Focus on Central Virginia - Discussing Invest 97L

Weather Headlines:

• Invest 97L has been designated for a rather vigorous tropical wave that just moved off the western coast of Africa. The National Hurricane Center indicates that this system has a medium - 60% - chance of becoming a tropical cyclone during the next 7 days as it moves west-northwestward across the tropical Atlantic.

• Some early, early model guidance suggests that 97L could develop into a major hurricane, which could go on to threaten the mid-Atlantic coast. Some people who enjoy hyping up weather events and spreading misinformation have latched onto this despite the fact the same model guidance also suggests 97L could go out to sea. It could suggests that 97L could go to Florida. It’s time to talk about why it’s not really time to talk about 97L yet. Yes, this is confusing. Yes, I’ll explain.

In Depth:

• The National Hurricane Center has designated a tropical wave moving off the coast of Africa toward the Cabo Verde Islands as Invest 97L (an “invest” is an area being monitored for tropical cyclone development, invest being short for “investigative area”). The global weather models have been projecting some tropical cyclone development in this part of the basin, known as the Main Development Region (MDR), for a little while now, and it looks like 97L will be the system that gets the ball rolling on that. NHC has given 97L a 60% (medium) chance of development during the next 7 days, and 97L should move generally west-northwestward across the tropical Atlantic during that time.

• The major issue with weather models is they sometimes lack skill. In the case of the GFS model, it is most skilled during the first 10 days, or 240 hours. Anything that happens after that point should be taken with a grain of salt. Case in point, the global models (GFS and Euro) are also run as ensembles - basically, collections of individual sub-models that are then taken together to determine what their consensus is, and these consensuses can often be more accurate than individual models…during that same 240 hour period. In the case of 97L, here is a screenshot of the latest (as of this writing) run of the GFS ensemble…

• On the image above, the GFS Ensemble has run a bunch of sub-models on 97L, and they all mostly follow the same track as they enter from stage right. Note how the individual sub-models become more spread out before they end at the red L’s - this is at 204 hours, which is within that 240 hour period. This is an indication that there is a great deal of uncertainty about the exact conditions at that point, and where a hurricane goes is highly dependent on where various things such as high pressure areas, other low pressure areas, fronts, etc. are located.

• One final example is the animation below - this is the GFS Ensemble, run from hour 96 to hour 300 (waaaaay beyond 10 days). Unfortunately, this animation doesn’t show tracks, so you’ll have to follow the little red numbers and orange dots as they move across the Atlantic…

• Based on this, 97L would seem to be more likely to go out to sea, but a number of tracks make their way to land anywhere from Florida to North Carolina. This is why we don’t put much stock in model forecasts this far out - although you can sometimes find trends that the models do eventually latch onto, there’s just too much uncertainty.

• This all boils down to one statement: it’s too early to say for sure where 97L is going, and it’s too early to say where 97L isn’t going. Anyone who tries to convince you that, at this early point, that a Category 5 killer hurricane is going to plow into the Outer Banks and obliterate the city of Richmond, is clearly looking for attention. You should always stick with official sources or other reliable outlets such as your local news or local professionals. Come back in about a week or so and we can get into the nitty-gritty about 97L.

• EDIT 8/10/25: NHC hurricane specialist Philippe Papin posted a thread on Bluesky with a somewhat more technical explanation of all of the above, and it’s absolutely worth your time if you’re interested. It does a great job of explaining the model skill issues I mentioned and provides some hard data to back it up.

One last thing…

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