Analysis: Many of Hurricane Michael’s ‘record-breaking’ claims don’t stand up to scrutiny
By Paul Homewood
While Michael was certainly a disastrous hurricane, three specific claims have been made about it, which don’t stand up to scrutiny:
- It was the biggest storm on record for the Florida Panhandle
- It was the third most powerful to hit the US, based on barometric pressure
- It was the fourth strongest in terms of wind speeds.
The first claim is plainly meaningless, given that the Panhandle is only a tiny part of the whole US coastline.
But what about wind speeds?
The claim is that Michael had 1-minute sustained wind speeds of 155 mph at landfall.
Yet the max wind gusts noted by the National Hurricane Centre (NHC) at landfall were 130 mph (although the instrument then failed). At nearby Panama City Airport, 129 mph was recorded.
Hurricane experts reckon that gust speeds are typically 30% higher than sustained speeds, so a gust of 130 mph would indicate a sustained wind speed of about 100 mph, making Michael a Category 2 hurricane.
Given some of the damage caused, this may be an underestimate though.
But where did the 155 mph figure come from?
It only appears once in the NHC’s regular bulletins:
The claim of 155 mph was based solely on SFMR measurements, which the NHC already admit are questionable.
[SFMR, or Stepped-Frequency Microwave Radiometer, has only been in use since the 1980s, and uses passive microwave emissions from the sea surface as a proxy for estimating surface wind speeds – see here]
Prior to the SFMR measurements, NHC was saying wind speeds at landfall were 150 mph, based on Hurricane Hunter aircraft data.
The difference between 150 and 155 mph may sound academic, but it makes a whale of a difference to the claims of 4th strongest.
At 150 mph , or 130 Kts, Michael would be only one of nine hurricanes on record as strong or stronger. During the 19thC, there may have been similarly strong storms, which went largely unobserved.
[Note – wind speeds are based on re-analysis work by NOAA’s Hurricane Research Division].
And, of course, it, fortunately, got nowhere near the Labour Day hurricane of 1935, Camille in 1969 or Andrew in 1992.
There is also another clue to the real strength of Michael, the storm surge.
Maximum surge seems to have been around 7 feet. I have heard this described on a news bulletin as “epic”, which is utter nonsense – this is not unusual for any hurricane.
By contrast, the storm surge during Camille was 24.6 feet:
A surge of just 7 feet would suggest that Michael’s wind speeds were much less than claimed.
There is one more clue.
NOAA use a variety of methods to estimate surface wind speeds. One uses data from a number of satellites.
Apart froThe first claim is plainly meaningless, given that the Panhandle is only a tiny part of the whole US coastline.m one outlier, all of the satellite data points to wind speeds of well below 120 Kts, well below NOAA’s official intensity estimate of 135 Kts.
From all of the information available, it is most likely that Michael was no more than strong Cat 3/ weak Cat 4 hurricane, with winds of around 110 to 115 Kts, or about 130 mph.
We still have the claim that Michael had the third lowest barometric pressure at landfall, only beaten by the Labor Day hurricane and Camille.
This is based partly on aircraft reconnaissance, and partly on ground observations:
Although the readings are no doubt correct, we know that Hurricane Hunter aircraft kept well away from the centre of the strongest storms in the early days, so we have no way of knowing whether other storms prior to Camille were as intense, unless surface observations were available.
The measurement neat Tyndall is from a Florida University WeatherFlow site.
WeatherFlow, according to their website, is:
WeatherFlow Inc. is a leader in the private sector weather industry, with over two decades of experience in applying the latest in observational, modeling, and forecasting technology to its clients’ most challenging problems..
With official weather observing networks historically focused on aviation, recent years have seen a dramatic increase in the number of public and private mesoscale observing networks (mesonets) installed to fill in the data gaps between official observing stations. State-sponsored networks like the Oklahoma Mesonet have contributed to significant advances in real time warning and detection of severe weather, while the proliferation of affordable home weather stations and the ability to post that data online have resulted in an explosion of ad hoc observational data available via the Internet.
Recognizing that specific applications and specific users have a need for high quality, high density, and consistent observational data, WeatherFlow operates the largest professional observing network in the United States, including the only large scale mesonets dedicated specifically to coastal zone and hurricane monitoring. Although often installed to meet one specific need, each station and mesonet is designed and operated to support multiple user communities and functions, providing a superior value by allowing the costs of installing and operating the networks to be spread across many customers – yielding better service for a fraction of the cost of a single-user system.
They set up networks of weather observation sites, in conjunction with a whole host of clients and partners, of whom Florida University is one.
In short, there are now many more weather observing sites than there used to be in the past.
The minimum pressure of a hurricane is confined to just a tiny part of it, at the centre. The odds of having equipment capable of measuring it at just the right place are much higher when you have thousands of sites. (Not to mention having equipment that is actually capable of operating during bad weather!).
How many hurricanes in the past have had much lower pressure than officially recorded? For instance, the deadly Indianola hurricane of 1886, which is estimated to have been 925 mb, or the Great Miami hurricane of 1926 at 930 mb.
We will never know. But what we do know is that by using modern networks with tens of thousands of weather sites, we are not comparing like with like.
Michael may have had the lowest pressure of any storm since Camille, but such claims cannot be made for earlier periods.