Tropical Storm Erika has now formed in the Atlantic. The system only needed a closed low level circulation all day long, and once it formed the NHC upgraded to a Tropical Storm at 5 pm. Currently, as of the 8 pm Advisory, the storm has winds sustained at 50 mph, but the convection has increased dramatically in the last few hours, so I wouldn't be surprised to see the winds go up at the next update. The low level circulation is currently outrunning the convection itself, but the last burst was much closer to the center than before. The system is still fighting dry air, and before the dry air can move out..and before the shear off to the northwest weakens, this system will have difficulty strengthening significantly. A weak hurricane could be possible in the next 72 hours if convection continues to pulse up like it has.
The two big questions are if the system can hold on and not pull a Danny...and where is it headed? Currently I think the main issue is the dry air, and this should become less of an issue as the system pulls northwest slowly. The 8pm advisory actually puts Erika as nearly stationary. This is likely because a new circulation is forming closer to the newest burst of convection, which is common in developing cyclones. This would actually cause some retrogression of the circulation back east...but only for a short time. I believe now that Erika has something going for it that the system will hold together and will be something to deal with in the near and long term future.
Currently there is a trough situated through the central Caribbean into the Bahamas, but this should move off to the west and only continue to ventilate Erika...as long as the low level circulation doesn't outrun the convection. If that occurs, then Erika might become completely sheared by this trough and fall apart...but I don't think that is the likely solution at this time. Erika will move northwest to just east of the Bahamas in the next 3-6 days. At this point Erika will likely be a moderate to strong Tropical Storm or weak Hurricane....with the current shear forecast. A boundary sagging along the east coast currently should begin to pull Erika north....however a building ridge of high pressure will come in right behind this boundary to the north holding Erika from pulling out all together....or at least that is what I see happening at this time.
Then the question will be how strong is this ridge? Will it hold Erika south off of the east coast, pull slightly east and then push Erika west towards the US? Or will Erika be strong enough to find any weakness...or develop a weakness, to move north and out to sea? Currently the European model forecasts a pull off to the northeast and out to sea while every other model builds the ridge in and pulls and stalls it out. The GFS never really develops the system that strongly and actually even moves it into the Gulf! There are a wide range of possibilities at this time, but knowing the European's consistency I wouldn't be surprised if it were right. Currently I think it is moving the system too fast, building in the ridge right behind Erika...which would allow it to sneak out. I think Erika won't move northwest fast enough to get to the weakness before the ridge builds in....which could be a bad scenario for the east coast.
PS: Jimena continues to move north towards the Baha and will make landfall along the central coast of the Peninsula as a Major Hurricane. The worst of the weather will miss Cabo, so that's good. The moisture from Jimena will move northeast into the US southwest and connect up with a frontal system moving in from the northwest in the northern and central Rockies and Plains.
