"Central pressure is measured in millibars, not megabytes"

Replacing "millibars" with "megabytes" might be the result of a too-helpful word processing program that does not have millibars in its dictionary. It's a fairly common phenomenon. That would make the mistake a result of bad proofreading rather than ignorance.

Sounds like Mark P nailed it. It's a great example of (I assume) Microsoft's obsessive dedication to adding a gazillion bells and whistles to its products instead of adding real functionality and utility!

Not if they're using my version of Word: I'm offered milliard, milliards, mill bars, milliars', and Millbrae - but not megabytes. Millibars and megabytes are a loooong way from each other, too - 7 out of 9 letters different, with only one substitution (e/r) being for adjacent letters. That makes the Cupertino Effect an unlikely scapegoat here, even with an initial typo...

I wonder if the draft report used MB instead of mb, rather than the full words. That would seem less insane.

It's an unlikely mistake for anyone even remotely familiar with computers, weather or atmospheric science. Or pretty much anything technical. I like to bang on the incompetence of bureaucrats in this administration as much as the next guy, but there is certainly enough genuine idiocy that you don't need to look for it in places where the problem might be carelessness rather than genuine incompetence. MartinM's suggestion looks reasonable.

If the way they do things is anything like my organization, I can see the following happening:

Technical guy writes document with "mb" or a similar abbreviation. Prior to release, the document goes to an administrative assistant for formatting and proofreading. Organizational standards require that all abbreviations are defined (on first use and/or in a list of abbreviations). Administrative assistant, who is not technical, erroneously determines that MB is the abbreviation for "megabytes" and places this definition in the document. (After all, that's what it meant in the last document that she proofed, and those geeks get all bent out of shape if you keep asking them the same question over and over again...)

So it strikes me as an unfortunate and embarrassing, but not particularly surprising, error to show up in a document.

Yes, a copyediting mistake from the abbreviation mb is certainly plausible. That suggests they use nontechnical proofreaders, though, which is a bit weird even if it's not mindbogglingly incompetent.

The title of this post reminded me to comment that I recently finished "Storm World" (I listened to it in audio form on my way to and from work). What jogged my memory was how hurricane pressure was always referred to both in millibars and in inches. I assume the inches measurement was in parentheses in the book. For some reason that always made my chuckle while I was listening to it. I really enjoyed the book though and have tried recommending it to climate change denialists that I've encountered on a Chicago Cubs message board. Not surprisingly, they have no interest in reading it.