The 13th named storm of the season, Marco formed from a cold-core low pressure area along the northern coast of Cuba on October 9, and tracked northwestward through the eastern Gulf of Mexico.

The cyclone combined with a cold front and the remnants of Hurricane Klaus to produce heavy rainfall in Georgia and the Carolinas.

By early on October 6, a low pressure area and circulation persisted over eastern Cuba in the middle levels of the atmosphere.

[1] Initially cold-core in nature, the system gradually built downward to the surface, and on October 9, the low developed a low-level circulation; at 1200 UTC the National Hurricane Center classified it as Tropical Depression Fifteen while located near the Cuban city of Caibarién,[2] though the cyclone was initially subtropical in character.

[2] After passing midway between Key West and the Dry Tortugas, Tropical Storm Marco adopted a steady northward track and quickly intensified, reaching peak winds of 65 mph (105 km/h) on October 11, while still southwest of Englewood, Florida.

[4] However, the cyclone continued its northward trajectory, the center remaining offshore, and it weakened to a tropical depression prior to making landfall near Cedar Key early on October 12.

[6] The cold front that absorbed the weakening low was to the storm's north on October 13,[2] though moisture from the remnants of Marco dropped heavy rainfall across the southeast United States for another day.

[11] Squalls from the storm spawned four tornadoes in the state,[7] one of which struck the city of Crystal River, destroying a mobile home and leaving 2,000 people without power for about an hour.

[7] On October 19, 1990, President George H. W. Bush declared several counties in Georgia as federal disaster areas, which permitted the use of emergency funds for victims.

[15] Rainfall from the combined remnants of Marco and Klaus extended into the Ohio Valley, with 3.67 inches (93 mm) recorded near Mountain City, Tennessee.

[7] In New York, the rainfall combined with moisture from Hurricane Lili, which triggered flooding that closed a portion of a railway line and a highway.