Summary
- Where it is now: The tropical wave is over the tropical coast of western Africa, in the vicinity of Guinea-Bissau, Guinea, The Gambia, and Senegal. It has not yet been marked by the Tropical Analysis & Forecast Branch (TAFB), but likely will be soon once it moves offshore. The tropical wave currently exhibits modest convective activity and is located within a bubble of locally higher total precipitable water values that extends southwestward offshore along a monsoon trough.
- Where it will be: The wave is expected to move off the West African coast later today and should be completely offshore by West African sunrise tomorrow. The disturbance will likely remain entangled within a monsoon trough during at least its first few days offshore, and will take some time to consolidate (if it does at all) as it tracks west. During this time, the wave is expected to sweep in vorticity from the surrounding monsoon trough; you can see one particular vorticity maximum at bottom-left in the image below that will likely be absorbed in some form by the tropical wave. The precise position of any resulting system will depend on where the wave consolidates, and models notoriously have a difficult time accurately depicting the evolution of tropical waves that have not left the African coast. That said, the vorticity maximum associated with the wave is expected to remain around 10–13°N over the next few days, reaching roughly 40°W sometime on Monday. Models are in decent agreement in a mid-level trough / frontal zone dipping down to around 30N over the central Atlantic towards the end of the week (EPS, GEFS), but whether this has significant implications on the storm's future track depends largely on the storm's intensity, assuming it develops at all. The disturbance may reach 60°W (roughly the longitude of the Leeward Islands) sometime between Thursday and next week.
- Model support: Not all of the deterministic guidance shows tropical cyclogenesis, though both the GFS and ECMWF show a tropical cyclone developing before the wave reaches the Lesser Antilles. Many of the EPS ensemble members depict the development of a low-pressure area tracking towards the Lesser Antilles, with a varying range of intensities ranging from disturbance to tropical depression to even low-end hurricane. The GEFS members also depict a generally weak disturbance taking similar, slightly north-of-west trajectories potentially towards the Lesser Antilles.
- What to watch for: While it is enticing to look at specific model depictions of the tropical wave developing into a fully-fledged tropical cyclone or even hurricane, as with any new tropical wave the main thing to watch is how convection develops around the wave, whether or not it can consolidate vorticity, and whether or not it can detach from the monsoon trough / ITCZ. Answers to those questions will become more apparent over the coming days.
Composite of total precipitable water overlaid on visible satellite imagery with surface observations valid ~12/13 UTC June 15. Source: SSEC RealEarth
And, per the latest NHC Tropical Weather Outlook:
Forecaster Bucci at the National Hurricane Center (800 AM EDT Thu Jun 15 2023) wrote:1. Eastern Tropical Atlantic:
A tropical wave is forecast to move off the west coast of Africa later today and early Friday. Environmental conditions are expected to be conducive for gradual development of this system while it moves generally westward to west-northwestward at 15 to 20 mph across the eastern and central tropical Atlantic during the early to middle part of next week.
* Formation chance through 48 hours...low...near 0 percent.
* Formation chance through 7 days...low...20 percent.
