Summary of active tropical disturbances in the Atlantic Ocean and model track projections. (Brian McNoldy)

We’ve entered prime time for hurricane season and are watching three areas of disturbed weather in the tropical Atlantic Ocean. Of these three systems, one has some potential to affect the U.S. coast — though it’s not a sure thing.

The system of greatest interest, is identified as “99L.” It is located 650 miles east of the Lesser Antilles, and we’ve been watching it since late last week. It has not been able to overcome the influence of dry air, and is still not even a tropical depression.


The majority of models do not forecast 99L to substantially strengthen, but the few that do bring it close to the Florida peninsula and Southeast U.S. coast early next week (7 to 10 days from now). At this point, it is not anything to be immediately concerned about, but certainly worth monitoring.


Track forecasts from a variety of global and regional models. “TCLP” is not a model, but is “climatology and persistence”. (UAlbany)

The westernmost of the three storms (west to east in the Atlantic basin), Fiona, is now a tropical depression centered about 650 miles southeast of Bermuda. It formed four days ago and weakened some this weekend. It is not forecast to strengthen, but it may not completely dissipate either in the next few days. It could make for a breezy weekend in Bermuda.


Surface winds (streamlines) and precipitable water (shaded background) across the tropical Atlantic. (earth.nullschool.net)

The easternmost tropical wave, or “90L,” is south of Cabo Verde and is much better organized than the previous waves to pass through the general area. It is very close to becoming a tropical depression, and will likely earn the name Gaston before 99L does. (If 99L is subsequently named, it will be called Hermine.)


Models agree this system will track out to sea, much like Fiona, turning to the north over the central Atlantic. But, unlike Fiona, model guidance indicates that this has a decent chance of becoming a fairly strong hurricane.


Tracks from the 20 GFS ensemble members, colored by intensity. The thick black line is the average of them. (tropicaltidbits.com)

Atlantic hurricane season to date

So far, six named storms have formed (including Fiona), two hurricanes (Alex and Earl), and no major hurricanes (Category 3 or higher). This compares with an average of four named storms, one hurricane, and 0 major hurricanes through this date — though these statistics rapidly ramp up in the coming weeks.

In terms of Accumulated Cyclone Energy, or ACE — a measure of not only the strength but also the duration of all storms that have developed — the season has produced just two-thirds of the average energy year-to-date. But that could all change quickly with a couple simultaneous hurricanes!


Accumulated ACE for 2016 (yellow) and for the 1981-2010 climatology (purple).