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Typhoon Meranti – The Facts v The Hype

September 14, 2016

By Paul Homewood   

 

h/t AC Osborn 

 

image

http://www.dailymail.co.uk/news/article-3788458/Super-Typhoon-Meranti-tears-Taiwan-wind-gusts-370km-h-sets-sights-China.html

 

Not for the first time in the last year or so, we find that a Pacific cyclone being grossly overhyped.

I must stress that this is not the doing of the media, they are simply being fed this information from official sources.

It is only in relatively recent years that cyclones have been monitored and measured by satellite, Before the 1980s, many would have been missed altogether as they often go nowhere near land. Others may only have been spotted by ship or land observation after they had reached maximum strength.

It is also important to understand that satellites do not actually measure wind speeds, speeds are estimated with the Dvorak technique using a variety of other information. It is well recognised that these estimates can be several mph out.

 

It is also relevant to point out the “actual” wind speeds, routinely reported in the media, are not “actual” at all, but the “operational warnings”, which are issued every six hours.

 

 

According to NOAA, Meranti peaked at 165 Kts (190 mph or 303 kph), for a six hour slot yesterday, based on the operational warning. However, when actual data from the Advanced Microwave Sounding Unit or AMSU, an instrument on NOAA operational polar-orbiting satellites, is used to estimate intensity, much lower wind speeds are obtained. Instead of 165 Kts, we actually get somewhere around 140Kts, or about 160 mph.

 

2016WP16_AMSUTSPL_201609141200

http://rammb.cira.colostate.edu/products/tc_realtime/products/storms/2016WP16/AMSUTSPL/2016WP16_AMSUTSPL_201609141200.GIF

 

While this would still make Meranti a Cat 5 storm on the Saffir-Simpson Scale, this would not be unusual for a mid Pacific typhoon.

 

It is no coincidence that we keep finding examples like this in the Pacific, where wind speeds have been grossly overstated. In the Atlantic, most strong hurricane tend to hit land, where monitored wind speeds would soon tell the true story.

 

wp1616

https://metoc.ndbc.noaa.gov/ProductFeeds-portlet/img/jtwc/products/wp1616.gif

 

JTWC now show Meranti tracking NW towards the China coast, with wind speeds of 125 Kts, or 144 mph, which would make it a Cat 4, with wind speeds forecast to weaken as it hits land.

This is still a major, and potentially damaging, storm, but nothing that does not come along regularly every year.

 

As I say, the Mail’s version of the story is covered by most of the media, including the Indian Express. However, they also quote Taiwan’s Central Weather Bureau:

Taiwan’s Central Weather Bureau warned that the Category 5 storm would threaten several southern and eastern cities, including Kaohsiung and Hualien, with strong winds, torrential rain and flooding.

Meranti, which grew in strength as it neared Taiwan, was carrying maximum winds of 216 km per hour (134 mph), meteorologists said.

This is 10 mph less than the JTWC figure.

 

One further point.

All the wind speeds mentioned are sustained winds over 1-minute. Often the media like to use gusts, as these sound much more scary. On this occasion, the Mail state, an enormous ‘super’ typhoon set to rip through China after leaving a trail of devastation in Taiwan has recorded wind gusts of up to 370 km/h .

As can be seen on the JTWC chart above, maximum gusts are only 150 Kts, or 172 mph.

10 Comments leave one →
  1. September 14, 2016 5:07 pm

    Nothing ruins truth like stretching it.

  2. September 14, 2016 6:16 pm

    Nice work Paul. I’ve been tracking tropical cyclones for a long time now and most of them tend to be greatly over-hyped. It is quite common for them to peak at great intensity well away from land and then weaken considerably before landfall, but the hype follows them to landfall. There are a few exceptions where these “super” storms hit land at peak intensity, but these are relatively rare.

    Estimating the peak winds of tropical cyclones still has a fair amount of uncertainty, probably around 10 to 20 percent with reconnaissance aircraft measurements because of sampling coverage constraints along with measurement error and even greater uncertainty for estimates based on satellite imagery and sensors which is all that is available for Western Pacific typhoons in recent years. Before aircraft and satellite measurements the uncertainties are huge and wind estimates have to be based largely on subjective damage reports.

    Over land at airports, winds are typically measured at 10-meters above the ground, and this is the height the estimated peak storm winds are supposed to represent. However, in strong storms over the ocean, wave heights may be on the order of 20 meters or more, so how meaningful is a wind at 10 meters above the ocean surface in these circumstances? Is that 10 meters above the wave troughs, or above the wave peaks, or the average of the two? Most of the ocean buoys that measure wind in storms have only 5-meter wind masts and are even more compromised by high waves.

    Another confusing aspect of storm reporting is that civilian and military agencies from the US use estimated peak 1-minute average for “sustained winds” whereas most other agencies outside the US use estimated peak 10-minute average for sustained wind (which yields lower speeds for the same given intensity). However, it is actually the wind gusts that do most of the damage, especially over land where surface roughness reduces 1-minute and 10-minute wind averages much more than peak gusts (the average/gust ratio is much lower over land than in coastal areas with lower surface roughness and is commonly less than 50% inland, especially for 10-minute averages). As a consequence, reported storm peak wind gusts even a short distance inland rarely exceed the estimated “sustained” wind speeds for these storms at landfall and very rarely reach the estimated peak gust levels except from tall towers or measurements at the immediate coast. On the other hand, with “super” storms there are usually few, if any accurate measurements from official weather stations at landfall because of power outages preceding the storm peak or actual damage to the wind equipment, so quite often only damage reports can be used to estimate the actual peak winds.

    • A C Osborn permalink
      September 15, 2016 11:25 am

      In most cases in low lying areas it is the storm surge which is most dangerous, you can build against high winds, but flooding is harder to deal with.

      • September 15, 2016 12:49 pm

        A C, agreed. However, there are a few “super” tropical cyclones with a relatively small extreme high wind area that do not generate as high of a storm surge as larger storms with lower peak winds spread over a much larger area, but cause tremendous wind damage when the storm center hits a highly populated area. A good example is Hurricane Andrew which hit the south side of the Miami area in Florida in 1992.
        https://en.wikipedia.org/wiki/Hurricane_Andrew

        Good examples of larger storms with much lower peak winds, but tremendous storm surge are Hurricane Ike hitting the Houston area in 2008 and hybrid storm Sandy hitting the US mid-Atlantic coast in 2012. Neither of these storms were classified as “major” hurricanes when they hit the US coast but caused extensive damage mainly from storm surge. Both of them caused more total damage than Andrew.

  3. Broadlands permalink
    September 14, 2016 6:32 pm

    History is not a strong point in the post-satellite era.

    Back in In 1924 there were several papers in the Monthly Weather Review on the long history of Far East typhoons by Coching Chu, From this can be gleaned that In the period 1904-1915 the average number of typhoons (winds at least Beaufort Scale 12) was nine. If you include all well-developed storms, the number increases to 20. I believe those are numbers that are about average now? Clearly, those large storms 100 years ago had nothing to do with man-made climate change.

    http://journals.ametsoc.org/doi/abs/10.1175/1520-0493%281924%2952%3C570%3AANCOTO%3E2.0.CO%3B2

  4. Bloke down the pub permalink
    September 14, 2016 6:57 pm

    The Mail obviously feels that its readership have been missing scary weather stories this year as the UK weather has been so benign.

    • 1saveenergy permalink
      September 14, 2016 9:28 pm

      But it’s unprecedented to have such catastrophic benign UK weather. Records from before records began, show that records have been broken & 97% of all tipping points have tipped. Try not to think of the children (you can be locked up for that & get you name in the Mail !!).

  5. Bob Jones permalink
    September 14, 2016 10:16 pm

    Meanwhile here in Hong Kong we seem to get fewer and fewer typhoons, or at least hits, as years go by

  6. Dave N permalink
    September 14, 2016 10:19 pm

    Still doesn’t excuse the Mail for not checking the info they receive

  7. Steven Fraser permalink
    September 15, 2016 3:18 am

    Forecast path now skims by the Taiwan north east coast, and heads toward southern Japan.

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