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April 2, 2004: Hurricanes are terrifying. They rip trees right out of the ground, hurl cars into the air, and flatten houses. Their winds can blow faster than 100 mph. Some hurricanes have been known to pull a wall of water from the ocean 20 feet high … then fling it inland, inundating miles of coast. No other storms on Earth are so destructive.

 

Right: A hotel in Gulfport, Mississippi, flattened by Hurricane Camille in 1969. [More]

Or so memorable. The most powerful hurricanes are talked about for decades, long after the floods subside and trees grow back. What child in Mississippi today hasn't heard of Hurricane Camille, the monster storm that traumatized their parents in 1969? Hurricanes are the only storms we actually name, like people, to help us remember.

 

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Naming hurricanes also helps prevent confusion. Sometimes there are two or more of the storms raging at the same time. Weather forecasters and storm trackers use names like Camille, Hugo and David to clarify which storm they're talking about. For these reasons, every hurricane gets a name. Always.

That is, until last week, on March 28th, when a nameless hurricane crashed into Brazil. The storm made landfall near Torres, a small town in the state of Santa Catarina about 500 miles south of Rio de Janeiro.

"This really caught everybody off guard," says NASA hurricane researcher Robbie Hood. "Hurricanes aren't supposed to be in that part of the world."

Weather satellites have been circling Earth for more than 40 years. During that time they've spotted hurricanes (also called "typhoons" or "cyclones") in the northern Atlantic Ocean, and on both sides of the equator in the Pacific and Indian Oceans, but never before in the south Atlantic.

 

Left: Hurricanes occur most often in the black-circled areas, and rarely outside. [More]

 

"Vertical wind shears in the south Atlantic are too strong for hurricanes," Hood explains. Winds in the upper troposphere (about 10 km high) are 20+ mph faster than winds at the ocean surface. This difference, or shear, rips storms apart before they intensify too much.

A typical hurricane starts out as a cluster of ordinary thunderstorms. Powered by heat from warm tropical waters and guided by Coriolis forces, the storms swirl together, joining forces to create a tropical depression … then a tropical storm … and finally a full-fledged hurricane. Wind shears in the south Atlantic usually stop this process at the stage of tropical depression.

There are exceptions. In 1991, for instance, the US National Hurricane Center documented a tropical storm off the coast of Congo. It lasted about five days as it drifted toward the central south Atlantic, but it never reached hurricane strength. (The minimum threshold for a hurricane is 74 mph winds.)

What was different about the March 2004 storm? Why did it become a hurricane? No one knows.

 

 

Above: The Brazilian hurricane on March 26, 2004, as seen by the Moderate Resolution Imaging Spectroradiometer (MODIS) on the Terra satellite. [Spectacular larger image] [More]

When the storm crashed into Brazil, local observers weren't even sure it was a hurricane. Brazil has no ground-based network of weather stations to measure wind and rain from tropical storms. "There are no 'Hurricane Hunters' in Brazil," adds Hood. "The storms are so rare."

Space satellites, however, gathered a great deal of data. "NOAA polar orbiting satellites measured the temperature of the storm's eye," says climate scientist Roy Spencer of the University of Alabama, Huntsville. "That told us how fast the winds were moving." It was a category 1 hurricane, he says, an estimate confirmed by NASA's wind-measuring QuikScat satellite. In addition, NOAA's GOES satellites and NASA's Terra and Aqua satellites took pictures of the storm at microwave, infrared, and visible wavelengths, allowing scientists to monitor the motions of moisture and heat energy through the storm--valuable data, indeed.

 

The TRMM spacecraft, a joint mission of NASA and the Japanese space agency, flew over the storm several times in the days before landfall, and it gathered perhaps the most revealing data of all. TRMM, short for Tropical Rainfall Measuring Mission, carries a precipitation radar, the only one in space. Beaming down through the clouds, the radar illuminated spiraling bands of rainfall; false color images of the storm resemble a pinwheel galaxy! Combining data from the radar and the spacecraft's microwave imager, researchers can estimate rain rates throughout the hurricane--from top to bottom, from eye to edge.

 

Right: A TRMM precipitation radar map of the March 28th south Atlantic hurricane. [More]

"This whole episode highlights the advantages of satellites for hurricane studies, especially where there are no aircraft standing by to fly through the storms," says Hood. "Satellites can monitor storms in all parts of the world."

But a problem remains: what to call them? The World Meteorological Organization maintains a list of hurricane names for every part of the world … except the south Atlantic. Sadly, the March 28th storm did damage to remember: 500 homes ruined, fishing boats sunk, at least two people dead and 1500 more homeless. Brazilians are going to be talking about the storm for a long time, and wondering about hurricanes to come.

South Atlantic hurricanes need names. Somebody somewhere, probably, is making a list.

 

Editor's note (April 7, 2003): This hurricane was too important to remain anonymous for long. The people of Brazil themselves have named it, unofficially, Hurricane Catarina, after the southern Brazilian state of Santa Catarina where the storm made landfall.