The U.S. and British Virgin Islands and Puerto Rico are under a tropical storm watch on Thursday, as a "disorganized" Tropical Storm Erika was moving northwestward in the Caribbean.</p><p>Erika has maximum sustained winds of 40 mph. Forecasters at the National Hurricane Center in Miami said gradual weakening of Erika "is likely during the next couple of days."</p><p>Although the system doesn't have a well-defined center of circulation, the storm overall is large, with tropical storm-force winds extending 230 miles from the center.</p><p>In the forecast advisories issued Thursday at 8 a.m., NHC forecasters said Erika was moving toward the west-northwest at 7 mph. The storm was about 40 miles southwest of St. Kitts in the Leeward Islands and about 220 miles east-southeast of San Juan Puerto Rico.</p><p>The official forecast track shows Erika crossing Puerto Rico early on Friday and weakening to a tropical depression, then moving past the northern coast of Hispanola and becoming a remnant low-pressure system approching the Turks and Caicos.</p><p>Although some computer models that NHC forecasters use show Erika strengthening, the official forecasts calls for the storm to dissipate within three days.</p><p>For the end of this week in the Keys, National Weather Service forecasters in Key West expect slightly-above-normal chances of rain, with showers most likely in the afternoon. Forecasters expect an average chance of rain for Saturday night through Labor Day.</p><p>The remains of Erika &mdash; as an open tropical wave or low-pressure area &mdash; could reach the Keys by Tuesday, forecasters said, and move west of the area by Wednesday.