Tropical Storm Erin has begun strengthening as it streaks west across the Atlantic and is on track to reach hurricane status as soon as Friday, prompting tropical storm watches in the northern Leeward Islands.

Erin’s sustained winds increased to 70 mph, just 4 mph shy of hurricane strength. The hurricane center said Erin should continue to strengthen through the weekend, when it should be moving near or north of the Leeward Islands, according to the official forecast path.

The National Hurricane Center (NHC) has warned that Tropical Storm Erin is expected to strengthen and could become a major hurricane over the weekend as it shifts just north of the northern Leeward Islands, raising the risk of flash floods, landslides and life-threatening sea swells.