Joaquin actually was born of an upper-level low that sat nearly stationary for over a week and gradually built down to the surface and acquired tropical characteristics. Evidence of the upper-level low extends back to beyond September 20! In this figure, there are slices of infrared satellite images shown every 12 hours for a week, and you can spot the same feature at nearly the same location east of the Bahamas the entire time.
|Track forecasts from a variety of global and regional dynamical models and consensus from the 06Z guidance. (UWM)|
|Intensity forecasts from a variety of global and regional dynamical models, statistical-dynamical models, and consensus from the 06Z guidance. (UWM)|
Vertical wind shear will be fairly strong over Joaquin until Thursday or so, which will be a key day to see if it intensifies quickly or not... because once it starts interacting with the trough that is expected to come off the east coast, the shear will increase again.
However, and this is really important, if it begins to lose tropical characteristics as it heads north, that does not make it less dangerous should it make landfall. A Sandy-like scenario is not something I'd predict this far out, but it's also not completely impossible and is something to be aware of. There are a lot of unknowns to be resolved before being too concerned about that possibility.
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