Watching Invest Areas

Well, it’s that time of year again. The US National Hurricane Center’s outlook has the yellow X of doom, and now even an orange blob of misfortune. This morning (Friday 16 June) we have this portent of potential future ruination:

So how should you read these tea leaves? First off, while the graphic is of some use, the valuable information is in the text that accompanies the graphic, on the NHC outlook page is right below the picture. Here is the text that goes with the above graphics:


Tropical Weather Outlook
NWS National Hurricane Center Miami FL
200 AM EDT Fri Jun 16 2023

For the North Atlantic…Caribbean Sea and the Gulf of Mexico:

  1. Eastern Tropical Atlantic:
    A tropical wave located near the west coast of Africa is producing disorganized showers and thunderstorms. Environmental conditions appear to be conducive for gradual development, and a tropical depression could form during the early to middle portions of next week while the system moves westward at 15 to 20 mph across the eastern and central tropical Atlantic.
  • Formation chance through 48 hours…low…near 0 percent.
  • Formation chance through 7 days…medium…40 percent.

Forecaster Cangialosi

These messages follow a set format with a very careful use of language that makes it really easy to decide if you need to panic or not. Each potential system is described and, if it is real threat, the following phrase will appear: Interests in <somewhere> should <do something>. If this phrase doesn’t appear, then the storm is nothing to worry about in the short run (next day or so), and probably not over the next week. If it does appear, it’s easy: if you are <somewhere>, then <do something>. If you aren’t <somewhere>, no need to worry yet if at all. Generally the pattern will start with “Interests in <somewhere> should monitor the progress” and once the storm actually spins up more specific actions will be detailed in the forecasts for the storm. The next thing to look at is the two “Formation Chance” lines, for the next two days, and over the next week.

At this point (6am Friday morning), the system described above doesn’t even really exist yet, the global models are showing a tropical wave moving off the coast of Africa potentially spinning up in to a system with a closed circulation – the first stage of tropical storm formation. Over the next two days there is little to no chance; but conditions are somewhat favorable over the next week as it moves out over water, so the forecaster gives it a 40% chance of becoming a tropical depression. Here’s what it looks like as the sun comes up … can you find it?

Not even an invest area … it’s a blob of clouds on the north edge of the Inter-tropical Convergence Zone (band of clouds).

The stages a storm progresses through are it’s a potential disturbance that is mentioned in the outlook, then as the forecasts start to converge it will be assigned a temporary ID in the Automated Tropical Cyclone Forecast (ATCF) system, then once it becomes either a sub-tropical or tropical storm, it will be assigned a permanent ID. ATCF ID’s consist of the storm basin (AL – Atlantic, EP – East Pacific (off of Mexico), CP – Central Pacific (Hawai’i), WP – West Pacific, IO – Indian Ocean, and SH for Southern Hemisphere. The basin is followed by a two digit ID number, and the year. The numbers from 90 to 99 are reserved as temporary ID’s and are recycled. These are so-called “Invest Areas”. This allows the computers to start tracking the storm before it is really technically a storm; if and when it does become a tropical system it gets a sequential ID starting at 1. So the first storm of the year will be AL012023, the second AL022023, and so forth. If this storm spins up it will probably first get the temporary ID AL922023 (90, and 91 have already been used recently), and if it becomes a storm it would get the permanent ID AL03 (AL01 was a sub-tropical system in January, AL02 was a minimal Tropical Storm Arlene from a few weeks ago that was so nothing, and I was so busy, I didn’t bother to comment on it 😛 .)

Often you will see the ATCF ID shortened to just the basin and storm number, leaving off the year – AL92. If that’s not enough, in order to increase confusion and ensure only professionals understand this (seriously, as a hold over from the era when every byte of computer space counted, and since the TC Vitals system uses it), there is also a shorter version of this identification that consists of a single letter and just the two digit ID. So in some places you will see it as “Invest Area 93L” – the “L” being shorthand for AL (Atlantic). Be careful, because in the shorthand system “A” is actually the Arabian Sea, so Cyclone Biparjoy, that just made landfall on the border of Pakistan and India, has the ATCF ID IO022023, but the shorter designation is 02A.

Generally it is my policy not to comment on a developing system until it is at least assigned a temporary ATCF ID. There are just too many tropical waves and potential disturbances during the year, and it’s just not worth getting excited about each and every one of them unless you profit from that sort of thing. In addition, prior to that time, dedicated models and vortex tracking are not being run, so there isn’t much data to base any discussion on (not that will stop some people).

As a final reminder, social media is a terrible way to get storm information, Recent changes to Facebook and Twitter have made a bad situation even worse, and sites that don’t pay them to “boost” posts are throttled. They sort and display posts by profitability and popularity, which means an older post with more circulation (but old, possibly inaccurate info) may be seen before later more accurate info. So make sure you check for current info. If you like these posts and would like them directly, you can subscribe below.


  1. Living on the east coast of south GA, you are my go to guy. So thankful you are back for the season!

  2. Thank you for all you do for us. You are our Calm in the Middle of the Storm. Always counting on you because you are the best!

  3. You do fantastic work and it’s appreciated. Please keep up the awesome expert efforts to keep us informed.

  4. Ditto to all the other comments. I’m visiting on the West Coast so getting the facts and accurate assessments is reassuring while away from home in Hilton Head.

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