Tropical Storm Rafael strengthening, heading toward Bermuda, forecasters say

MIAMI (CNN) - Tropical Storm Rafael churned in the central Atlantic early Monday as it approached hurricane strength, forecasters said.

Maximum sustained winds increased to 70 mph late Sunday, according to the National Hurricane Center in Miami. The storm was centered about 235 miles (380 km) north-northeast of San Juan, Puerto Rico, and was swirling north-northwest at 10 mph.

"Some additional strengthening is forecast ... and Rafael could become a hurricane on Monday," the hurricane center said.

A projection map shows Rafael headed toward Bermuda later this week.

Officials there issued a tropical storm watch Sunday and told residents that they expected the storm to affect the British territory on Tuesday.

While the National Hurricane Center predicted Rafael will stay well to the east of the Bahamas through Monday night, it did warn of life-threatening surf conditions and rip currents on the eastward-facing beaches of the Bahamas over the next few days.

Forecasters expect Rafael to leave between 4 to 8 inches of rain over the northern Leeward Islands, with some pockets getting as much as 12 inches.

"These rains could cause life-threatening flash floods and mudslides, especially in areas of mountainous terrain," the hurricane center said.

Rainfall amounts of 1 to 3 inches are possible in the Virgin Islands, Culebra and Vieques, forecasters said.

CNN's Chandler Friedman contributed to this report.