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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100th anniversary of the 1926 Great Miami Hurricane

The Great Miami Hurricane of 1926 made landfall in Miami on the morning of September 18, 1926.

I am publishing this post one month ahead of the anniversary to share some new wind speed maps I created, which I hope can be useful to the community as the centennial approaches.

Miami-Dade County has had 12 major hurricanes (Category 3+) pass within 20 miles in the past century. There were two in 1926, including the Great Miami Hurricane, then the others were in 1929, 1935, 1945, 1947, 1948, 1950 (King), 1960 (Donna), 1965 (Betsy), 1992 (Andrew), and 2005 (Wilma).  That's an average return period of 8.3 years, but clearly, they aren't bound to that average.  Four of the twelve occurred in just six years from 1945-1950. Luckily, there have been zero in the past 21 years.

Tracks of the 12 major hurricanes that passed within 20 miles of Miami-Dade County from 1926-2025.

But even with that infamous list of storms, the Great Miami Hurricane of 1926 keeps its place in history. If any of them were to occur this year, the Great Miami Hurricane would still rank as the most destructive and costly.  Some might wonder why 1992's Andrew doesn't top that list... it was very small and the extreme winds in the eyewall missed downtown Miami. The 1926 hurricane was also extremely intense, but much larger and the eyewall passed directly over Miami. In 2026, the impact from an identical hurricane would be unimaginable and unsurpassed.

Please peruse this webpage I created to showcase the new surface wind maps, and reach out to me with any questions you may have:

Great Miami Hurricane of 1926

One of the surface wind field maps available at https://bmcnoldy.earth.miami.edu/tropics/miami26/. Several storm parameters needed to be carefully estimated using what data are available. The decay of wind speed over land is intentionally smoothed, and modern urban areas in the land use dataset are handled to approximate what it may have been one century ago.

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Bertha bringing unsettled weather to northern Gulf coast

Shortly after my previous post, Invest 91L was upgraded to Tropical Depression Two, then late Monday night, it was upgraded to Tropical Storm Bertha... the second named storm of the season.

It has barely moved since it formed but is gradually oozing westward just off the Gulf coast. That slow motion will continue over the next several days as it scrapes along the coastline.  Tropical storm watches and warnings are in effect for the coastal Florida panhandle over to western Louisiana.  On the cone graphic below, remember the cone does NOT show where impacts will be experienced, only the likely area where the center of the storm will track. [Cone refresher]

As you can see in the satellite animation at the top of the post, the storm is extremely sheared, with the surface center exposed and the thunderstorm activity displaced to the south.  That significant vertical wind shear will keep the storm from intensifying much.

The only relatively minor impact will be storm surge of 2-4 feet along Mississippi and eastern Louisiana... the rain should not be a big problem because the bulk of the messy part of the storm will remain over the Gulf of Mexico.  The stronger side of the storm in terms of wind is also more over the Gulf and less over land, but the graphic below shows the probability and most likely arrival time of tropical storm force winds. Most places over land are under a 50% chance of seeing such winds.

Bertha is still a name from the original set of rotating lists... first used in 1984 and every six years since.  So this is its 8th time in use and will be certainly be around for a 9th time in 2032. [Storm naming and retiring refresher]

 

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