<blockquote>
<p>A similar question talks about &quot;invests&quot; but that question mentions those numbers ranging from 90-99, these numbers were in a different range, so if they are related what do the lower numbers mean?</p>
</blockquote>
<p>The US <a href="https://ftp.nhc.noaa.gov/atcf/README" rel="nofollow noreferrer">Automated Tropical Cyclone Forecast (ATCF)</a> provides somewhat of a hint, with names of the form <code>&lt;basin&gt;&lt;storm-number&gt;</code> included in the file names and has this to say about <code>&lt;storm-number&gt;</code>:</p>
<ul>
<li><code>&lt;storm-number&gt;</code> = 01 - 30<br />
&quot;Numbered storms with forecasts issued and numbers are <em>not</em> recycled until the next season&quot;</li>
<li><code>&lt;storm-number&gt;</code> = 90 - 99<br />
&quot;Invest, areas of interest watched by forecasters for possible development and these numbers are re-used periodically throughout the season&quot;</li>
<li><code>&lt;storm-number&gt;</code> = 80-89<br />
&quot;Internal training storm numbers which are to always be ignored&quot;</li>
</ul>
<p>The numbers 31 to 79 are currently unused or are put to other uses. Numbers 50-79 are reserved for other uses. The ATCF has a hard-coded limit on numbered storms of 49 to make way for those reserved numbers.</p>
<p>The <code>&lt;basin&gt;</code> part of the ATCF descriptors apply only to the three regions monitored by the US: The Atlantic, western Pacific, and central Pacific. These are typically two letter designators as opposed to the single letter designators used for invests, sometimes all caps, other times lower case in the ATCF file names. The basin identifier typically but does not always precede the storm number.</p>
<p>This final part is just a guess. I suspect the international group that covers aviation charts wants a consistent naming scheme that covers the globe. They appear to have followed the scheme used for invests: A two digit storm number that in contrast to invests does not recycle over the course of a tropical weather season, followed by a single character basin identifier. The storm number most likely is supplied by the meteorological organization responsible for monitoring the basin in question.</p>

CC BY-SA 4.0
2024-09-28T17:05:12.400Z
2024-09-28T17:05:12.400Z
David Hammen
<p>I am looking at an aviation weather chart and see T.S Isaac 10L and Hurricane Helene 09L and hurricane John 10E.</p>
<p>What do these numbers mean after the name (10E, 10L, 09L) ?</p>
<p>A similar question talks about &quot;invests&quot; but that question mentions those numbers ranging from 90-99, these numbers were in a different range, so if they are related what do the lower numbers mean?</p>

CC BY-SA 4.0
2024-09-26T16:28:33.220Z
Kind of related: https://earthscience.stackexchange.com/q/26421/18081
Jean-Marie Prival
CC BY-SA 4.0
2024-09-26T22:45:06.663Z
This question is similar to: [Why are these three "disturbed weather" events called "Invest" and what to the subsequent numbers and letters mean?](https://earthscience.stackexchange.com/questions/26421/why-are-these-three-disturbed-weather-events-called-invest-and-what-to-the-s). If you believe it’s different, please [edit] the question, make it clear how it’s different and/or how the answers on that question are not helpful for your problem.
David Hammen
CC BY-SA 4.0
2024-09-26T22:46:01.503Z
I wouldn't just say that this question is "kind of related" to the other. I voted to close this question as a duplicate.
David Hammen
CC BY-SA 4.0
2024-09-27T06:57:39.303Z
@DavidHammen No, the number ranges are different, so it must be another kind of classification, even if they are related. Voted to leave open.
Jean-Marie Prival
CC BY-SA 4.0
2024-09-28T14:59:22.080Z
@Jean-MariePrival I agree; I have retracted my VTC.
David Hammen
<meteorology><tropical-cyclone>
What does 10E, 09L, 10L mean after a hurricane or tropical storm name
Name
# What does 10E, 09L, 10L mean after a hurricane or tropical storm name

(Asked by: username_0 on 2024-09-26)

I am looking at an aviation weather chart and see T.S Isaac 10L and Hurricane Helene 09L and hurricane John 10E.

What do these numbers mean after the name (10E, 10L, 09L) ?

A similar question talks about "invests" but that question mentions those numbers ranging from 90-99, these numbers were in a different range, so if they are related what do the lower numbers mean?

**Tags:** meteorology, tropical-cyclone

> **Comments:**
> **username_1**: Kind of related: https://earthscience.stackexchange.com/q/26421/18081  
> **username_2**: This question is similar to: [Why are these three "disturbed weather" events called "Invest" and what to the subsequent numbers and letters mean?](https://earthscience.stackexchange.com/questions/26421/why-are-these-three-disturbed-weather-events-called-invest-and-what-to-the-s). If you believe it’s different, please [edit] the question, make it clear how it’s different and/or how the answers on that question are not helpful for your problem.  
> **username_2**: I wouldn't just say that this question is "kind of related" to the other. I voted to close this question as a duplicate.  
> **username_1**: @username_2 No, the number ranges are different, so it must be another kind of classification, even if they are related. Voted to leave open.  
> **username_2**: @username_1 I agree; I have retracted my VTC.  

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## 1 answers

### Answer by username_2 on 2024-09-28. Score: 2

> A similar question talks about "invests" but that question mentions those numbers ranging from 90-99, these numbers were in a different range, so if they are related what do the lower numbers mean?

The US [Automated Tropical Cyclone Forecast (ATCF)](https://ftp.nhc.noaa.gov/atcf/README) provides somewhat of a hint, with names of the form `<basin><storm-number>` included in the file names and has this to say about `<storm-number>`:

* `<storm-number>` = 01 - 30  
  "Numbered storms with forecasts issued and numbers are *not* recycled until the next season"
* `<storm-number>` = 90 - 99  
  "Invest, areas of interest watched by forecasters for possible development and these numbers are re-used periodically throughout the season"
* `<storm-number>` = 80-89  
  "Internal training storm numbers which are to always be ignored"

The numbers 31 to 79 are currently unused or are put to other uses. Numbers 50-79 are reserved for other uses. The ATCF has a hard-coded limit on numbered storms of 49 to make way for those reserved numbers.

The `<basin>` part of the ATCF descriptors apply only to the three regions monitored by the US: The Atlantic, western Pacific, and central Pacific. These are typically two letter designators as opposed to the single letter designators used for invests, sometimes all caps, other times lower case in the ATCF file names. The basin identifier typically but does not always precede the storm number.

This final part is just a guess. I suspect the international group that covers aviation charts wants a consistent naming scheme that covers the globe. They appear to have followed the scheme used for invests: A two digit storm number that in contrast to invests does not recycle over the course of a tropical weather season, followed by a single character basin identifier. The storm number most likely is supplied by the meteorological organization responsible for monitoring the basin in question.


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