Tropical Cyclone Emma was a weak but unusually large
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. Depend ...
that affected a substantial portion of
Western Australia
Western Australia (commonly abbreviated as WA) is a state of Australia occupying the western percent of the land area of Australia excluding external territories. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to th ...
during the
2005–06 Australian region cyclone season. Forming out of an
area of low pressure
In meteorology, a low-pressure area, low area or low is a region where the atmospheric pressure is lower than that of surrounding locations. Low-pressure areas are commonly associated with inclement weather (such as cloudy, windy, with possible ...
on 25 February, the precursor to Emma slowly tracked southward. Although classified tropical, the structure of the system represented that of a
monsoon
A monsoon () is traditionally 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 annual latitudinal oscil ...
al storm. However, low
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 horizontal ...
and well-developed
outflow
Outflow may refer to:
*Capital outflow, the capital leaving a particular economy
*Bipolar outflow, in astronomy, two continuous flows of gas from the poles of a star
*Outflow (hydrology), the discharge of a lake or other reservoir system
* Outflow ...
gradually allowed
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 convec ...
to develop near the
centre of circulation. As the system approached the
Pilbara
The Pilbara () is a large, dry, thinly populated region in the north of Western Australia. It is known for its Aboriginal peoples; its ancient landscapes; the red earth; and its vast mineral deposits, in particular iron ore. It is also a glo ...
coastline of Western Australia on 27 February, it intensified into a Category 1 cyclone and attained peak 10-minute sustained winds of . 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
The Great Australian Bight is a large oceanic bight, or open bay, off the central and western portions of the southern coastline of mainland Australia.
Extent
Two definitions of the extent are in use – one used by the International Hydrog ...
.
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 floodwaters. The most significant damage took place along the
Murchison River which swelled to roughly 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
In meteorology, a low-pressure area, low area or low is a region where the atmospheric pressure is lower than that of surrounding locations. Low-pressure areas are commonly associated with inclement weather (such as cloudy, windy, with possible ...
that formed to the southeast of
Java
Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's List ...
on 22 February 2006. Over the following few days, a
monsoon
A monsoon () is traditionally 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 annual latitudinal oscil ...
al
trough
Trough may refer to:
In science
* Trough (geology), a long depression less steep than a trench
* Trough (meteorology), an elongated region of low atmospheric pressure
* Trough (physics), the lowest point on a wave
* Trough level (medicine), the l ...
developed over the
Timor Sea
The Timor Sea ( id, Laut Timor, pt, Mar de Timor, tet, Tasi Mane or ) is a relatively shallow sea bounded to the north by the island of Timor, to the east by the Arafura Sea, and to the south by Australia.
The sea contains a number of reefs, ...
, leading to an increased likelihood of
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. Depend ...
formation from the initial low within several days.
On 25 February, the
Australian Bureau of Meteorology
Australian(s) may refer to:
Australia
* Australia, a country
* Australians, citizens of the Commonwealth of Australia
** European Australians
** Anglo-Celtic Australians, Australians descended principally from British colonists
** Aboriginal Aus ...
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
10-minute sustained) before moving over land in
Western Australia
Western Australia (commonly abbreviated as WA) is a state of Australia occupying the western percent of the land area of Australia excluding external territories. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to th ...
.
Early on 27 February, the
Joint Typhoon Warning Center
The Joint typhoon Warning Center (JTWC) is a joint United States Navy – United States Air Force command in Pearl Harbor, Hawaii. The JTWC is responsible for the issuing of tropical cyclone warnings in the North-West Pacific Ocean, South P ...
(JTWC) classified the system as a
tropical depression
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 ...
.
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
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 horizontal ...
and underneath an
anticyclone
An anticyclone is a weather phenomenon defined as a large-scale circulation of winds around a central region of high atmospheric pressure, clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere as viewed from abov ...
,
convective activity was mostly present in the system's large