SAN JUAN, Puerto Rico (AP) — Two tropical storms advanced across the Caribbean on Saturday night as potentially historic threats to the U.S. Gulf Coast, one dumping rain on Puerto Rico and the Virgin Islands while the other was pushing through the gap between Mexico's Yucatan Peninsula and Cuba.

Tropical Storms Laura and Marco were both projected to approach Louisiana at or close to hurricane force just two days apart next week. A hurricane watch was issued for the New Orleans metro area, which was pummeled by Hurricane Katrina in August 2005.

Two hurricanes have never appeared in the Gulf of...