Wednesday, September 2, 2026

Invest numbers / Disturbance identifiers

 

Those codes are invest numbers / disturbance identifiers used by tropical cyclone warning agencies to track systems before—or sometimes after—they become named tropical depressions or storms.

The format is basically:

NN + basin letter

where NN is a sequential number and the final letter identifies the ocean basin.

ExampleMeaningBasin
05LSystem number 05North Atlantic
12ESystem number 12Eastern North Pacific
01WSystem number 01Western North Pacific

The basin letters are the important part:

  • L = North Atlantic, including the Caribbean Sea and Gulf of Mexico
  • E = Eastern North Pacific
  • C = Central North Pacific
  • W = Western North Pacific
  • A / B = North Indian Ocean
  • S / P = Southern Hemisphere basins, depending on location

An important distinction

You might see something like Invest 95L. That is not the fifth tropical cyclone of the year.

Numbers 90–99 are normally reserved for invests—areas of disturbed weather that forecasters are specifically investigating for possible tropical development. The numbers can later be reused.

 

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