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Deconstructing Super Typhoon Yolanda

November 13, 2013

By Paul Homewood

 

With special thanks to John Fuller and Agar012

 

Now we have had a few days to reflect on the terrible events of last week, we can start to piece together some of the facts.

First of all, as it is the thing that really matters above all, fatalities. The good news, if it can be termed that, is that the death toll is likely to be around 2000 to 2500, according to the Philippine President. This is much less than the 10,000 originally feared to have died.

As far as the storm itself was concerned, the official statistics from the Philippine Met Agency, PAGASA, remain the same as those issued at the time. The table below compares these with the original satellite estimates put out by the Joint Typhoon Warming Centre, JTWC, and that were subsequently used by the media around the world to claim that Yolanda was the “strongest storm ever”.

 

 

  PAGASA JTWC
Sustained Wind Speed mph 147 195
Gust mph 171 235

http://www.ndrrmc.gov.ph/attachments/article/1124/Update%20SWB%20No.6%20re%20TY%20YOLANDA%205AM.pdf

http://www.webcitation.org/6KyWsFio5

http://www.bbc.co.uk/news/world-asia-24878801

 

As far as sustained wind speeds are concerned, the PAGASA numbers are based on 10-minute averages, whilst the JTWC are on 1-minute averages, so the latter are always likely to be higher. Is it possible then to draw any conclusions?

According to hurricane expert, Chris Landsea,

One complication with the use of the 1 min averaging time for the standard for sustained wind in the Atlantic and Northeast Pacific tropical cyclone basins (where the United States has the official World Meteorological Organization tropical cyclone advisory responsibilities) is that in most of the rest of the world, a 10 min averaging time is utilized for "sustained wind". While one can utilize a simple ratio to convert from peak 10 min wind to peak 1 min wind (roughly 12% higher for the latter), such systematic differences to make interbasin comparison of tropical cyclones around the world problematic. “

 

So on this rule of thumb,adding 12% to the PAGASA number would increase it to 164 mph, on 1-minute averages.

Jeff Masters also mentions  that other studies suggest a ration of 1.14, which would give a figure of 167 mph. He also points out that the Japanese Meteorological Agency estimate 145 mph, using satellite based 10-minute averages, therefore backing up the PAGASA version.

There is still, therefore, a big gap between JTWC and the others. A clue to this difference is given by Masters:

Haiyan’s strongest winds occurred on the south shore of Samar Island and the city of Guiuan (population 47,000), where the super typhoon initially made landfall with 1-minute average winds estimated at 195 mph. This estimate came from the Joint Typhoon Warning Center, and was based on satellite measurements. We have no ground level or hurricane hunter measurements to verify this estimate. Typhoon and hurricane maximum wind speed estimates are only valid for over water exposure, and winds over land are typically reduced by about 15%, due to friction. This would put Haiyan’s winds at 165 mph over land areas on the south shore of Samar Island.

So how does all this compare with earlier hurricanes and is there any justification for the “strongest ever” claims.

Hurricane Camille in 1969 is generally accepted as the strongest in recent decades. NOAA describe the wind speeds:

The actual maximum sustained winds will never be known, as the hurricane destroyed all the wind-recording instruments in the landfall area. The estimates at the coast are near 200 mph.

The “Atlantic Hurricane Season of 1969”, published at the time offers more detail:

 

image

image

 

Note that 180 knots = 207 mph, and 175 knots = 202 mph.

Quite simply Yolanda and Camille cannot be seriously compared with each other.

It is probably also worth taking note of these two statements.

Mr. Paciente  [a forecaster with the Philippine government’s national weather agency] stated:

Before the typhoon made landfall, some international forecasters were estimating wind speeds at 195 m.p.h., which would have meant the storm would hit with winds among the strongest recorded. But local forecasters later disputed those estimates. “Some of the reports of wind speeds were exaggerated,”

The Philippine weather agency measured winds on the eastern edge of the country at about 150 m.p.h., he said, with some tracking stations recording speeds as low as 100 m.p.h.

Roger Edson, the science and operations officer at the United States National Weather Service in Guam said

195 m.p.h. winds would put the storm “off the charts,” but he acknowledged that satellite estimates require further study on the ground to determine if they were accurate.

 

Wind Gusts

As well as the discrepancies in sustained wind speed, there is also a big gap in the claimed top gusts. Chris Landsea also has a useful rule of thumb:

Gusts are a few seconds (3-5 s) wind peak. Typically in a hurricane environment, the value of the maximum 3 second gust over a 1 minute period is on the order of 1.3 times (or 30% higher than) than the 1 min sustained wind.

So, assuming 164 mph sustained winds, we would expect gusts of 213 mph. Whereas JTWC estimated 235 mph, the figure officially recorded by PAGASA was only 171 mph, which suggests the sustained speeds may have been slightly lower than we have assumed.

 

Atmospheric Pressure

The lowest atmospheric pressure of Yolanda was 895 hPa. Within just the Western Pacific Basin, there have been 20 storms with lower pressure since these figures began to be reliably collected about 60 years ago. The lowest pressure recorded was 870 hPa, with Typhoon Tip in 1979.

Together with ties, typhoons with Yolanda’s atmospheric pressure or less can be expected every couple of years in the Western Pacific. Fortunately the vast majority of these never see land, or do so only after significant weakening.

 

Storm Surge

Both CNN and the BBC talk about 40 to 50 feet storm surges , yet the official Philippine body responsible for these matters, NOAH, using JMA models, on 7th November forecast about 5 meters or less for the day after when the storm hit land.

Once again, it appears that some media reports have been wildly overhyped.

 

image

http://blog.noah.dost.gov.ph/2013/11/07/list-of-localities-typhoon-yolanda-highest-predicted-storm-surge-and-tide/

 

Historical Trends

PAGASA show a couple of graphs plotting the number of tropical cyclones from 1948 to 2004. There seems to be little in the way of trends either way.

 

TC Graph

image

http://kidlat.pagasa.dost.gov.ph/cab/main.htm

 

There is a fear that although typhoons are not becoming more frequent, they may be getting more intense. However, given the lack of accurate data from even just a few decades ago, it is difficult to see how any real conclusions can be made.

 

Summary

It seems reasonable to conclude that Yolanda was a Category 5 storm, i.e. that 1-minute wind speeds were at least 157 mph. However, it was clearly a much less powerful storm than Camille, and arguably many others in recent history.

It is, fortunately, a rare occurrence for storms of Yolanda’s strength to cross land, but sometimes it does happen.

The sensationalist and overhyped reporting of much of the media immediately after the tragedy was, in my view, utterly disgraceful.  Perhaps in future, they might care to check the facts first.

11 Comments
  1. gregole permalink
    November 14, 2013 12:24 am

    Paul,

    Thanks for the good work here.

    Yes I agree media hype and disaster-mongering warmista misstatements have been “utterly disgraceful”. It is bracing however to have facts on Yolanda now easily at hand as summarized here.

  2. Jamie Valero permalink
    November 14, 2013 1:28 am

    I am not qualified to make a scientific assessment of your claims here, but this I can tell you as a Filipino living here in the Philippines:

    My subjective opinion is that there are more typhoons in recent years, and this is the only time in my memory when there is this prospect when there might be a typhoon on Christmas. When I was a kid, typhoons typically start on May or June, and end on October. This year, we started getting typhoons this January, and it seems we’ll continue getting them well until December.

    And so while my educated, objective mind understands your arguments – my experience disagrees with the rationalizations you have made. And when your science disagrees with my personal experience, I think at the very least it is worth it to reexamine your argument.

    Firstly, the Philippine government has done a lousy job assessing the typhoon situation here in the Philippines. In the first day in the aftermath of the typhoon, politicians start claiming credit for disaster preparedness and low casualties – only to have their foot in their mouths afterwards when people all over the Philippines started looking for their loved ones.

    Second, the government has a track record of shooting messengers for bad news – at least one senior PAGASA official has been fired in the current administration, and a lot of their veterans have looked for other jobs overseas because of low morale and pay. Also, based on local news reports a lot of PAGASA’s monitoring equipment got trashed by the typhoon.

    As a Filipino, I am used to our local media somewhat toeing the local government line. It is a strange experience for me to see this same phenomenon for a foreign blogger.

    [FYI: I came across this because I am one of many volunteers populating online databases with lists of survivors and missing people in the typhoon, and collating online data about the typhoon. The Google Person Finder, among others, probably has more accurate tallies of missing people, because a vast majority are not reporting missing people to the government.]

  3. americantechie permalink
    November 14, 2013 1:31 pm

    Thanks for the mention. You started a great conversation with the first Yolanda post and it has been interesting digging into all of this. That was a bit of work. Maybe the media is just too lazy. 😉

    I too live in the Philippines. If it seems we have had a lot more typhoons lately, it’s because we have! I have been under three typhoon warnings in as many weeks. Luckily I was on the edge of Yolanda in Negros Oriental and we barely got touched. Zoraida did a lot more damage here with flooding. I think we have had something like 19 typhoons this year while normally we average around 5.

    The problem is, that’s a pretty small data set to work with. As you have pointed out, we haven’t even had decent ways to measure typhoons for long. And even today our methods aren’t great and we have to rely on “storm hunters” to get hard data.

    Then once we have data, we have different organizations interpreting that data differently. Then we have the media to totally blow everything, delivering crap reporting to the masses. As we have found, getting hard data can also be difficult. And sometimes, that data is just a wild estimate.

    I think we need more “citizens” digging up that data and asking questions. Even if we get some things wrong. We keep carrying the conversation and and get closer to the truth.

    Blog on!

  4. b4llzofsteel permalink
    November 14, 2013 9:18 pm

    The good news about the death toll is not as “good” as you think. Today the UN increased the number to 4.460.

    I too lived in the RP for some time and I can confirm, many times things are not what they seem to be… Toss Tayo!

    • November 15, 2013 9:26 am

      Apparently this number has now been retracted. The reality though is that nobody will ever really know.

      http://www.wthr.com/story/23970841/2013/11/14/un-reports-4460-dead-in-philippines-typhoon

      • b4llzofsteel permalink
        November 15, 2013 2:13 pm

        Duly noted, Paul, haven’t seen the retraction. The constant juggling with facts and figures is truly annoying and unprofessional.

        Seeing the total devastation it’s a miracle that “only” 2.300 died. I wonder if the missing people are also included innthe official numbers. I’ve herad that small islands are completely flattened, nobody knows what happened with the inhabitants.

  5. Scott Scarborough permalink
    November 17, 2013 12:20 am

    Paul,

    I have a question. If Jeff Masters knows that wind speeds from satellite have to be reduced by 15% when the typhoon hits land why did he report the 195 mph estimate of Yolanda at landfall when he knows it should have been reduced 15%? Is he promoting Climate change to such a degree that he knowingly and shamelessly reports the wrong values?

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