11:15 p.m. Update: After having been upped to 60 mph earlier, Alberto’s maximum sustained winds are now clocked at 50 mph. A Tropical Storm Watch has been issued for the South Carolina coast from the Savannah River to South Santee River (see tropical storm-force wind probabilities here). Dangerous surf is possible along the South Carolina and Georgia coast through Monday. The National Hurricane Center expects little change in Alberto’s strength during the next 48 hours.

This NOAA satellite image taken Saturday, May 19, 2012, shows Tropical Storm Alberto 140 miles (225 km) east of Charleston, S.C. (AP Photo/Weather Underground)

Tropical storm-force winds extend 45 miles from the center of Alberto, which is about 140 miles east-southeast of Charleston, S.C., and expected to move very slowly to the southwest through Sunday. Currently there are no hazards associated with Alberto that are affecting land. The National Hurricane Center says that “only modest intensification is expected,” but that a Tropical Storm Watch could be issued for a portion of the Carolina coast this evening.

CWG hurricane expert Greg Postel had this to say earlier today (before Alberto officially formed):

There is an abundant supply of relatively cool & dry nontropical air on the U.S. coast, from Maine to Florida, that is ready to be inhaled. The circulation is right now sitting above the Gulf Stream, so there may be some brief opportunity for maturation ... but, once it moves away from that friendly spot, the environment will be stacked against further development

Interestingly, the National Hurricane Center notes that this is the first time a tropical storm has formed in both the Atlantic and Eastern Pacific before the official June 1 start of hurricane season. Tropical Storm Aletta, which formed earlier this week in the Pacific, is no longer tropical in nature.