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Hurricanes can get much, much bigger and stronger than we have so far seen in the Atlantic. The most intense Pacific storm on record was Super Typhoon Tip in 1979, which reached maximum sustained winds of 190 mph near the center. On its wide rim, gale-force winds (39 mph) extended over a diameter of an astonishing 1350 miles. It would have covered nearly half the continental United States.

“More than half the total hurricane damage in the U.S. (normalized for inflation and populations trends) was caused by just five events,” explained MIT hurricane expert Kerry Emanuel in an email. Storms that are Category 4 and 5 at landfall (or just before) are what destroy major cities like New Orleans and Galveston with devastating winds, rains, and storm surges.

In Part 2, we’ll look a little more in detail at Katrina (and Gustav), and why they weren’t (and probably won’t be) as strong and hence as devastating at landfall as they could have been.

But let’s first ask, How did Katrina turn into a powerful Category 5 hurricane ? The National Climatic Data Center 2006 report on Katrina begins its explanation by noting that the surface temperatures (SSTs) in the Gulf of Mexico during the last week in August 2005 “were one to two degrees Celsius above normal, and the warm temperatures extended to a considerable depth through the upper ocean layer.” The report continues, “Also, Katrina crossed the ‘loop current‘ (belt of even warmer water), during which time explosive intensification occurred. The temperature of the ocean surface is a critical element in the formation and strength of hurricanes.”

An important factor was that the ocean warming had penetrated to a considerable depth. One of the ways that hurricanes are weakened is the upwelling of colder, deeper water due to the hurricane’s own violent action. But if the deeper water is also warm, it doesn’t weaken the hurricane. In fact, it may continue to intensify. Global warming heats both the sea surface and the deep water, thus creating ideal conditions for a hurricane to survive and thrive in its long journey from tropical depression to Category Four or Five superstorm.

A 2005 study, “Penetration of Human-Induced Warming into the World’s Oceans,” led by Scripps Institution of Oceanography compared actual ocean temperature data from the surface down to hundreds of meters (in the Atlantic, Pacific, and Indian oceans) with climate models and concluded:

A warming signal has penetrated into the world’s oceans over the past 40 years. The signal is complex, with a vertical structure that varies widely by ocean; it cannot be explained by natural internal climate variability or solar and volcanic forcing, but is well simulated by two anthropogenically forced climate models. We conclude that it is of human origin, a conclusion robust to observational sampling and model differences.

This figure shows what they found:

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I reprint this post from TPM election central (a must read blog for political junkies), having already borrowed its headline:

Priorities, priorities.

Check out this Karl Rove quote buried in a Fox News article about the threat Hurricane Gustav poses to the GOP’s convention plans:

“The Republicans can’t seem to get a break when it comes to August and when it comes to the weather,” said Rove, a FOX News analyst. “I know this is being thought a lot about in Washington and at the White House and discussed and I suspect they will monitor it carefully and figure out what to do.”

Yeah, Katrina (which hit in August 2005) was really rough on those Republicans, no question about it.

You can’t make this stuff up!

For more on the implications of Gustav on the RNC, see the Washington Post’s piece today, “GOP Considers Delaying Convention.” The piece warns that, “Gustav threatens to provide an untimely reminder of Hurricane Katrina. A new major storm along the Gulf Coast would renew memories of one of the low points of the Bush administration.” It also notes that, “A hurricane in the Gulf of Mexico could also cast unwelcome attention on the offshore oil rigs that McCain has championed as a solution to rising gasoline prices.”

But the article has two unintentionally funny parts:

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On August 23, 2005, a tropical depression formed 175 miles southeast of Nassau. By the next day, it had grown into tropical storm Katrina and was intensifying rapidly. Early in the evening on August 25, Hurricane Katrina made landfall near North Miami Beach. Even though it was only a Category 1 storm, with sustained wind speeds of about 80 miles per hour, it caused significant damage and flooding, and took 14 lives.

The hurricane’s quick nighttime trip across Florida barely fazed the storm. Entering the Gulf of Mexico’s warm waters quickly kicked Katrina into overdrive, like a supercharged engine on high-octane fuel. Hurricanes fuel themselves by continually sucking in and spinning up warm, moist air.

On August 28, Katrina reached Category 5 status, with sustained wind speeds of 160 mph and a pressure of 908 millibars. A few hours later, wind speeds hit 175 mph, which they maintained until the afternoon.

At 4:00 pm, the National Hurricane Center warned that local storm surges could hit 28 feet, and “Some levees in the Greater New Orleans Area could be overtopped,” a warning that was tragically ignored by federal, state, and local emergency officials. Over the next 14 hours, Katrina’s strength dropped steadily. When the hurricane’s center made landfall Monday morning, it was a strong Category 3, battering coastal Louisiana with wind speeds of about 127 mph. The central pressure of 920 millibars was the third lowest pressure every recorded for a storm hitting the U.S. mainland.

The devastation to the Gulf region was biblical. The death toll exceeded 1300. The damage exceeded $100 billion. [Combined with the effects of Hurricane Rita] two million people were forced to leave their homes, more than were displaced during the 1930’s Dust Bowl. One of the nation’s great cities was devastated.

About 20 miles to the west of the second Gulf landfall was the small town named Pass Christian, Mississippi, where my brother lived with his wife and son.

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That headline is lifted from Drudge. Needless to say, he left out “… and on the third anniversary of Hurricane Katrina, where both Bush and McCain were AWOL” (see TP’s “As Katrina hit, McCain celebrated 69th birthday with Bush“).

Track the storm with the National Hurricane Center here. Best hurricane blog here.

Readers of this blog know that my brother lost his home in Katrina three years ago, which is probably the main reason I began this blog in the first place (see “100 Katrinas and the Launch of Climate Progress“).

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