Hurricane Danny is the first hurricane of the Atlantic season and of course right on schedule we have already seen social media posts making broad statements about the threat to the U.S. blah blah blah so Joestradamus thought this would be a very good time to illustrate what the atmosphere has to look like for a hurricane to come up the east coast.
First off, its not an easy thing for it to happen. Essentially everything has to be perfect in terms of the flow aloft. The maps below of the upper air flow will give you an idea of what it needs to look like
What i have done is overly the the required flow you need to see (or something close to this) over last night’s run of the European. This is for 6 days from now and assuming the model forecast is correct you can see the difference between what is being shown by the model and what you need to have.
The hurricane track (in theory) is shown by the green line. If the upper air flow shown in black were correct the hurricane would be picked up by that trough and move up the coast. The other variable is that the trough has to hold position as the hurricane recurves. So the timing of all this would have to be nothing short of perfect in order for a hurricane to track up the east coast and hit the northeast.
This leads us to another issue in that the atmosphere is not a static thing. It is changing over time (most of the time). Last night’s European in the long range WOULD NOT FAVOR a storm moving up the coast.
Now we have the European out to day 8 and you can see the forecast flow is west southwest along and off the east coast. So let’s say a hurricane were to be moving around the western edge of the upper high, it would recurve to the northeast and away from the coast. While there is troughing in the east, the trough is too broad. It is not sharp as I illustrated above. So this is not the kind of upper air pattern you would see for an east cast hurricane threat.
Now lets go out to day 10. The trough in the east is there but again it is still rather broad. Again with this look there is no northeast coast threat possible. Now from a purely speculative point the ridge might be strong enough to bring the hurricane close to say the Bahamas or off the Florida coast. But that is purely speculative and we are talking here about the northeast and not the southeast. Even the southeast coast of the US might not be threatened by this because of the broadness of the trough. This is one model view of the atmosphere. Now lets take a look at another.
The GFS look is completely different from the European. It pulls the trough off the east coast and builds a blow torch ridge from the Western Gulf of Mexico and forces the jet stream up into the northeast and Canada. It drives a deep trough off the west coast and there is no ridge in the west. This look would mean no recurvature if the ridge off the east coast is strong enough and drive any tropical system further west. But again this is not the look you would see for an east coast threat. Longer range the GFS would mean a late August early September very warm pattern while the European would be much cooler and probably below normal temps. Both would mean no hurricane threat for the northeast. These 2 model solutions could not be more different in terms of the long range outcome but they both would mean the same thing regarding hurricane threats for the northeast. Assuming either look is correct, it can’t happen.