12 September 2021

No active storms on peak of the season, but lots to watch

From last Thursday's post on the peak of the hurricane season, I mentioned that the peak of the season is generally the second week of September, but if a specific date has to be chosen, I recommended September 12th (today). As of this writing, we happen to have zero active tropical cyclones on September 12th... but a whole lot to talk about.

The National Hurricane Center is highlighting five areas of potential formation within the next five days, two of which I'll focus on because of their eventual potential impacts.  But the five areas are shown above, with yellow indicating an area with a low probability of formation, orange is medium, and red is high.

The one of immediate concern is a disturbance in the Bay of Campeche, which has been a feature of interest for the past few days since it was north of Honduras then drifted across the Yucatan peninsula.  This is identified as Invest 94L, and is quite likely to become at least a tropical depression by later today.

Models are in good agreement on a track toward the north, scraping the Mexico/Texas coastline over the next few days, dropping heavy rain along the way.  They're also in good agreement on it remaining relatively weak -- none have it reaching hurricane intensity (but let's not rule that out completely... after all, it's mid-September!).  As of now, the greatest threat posed by this system is the rain, and significant totals are expected over southeast Texas and southern Louisiana in the next five days, which will inevitably result in flash flooding.

The next feature I'll highlight is an easterly wave that's still over Africa... but models have been consistently bullish on its development and eventual track through the deep tropics.  There's another easterly wave centered over Cabo Verde too (Invest 93L), but that one is less likely to develop and more likely to take a track toward the northwest.  Since there's so much going on, I'll just focus on the one still over land.

The American (GFS, top) and European (ECMWF, bottom) global model ensembles are shown below... these are the trackable low pressure centers out through the next ten days from the most recent run.  When you look at long-range forecasts of activity, it's important to not focus on details.  Blur your eyes, look for trends in the percent of members that develop it and the general placement of the tracks.  From this, we can be quite confident that the easterly wave will develop, that it's likely to become a hurricane, and that it could be a threat to the eastern Caribbean next Sunday-Tuesday.

The area north of the Bahamas that's shaded in orange on the map at the top of the post is not a current disturbance at all, but rather an area where one could form later in the week. *IF* something is able to develop there, it could have impacts from North Carolina up into the northeast U.S. in the Friday-Saturday timeframe, but it does not appear to be a big concern at this point.  Something to keep an eye on if you're in that area though.

The next names on the list are Nicholas, Odette, and Peter.  All three of those names are originals from the 1979 list, but they have only been used once before (2003)!

And finally, an update on the progression of Accumulated Cyclone Energy (ACE) for the season: it's at about 143% of average for the date, using a 1971-2020 climatology.  This season's ACE is 1.4 times higher than 2020's was on this date, but way lower than mega-seasons like 2017, 2008, 2005, 2004, etc. In other words, it's noteably high, but very far from touching any records.

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