Well Irene certainly was weaker than I and most forecast it to be as it passed through the Outer Banks and northeast US. The pressure-wind relationship did not work well as Irene had a central pressure more representative of a category 3 hurricane not a category 1 storm. It still brought damage and will likely end up a costly storm, but it looks like the worst case was avoided. Jose brushed Bermuda and is dissipating so I will not discuss him.
This system looks to be a classic long tracking Cape Verde Atlantic cyclone that has a great chance to become a major hurricane. The system is at a far south latitude down around 9.5N and at the moment not a strong system. The SHIPS guidance is currently showing around 20 knots of easterly shear over the system which should weaken in the next 24 hours. TD #12 will likely strengthen into Tropical Storm Katia in the next 12-24 hours and then likely strengthen at a more rapid pace as we approach the middle of the week. Both the SHIPS and LGEM intensity guidance show a hurricane by Wednesday morning and a major hurricane by Thursday. I think TD 12 is Katia in the next 12-24 hours and a hurricane in 48-72 hours and likely a major by this weekend.
The system is at a far south latitude and as you can see by the attached analog graphic, many that have formed at this far south of a latitude have ended up striking or at least threatening the US. That is obvious no guarantee of anything though, just a frame of reference. Katia will be steered just north of west the next 5 days as a subtropical ridge to her north keeps the storm on this track.
As the system approaches the 50-60W longitude this weekend the models forecast a cut off low with an associated trough just off the east coast. This will weaken the western periphery of the subtropical ridge and Katia could begin to move more towards the WNW or NW. It is interesting to note that the operational 12z GFS is further north and slower than many of the ensemble members. The GFS recurves the system near 65W with a threat to Bermuda. The 12z GFS Ensemble mean though is much further west and faster and most members are looking threatening to the southeast coast in about 10-12 days. The new 12z ECMWF is further west and quicker than the 00z run in fact it is very threatening at day 10 with a strong hurricane, a western Atlantic ridge, and a cut off low over Florida. One thing we will have to watch in future model cycles is a splitting trough and a leftover cutoff low in the southeast. This is usually the catalyst in getting a southeast landfalling hurricane like Hugo or Fran.
The overall pattern looks to favor a persistent trough in the eastern half of the US so a re-curve is certainly possible just of the US coast. However, it is way too early to be confidence at all in how the timing and depth of the troughs will materialize. There is a higher change in my opinion that this re-curves than at this time when we were looking at Irene. But there is a chance it could threaten the US in about 12-14 days, so stay tuned.
A tropical wave in the western and central Caribbean is forecast to move into the Gulf this week. Some models have hinted at this area camping out in the Gulf and slowly developing. The 12z GFS and ECMWF have a tropical storm off of Galveston by late this week. This is a possibility and will have to be watched. The models show little movement to this system as it sits off the Texas coast and then edges inland around Labor Day. It will be tricky with several troughs moving across the Midwest and Northeast, if the system is far enough east and north and could get nudged north by one of these if not, it will likely move into Texas early next week.
A strong wave is also set to emerge off the African coast tomorrow and global models also show some development with this system. It is the heart of Cape Verde season so all these waves have to be watched for development.