Tuesday, Oct. 3, 2006 | The early morning clouds looked menacing, but just covered San Diego in a brief rain shower.

The worst was yet to come.

After the rain passed, barometers began plummeting more than had ever been recorded. A dangerous storm was zeroing in on San Diego.

“The whole heavens seemed closing in with bank upon bank of dark, heavy, ominous-looking clouds,” wrote a correspondent for the Daily Alta California. “… Very heavy gusts of wind came driving madly along, completely filling the whole atmosphere with thick and impenetrable clouds of dust and sand.”

The dust clouds were so thick that they blotted out the midday light. Gales tore through roofs and ripped ships off their anchors. By noon, the Point Loma lighthouse keeper had abandoned his post, fearing the tower’s collapse.

It was Oct. 2, 1858. The only recorded hurricane to ever strike San Diego was wreaking havoc.

One-hundred-and-forty-eight years later, the Category 1 storm strike – and the knowledge that it will eventually happen again – connects San Diego to a controversial scientific debate about the effects of the earth’s changing climate on hurricanes.

Most scientists agree about the fundamental science of global warming: the idea that man-made carbon dioxide emissions are increasing the earth’s temperature. But they disagree about its many implications, including its effects on hurricanes.

While studies show that the oceans’ average temperature has increased between one-half and one degree Fahrenheit over the last century, scientists disagree about whether that jump is producing stronger hurricanes.

Several recent studies say the global temperature boost is notably increasing the strength of hurricanes, which feed on warm, tropical water. But some scientists remain skeptical about whether a one-degree Fahrenheit increase in sea surface temperatures has had any measurable impact.

As meteorologists and researchers sort out their differences, some are examining the deeper questions prompted by the asserted connection between global warming and stronger hurricanes.

Could warmer oceans change the threat of hurricanes? Could the tropical cyclones reach farther, fueled by warmer oceans? In San Diego, will global warming increase or decrease the small risk of a hurricane strike?

“That’s a very interesting question,” said Benjamin Santer, a senior climate researcher at the Lawrence Livermore National Laboratory in Livermore, Calif., who has linked global warming to ocean temperature increases in hurricane breeding grounds. “Whether the geographical distribution of hurricanes will remain the same in a warmer world is unclear – and is definitely a subject for serious scientific research.”

Kerry Emanuel, a meteorology professor at the Massachusetts Institute of Technology who is modeling long-term hurricane risk, said the implications for San Diego are still unclear. But other regions are seeing “significant changes,” he wrote in an e-mail.

The 1858 San Diego storm highlights a chief complaint of those scientists who question the link between storm strength and global warming. They say that better data on modern storms may be responsible for an increase in Category 4 and Category 5 hurricanes being recorded around the world.

Christopher Landsea, who documented the 1858 hurricane and published a 2004 report on its implications, said the Atlantic hurricane basin has a fairly complete database, thanks to recon flights flown into the storms for the last sixty years. But other areas lag behind, and may have been hit by storms that were actually stronger than has been recorded.

When a hurricane struck Brazil in March, it was hailed as the first to hit the country. But the coastal area where it hit – 500 miles south of Rio de Janeiro, has only been settled for a few decades. Landsea, science and operations officer at the National Hurricane Center in Miami, points out that satellite imagery for that region only dates back about 40 years.

And while attention often focuses on the Atlantic hurricane season, its storms represent just a fraction – about 11 percent – of tropical cyclones each year.

While the Brazil and San Diego storms are both anomalies, a stronger historical record exists in San Diego. Landsea said he is certain that only one hurricane has hit the city in the last 150 years. But the San Diego hurricane had gone undocumented until Landsea’s 2004 report.

“I think it gives us a perspective that even 100 years’ worth of records can be incomplete in describing what happened,” Landsea said.

The 1858 storm’s discovery has had clear implications in San Diego, where historians had acknowledged the storm’s strike, but where meteorologists had not.

“It kind of served as a wake-up call,” said Ivory Small, science and operations officer for the National Weather Service’s San Diego office. “This kind of thing can happen. Before, we had an idea that it was possible, but it had never happened, according to what we knew. When you know that something has happened before, you know the possibility is there.”

While hurricanes regularly hit the Baja California coast, their basic engineering steers them away from San Diego. They tend to move to the north-northwest, which sends most out into the Pacific Ocean.

The hurricanes that do track north often sputter and weaken as they approach San Diego. The waters around California are simply too cold for the slow-moving storms, which feed on tropical water above 80 degrees Fahrenheit. Summer water temperatures in San Diego typically peak in the 70s.

But Small said San Diego’s risk comes from the rare fast-moving storm, one that may move 16 knots an hour instead of the typical 8 knots. When that happens, storms can hit the area before they decrease in intensity. It has happened before. Small points to Hurricane Kathleen, a Category 1 storm that reached California in 1979 as a tropical storm, flooding arid stretches of Imperial County.

El Nin˜o conditions – such as existed in 1979 and are back again this year – play a facilitating role. That term describes the periodic warming of ocean temperatures off South America’s western coast. During a 1997 El Nin˜o, Hurricane Linda strengthened to a Category 5 and briefly threatened Southern California with 200 mph gusts. It never made landfall, instead turning west.

In all, four tropical storms have hit Southern California.

Landsea believes the 1858 storm – a Category 1 hurricane with winds around 75 mph – is the strongest that could be expected in San Diego. It wouldn’t be strong enough to cause structural damage, but would bring widespread power outages and blow down trees. Harbors and boats would receive a lot of damage, Landsea said.

Rainfall and flash flooding could cause major problems, he said.

The 1858 storm left little record of severe financial damage. No deaths were recorded. But San Diego was little more than an outpost then, with fewer than 800 residents. Countywide, the population was just 4,325. Today, 2.9 million people live in the county.

If the same storm happened today, Landsea estimated it could do hundreds of millions in damage, possibly as much as $1 billion.

“I’m just hoping it does not happen for a looooong time,” Small said. “Because that’s a very serious event, very serious.”

Please contact Rob Davis directly with your thoughts, ideas, personal stories or tips. Or send a letter to the editor.

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