It developed out of the interaction between a cold front and an upper level trough on October 10 located to the south of Bermuda, and quickly strengthened as an extratropical storm.

On Bermuda, winds from the precursor extratropical storm produced moderate damage, primarily to power lines and marine interests.

In Atlantic Canada, Tropical Storm Karen produced light winds and rain, but caused minimal damage.

Based on its organization, the system developed into Subtropical Storm One early on October 12 while located about 35 miles (56 km) south of Bermuda.

[1] Convection continued to develop, and organized into a ring around the eye as Karen reached its peak intensity of 80 mph (130 km/h) on October 14 while located about 400 miles (640 km) south of Halifax, Nova Scotia.

[1][3] Karen quickly weakened as it moved over cooler waters,[3] and late on October 14 it degenerated back into a tropical storm as it accelerated northward.

[4] Convection gradually decreased,[5] and Karen made landfall on southwestern Nova Scotia with winds of 45 mph (72 km/h) on October 15.

[1] Karen retained its tropical characteristics during and after making landfall, based on a research flight out of Halifax intended to study the early stages of extratropical transition.

[6] Under the influence of a mid-latitude system, the storm turned sharply to the northeast, and after losing the remaining of its convection it became extratropical shortly after landfall.

Continuing northward, the remnant low quickly weakened, and dissipated as it was absorbed by a larger extratropical storm over the Gulf of Saint Lawrence.

In addition, heavy rainfall warnings were issued for large portions of Nova Scotia including Halifax, southeastern New Brunswick, Fundy National Park, and Prince Edward Island.

Skewed to the left side of the transitioning storm,[6] the rainfall was beneficial for the drought-stricken areas of Nova Scotia and New Brunswick.