Sept. 24 (UPI) -- A 6.0-magnitude earthquake rocked Puerto Rico as the island prepares to be hit by Tropical Depression Karen on Tuesday.
The earthquake struck at 11:23 p.m. Monday some 38 miles north-northwest of San Antonio out in the Atlantic Ocean at a depth of 3 miles, the United States Geological Survey said. There is no tsunami warning in effect.
There were at least eight aftershocks, with the strongest occurring seconds later, measuring at a magnitude 5.1 magnitude, the USGS said.
Puerto Rico Mayor Wanda Vazquez Garced reminded the island's citizens to remain calm.
"We hope everyone is well and we have no harm in the face of the strong tremor," she said via Twitter.
The earthquake occurred as the island territory was hunkering down in anticipation of Tropical Depression Karen, which was nearing Puerto Rico and was forecast to lash the island with heavy wind and rain on Tuesday.
The National Hurricane Center said in its 2 a.m. Tuesday update, that the storm was about 150 miles south of San Juan with sustained winds of 35 mph and was moving north at 8 mph. Tropical storm warnings were in effect for the island.
The island had already closed schools for Tuesday in preparation of Karen whose center is forecast to either pass near or over the island later Tuesday.