Tropical Storm Isaias likely to become first hurricane of the season

The area of concern I mentioned in last Wednesday's post was upgraded to Tropical Depression 9 on Tuesday afternoon and then to Tropical Storm Isaias on Wednesday morning. There is high confidence that it will intensify in the central Gulf of Mexico and become the first hurricane of the 2026 Atlantic season, nearly one month later than the previous record-latest first hurricane formation, which was September 11.

The official forecast from early Wednesday morning brings Isaias up to a borderline Category 2-3 hurricane in the central Gulf, then shows some weakening prior to landfall overnight on Friday, likely between New Orleans LA and Panama City FL.  Tropical storm force winds should arrive along the north-central Gulf coast on Friday evening.

Rainfall and storm surge impacts will be noticeably more severe for places to the right of the track... for example, roughly Mobile to Tampa. Storm surge guidance isn't available yet, but stay closely tuned to the NHC webpage for the latest... storm surge will likely be fairly significant.

The storm will also be moving rather quickly by the time it makes landfall, so the wind impacts will also be carried further inland than "normal", again, primarily to the right of the track.

I brought this up in my annual "cone" refresher post, but remember that the intensity forecast also contains uncertainty, just like the track does. You can see the track forecast cone above, but here's my take on the intensity forecast cone, as of Wednesday morning's Advisory #3. The cone is based on NHC's intensity forecast errors over the previous five seasons.

With an active tropical storm (and likely hurricane soon), the Accumulated Cyclone Energy will get its biggest boost of the entire season by far.  As of today, it's at about 11% of average, but the next 3 days could nudge that up to approximately 16-20% of average.

Some name history: Isaias (pronounced ees-ah-EE-ahs) was first introduced to List 6 (the one we're using this year) in 2014... it replaced Ike after the 2008 season. In 2014 however, the name never got used because the very quiet season ended with Hanna. It was used in 2020 and now in 2026. It most likely will not get retired this year, so we'll see it again in 2032.

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Eyes still on southern Gulf of Mexico for next potential storm

I chose the title of this post to mimic the one from last Wednesday, because that post hardly needs any updating today! The area I highlighted six days ago is coming together... it's currently tagged as Invest 92L but is close to becoming the season's 9th named storm, Isaias. As of Tuesday morning, it's located in the far western Gulf of Mexico and has had a significant flare-up of strong thunderstorm activity over the center.

And, as mentioned last Wednesday, if it forms, it has good odds of becoming the season's first hurricane. Recall that within the past century and within the more reliable satellite era (mid-1970s), the record-latest first hurricane formed on September 11. Will 2026 finally get its first hurricane this week? If not, the chances start dropping off quickly in the final six weeks of the season.

The tracks shown below are from the operational (left) and experimental (right) Google Deepmind ensemble. They provide some confidence in a track forecast because there is so little spread among the members. But the majority of them are also quite bullish on the intensity. Even in the 1000-member version of the ensemble (not shown), this has a roughly 70% chance of becoming a hurricane.

https://www.weathernerds.org/models/fnv3.html

Among the ensemble and deterministic models, the timing of landfall is fairly tight around Friday afternoon into Saturday morning. However, the intensity at landfall is another story... very little agreement among models with an enormous range from tropical depression to Category 3 hurricane.

It does not appear that time, moisture, or water temperature will hinder the storm's potential for substantial development, but wind shear probably will. The current wind shear in the western Gulf is moderate and the forecast wind shear in the northern Gulf is substantial, so even if the system does develop in the next couple of days, its final day or two should be greeted by a wall of strong vertical wind shear which would weaken it. With that in mind, the intensity forecasts shown above that indicate a peak intensity in the 48-72-hour window followed by weakening seem more likely to me.

A feature that could play a role in the storm's evolution at the end of the week is an anticyclonic warm eddy in the central Gulf. There is deep warm water there that could provide a temporary boost to a system which should be beginning its battle against increasing wind shear.

https://bmcnoldy.earth.miami.edu/tropics/sectors/

The sea surface temperature under Invest 92L is currently about 31°C and will only decrease to about 29°C as it approaches the Gulf coast -- all plenty warm to sustain a hurricane of any intensity.

https://bmcnoldy.earth.miami.edu/tropics/sectors/

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Eyes shift to southern Gulf of Mexico for next potential storm

Fay and Hanna have dissipated, and the Atlantic will be quiet for a week or so, then the long-range models begin hinting at something brewing in the Bay of Campeche in the southern Gulf of Mexico. If this ends up developing into the ninth named storm, the next name on the list is Isaias. But it's a looong way off.

As of the Wednesday morning cycle, the 1000-member Google Deepmind ensemble gives this a 27% chance of becoming a tropical storm late next week, and of those members, they show a 60% chance of it becoming the season's first hurricane and even a 22% chance of reaching major hurricane intensity (Cat3+). Other AI and conventional ensembles agree with a decent chance of something forming here in 7-10 days. There's a LOT of uncertainty of course, but the signal in the models is there.

Image from https://tcatlas.org/realtime_ir.html

This area is not as favored for development in early October.as one might think, at least for storms that eventually reach hurricane intensity. The last one that did so was Milton in 2024, then Roxanne in 1995, then Fern in 1967. It's a very short list.

Just for curiosity's sake, I ran some preliminary homogeneous track and intensity verification statistics on the meager activity so far this season. This covers Arthur through Hanna, and you can see on the charts that there are actually ZERO 5-day (120-hour) verification times, but it's what we've got. All six of the 4-day (96-hour) verifying forecasts come from Fay.

For track, the Google Deepmind ensemble mean (GDMI) leads the pack overall, then it gets a bit more noisy. The National Hurricane Center's forecasts (OFCL) were very closely aligned with GDMI except for the six forecasts for Fay when the model was superior.

For intensity, it's definitely a mixed bag, but the thing I see is the two consensus aides, HCCA and IVCN, did the best overall. The Google Deepmind ensemble mean was quite good too, but lost a little bit of ground on the 4-day forecasts of Fay. Also worth noting is that the HWRF hurricane model (HWFI) beat the NHC's average forecast error at every lead time -- none of the other hurricane models did that (HMNI, HFAI, HFBI, CTCI).

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