Cyclone Alu (GaryKJR)

Cyclone Alu (also known as Severe Tropical Cyclone Alu) was the most intense Australian tropical cyclone on record, with a minimum barometric pressure of 892 mbar (26.34 inHg) and 10-minute sustained winds of 160 mph (260 km/h). It caused catastrophic damage in southeastern Papua New Guinea after making landfall there as a strong Category 4 cyclone on the Australian scale. The precursor to Alu was a tropical low that formed near the island of New Ireland on January 12. At 12:00 UTC on January 13, the low developed into a tropical depression. Six hours later, it strengthened into a tropical storm. Shortly after becoming a tropical storm, Alu underwent explosive intensification. In a 30-hour period, Alu's barometric pressure dropped from 994 mbar (29.35 inHg) to 892 mbar (26.34 inHg), and its 10-minute sustained winds increased from 60 mph (95 km/h) to 160 mph (260 km/h). At its peak on the afternoon of January 15, the Joint Typhoon Warning Center (JTWC) reported that Alu was an extremely powerful Category 5-equivalent cyclone on the Saffir-Simpson hurricane scale with 1-minute sustained winds of around 190 mph (305 km/h).

Due to land interaction and an eyewall replacement cycle, Alu began to weaken quickly. At 18:00 UTC on January 16, it made landfall near Alotau, Papua New Guinea as a strong Category 4 cyclone on the Australian scale. After emerging into the Coral Sea, Alu continued to weaken. By midday on January 18, Alu had weakened to a Category 1 tropical cyclone. Later that day, Alu began to restrengthen. Early on January 21, Alu reached its secondary peak intensity as a Category 3 tropical cyclone with 10-minute sustained winds of 80 mph (130 km/h) and a minimum barometric pressure of 973 mbar (28.73 inHg). Three hours later, Alu made landfall near Yarraden, Queensland. Alu briefly entered the Gulf of Carpentaria on January 22 before making another landfall near Burketown, Queensland early on January 23. At around 06:00 UTC on January 24, Alu degenerated into a remnant low while located about 225 miles (362 kilometers) northeast of Alice Springs.

Because of Alu's extremely rapid and unprecedented rate of intensification, residents of southeastern Papua New Guinea were given little time to prepare or evacuate. This lack of preparation lead to catastrophic damage and loss of life. A storm surge of up to 25 feet (7.6 meters) in some places led to widespread flooding. In mainland Milne Bay Province alone, 2,233 people died. 90% of the buildings in the town of Alotau, which suffered a direct impact from Alu, were damaged or destroyed. In the D'Entrecasteaux Islands, which Alu passed through as a weakening Category 5-equivalent cyclone on the Saffir-Simpson hurricane scale, 627 people died. Normanby Island, Fergusson Island, and Goodenough Island were declared uninhabitable for nine months after the storm. Volunteers reported that every building in the town of Esa'Ala was destroyed by Alu. 10 people were killed in Port Moresby because of flooding caused by Alu's outer rainbands. Local flooding in Oro Province and Central Province lead to 26 fatalities and severe property damage. In Australia, the effects of Alu were not nearly as severe. This can be attributed to both the storm not being able to fully restrengthen after interacting with Papua New Guinea and Australia's effective tropical cyclone warning system. A storm surge of around 12 feet (3.7 meters) resulted in significant beach erosion and coastal flooding. Three people were killed in Queensland when their house collapsed. Alu's remnants produced heavy rainfall in the Northern Territory. Overall, Alu caused 2,901 fatalities and $12.41 billion in damage.

Meteorological history
On January 12, a tropical low formed near the Papua New Guinean island of New Ireland. As a result of it being located within an area of extremely low wind shear and sea surface temperatures of around 90°F (32°C), the system began to intensify quickly. Early on January 13, a large burst of convection prompted the Joint Typhoon Warning Center (JTWC) to issue a Tropical Cyclone Formation Alert for the disturbance. At 10:00 UTC that day, the JTWC classified the system as Tropical Cyclone 05P. Two hours later, TCWC Port Moresby initiated advisories on the system, naming it Alu. For the next day, Alu slowly traveled southwards as it continued to strengthen. From January 14 to January 15, Alu underwent explosive intensification. In approximately 30 hours, Alu's minimum barometric pressure dropped from 994 mbar (29.35 inHg) to 892 mbar (26.34 inHg) and its 10-minute sustained winds increased from 60 mph (95 km/h) to 160 mph (260 km/h). During this period, Alu developed excellent poleward and equatorward outflow and cloud tops of below -120°F (-84°C) that wrapped around an eye 21.2 miles (34 kilometers) in diameter. On the afternoon of January 15, Alu reached its peak intensity with a minimum barometric pressure of 892 mbar (26.34 inHg). At 12:00 UTC that day, the Australian Bureau of Meteorology reported that Alu was a Category 5 cyclone on the Australian scale with 10-minute sustained winds of 160 mph (260 km/h). The Joint Typhoon Warning Center, however, reported that Alu was a Category 5-equivalent cyclone on the Saffir-Simpson scale with 1-minute sustained winds of 190 mph (305 km/h). These measurements made Alu the strongest Australian region tropical cyclone on record in terms of barometric pressure, 10-minute sustained winds, and 1-minute sustained winds. Shortly after achieving peak intensity, Alu began to steadily weaken as a result of upwelling, interaction with the mountainous terrain of southeastern Papua New Guinea, and an ongoing eyewall replacement cycle. The storm also turned westward in response to a ridgeto its northwest. By 16:00 UTC on January 16, Alu had weakened to a Category 4 cyclone on the Australian scale. Later that day, Alu made landfall near Alotau, Papua New Guinea with 10-minute sustained winds of 125 mph (200 km/h) and a minimum barometric pressure of 923 mbar (27.26 inHg). Early the next day, Alu emerged into the Coral Sea as a weak Category 4 cyclone and started to weaken more rapidly due to increasing vertical wind shear. By midday on January 17, Alu's eye had completely dissipated. Over the next day, Alu became more disorganized and lost much of its deep convection.

On January 18, Alu began to restrengthen as conditions around the system became more favorable. At 18:00 UTC on January 19, Alu strengthened into a Category 3 cyclone. Because of a high-pressure system located to its east, Alu turned southward. The presence of a ragged eye on satellite imagery prompted the Joint Typhoon Warning Center to upgrade Alu to a Category 2-equivalent cyclone on the Saffir-Simpson scale at 12:00 UTC on January 20. Early on January 21, Alu reached its secondary peak intensity as a low-end Category 3 cyclone on the Australian scale with 10-minute sustained winds of 80 mph (130 km/h) and a minimum barometric pressure of 973 mbar (28.73 inHg). Three hours later, Alu made landfall near Yarraden, Queensland. After making landfall, Alu weakened considerably. By 18:00 UTC on January 21, thunderstorm activity near the center of the storm had decreased significantly.

Early on January 22, Alu entered the Gulf of Carpentaria as a high-end Category 1 cyclone. Due to dry air intrusion and high amounts of vertical wind shear, it was not able to restrengthen before making landfall again near Burketown, Queensland with 10-minute sustained winds of 40 mph (65 km/h) and a minimum barometric pressure of 1005 mbar (29.68 inHg). Six hours later, Alu weakened to a tropical low and began to accelerate southwestward. On January 24, after its low-level circulation center had become entirely devoid of convection, Alu degenerated into a remnant low while located about 225 miles (362 kilometers) northeast of Alice Springs.

Papua New Guinea
On January 13, shortly after Alu was named by TCWC Port Moresby, Papua New Guinea's National Weather Service issued tropical storm warnings for coastal communities in East New Britain Province, West New Britain Province, and southern New Ireland Province. Later that day, the National Weather Service issued tropical storm warnings for all coastal and inland communities in Milne Bay Province and Central Province and encouraged people in the area to prepare extensively for the storm. Many people heeded this warning; in these two provinces, all businesses and schools, with the exception of designated emergency shelters, were closed, groups of people placed sandbags on beaches, and the vast majority of stores sold all their supplies. The Government of Papua New Guinea sent food and water to numerous communities on the coast of the Papuan Peninsula. Following Alu's period of explosive intensification, the tropical storm warnings which had previously been in effect for the islands of New Britain and New Ireland were discontinued; the tropical storm warning which was in effect for Milne Bay Province and Central Province was upgraded to a tropical cyclone warning, and the warned area was extended to include Oro Province. Due to its remarkable and unprecedented rate of intensification, the precautions taken by residents of southeastern Papua New Guinea were largely incapable of protecting them from the storm surge, which reached around 25 feet (7.6 meters) in some location, heavy rainfall, and strong winds caused by Alu; therefore, in Papua New Guinea, damage and loss of life was extensive and catastrophic.

Australia
On the afternoon of January 19, approximately two days before Alu made landfall in Queensland as a Category 2 tropical cyclone on the Saffir-Simpson hurricane scale, the Bureau of Meteorology issued a tropical cyclone watch for the eastern coast of Queensland between Archer River and Cairns. The next day, the tropical cyclone watch for this region was upgraded to a tropical cyclone warning. Before the storm made landfall, local officials evacuated the towns of Yarraden and Coen; Oyala Thumotang National Park and Kutini-Payamu (Iron Range) National Park were evacuated as well. Residents that refused to leave these areas were encouraged to stay inside until the storm passed and it was deemed safe for them to leave. Television and radio stations advised people in Queensland to gather food and water and do whatever they could to protect their houses from structural damage. On January 21, a cyclone watch was issued for the coast of Queensland between Karumba and Nicholson. Early on January 22, the tropical cyclone watch was upgraded to a tropical cyclone warning. Schools in the area were closed for several days as the storm approached the northwestern coast of Queensland. Heavy rainfall from Alu prompted the Bureau of Meteorology to issue a flood warning for much of the Northern Territory.

Records
Cyclone Alu formed in TCWC Port Moresby's area of responsibility, which encompasses the area around the country of Papua New Guinea. Tropical cyclones rarely form in this region. Alu was the first storm to be named by TCWC Port Moresby since Severe Tropical Cyclone Guba. Guba was a Category 3 cyclone on the Australian scale that developed in November 2007. It caused severe flooding in southern Papua New Guinea, partly because of its erratic movement.

One of the most notable aspects of Alu was its explosive intensification and intensity. Alu's minimum barometric pressure dropped by 102 millibars in a 30-hour period, surpassing Hurricane Wilma of 2005, which experienced a barometric pressure drop of 100 millibars in 30 hours. This rate of intensification was slightly slower than Super Typhoon Forrest of 1983, however, which experienced a barometric pressure drop of 100 millibars in less than a day. At its peak, Alu had 10-minute sustained winds of 160 mph (260 km/h), 1-minute sustained winds of 190 mph (305 km/h), and a minimum barometric pressure of 892 mbar (26.34 inHg). This made it the strongest cyclone on record in the Australian region. Previously, Cyclone Inigo, which had 10-minute sustained winds of 150 mph (240 km/h), 1-minute sustained winds of 160 mph (260 km/h), and a minimum barometric pressure of 900 mbar (26.58 inHg), held this title.

Due to its slow movement, Alu dropped torrential rainfall on much of southeastern Papua New Guinea, causing landslides and widespread flooding. Mount Vineuo, the highest point of Goodenough Island, received 114.87 inches (2,918 mm) of precipitation in a three-day period; this measurement makes Alu one of the wettest tropical cyclones on record. The main reason for this large amount of rainfall is a process known as orographic lift. This process involves the forcing of air masses to higher elevations, which can create precipitation and clouds.

Retirement
When a tropical cyclone forms in TCWC Port Moresby's area of responsibility, its name is automatically retired. Because of this policy and the widespread damage and loss of life caused by the storm, the name Alu was retired by the World Meteorological Organization (WMO); it was replaced with Nou, which was the first name on TCWC Port Moresby's standby list at the time.