(CNN) — Major Hurricane Lee will continue to grow in size and slow down ahead of a crucial northward turn midweek, which will determine the extent and severity of its impact on the Northeast, New England, Bermuda and Canada.

Lee was a 120-mph, Category 3 hurricane on Monday morning, located well north of the Leeward Islands and Puerto Rico in the Atlantic Ocean. Its intensity could oscillate over the next couple of days as it stalls out before its turn to the north, but is expected to weaken as it does so.

The final track of the storm after it passes by Bermuda on Thursday or Friday remains highly uncertain because the slowdown is also delaying key forecast details. Exactly when, where and how fast Lee makes its northward turn will determine how close it tracks to the East Coast on its nearest approach over the weekend – details that could come more into focus as soon as Wednesday.

If Lee tracks farther to the west before its northward turn, areas north of the Carolinas – particularly eastern New England and Atlantic Canada – could be more at risk of rain, wind and coastal flooding. If the storm turns more abruptly, it would track more to the east and lessen the risk to the entire Eastern Seaboard.

Bermuda could be spared a direct hit, but may still experience strong winds and heavy rain as Lee tracks just to its west.

The exact track, even if off the coast of the US, will be extremely important because the size of Lee’s wind field will continue to grow as it moves north and weakens over cooler water. As of Monday morning, hurricane-force winds extended 75 miles from Lee’s center, up from 45 miles early Sunday. Tropical storm-force winds extended 185 miles from its core.

The storm’s large wind field means that even if Lee stays a couple hundred miles off the coast of New England, people along the coast could still experience strong winds, rain and coastal flooding. Larger storms could also displace more water and cause more coastal flooding issues.

Regardless of its final track, the storm will send big waves to a growing area of the East Coast throughout the week as it tracks northward off the coast. This will cause coastal erosion, dangerous surf and life-threatening rip currents at beaches.

Dangerous surf was already happening along the Florida coast and on many of the far eastern Caribbean islands as well as the British and US Virgin Islands, Puerto Rico, Hispanola, the Turks and Caicos, the Bahamas and Bermuda.

Rip currents have already killed 71 people in the US this year, preliminary National Weather Service data shows, including three people in New Jersey who died in rip currents kicked up in the wake of Hurricane Franklin last week.

Lee, which was a Category 1 storm Thursday, intensified with exceptional speed into rare Category 5 status as it moved west across the Atlantic, more than doubling its wind speeds to 165 mph in just a day.

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