A Detailed Look at the Category 5 Winds of Cyclone Tracy

Cyclone Tracy devastated the city of Darwin on Christmas Day, 1974. The storm caused more wind-related fatalities than any other tropical cyclone in a developed nation since 1950 and nearly led to the abandonment of half the city.

□ The city of Darwin, which sits alone atop Australia’s northern coastline, experienced a large surge of development in the years following World War II. Despite the existence of fairly standard building regulations, much of the city and its suburbs were constructed quickly in the 50’s and 60’s, causing many developers to turn a blind eye to the structural codes (Risk Assessment Model). As the city had not experienced a severe cyclone in many decades, the new suburban neighborhoods were built primarily with the tropical heat in mind. To take advantage of afternoon breezes, homes were elevated atop cement pillars and fitted with louvres for ventilation. By 1970, more than 40,000 people called the growing city home.

On December 22nd, 1974, a swirling mass of rain entered within range of the Darwin radar. The storm, named Cyclone Tracy the previous evening, appeared small and meek as it spun ever so slowly to the southwest. False alarms were commonplace in the tropics, and few paid much attention to radio warnings as the cyclone changed direction and slowly moved into the Beagle Gulf. Cyclone Tracy was an exceptionally small storm, being able to fit entirely within the 40 mile wedge between Bathurst Island and mainland Australia.

Composite radar view of Cyclone Tracy on the evening of December 24th, with the city of Darwin highlighted in yellow. The eyewall surrounding the storm is unusually compact and symmetrical. Despite the center of the storm being a mere 15 miles from Darwin, the city was experiencing only moderate rain and breezy conditions. The most intense winds in the cyclone extended only a few miles beyond the edge of the eye.

Cyclone alerts warned that “very destructive winds” of 75mph (120 km/h) with gusts to 94mph (150 km/h) were expected to hit the area late Christmas Eve. Many residents boarded up their windows while some chose to wait-and-see with the impending storm, which was forecast to be of only moderate intensity – the equivalent of a minimal Category 1 hurricane in the Atlantic.

Only a dozen miles offshore, the eye of Cyclone Tracy contracted to less than seven miles in width. The storm would become the smallest tropical cyclone in history, with winds over 38mph (60 km/h) extending only 30 miles from the center of the storm, and hurricane force winds extending less than eight miles.* Unbeknownst to meteorologists at the time, the storm had significantly stronger winds than originally estimated, and was gaining intensity as darkness fell over Darwin the night of Christmas Eve.

*Tropical Storm Marco in 2008 became the smallest tropical cyclone in history, with gale force winds extending only 10 miles from its center. The storm was significantly weaker, however. No storm of greater intensity has ever approached the tiny diameter of Cyclone Tracy..

Obliterated homes in Darwin’s northern suburbs.

The Storm

Winds picked up across Darwin shortly after 11pm as a few brave holiday partygoers left city pubs and headed home. By 12am Christmas morning, gusts of 50mph (80km/h) were being recorded at the Darwin Airport, and the winds were increasing with each passing minute. Around 1am, serious damage began to occur as hurricane force gusts reached the coastline.

Convection surrounding Tracy’s pinpoint eye intensified throughout the night, causing the storm’s central pressure to drop to 950mb, or perhaps a bit lower. Later analysis concluded that Cyclone Tracy entered a period of “explosive deepening” in the hours prior to making landfall, causing the storm’s eye to contract to only 5 miles in width (Sydney Morning Herald, 1975). The cyclone’s extremely slow forward pace, under 5mph, meant that sections of Darwin were to experience hurricane force winds for more than three hours.

Wind trace from the Darwin Airport, located three miles inland and near the center of the storm’s path. Winds rapidly increased after 2:30am as the powerful eyewall came shore. A peak gust of 135mph (217 km/h) was recorded just before the anemometer failed at 3:10am. The failure likely coincided with the commencement of the storm’s highest winds, which likely intensified before the calm of the eye reached the area 40 minutes later. A false reading was created at the end of the trace as the instrument failed. (Mason and Haynes)

Severe damage at the RAAF base in Darwin. An Indonesian DC3 airplane, which had been anchored to multiple 44-gallon drums filled with concrete, was lifted and thrown completely over a nearby hangar (visible above). Many of the destroyed aircraft were later placed in the Darwin Air Museum as a memento to the cyclone. (RAAF)

Around 3am, homes near the coast began to experience the full force of Cyclone Tracy. Darwin residents, initially concerned with the damage to their homes, soon realized their lives were in danger. Just north of downtown, priest Ted Collins made a brief audio recording of the storm as it roared like a jet engine over town (best heard with headphones on high volume). Flying debris from thousands of disintegrating homes filled the air, puncturing boarded windows and banging loudly against the sides of homes. Terrified residents huddled in their bathrooms as their homes shook violently amidst the thundering winds. Slightly south of the worst conditions, a survivor from Fannie Bay described her experience:

One of the living room windows went. And, shortly thereafter, the louvers burst in the bedrooms. Next, I saw the hatch to the attic pop up, so I knew the roof was going. You could hear the tin being torn from the roof by the fierce wind…By this time the water was pouring through the windows and we were lying cold and wet. I could feel the movement of the floor under me and the shuttering of the house. (Gil Jennex)

Farther north, 17-year old Amanda White (nee Mills) was weathering the storm at her father’s home in Rapid Creek:

At one point the winds were so loud that it didn’t seem they could get any stronger. I could hear the roof being torn off, and then something large smashed through the bedroom wall and took some of the house along with it. Before I could get a good grip on the counter, the whole structure came apart. My arm was badly crushed from a piece of timber. All I felt I could do was pray that I wouldn’t feel any pain, if it took me or not.

Final view of Cyclone Tracy, around 5am, before the radar failed. The storm’s eye contracted to only 5 miles in width in the hours before landfall (Mason and Haynes, 2010). As the leading edge of the back eyewall began impacting the airport, the radar failed, effectively ending all local analysis of the storm.

Extreme wind damage in Casuarina, one of Darwin’s northern suburbs. Entire forests were stripped of leaves and branches by the storm, an indication of extreme intensity. (Image by Rick Stevens)

The eye provided a brief 40 minute respite, confusing many into thinking the storm had passed. Survivors described the back eyewall of the storm as even more fierce than the front, accompanied by a roar that was heard several minutes before the winds recommenced. Due to the storm’s slow speed, the severe nature of the “second wind” was unusual. Some researchers later concluded that the winds in the western eyewall may have appeared more intense due to the multitude of debris left behind by the first half of the storm. Others researchers believe the storm continued to intensify slightly after landfall. One study also concluded that “decreased fetch roughness” in the back eyewall may have led to their increased intensity in the northern suburbs (Mason and Haynes).

By daylight on Christmas Day, 71 people had been killed directly by the storm. Most of the 50 fatalities that occurred on land were in the northern suburbs, where the most extreme damage occurred. A detailed report on 46 of the fatalities concluded that 33 of the victims were crushed by collapsed buildings, and another 13 deaths were related to flying debris, mostly from slicing pieces of metal but also from “penetration” by flying timber. Injuries sustained from being blown out of elevated houses was also a contributing factor in some of the deaths (Mason and Haynes). In one instance, an injured man sought shelter in a neighbor’s home during the eye of the cyclone, only to be killed when the house was leveled in the second half of the storm.

Cyclone Tracy caused more wind related fatalities than any other tropical cyclone to impact the United States or Australia since the turn of the 20th century. Hurricane Andrew, which struck a more populated area as a Category 5 hurricane in 1992, caused only 14 wind-related deaths. The high number of victims is likely the result of four factors – the extreme intensity of the winds, the duration of the slow-moving cyclone, the building construction in the area and the lack of evacuation preceding the storm (Griffith Review).

Image of trees that were stripped of leaves and branches by Cyclone Tracy. Such damage is generally only seen in powerful tropical cyclones with wind gusts exceeding 150mph. (Northern Territory Library)

A bus at the RAAF base was flipped multiple times and crushed by Cyclone Tracy (RAAF).

Debate still exists over the exact strength of Tracy’s winds. Observations at the Darwin Airport indicated that sustained winds were rapidly intensifying when the instrument failed at 3:10am. According to the on-hand weather observers, the calm center reached the airport at 3:50am, so the 40 minutes preceding the eye, as well as the back eyewall of the cyclone, were not recorded. Therefore, it is probable that wind gusts significantly higher than 135mph affected the airport, which was south of the worst affected areas.

Another notable variable is the pressure gradient of the cyclone. Observations in northern Darwin indicate that Tracy had a pressure gradient of 5.5mb per kilometer, or 8.8mb per mile (Courtney and Knaff, 2008). Such a steep gradient is comparable to some of the most intense Category 5 hurricanes in the Atlantic. While the central pressure of the storm was likely somewhere between 946 and 950mb, typical of a strong Category 3 hurricane in the Atlantic, the storm’s small size compressed the pressure difference into an unusually small area.

At left, an apartment building that lost its upper floor. At right, a devastated home in Rapid Creek.

The official report following the cyclone estimated peak gusts reached 150mph, or 240 km/h (Bureau of Meteorology Report). A more recent study suggests that maximum gusts were more likely around 162mph, or 260 km/h (Mason and Haynes). Some unofficial estimates place the highest gusts at 185mph (300 km/h) (Sydney Morning Herald, 1975). Considering the severity of the damage, including dozens of flipped vehicles and the deformation of thick steel beams, it is probable that many locations experienced gusts greater than 160mph.

A number of meteorologists have suggested that vortices imbedded in the storm’s eyewall (later identified as “miniswirls” following Hurricane Andrew in 1992) may have been responsible for some of the more extreme damage. Evidence pointing to the existence of violent, small-scale wind features included a refrigerator that was found imbedded in the side of a water tower 50ft above the ground (Sydney Morning Herald, 1975). Pilots in the area also sighted tornadic vortices within the storm.

Cyclone Tracy officially remains a Category 4 on the Australian Cyclone Scale, with sustained winds between 100mph and 123mph. The damage caused by the storm, however, suggests that the cyclone was significantly more intense.

Vehicles flipped by Cyclone Tracy. The car at distance appears to have been tossed from a parking stall, perhaps as far as 20ft. There does not appear to be any nearby wall which could have provided upward lift, as is commonly the case when cars are moved by hurricanes. A recent study that placed vehicles in wind tunnels concluded that winds of 150 to 180mph were required to overturn minivans at less “sensitive” angles (Lyons, 2009).

A car was blown into the pool of the Darwin Travelodge in downtown.

Extreme damage from Cyclone Tracy. At far right, a large steel electricity pole that was twisted and snapped by the storm’s violent winds. Cyclone Tracy remains the most damaging weather event in Australian history, and one of the most violent windstorms ever documented.

Inside the Category 5 Winds of Hurricane Andrew

Hurricane Andrew was the most damaging single windstorm in world history. Whereas most catastrophic hurricanes are defined by their storm surges and flooding, Andrew proved that the winds in tropical cyclones can be just as devastating. (Image courtesy of Michael Laca)

After decades of relative inactivity in the Atlantic basin, Hurricane Andrew marked the first time in modern history that a Category 4 or Category 5 hurricane had directly threatened a large American city. As people across the country watched, the tightly wound storm took aim on downtown Miami. On August 23rd, 1992, journalists and camera crews positioned themselves in iconic areas throughout the city. By 1am on August 24th, winds were howling across Dade County. Employees at the National Hurricane Center, then located in Coral Gables, had the dual task of monitoring the storm and protecting themselves as windows shattered in the upper floors of their building.

Hurricane Andrew strengthened up until, and slightly after, its South Florida landfall. The storm was extremely well shaped, and easily had the most intense and symmetrical eyewall ever captured up-close by land-based radar.

At the break of dawn, the eye of the storm was entering the Gulf of Mexico and the winds across Dade County had begun to die down. Daylight revealed extensive damage across the city of Miami and Coral Gables. Strangely, however, there was little word from areas farther south. A last minute dip in the storm’s path meant that the urbanized areas south of Miami, from Kendall to Florida City, had taken the brunt of the storm. Despite the widespread use of video cameras in the early 90’s, no clear footage exists of the storm at its height. Nearly all of the videos taken south of 152nd Street end abruptly at 4am.

Few videos exist of Hurricane Andrew’s landfall in Dade County. At top left, a clip from a journalist and his cameraman as they filmed the hurricane throughout the city, spending the majority of the storm on South Beach. At bottom left, Dennis Smith from the Weather Channel broadcast live footage of the hurricane in Coral Gables. At right, storm chaser Michael Laca recorded the duration of the storm in Coconut Grove. All three of these films were taken well north of the worst affected areas.

News helicopters and emergency crews quickly realized the extent of the damage. Cities to the south of Miami had taken the full force of the Category 5 hurricane, leaving tens of thousands of people homeless. Nearly everyone who lived south of 152nd Street seemed to agree that “something unusual happened” between 4am and 6am the morning of August 24th. In the words of one Homestead resident –“I’ve been through plenty of hurricanes, and all of them together was nothing compared to this.”

Tests in wind tunnels have found that winds of 130mph are required to overturn a minivan at its most sensitive angle, and winds of 150mph to 180mph are needed for them to be flipped at other angles (Schmidlin, 2003). Hurricane Andrew overturned more cars than any hurricane in history. At left, two vehicles in Homestead were flipped end over end inside a garage. At right, a U-Haul truck was blown atop the roof of a building. In both cases, the proximity of the vehicles to buildings likely contributed to their movements. (NOAA Photo Library)

Hurricane Andrew’s right front quadrant came ashore in the vicinity of Cutler. As would be expected, the maximum storm surge of 17ft occurred in this area. Due to the storm’s fairly rapid forward speed, the most extreme winds should have occurred along the immediate coastline of Cutler and East Perrine. And indeed, the damage was astounding. Trees in the area were stripped bare, and some homes near the shoreline were unroofed and partially leveled by wind gusts in excess of 175mph. The Pinewood Villas, a one-story apartment community in Cutler Ridge, experienced some of the most severe wind damage in the area. Several apartment buildings in the complex were completely leveled, and the remaining units suffered extensive internal damage as doors were ripped from their hinges. Professor Fujita toured the damage at the Pinewood Villas and noted the inconsistent nature of the destruction, which was reminiscent of the narrow streaks of damage left by tornadoes.

At left, a seven-story Holiday Inn was gutted of furniture and some interior walls by the hurricane. At right, a view of damage in Pinewood Villas, one of the areas Professor Fujita visited. He deemed some of the building damage to be of F3 intensity. (NOAA Photo Library)

A little farther inland in Cutler, the hurricane punched through the windows and walls of large retailers and completely gutted a two-story furniture store. Due to Andrew’s incredible power and brisk westward motion, areas well inland were affected by wind gusts over 150mph. The Tamiami Airport, located 10 miles from the coast, suffered tens of millions of dollars in damage. Airplanes were flipped and rolled into piles, and the airport’s hangars were shredded to their metal frames.

During the storm, even though routine weather observations had ceased operation, the official weather observer at the airport continued to keep track of the station’s wind dial. Around 4:45am, he noted that the needle became pegged at a position beyond the instrument’s peak value (later shown to be a bit over 120mph). The needle remained fixed at this point for three to five minutes before dropping to zero as the anemometer failed. The weather observer reported that the winds increased in intensity for another 30 minutes, so it is quite likely sustained winds well over 120mph affected the Tamiami Airport (NHC, 1992).

At left, damage to the Tamiami Airport, which was located 10 miles from the coastline and north of the storm’s eye. At right, the devastated Dadeland Mobile Home Park, which was located several miles east of the airport.

Andrew was a rather fast moving storm, so winds in the northern half of the eyewall should have been more than 35mph stronger than winds in the southern eyewall. Despite the destruction in Cutler and Perrine, however, even more intense damage was found farther south. Arguably the most severe wind damage caused by the hurricane was four miles inland in Naranja Lakes, a small community just north of Homestead. The devastation was unusual because the area was near the geographic center of the storm’s path, well away from the onshore winds that affected Cutler Bay. Even more unusual, survivors in Naranja Lakes and Homestead told surveyors that the most extreme winds occurred during the back-eyewall of the hurricane. One woman in Naranja Lakes was fatally injured as her home was destroyed by southerly winds following the passage of the eye.

Extreme damage in Naranja Lakes. The home at left is where Mary Cowin was killed after being impaled by a piece of debris. At right, a streak of leveled buildings through Naranja Lakes that may have been the result of a “mini-swirl.”  Eyewitness statements indicated that the most extreme winds impacted the area around 6am (Powell, 1995). While the exact conditions that led to the extreme damage is unknown, it is theorized that powerful downdrafts may have occurred within the convection cells. (NOAA Photo Library)

Aerial view of damage in Naranja Lakes. Like many properties in the area, buildings that were not leveled still suffered severe internal damage as winds entered residences through windows and doorways. (Image by Carl Seibert)

Radar views of the hurricane provided some clues as to why its southern eyewall caused such incredible damage in Naranja Lakes, Homestead and Florida City. The Miami radar failed as the leading edge of Andrew’s eyewall came ashore, and the Key West radar ceased functioning when the power went out across the region, so no radars within 200 miles of Homestead captured the hurricane as it crossed the coastline. Radar in Tampa, however, was able to fill in the gap, though with slightly less detail due to its distance. As the hurricane came ashore, radar images showed powerful convection cells forming over Homestead and nearby areas in the storm’s southern eyewall. It is likely these dense cells of precipitation led to extremely intense bursts of wind that may have reached 200mph.

View of massive convection cells in Hurricane Andrew’s southern eyewall. These features may explain why the most intense damage was not found in areas affected by Andrew’s right-front quadrant, traditionally the most violent section of a hurricane. The convection cells were not as visible in the storm’s back eyewall, where the most intense winds may have occurred, possibly due to interference from precipitation to the west.

The approximate position of the radar velocities. Areas beneath the bright orange cell include Naranja Lakes and the Homestead Air Force Base.

Images of some of the strongest hurricane winds ever filmed. At left, storm chaser Mike Theiss’s footage of the strongest hurricane winds ever captured on video during Hurricane Charley. Peak wind gusts in the film are likely between 150 and 160mph. At right, legendary storm chaser Jim Leonard captured gusts of 130mph or more whipping through palm trees in Puerto Rico during Hurricane Georges. Peak wind gusts in Hurricane Andrew may have topped 200mph.

The winds that affected Homestead, Florida City and Naranja Lakes were like nothing that has ever been filmed before. Deep convection in Hurricane Andrew’s southern eyewall likely led to near complete white-out conditions during the peak of the storm. Survivors described the roar of the storm as being so loud that “you could barely hear someone screaming next to you.” Lisa Frantz, a Los Angeles resident who survived the storm in her mother’s home in Florida City, described the impact of the storm:

The whole home shook as if it was going to be ripped from the ground. We could hear furniture banging against the walls and being blown out the windows. You could hear some of the gusts right before they hit – it sounded like jet planes were taking off right over us…I was sure we both were going to die.

At left, saplings in a South Dade County nursery were blown to the ground by extreme surface winds. At right, a building that was completely leveled in Naranja Lakes. (Images courtesy of Michael Laca)

Unlike most US hurricanes, the majority of Hurricane Andrew’s deaths were caused by its winds. Falling trees are generally the biggest killer, but the deaths in South Florida were more consistent with tornado-related fatalities. Half of the 15 deaths directly attributed to the storm occurred in the collapse of frame homes or apartment buildings. Additionally: two men sheltering together in a metal storage trailer west of the Tamiami Airport were killed when the container was flipped several times. One man, who was also more than 12 miles inland on SW 198th Street, was killed by flying debris while running for shelter after the building he had been in collapsed. Two more deaths occurred in two separate mobile homes that were obliterated. Only one of the deaths was the result of drowning. (Natural Disaster Survey Report, 1993). A third of the deaths occurred more than 10 miles inland.

Extensive research in the decade following the storm concluded that Hurricane Andrew was significantly stronger than previously estimated (the official intensity at landfall in Homestead was originally 145mph). In 2002, the hurricane was posthumously upgraded to a Category 5 with maximum sustained winds of 175mph. At landfall in Homestead, the storm’s winds are now estimated to have been 165mph, even though the storm’s lowest pressure of 922mb was recorded at this time. The complicated and isolated nature of the wind features in Hurricane Andrew make a single intensity estimate almost impossible to calculate.

At left, view of the NHC’s updated wind contour map of Hurricane Andrew at South Florida landfall. Despite being vastly more accurate than the official intensity prior to the 2002 addendum, the contour map still is unable to account for the extreme wind damage south of Cutler Bay. At right, the contour map overlaying a map of the area.

Hurricane Andrew remains one of only three Category 5 hurricanes to ever make landfall in the United States.* The storm redefined the concept of a hurricane to a whole new generation and left lasting scars in South Florida that are still visible 20 years later. More than anything, the storm highlighted the continued discrepancies that exist between National Hurricane Center estimates and the actual surface conditions in landfalling hurricanes.