Two Weather Offices Watched The Same Storm. They Wrote Down Different Numbers.

When a typhoon crosses the Philippines, more than one weather office is watching it.

Japan runs one. The United States Navy runs another. China, Hong Kong and Korea each run their own. They all look at the same storm, and they all write down how fast its wind is blowing.

They do not write down the same number.

Haiyan Was Two Different Storms On Paper

Haiyan hit the Philippines in 2013. It is one of the strongest storms ever recorded anywhere.

The US office wrote down 170 knots. The Japanese office wrote down 125 knots. That is a gap of 45 knots for the same storm on the same day.

Neither office is lying. Here is why.

They Are Timing The Wind Differently

Wind is gusty. It speeds up and slows down all the time. So to say how fast it is blowing, you have to pick a length of time and take the average.

The US office averages over one minute. Japan averages over ten minutes.

A ten-minute average is always a smaller number, because the quiet moments get mixed in with the strong ones. So part of the gap is just the clock, not the storm.

But The Clock Does Not Explain It

If the clock were the whole story, the gap would always work the same way. It does not.

I compared 17,244 moments where both offices wrote down a number for the same storm at the same hour.

For weak storms, Japan's number is bigger, by about 7 knots. A ten-minute average cannot be bigger than a one-minute one. So that gap is not the clock.

For medium storms, the two offices write down exactly the same number.

For the very strongest storms, the US number is 35 knots higher.

Why This Matters When A Storm Hits

Nobody evacuates a town because of a number. They evacuate because of a word: is it a typhoon or not?

I looked at every moment a storm was over Philippine land and both offices had written a number. There were 840 of them.

In 19.88% of those moments, one office said typhoon and the other did not.

And it goes mostly one way. The US office said typhoon on its own 158 times. Japan said typhoon on its own only 9 times.

Forty Years, And It Has Not Got Better

You might think better satellites would fix this. They have not.

In the 1980s the middle gap was 12 knots. In the 1990s it grew to 20 knots. In the 2020s it is 17 knots.

It got wider, then stayed there.

Three Things I Cannot Tell You

Which office is right. There is no way to go back and measure Haiyan properly. Both numbers are careful guesses from satellite pictures. I can only show that they differ.

What happens when one office says nothing. Japan only writes a number once a storm is strong enough. I left out 13,247 moments where only one office spoke. Counting silence as agreement would have made the gap look much smaller than it is.

What any of it cost. This record holds wind and position. It holds no damage, no deaths, no houses.