With winds of 60 mph (95 km/h) and strengthening, the subtropical storm initially drifted northeastward. On December 13, a ridge of high pressure to its north forced the storm southeastward, and the following day the storm turned to the south after an upper-level cold-core low developed over the system. A break in the ridge resulted in the storm turning to the northeast, with its forward motion accelerating to nearly 40 mph (65 km/h). After turning to the northwest on December 17, the high pressure system again halted its northward movement, leaving the storm drifting south-southeastward. Conditions favored further strengthening, and the subtropical storm reached 70 mph (115 km/h) winds on December 18. Satellite imagery estimated the storm attained hurricane status on December 19, and a day later ship near the center reported winds of 75 mph (120 km/h). Based on the wind report, as well as a minimum central pressure of 980 mbar and a well-defined eye, the storm was classified as Hurricane Lili while located 730 miles (1,180 km) east of Bermuda.