Uncertainties remain about the weekend East Coast low

Even though Faux weather channel is hyping this like it's Sandy's unnamed sibling, the low (as of this moment) has not yet developed.

National Weather Service https://www.weather.gov/
offices are issuing warnings and advisories as a precaution, but the discussions reveal uncertainties about the low's development and path.

Some examples for north of SC:

Wakefield (near Richmond VA):

(snip)
A coastal low is still expected to impact the region from later
Saturday into at least Sunday. However, a good deal of forecast
complexities remain. There is good agreement among the model
guidance that the aforementioned low that develops offshore of GA/FL
later today will slowly lift north toward the NC/SC coast Saturday.
Beyond that time, there remains larger-than-normal divergence across
the deterministic and ensemble guidance. There are differences on
both the track and evolution of the low, as well as the strength. In
general, the GFS/GEFS suite continues to advertise a more well-
defined low that tracks near or just offshore of the VA/NC coasts
Saturday night into Sunday. The EPS/ECMWF suite shows a weaker, less-
defined, and more sprawling low that initially remains to our S
Sunday, with a secondary low eventually becoming the dominant
feature offshore the northern Mid-Atlantic and southern New England
coasts by Monday. The Canadian and NAM also track the low northward
near our coastline, but they are a bit more offshore than the GFS.
It will be interesting to see how CAMs handle and depict this low as
we get closer to the event. In fact, some of the currently available
CAMs show some potential for mesoscale enhancements to the low
strength and winds/rain.
(snip)

Mount Holly (Philadelphia):
(snip)
What has changed: There have been no significant changes to the
forecast or messaging for the storm with this update. There
still remains a fair amount of certainty regarding the details
of the evolution of the coastal storm and its ultimate degree of
impacts. There are still 2 potential solutions, which are most
evident in the differences between the 00Z GFS and ECMWF model
runs. A stronger storm that tracks closer to the coast will
result in much more severe impacts (similar to the 00Z GFS
solution). A somewhat weaker storm that tracks farther offshore
will result in less severe, but still potentially significant
impacts to the immediate coast. Guidance will likely continue to
struggle and vary from run to run with this system until it
actually forms a well defined low pressure center sometime
Saturday or Saturday night. All previously issued watches remain
in effect at this time due to the continued uncertainty in
timing, severity, and inland extent of impacts.
(snip)

Upton (NYC):
(snip)
Developing low pressure associated with a southern stream
shortwave will slowly track northward along the southeast coast
Saturday night and then along the Middle Atlantic coast on
Sunday. Large high pressure will remain over northern New
England and the Canadian Maritimes. A northern stream shortwave
will settle over the northeast by Sunday. These two systems will
interact with another, ultimately phasing into one trough
sometime late Sunday into Sunday night.

These interactions are difficult for the modeling to handle and
lead to some uncertainties with the track and intensity of the
surface low. An example of this can be seen with the 00z ECMWF
and ECMWF-AIFS, which show a faster northern stream that does
not phase into the southern stream until late Sunday night into
Monday. There even hints at this in the latest ensembles for
both modeling systems. This scenario would let the coastal low
to the south remain elongated and further away on Sunday before
getting captured with the phase and pushed back towards the
coast on Monday. This would delay the most significant impacts
till Sunday night and Monday. The overall model ensemble
consensus does not agree with this scenario, but it does
illustrate the complexity of the pattern and why uncertainty is
quite high despite this event occurring in 3-4 days.
(snip)