As the humorous NHC morning discussion said, the Don is dead, as Tropical Storm Don died quickly as it came ashore in south Texas. Don behaved pretty well and as the global models insisted and most of the tropical models, Don never really got its act together due to the dry environment in the NW Gulf of Mexico.
So Don is gone and now we set our sights on Invest91 in the central Atlantic. The NHC as of 8am now gives this wave a 70% chance of development in the next 48 hours. Morning satellite images show a large wave with some hints of a circulation in the visible satellite imagery. IR satellite shows decent convection but certainly not very strong or well organized yet. This seems to be one of those systems that takes some time to initially organize, but since it is rather large once it does it could intensify rather quickly. I think that will likely be upgraded to a depression by tonight or within in the next 24 hours and likely Emily within 48 hours.
Invest91 is being steered slightly north of west by a strong upper ridge to its north and northeast. The system will approach a weakness between this ridge and a strong ridge over the south-central US early next week and will begin moving a bit more WNW which will take it towards the central and/or northern Islands it appears by Monday night and Tuesday morning. The models have slowed the timing of this down but almost all show this as a threat to the central and northern Islands and Virgin Islands except for the HWRF which is a little northeast of the Islands. After future Emily affects the Islands it appears it will either target Puerto Rico and Hispaniola or move just north of those islands possibly near the Bahamas. The global models show this weakness lifting out but an upper low being left behind off the southeast coast. How strong this upper low is or if it is real is not clear, the 6z GFS particularly shows this. They global models also show another trough quickly diving in by 5-8 days which would likely catch future Emily and turn her out to sea.
What we are seeing are the models showing a fundamental change to the synoptic weather pattern as we head into August. So far this summer the predominant pattern has featured a trough out west, and a ridge centered over the Midwest with a narrow trough off the east coast. The pattern we are heading towards will feature the trough being further west, possibly over the northeast or Great Lakes. This could lead to a pattern that any storm that approaches the southeast coast will have a good chance of recurving thanks to this trough with storms that sneak into the Caribbean likely heading for Mexico. This is just speculation but this is what the pattern is shaping up to be through mid-August, if the models are correct. Of course if this is a stable pattern there will be periods of waxing/waning which would allow for storms to have an opportunity to take a different path during those periods.
As far as intensity goes I think Invest91 will be a depression within 24hours, Emily within 48 hours, and possibly a hurricane in 72-96 hours possibly as the storm is impacting the Islands. The intensity guidance shows the storm peaking in about 96 hours around 75-90 knots or in the category 2 hurricane range. As Emily approaches the weakness in 3-4 days shear could increase a little, but probably not enough to weaken the storm too much but perhaps halt the strengthening. Interaction with land could also affect the storm. Once Emily pulls away from the Islands by the middle of next week assuming she misses Hispaniola she could strengthen again.
In summary, I think Invest91 will be Emily and poses the risk to hit the northern and central Islands possibly as a hurricane. Beyond that as of now the models are showing a pattern that would seem to favor a re-curve off the southeast coast, but that could change. We will see.