Hi guys, here's an email I sent out to the t-storm list folks... thought I'd share it here.
The GFS operational model is indicating a potential eastern MDR-type genesis event coming up in 2-3 days. This shows up pretty nicely in maps of GFS rainfall/925 hPa vorticity/200 mb wind maps:
What's interesting is the GFS op is indicating that convection will fire up just off the coast of West Africa between 06-12Z tomorrow, forming an area of low-level cyclonic vorticity over the ocean. This times well with the coherent diurnal cycle of convection at the West Africa coast, where convection is most prominent over the ocean, straddling the coast of West Africa between 06-12Z, with a minimum of convection over the coastal region.
The GFS then fires up afternoon convection downstream of the Guinea Highlands region, or more specifically the Fouta Djallon's, between 15-21Z, also developing a low-level cyclonic relative vorticity signature. At this time, the model keeps the convection active over the ocean. Between 06-12Z July 10, the GFS suggests that the vorticity centers will merge just off the coast of West Africa, and what looks to be a depression or tropical storm spins up soon after.
Alan Brammer's dprog(dt) maps indicates that there's a moderate-strong African easterly wave propagating across West Africa and out over the Atlantic during this interaction: http://www.atmos.alb.../abrammer/maps/
This also times well with a strong MJO event currently over the Indian Ocean (http://www.atmos.alb...m.MJO.5S-5N.png
; VP200 anomalies shaded, MJO filtered VP200 anomalies contoured where dashed = upper-level divergent phase of the MJO), suggestive that the Atlantic is in an intraseasonal state favorable for increased African easterly wave activity and also developing tropical cyclones.
Now the only thing that worries me is there is a 2 standard deviation convectively suppressed atmospheric Kelvin wave pushing over the western MDR. Currently, the eastern Atlantic/West Africa is still in a state relative to the suppressed Kelvin wave where the upper-level easterly, low-level westerly wind phase will be impacting the region for the upcoming few days... http://www.atmos.alb...c_analyses.html
This relative Kelvin wave location, in conjunction to the robust AEW pushing across Africa and the state of the MJO, may all act together to spin up an east Atlantic storm... however there will only be a 2-3 day window. If the GFS verifies, it will be a very big "win" in the modelling community to correctly represent the current, complex state of convection in the tropics.
That being said, I do have some concerns with the forecast beyond 2-3 days, as the GFS has been dropping the ball with propagating the strong suppressed Kelvin wave phase eastward once in forecast mode:
For the past week, the model has been holding the convectively active phase of the MJO/CCKW over Africa instead of continuing it off to the east. You can see this clearly in the 1-week MJO phase-space diagram verification maps that the CPC puts out: http://www.cpc.ncep....lidphase-W1.gif
I've noticed, and I'm sure others have as well, that land masses such as S. America, Africa, and the Maritime Continent, tends to act as a barrier for the eastward propagation of the MJO/CCKWs. It appears that this is happening again, holding the negative VP200 anomaly stationary over Africa instead of bringing that suppressed Kelvin wave across the region (http://www.atmos.alb...om.30.5S-5N.gif
Nevertheless, I will be watching this case quite closely as it has a lot of similarities to the 2006 Tropical Storm Debby Case (with the main exception that instead of an upstream suppressed Kelvin wave phase, it was the convectively active phase of a CCKW passing).