Hurricane Jose, a Category 1 storm packing winds of about 135 kilometres per hour (85 miles per hour), is approaching the Caribbean hot on the heels of Irma, but will likely bypass land, according to the French weather service.
Weaker than Category 5 Hurricane Irma -- which has flattened almost everything in its path as it nears Florida -- Jose will likely strengthen to at least a Category 2 storm, forecaster Etienne Kapikian told AFP.
"On Saturday, it will pass a few hundred kilometres north/northeast of Saint Martin Island and Saint Barthelemy, probably as a Category 2" storm, he said.
On the 5-level intensity scale, Category 2 tropical storms carry winds of 154-177 km/h (96-110 mph), strong enough to cause life-threatened damage.
Category 5 storms have sustained winds -- at least a minute -- of 252 km/h or higher.
Even if Jose does not make direct landfall, it is likely to dump a lot of rain on islands already ravaged by Irma, which has been blowing at nearly 300 km/h for more than 33 hours -- a record.
"Those are not ideal conditions for carrying out rescue operations," Kapikian said.
Another Category 1 tropical storm brewing in the Gulf of Mexico, Hurricane Katia, "will probably make landfall in the northern part of the Mexican state of Veracruz before Friday," he added.
Katia is poised to deliver large quantities of rain along the Mexican coast.
The Atlantic basin has not seen three simultaneous hurricanes since 2010.