However, after entering the warm waters of the Gulf of Mexico on August 23, Marco briefly intensified into a hurricane, only to quickly weaken later that evening due to another rapid increase in wind shear.

At 00:00 UTC on August 16, the National Hurricane Center (NHC) began monitoring a westward-moving tropical wave over the Central Atlantic that had the potential for development.

[2][3] The disturbance quickly moved westward at a speed over 20 mph (32 km/h), which initially limited its development as it passed through the Windward Islands and into the Caribbean Sea.

This allowed the depression to intensify, and the NHC upgraded the system to Tropical Storm Marco in the northwest Caribbean at 00:00 UTC on August 22.

[7] Marco was able to strengthen quickly as a small system, reaching its initial peak intensity of 65 mph (100 km/h) and 992 mbar (29.29 inHg) just 18 hours after being named,[3] with an almost closed eyewall being observed by Hurricane Hunters.

[11] This weakening period proved to be short-lived, as the shear relaxed somewhat when Marco moved into the warm waters of the Gulf of Mexico on August 23.

[12] Marco strengthened into a Category 1 hurricane at 12:00 UTC on August 23, and simultaneously reached its peak intensity with 1-minute sustained winds of 75 mph (120 km/h) and a minimum central pressure of 991 mbar (29.26 inHg).

[14] Wind shear continued to plague the system as it turned westward near the Louisiana coastline, and Marco rapidly weakened to minimal tropical storm strength by 18:00 UTC.

[3][16] Afterward, Marco weakened further and fell to tropical depression intensity just offshore of Louisiana, near Grand Isle, at 03:00 UTC on August 25, before degenerating into a remnant low three hours later.

[3][17][18] The remnant low continued to spin down as it slowly moved westward along the Louisiana coastline, ahead of the approaching Hurricane Laura, before opening up into a trough at 00:00 UTC on the next day.

[19][20] When Marco moved to the north instead of northwest, a Tropical Storm Warning was issued by the Government of Cuba for the Pinar del Río Province and the Isle of Youth.

[28] A tornado watch was issued for southeast Alabama, the Florida Panhandle, Southwest Georgia, and United States coastal waters at 20:40 UTC on August 24.

[29] The Instituto Meteorológico Nacional of Costa Rica reported that heavy rain from the indirect effects of Marco affected parts of the country for three days.

[1] While traversing the Yucatán Channel, Marco brought heavy rain to parts of Pinar del Río Province in Cuba on August 23.