns, including Wickham, Karratha and Dampier. Fishing is the main industry...
, Roebourne
Roebourne, Western Australia
Roebourne is an old gold rush town in Western Australia's Pilbara region. It is 202 km from Port Hedland and 1,563 km from Perth, the state's capital. It prospered during its gold boom of the late 19th century and was once the biggest settlement between Darwin and Perth...
, Wickham
Wickham, Western Australia
Wickham is a townsite located 1,572 km north of Perth and 13 km north of Roebourne in the Pilbara region of Western Australia.-History:...
, Dampier
Dampier, Western Australia
Dampier is a major industrial port in the north-west of Western Australia. The Dampier Port is part of the Dampier Archipelago. The port services petrochemical, salt, iron ore and natural gas export industries. Rio Tinto exports large volumes of iron ore through the port, and in September 2010...
, Karratha
Karratha, Western Australia
-Facilities:A range of hotel, motel, B&B and caravan/RV accommodation is available for visitors. However, as the town is booming, accommodation is often hard to come by.The town has restaurants, a tavern, two hotels and two night clubs...
, and Mardie. Residents in these areas were advised to evacuate if necessary and ensure that all cyclone preparations had been completed. Shelters were also opened for residents who sought need for one. Schools throughout the Pilbara region were also closed for several days as a result of the storm.
Due to the low intensity of the storm at landfall, little or no wind damage took place from Emma. On land, sustained winds were recorded up to 78 km/h (48.5 mph) and gusts up to 95 km/h (59 mph). 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 0.8 m (2.6 ft) was recorded at Dampier but, no damage resulted from it. Heavy rains produced by the storm caused moderate to severe flooding in Western Australia. In Karratha, six people were rescued from two cars after they became stranded on a flooded road. Total rainfall from the storm was recorded at 308 mm (12.1 in) in the city. Localised flooding was reported in Pannawonica
Pannawonica, Western Australia
The town of Pannawonica is an iron-ore mining town located in the Pilbara region of Western Australia, near the Robe River, about 200 km south-west from Karratha...
. Some buildings reported minor flooding but overall structural damage was minimal. The 190 mm (7.5 in) of rain that fell in a 24-hour span in Karratha pushed the city above its annual average rainfall totals in the first two months of the year. Near the Yarraloola Station, the Robe River
Robe River
Robe River is a river in the Pilbara region of Western Australia.The headwaters of the river rise in the Hamersley Range near Marana Spring then flow in a north westerly direction past the Robe River-Deepdale mine, crossing the North West Coastal Highway near the Pannawonica turnoff then...
overflowed its banks, inundating the area and forcing the evacuation of everyone in the homestead. In the Gascoyne region 30 cattle drowned after flood waters rapidly overtook a pasture.
In the Murchison region, rainfall exceeding 100 mm (3.9 in) brought the worst floods in decades, inundating numerous farms and causing substantial agricultural losses. Two weeks after the storm passed, the mouth of the Murchison River
Murchison River (Western Australia)
The Murchison River is the second longest river in Western Australia. It flows for about from the southern edge of the Robinson Ranges to the Indian Ocean at Kalbarri. It has a mean annual flow of about 200 million cubic metres.-Course:...
was closed after a ship became stranded in the swollen river. By 14 March, the river had broadened to roughly 20 km (12.4 mi) in places normally 500 m (1,640.4 ft) in width. These values marked the largest flood ever recorded in the river's history. Officials distributed sandbags to build temporary levee
Levee
A levee, levée, dike , embankment, floodbank or stopbank is an elongated naturally occurring ridge or artificially constructed fill or wall, which regulates water levels...
to protect low-lying areas. The largest operation took place at Kalbarri
Kalbarri, Western Australia
Kalbarri is a coastal town in the Mid West region located 592 km north of Perth, Western Australia. The town is found at the mouth of the Murchison River and has an elevation of...
, near the mouth of the river, where 60 firefighters and 18 volunteers worked to put up 9,000 sandbags. The Billabalong and Twinpeaks stations were also isolated from surrounding areas after the Murchison River inundated the area. Several stations in the area remained under water for over a month and farmers requested urgent assistance from the government to help alleviate losses. Initial damage from the storm was placed at A$
Australian dollar
The Australian dollar is the currency of the Commonwealth of Australia, including Christmas Island, Cocos Islands, and Norfolk Island, as well as the independent Pacific Island states of Kiribati, Nauru and Tuvalu...
1 million ($706,580 USD
United States dollar
The United States dollar , also referred to as the American dollar, is the official currency of the United States of America. It is divided into 100 smaller units called cents or pennies....
).
Flood waters from the Murchison River finally began to recede on 17 March; however, it took several weeks for the river to return to its normal level. Although Emma had only minor effects in Carnarvon
Carnarvon, Western Australia
Carnarvon is a coastal town situated approximately 900 kilometres north of Perth, Western Australia. It lies at the mouth of the Gascoyne River on the Indian Ocean. The popular Shark Bay world heritage area lies to the south of the town and the Ningaloo Reef lies to the north...
, the town enacted a A$14 million ($10 million USD) flood protection plan in the wake of the storm. The plan would lead to the construction of new levees in areas surrounding the town and keep flood waters within Nicol Bay Flats. Additionally, four sections of the North West Coastal Highway
North West Coastal Highway
North West Coastal Highway in Western Australia is a generally north-south Western Australian highway which links the fishing town of Geraldton with the iron ore port of Port Hedland. It is long, and constructed as a sealed 2-lane single carriageway with overtaking lanes in some parts. It was...
were set to be upgraded for similar reasons. Due to the combined effects of Cyclones Clare, Darryl, Jim, Emma, Kate and Glenda, gold production in Australia fell by 8 percent, resulting in earnings losses of A$130 million.
See also
- 2005–06 Australian region cyclone season
- List of cyclones in Western Australia