How do Invest storms get numbered?

[Michele B]

I mean, I get it...they’re called “invests” b/c they are going to. be investigated for tropical development.

But how do they get numbers? It seems like they ALL get numbers between 91 and 96 No higher- no lower. So what is the system for numbering them? Or is there one?

Thanks for taking the time to help a newbie with a dumb question!

[toad strangler]

Invests are numbered 90 through 99 and are rotated in chronological order. Once 99 is used it reverts back to 90. Also each basin has a distinct letter that follows the number. In the Atlantic, that letter is “L”

[wxman57]

To further the explanation, all storms in the Atlantic are given a 2-digit number for identification (AL01, AL02, etc.) in a database. Those numbers are for designated systems (depressions, tropical storms, hurricanes). The NHC needed to use a classification range that was above the highest number of active storms that might be seen in a season, so they use 90-99 for invests. Test storms are given a range of 80-89, I believe. That leaves 0-79 for designated storms or for other testing purposes.