ECMWF goes west with Invest 92L; East Coast At Risk

Pre-reading notes: ECMWF did well with track of Hurricane Irene but did not do too well with strength in forecasts. We are using ECMWF only because we believe this is the more important model of the GFS/ECMWF comparison. This bulletin is for August 29.

The 12z ECMWF run has fled west with Invest 92L, posing a potentially serious threat to the East Coast yet again. While Hurricane Irene was a minor hurricane (below category 3) at landfall, this system, which would be called Katia, could pose a significant risk to the East Coast (EC) if this verifies.
The time period we are looking at today is the September 6-8 area, when 'Katia' could begin to approach the Florida region. Each image is 24 hours from the previous image.

September 6

So here is 'Katia' on September 6. She is storming NW towards the Florida area. If this were to verify, Katia would likely scrape up the Florida coast and probably come dangerously close to the OBX region again, possibly hitting New England by the time it all ends. However, there remains the potential of Katia going out to sea after the OBX hit instead of New England.

September 7

September 7 features Katia growing massively in size and strengthening as a result. The big question going around is how storms like this manage to sometimes go out to sea. Here's the thing. Another ridge (high pressure) is forecast to develop in the CONUS (continental US) and move eastward. There appears to be a trough of low pressure moving eastward. Depending on how strong or weak it is will determine the ultimate track. If the trough is stronger, the storm will go out to sea (OTS). If it is weaker, as the ECMWF has picked up on here, the storm will have a shot at an East Coast landfall. If you don't understand all of that, focus in on the italicized part.

September 8

At this point, Katia is a monster. She has grown exponentially and strengthened a deal more in a one day period. The ECMWF continues bringing up the storm NW towards the East Coast.

You might be asking 'Okay, so when does the decision making come on whether this trough will make the storm go out to sea or towards the US?' That is an excellent question. Comparing other models against the ECMWF, it looks like we cannot answer that right now, but it would come beyond 5 days from now, so a lot of model watching is to be done.