Water dripping from outdoor HE furnace vent
As isherwood notes, burning natural gas creates carbon dioxide and water vapor. Since high-efficiency furnaces try to draw as much heat as possible from the burned gasses, you're going to get water condensation, and that has to be dealt with explicitly.

As isherwood also notes, the combustion vent pipe should be sloped back to the furnace so that any condensate drains back into the furnace, and then into the furnace's condensate drain system (generally a pump into the sanitary sewer system). It sounds like the vent slope is wrong in your case, so that the condensate either accumulates in the pipe or drains outside. If it just drains outside then that seems like an annoyance at most; if it actually accumulates in the pipe then your furnace exhaust could be blocked.

Since you're in the northeast (as am I), with freezing winters, then this could get more interesting; you could get some serious furnace-cicles from your vent pipe, which may even block it in very cold weather.

In summary, none of this seems urgent or dire, but you should keep an eye on the vent outlet to see what the consequences are.

Edit: I checked condensing boiler installation manuals from Lochinvar, Bosch, Weil-McLean, Munchkin, Rinnai, Burnham, and Williamson-Thermoflo, and every manufacturer specified that the exhaust pipe must be pitched a minimum of 1/4 inch per foot back towards the boiler to allow drainage of condensate.