The evolution of Hurricane Irma’s disinformation campaign

Is Irma The Most Powerful Atlantic Storm?

http://www.telegraph.co.uk/news/2017/09/06/hurricane-irma-latest-live-news-strongest-ever-atlantic-storm/

There seems to be a lot of disinformation about Irma being the “most powerful Atlantic Ocean storm in recorded history” with sustained winds of 185 mph, such as the Telegraph above. I also heard the same comment on ITV News yesterday.

As I pointed out yesterday:

Four other storms have had winds as strong in the overall Atlantic region but they were in the Caribbean Sea or the Gulf of Mexico, which are usually home to warmer waters that fuel cyclones.

Hurricane Allen hit 190 mph in 1980, while 2005’s Wilma, 1988’s Gilbert and a 1935 great Florida Key storm all had 185 mph winds.

In other words, there have now been four hurricanes as strong or stronger since 1980, about one every decade, and certainly nothing like the “unprecedented” impression left by the headlines.

And as we know, prior to Allen in 1980, we had very little in the way of measurements in mid-ocean.

A closer look at the Labor Day Hurricane of 1935, widely acknowledged to be by far the most powerful storm to hit the US, emphasizes this fact.

According to HURDAT:

The Labour Day Hurricane was the strongest hurricane to ever make landfall in the United States, based upon its central pressure of 892 mb. The maximum sustained winds at landfall in the Florida Keys are estimated to have been around 185 mph.

http://www.aoml.noaa.gov/hrd/hurdat/metadata_master.html

And as Chris Landsea’s reanalysis highlighted, wind speeds were probably even higher, up to 164 kt, or 189 mph:

http://www.aoml.noaa.gov/hrd/Landsea/landsea-et-al-jclimate-2014.pdf

Wind speeds were almost certainly even greater offshore prior to landfall, but in those days there was no way to measure them. Any anemometers in the area would have been destroyed in such high winds.

Therefore meteorologists relied heavily on measurements of pressure, and it is this which casts suspicion on claims about Irma.

If we look again at the five hurricanes listed above, we find:

https://en.wikipedia.org/wiki/List_of_Category_5_Atlantic_hurricanes

Wind speeds don’t always correlate exactly with pressure, but pressure is usually a pretty good guide.

And we can see that Irma is not in the same league as the others.

The wind speeds estimated for Irma may be right, but if so it would indicate that they were underestimated for the other storms.

Meanwhile, the early indications are that Irma is gradually losing strength, now down to 175 mph.

http://abcnews.go.com/US/hurricane-irma-slams-caribbean-florida-face-direct-impacts/story?id=49645643

But the models still have little idea about where it is heading.

http://abcnews.go.com/US/hurricane-irma-slams-caribbean-florida-face-direct-impacts/story?id=49645643

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