Many people have been obssessing about 99L, the GOM frontal disturbance, and the remnants of Chantal (extratropical transition). The recent demise of 99L led to "dead" pronouncements. 99L is an ill system; but if it fizzles, I think the real action will begin to commence shortly - I see several promising systems. We should not overlook the large changes across the basin. I think the transition to a favorable regime is assured - the upper-air pattern indicates a conducive environment will enhance activity over the next few weeks. The climatological upward swing will likely occur over the next several days. It may occur sooner than we think...
Firstly, the strong 500 mbar Azores ridge has weakened. Strong easterlies have weakened - favorable convective parameters have materialized. The recent mid-level air mass has been extremely hostile to MDR/Cape Verde development - the strong SAL capped convection. Recently, that has changed. The dry air has moderated amid a low-level surge of moisture from the African continent. The SAL's aerial coverage is slowly diminishing. It is clearly visible in conventional imagery. Note the favorable gap between 21N and the equator. Low-level convergence is extremely favorable across the tropical Atlantic Ocean - the African easterly jet has enabled vorticity across the area.
Secondly, the ITCZ has lifted northward as the ridge weakened. Several impressive waves have been moving westward across the continent during recent months. Currently, I can count THREE (possibly four) well-defined wave axes over the interior of Africa. The environment is good across portions of the basin. A favorable subtropical upper high should provide good diffluence between 20W and 50W. Heat content is sufficient for organization. I'll highlight several areas.
1) The wave near 40W and 10N should garner observations. A weak anticyclone is located in the vicinity. Satellite observations suggest a slow decrease of wind shear. Critical mid-level moisture has intruded into the area - that trend would indicate an increasingly conducive environment for slow development. The environment is improving further west, too. Its chances are more significant than 99L, and recent trends indicate moisture may be increasing over the eastern Caribbean. This is the one to watch for development within the next few days.
2) There is a great wave over extreme western Africa. Convection has maintained itself over water ahead of the axis - the curvature and mid-level rotation is extremely articulate. Observations suggest a possible low forming near 12N. A sfc low may form as the axis approaches the coastline. SAL is lower; I would watch this system. The large expanse of convection could provide a bountiful source of moisture. Conditions are conducive ahead of the wave, so it should receive attention. It could influence another wave to the west, too.
3) Another west African wave carries a good signature. It should be monitored as it follows the first wave.
What do you think?
