Tropical Depression 5 forms, Dolly dissipates

Since my previous post last Thursday, the tropical Atlantic has been fairly quiet.  Tropical Storm Dolly dissipated into an open wave on Friday morning, just one day after it formed. There's a very slim chance that it redevelops this weekend... more on that at the end. Elsewhere, a disturbance in the northwestern Gulf of Mexico organized into Tropical Depression 5 on Monday afternoon. If it reaches tropical storm intensity, the next name is Edouard.

At 5pm Eastern, TD5 is located just off the central Louisiana coast and is forecast to track northwest toward the Houston area on Tuesday as it slowly intensifies. 

Even if it does briefly reach tropical storm intensity on Tuesday, it has little time before landfall, so flooding rain will be the primary threat. Fortunately, the depression is very small, so impacts such as storm surge and heavy rain are also going to be fairly limited in scope.

The remnants of Tropical Storm Dolly are near the northern coast of Hispaniola and barely discernible. The odds of regeneration have decreased drastically in the past day, but the disturbance will travel toward the Bahamas and then Florida the rest of the week, bringing heavy rain with it.

Looking at where the season stands relative to climatology as we wrap up August, the Accumulated Cyclone Energy is 10% of average. In terms of storm counts, there have been 4 named storms, 0 hurricanes, and 0 major hurricanes. The average by now is 6, 2, and 1.  By any measure, this is an incredibly slow start to a season, and with a strong El Niño developing, Atlantic activity should remain suppressed for the remainder of the season. However, "suppressed" doesn't mean zero... just less than average. We are in the heart of the season and need to remain vigilant. 

In terms of ACE, the hurricane seasons since 1950 that had a slower start than 2026 were 2022, 1988, 1984, 1977, and 1967. 2022 and 1988 were during a La Niña, 1984 was fairly neutral but headed into La Niña. 1977 was a weak El Niño, and 1967 was neutral. So 2026 is the only one among these that is a strong El Niño.

If you're curious if there has ever been a season without any hurricanes, the answer is yes, at least that we know of. In the historical record which extends back to 1851, the only years with no hurricanes were 1914 and 1907.  Inspecting their ENSO phases, 1914 was a strong El Niño and 1907 was neutral.

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Tropical Storm Dolly forms in eastern Atlantic

The easterly wave I mentioned in Tuesday's post (Invest 96L) has been upgraded to Tropical Storm Dolly... the fourth named storm of the season.  Zooming in on the storm with some enhanced satellite imagery, we can see the mostly-exposed surface circulation and the thunderstorm activity displaced to the south of the center... and indication of some dry air and northerly wind shear.

The forecast from the National Hurricane Center as of 11am Eastern maintains it as a tropical storm for the next three days then dissipates.  Model guidance supports this with few exceptions, so the chance of this being a serious threat to the Leeward Islands and eastern Greater Antilles this weekend is very slim.

Here's where looking at ensembles is useful... to explore the spread of potential outcomes in the coming week+. Among the American GFS ensemble, the European ECMWF ensemble, and the Google DeepMind ensemble, you'd be hard-pressed to find any support for this to survive the next few days. Even the 1000-member DeepMind ensemble has zero members surviving much beyond the Leeward Islands. So the NHC forecast comes with a lot of confidence.

As I mentioned in the previous post, the name Dolly has been in circulation in the modern naming scheme since 1996 (it replaced Diana which was retired after the 1990 season). So, this is the 6th Dolly: 1996, 2002, 2008, 2014, 2020, 2026.  It's hard to ignore the connection with Dolly Parton's recent passing this year, but my connection to that list is seeing the real Dolly in concert in August 2008 (the 3rd tropical Dolly).

The Accumulated Cyclone Energy (ACE) is at about 12% of average for the date, and the forecasts don't show Dolly contributing too much to the tally. However, just because it's a slow season, we are entering the heart of it and even a single strong hurricane making landfall somewhere can make it a really bad season for that area.

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Deep tropics waking up as we enter the heart of hurricane season

Like clockwork, our eyes are drawn to an active disturbance near Cabo Verde. "Cabo Verde season", in fact, gets its name for the constant march of easterly waves that exit the African coast and begin their westward trek across the deep tropics... some of which become long-track tropical cyclones -- most prolifically from mid-August through early October.

Invest 96L is currently centered about 200 miles south of Cabo Verde and has very good odds of becoming the next named storm of the season, Dolly. Models are in good agreement on a west-northwest track for the next 4-5 days, then there is some notable divergence. The forecasts with weaker intensities tend to stay on a west-northwest track, bringing it near the northern Leeward Islands by about Sunday, while the forecasts with stronger intensities tend to start turning it toward the north around that time.

If it takes the more northern route, Bermuda should be on alert late next week. However, even if it does take the more southern route, conditions could become more favorable for development as it passes north of Puerto Rico and Hispaniola, and places like the Bahamas, Cuba, and Florida should be watching this very closely for mid-late next week. The skillful Google DeepMind ensemble has been showing that scenario, though it's too far out now to be too concerned.

The Google DeepMind ensemble, showing forecast tracks from what is currently Invest 96L. All members fail to develop it until this weekend, then several of them do near the Bahamas around next Wednesday. The positions of the low pressure centers shown here are on Thursday evening (September 3). The colored background image is the sea surface temperature.

Later this week, this could become the first hurricane of the season. Over the past five decades, the median date of first hurricane formation is August 6. In recent years, we have had some much later first hurricanes: September 2 (2022), September 11 (2013), and September 11 (2002), so this is far from record late in the season.

Elsewhere, Invest 95L is located northeast of Bermuda and also has a chance of becoming a named storm, though its window for development is not very long. After Dolly, the next name is Edouard. Both Dolly and Edouard have been on the rotating list of names since 1996 (Dolly since 1996 and Edouard since 1984).

If it does manage to develop, it would remain fairly weak and track toward the north-central Atlantic... perhaps becoming relevant to the British Isles in 5 days or so as an extratropical cyclone.

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