Tracy was tiny, but don't let her size fool you. She punched like a heavyweight fighter, and she knocked Darwin out cold.

A fantastic look back on one of Australia most memorable events. Written by SSA friend Jamie Duncan.

By Jamie Duncan
MELBOURNE, Dec 23 AAP - Tracy was tiny, but don't let her size fool you. She punched like a heavyweight fighter, and she knocked Darwin out cold.

Tracy was the world's smallest tropical cyclone. Her gale-force winds - not even her destructive winds - extended only 50km either side of the eye.

But when Tracy roared in early on Christmas Day 1974, her narrow, destructive core rolled right over Darwin and flattened the city of about 45,000 people in a few short hours, killing at least 66 people.
Ian Shepherd, a senior meteorologist at the Bureau of Meteorology's Darwin office, says the cyclone began as a tropical depression formed in what he called "a sweet spot" in warm waters of the Arafura Sea on December 20, 1974.

It intensified to cyclone strength by 9.30pm local time the following day and drifted slowly southwest.

From 9am on December 23, Tracy began to change direction dramatically, swinging to the southeast over the next 24 hours as she rounded Bathurst Island, north of Darwin.

By 9am Christmas Eve, Darwin's fate was sealed.
"It's extraordinary, really, that it did that dogleg right around the corner of Bathurst Island and set up a beeline straight for Darwin," Shepherd says.
"You couldn't have had a worse scenario for Darwin, really."
It's thought westerly winds from a strengthening monsoon trough north of Australia pushed the cyclone suddenly southeast towards Darwin.

Shepherd says forecasters in 1974 had only two satellite images a day and readings from one weather station as Tracy advanced.
Despite this, the Bureau of Meteorology did "a very good job" warning Darwin of the impending disaster.
But two things got in the way: the festive season and Cyclone Selma, which weeks before gave Darwinians a near miss.

"People weren't really on the ball with this particular cyclone and, being Christmas Eve, people had other things on their minds," Shepherd says.
Tracy's true strength may never be known.
A barometer at Darwin Airport measured the central pressure at 950hPa but the anemometer was destroyed before the eye arrived. The highest wind gust it recorded was 217km/h.

Shepherd says official estimates initially found Tracy was a category-four cyclone with peak gusts of 220km/h to 230km/h.
"More recent research suggests it could have been a weak category-five cyclone as it was offshore and approaching Darwin," he says.
"The current estimate is 240- to 260km/h."
Modelling by leading researcher Greg Holland found the shape of Tracy's eye may have distorted and elongated as it crossed the coast, causing even more intense localised gusts as it tried to regain its normal circular shape.

"The theory is that in Darwin, the rear edge of the eye wall was a little stronger than the leading edge in some parts because of the re-organisation of that eye area as it came ashore - but we'll never know, of course," Shepherd says.
"What is interesting is the narrowness of the trail of damage. It carved a path right through the main suburbs of Darwin, and by the time it was 40 or 50km inland it was pretty much weakening out."

Why was Cyclone Tracy so small?
Shepherd says there is no clear answer, although where cyclones form may influence their size.
"Cyclones in the northwest Pacific have a wide expanse of ocean in which to form and they tend to be much larger," he says.
"The ones tucked in against the Australian coast tend to be smaller, but we haven't got a really good answer."
Tracy disappeared as abruptly as she arrived. By mid-morning on Christmas Day, she had devolved into a tropical rain depression.
Gone, but not forgotten, 40 years on.

TRACY BY THE NUMBERS
Life span: December 20-25, 1974
Peak recorded central pressure: 950hPa
Strongest recorded wind gust: 217km/h
Estimated peak wind gust: 240-260km/h
Extent of gale force winds: 50km from eye
Eye width: 12km (mean)
Storm surge: 1.6m at Darwin Harbour, 4m at Casuarina Beach
Death toll: 66
Injuries: 145 serious, 500+ minor injuries

(Source: BoM, Northern Territory Library)
(Image: December, 1974. Darwin, NT. Then Prime Minister, Mr. Gough Whitlam, M.P. (first white car) inspects the wrecked suburb of Casuarina after Cyclone Tracy hit Darwin.)