Everything you need to know about “super typhoons”

November 8, 2013

One of the strongest tropical storms on record — Super Typhoon Haiyan — slammed into the Philippines Friday morning, killing an estimated 2,000 people so far and forcing hundreds of thousands to flee their homes. The storm is expected to hit Vietnam next.

Not a fun scene after Haiyan. (AP) Not a fun scene after Haiyan. (AP)

Our colleagues over at Capital Weather Gang have been doing a fantastic job covering this incredibly large storm in all its destructiveness. So go there for detailed updates.

But below is a very basic overview of "super" typhoons, their horrible ways, and whether they're really so unusual:

What is a typhoon?

It's basically the same thing as a hurricane. Both are tropical cyclones — rapidly rotating storms that typically form in warm tropical waters and feature low pressure centers, high winds, and lots of rain.

If the storm originates in the Atlantic or Northeast Pacific, we call them "hurricanes." If they form in the Northwest Pacific, they're called "typhoons." Elsewhere, they're called "cyclones." But they're all the same thing. Big tropical storms.

What makes a typhoon a "super typhoon"?

That's the term that weather agencies use for particularly severe tropical cyclones, although the precise definition can vary from country to country.

The U.S. Navy's Joint Typhoon Warning Center deems a typhoon "super" when the wind speed reaches 130 knots, or 150 miles per hour. That's roughly equivalent to a Category 5 hurricane — again, it's a really, really massive storm.

So how intense is Super Typhoon Haiyan?

Pretty intense. Before hitting land on Friday, the storm's winds reached estimated sustained speeds of 195 miles per hour, with gusts rising above 220 miles per hour. Those are some of the highest wind speeds ever recorded. Here's what the storm looked like from space:

View of Haiyan and night lights over Asia Thursday morning EST (13:00 UTC) or Thursday night local time (EUMETSAT via Flickr)
View of Haiyan and night lights over Asia Thursday morning EST (13:00 UTC) or Thursday night local time (EUMETSAT via Flickr)

Is Haiyan the strongest tropical storm ever?

Possibly, although it's hard to tell for certain. As Nate Cohn explains, the most precise way to measure a tropical cyclone's intensity is to fly surveillance aircraft into the eye of the storm and drop instruments to measure wind speed and air pressure. Those aircraft aren't available in this case. Instead, the Joint Typhoon Warning Center is using satellite estimates to track Haiyan.

Those measurements suggest that Haiyan may end up being one of the most intense storms of the satellite era. Indeed, before making landfall, the storm appeared to be approaching the top end of the intensity scale for tropical cyclones — about as intense a storm as is physically possible.

At its peak, Haiyan appeared to be more intense than Katrina, albeit covering a smaller area:

Comparison of super typhoon Haiyan and hurricane Katrina at peak intensity (Weather Decision Technologies using NOAA imagery)

Jeff Masters of Weather Underground argued that when Super Typhoon Haiyan hit the Philippines on Friday morning, it may well have been the most powerful tropical storm to make landfall on record. He has a detailed look at the numbers and some of the discrepancies in measurements over the years.

(Update: There are, however, conflicting accounts of how intense the storm actually was when it hit land. The AP reports that Haiyan had sustained winds of 147 miles per hour and gusts of 170 miles per hour. If true, Haiyan would be more akin to a Category 4 hurricane and just short of a Category 5. But different agencies appear to disagree on the numbers here.)

Why are super typhoons so deadly?

Same reason hurricanes are deadly. High winds, lots of rain, flooding. In the Philippines, heavy rains can often cause the most death and destruction in the mountainous regions, since they can trigger flash floods and mudslides.

How much damage will Haiyan do?

So far, Haiyan seems to wreaked a fair bit of havoc. Here's Jeff Masters: "Wind damage on the south shore of Samar Island in Guiuan (population 47,000) must have been catastrophic, perhaps the greatest wind damage any place on Earth has endured from a tropical cyclone in the past century. A massive storm surge must have also caused great destruction along a 20-mile swath to the north of where the eye hit, where Project NOAH was predicting a 17 foot (5.3 meter) storm tide."

There was one bit of mercy, however: "Fortunately, the storm’s fast forward speed of 25 mph cut down the amount of rain the storm dumped, compared to typical typhoons that affect the Philippines. Hopefully, this will keep the death toll due to flash flooding relatively low. Flash floods are usually the biggest killer in Philippine typhoons."

The other bit of good news is that Manila, home to 12 million people, is expected to escape the worst of the typhoon's winds and surges (though it does lie in the storm's path).

Have there been an unusual number of typhoons this year?

It's difficult to say. So far, the 2013 Pacific Typhoon season has seen 30 storms, 13 typhoons, and five "super typhoons" — including Haiyan (although the latter count is unofficial). But the season's not necessarily over yet.

Those 30 storms makes this the most active Pacific Typhoon season since 1994. On the other hand, those five "super typhoons" aren't necessarily unusual. Between 2002 and 2012, there appear to have been seven years with at last five super typhoons in the Western Pacific.

What about other types of tropical cyclones? Why haven't we heard about hurricanes in the U.S. this year?

Yep, the above numbers are only for the Pacific Typhoon season. But there are tropical cyclones elsewhere in the world, too: There's also the Atlantic hurricane season, the Pacific hurricane season, the North Indian Ocean cyclone season, the Australian cyclone season, and so forth.

Trends are different for different regions. The 2013 Atlantic hurricane season has been particularly quiet so far, with not a single hurricane making landfall this year (although the season doesn't end until Nov. 30).

Over at Climate Central, Andrew Freeman recently explained some of the reasons for the unexpectedly quiet Atlantic season: "large areas of sinking air, frequent plumes of dry, dusty air coming off the Sahara Desert, and above-average wind shear." Brian McNoldy has an even more detailed analysis of the hurricane lull over at Capital Weather Gang.

What are the long-term trends in tropical cyclones?

It's not very clear. Last year, three researchers at the University of Colorado and the Naval Research Laboratory did their best to reconstruct a worldwide database for hurricanes or typhoons that made landfalls between 1970 and 2010.

Their conclusion? "The analysis does not indicate significant long-period global or individual basin trends in the frequency or intensity of landfalling [tropical cyclones] of minor or major hurricane strength." Here's the chart:

hurricane frequency

(And, for those curious, here is a preliminary estimate by the authors extending the data out to 2012.)

The authors of that paper, Jessica Weinkle, Ryan Maue, and Roger Pielke Jr., note that the economic damage from tropical cyclones does appear to be increasing worldwide. But this may be a function of people building more buildings in areas prone to hurricanes and typhoons, rather than an uptick in storm intensity or frequency.

The Intergovernmental Panel on Climate Change (IPCC) came to a similar conclusion in its recent report: As best anyone can tell, tropical storms aren't getting any more or less frequent worldwide: "Current datasets indicate no significant observed trends in global tropical cyclone frequency over the past century and it remains uncertain whether any reported long-term increases in tropical cyclone frequency are robust."

The IPCC adds that there has been a marked increase in intensity for the very strongest tropical cyclones in the North Atlantic since the 1970s, but it's unclear what's causing this. And there's less data to indicate a change in cyclone intensity elsewhere in the world. It might be happening — here's one 2008 study suggesting that the strongest typhoons in the northwest Pacific may be getting stronger — but it's difficult to say for sure.

Could global warming make tropical cyclones more destructive?

Yes — though with caveats. It's still not entirely clear what effect climate change will have on the tropical cyclones themselves. The latest IPCC report said it was "likely" that tropical cyclones around the world would get stronger as the oceans heat up, with faster winds and heavier rainfall. But the overall number of hurricanes in many basins was likely to "either decrease or remain essentially unchanged." (Here's a longer discussion of this topic.)

There is, however, an important asterisk here: Climate scientists are much more confident that sea levels will keep rising as the oceans warm and glaciers and ice caps melt. And that will escalate the risk of storm surges when tropical cyclones do hit, particularly in low-lying areas. That alone will make storms more destructive, even if the number stays the same.

What sites should I be reading if I want to stay on top of super typhoon news?

--Definitely our colleagues at Capital Weather Gang.

--Climate Central has consistently excellent coverage.

--So does Jeff Masters at Weather Underground.

--Ryan Maue's website has some excellent data on trends in global tropical cyclone activity.

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