Tropical Storm Fiona is on the decline but may pave the way for a new storm — which may earn the name Gaston — which could become more menacing.

Fiona is still spinning in the central Atlantic, clashing with dry air and increasing wind shear. It is now forecast to weaken to a tropical depression by the end of the weekend.

Meanwhile, a potent easterly wave that left the African coast Tuesday is getting better organized and should have a clearer path to becoming something more powerful.


Although not even a tropical depression yet, the disturbance near the Cape Verde islands is heavily favored by models to develop and strengthen. Should it attain tropical storm strength, it would earn the name Gaston.

The “Cape Verde season” is just getting started, and the tropical cyclone conveyor belt between Africa and the Lesser Antilles can get preconditioned (moistened) by previous disturbances passing nearby — which may have succumbed to the relatively hostile early-season environment. Fiona turned northward fairly early, but it did help to sweep out dusty dry air in the 1,700-mile-long channel between Africa and about 45 degrees West longitude.

Enhanced satellite image over the eastern Atlantic, where the warm colors indicate the presence of a dry Saharan Air Layer. Fiona is toward the top, while the disturbance of interest (pre-Gaston??) is at the bottom. (UW-CIMSS)

The midlevel air between 45 and 70 degrees West is still on the dry side, but if the disturbance organizes fairly quickly and is not ripped apart from wind shear, it could remain isolated from that. Most models, though not all, forecast Gaston to form and become formidable.

The track projections for the system that may become Gaston, shown below, are from regional and global models and cover the next five days. As you can see, many place Gaston on a collision course with the Lesser Antilles.

Five-day forecast tracks from a suite of model guidance for 99L.

Models present a range of scenarios for the intensity of would-be Gaston. Some only strengthen the system modestly, but some significantly.

On the graph below, you can see the range of intensity predictions among the models — ranging from a tropical storm to a major Category 3 hurricane over the next several days. Models typically have a hard time predicting the intensity of weak, fledgling disturbances since they are very sensitive to minor changes.


So, will Gaston form in the coming few days? There is no way of knowing for certain, but the odds are good. Also, another over continental Africa is likely to be something to watch once it emerges in the Atlantic, and the name after Gaston is Hermine.