MIAMI, FL (CNN) — It was a picture perfect start to the Memorial Day weekend for beachgoers basking in sunny skies from northeastern Florida to South Carolina -- but it won't last long.
They can thank subtropical storm Beryl, which gained strength Saturday evening and threatened to dump several inches of rain and bring heavy winds just in time to put a damper on a part of the long holiday weekend.
Even before a drop of precipitation had fallen ashore, Beryl already rustled up ocean water and prompted "red flags" -- warning people to stay out of the surf -- around the region Saturday. The National Weather Service reported at least 20 people were rescued off Tybee Island, Georgia, located 15 miles east of Savannah, by 12:20 p.m. due to rip currents.
After being stalled in the western Atlantic Ocean earlier in the day, Beryl was churning southwest at a rate of 6 mph, according to an 8 p.m. ET National Hurricane Center advisory. It was then centered about 220 miles southeast of Charleston, South Carolina, and 290 miles east of Jacksonville, Florida.
Beryl got stronger over the course of Saturday, boasting maximum sustained winds of 50 mph and even stronger gusts by evening.
The storm is forecast to maintain that strength with "little change" expected as it turns toward the west by late Sunday. At that point, its center should be over land in portions of the U.S. Southeast, the Miami-based agency said.
The prime sandcastle-making and tanning conditions that many experienced Saturday from St. Augustine, Florida, up the Atlantic Coast to Hilton Head Island, South Carolina -- where high temperatures in the high 80s and low 90s and sunny skies were the rule --could change drastically by Saturday night and more likely into Sunday and Monday.
The National Weather Service is forecasting a good chance of rain and possible tropical storm conditions in places such as Jacksonville, Florida, through the rest of the long weekend.
A tropical storm warning -- indicating that, beside rains, winds stronger than 39 mph are expected to strike within 36 hours -- now is in effect for a large swath of coast from the border of Volusia and Brevard counties in Florida up to Edisto Beach, South Carolina. There is a less severe tropical storm watch that extends from Edisto Beach north to the South Santee River.
Rain totaling 3-6 inches is expected from northeastern Florida to southeastern North Carolina, the hurricane center said.
Rising water will flood normally dry coastal locales, especially around high tide. Beryl also is forecast to spur a significant storm surge and possibly "dangerous surf conditions."