• Bryan Norcross

Two systems to watch in the Atlantic as Danny dies over the Southeast

The two tropical disturbances we’ve been following are continuing their treks over the open ocean. Neither are expected to develop, if they ever do, right away. But both bear watching.



Tropical Storm Danny spun up just off the Carolina and Georgia coast yesterday afternoon, and quickly moved inland. The Remnants of Danny are dying out over the Southeast, but still dumping heavy rain.


The upper-level part of the system has become disconnected from the lower circulation, which is what gets tracked on a map. So while the National Hurricane Center is locating the center over Georgia, the heaviest rain has already moved into Alabama. There is a threat of isolated flooding today from the tropical downpours.


Danny’s sudden strengthening yesterday was a bit of a surprise, but not unheard of. The system moved over the Gulf Stream, which gave it some extra energy. The upper-level winds apparently let up just enough to allow it to develop. But probably most importantly, the interaction with the coastline enhanced the circulation.


When small-diameter systems encounter land, the wind blowing off the ocean gets deflected left. This phenomenon called coastal convergence can have the effect of shrinking the diameter of the rotation of the air. Like an ice skater speeds up by pulling in her arms, the winds go faster, and in this case, we got a short-lived tropical storm.



Out in the tropical Atlantic, Tropical Disturbance #1 is still embedded in lots of Saharan dust with moderately hostile upper-level winds. The National Hurricane Center is giving it a low-medium chance of becoming at least a tropical depression later this week. In any case, it likely will reach the eastern Caribbean islands late tomorrow with some gusty winds and squalls.


The long-range computer forecast models don’t show any significant development, but we’ll keep an eye on it because of where it’s located in the Atlantic.


To its southeast is Tropical Disturbance #2, which consolidated out of the broad area of disturbed weather off the coast of Africa. This system is on a more southerly track than Disturbance #1, so it’s missing some of the Saharan Dust.


The National Hurricane Center is only giving this disturbance a slight chance of developing in the next 5 days, although some long-range computer forecast models show it organizing and moving through the Caribbean.


Remember that ALL forecasts for undeveloped or just-developing systems are highly uncertain, so we don’t really pay much attention to computer models for systems like this. They are prone to bounce around with different forecasts morning and night and between the various models. That’s the case here.


The point is, don’t pay attention to any single-model map you see on social media. They don’t mean anything at this point.


Nothing else seems imminent in the Atlantic, although the large area of disturbed weather over and near Africa persists, so of course we’ll keep an eye on that for developments.