Remember, pressure is relative when it comes to wind speed. For a tropical storm -- not a hurricane -- the wind field balance is going to have some contribution from the environmental pressure gradient. Pressures around the storm are relatively high, helping to contribute to the strong winds. I believe that the surface winds may not quite be 70mph (picking nits here), but they aren't 50mph either. The NHC and the hurricane hunters know what they are doing out there...

A few years ago, we had a tropical storm with a pressure near/over 1020mb, embedded within a region of higher pressures (~1040mb). While most hurricanes have pressures under 990mb, you can see them with pressures in the 990-1000mb range as well (admittedly rare). Franklin's likely not a hurricane, but it's trying to get there.