Tropical Storm Rafael is coming soon. It poses an uncertain threat to the U.S. Gulf Coast

Tropical Depression Eighteen churns in the Caribbean Sea on the morning of Nov. 4. (CNN Weather via CNN Newsource)

A rare November tropical threat could impact the United States over the weekend amid an unusual and relentless hurricane season that shows no signs of letting up.

Tropical Depression Eighteen formed in the Caribbean Sea on Monday morning and is forecast to strengthen and become Tropical Storm Rafael on Monday afternoon. It will then strengthen into a hurricane by midweek while tracking over the northwestern Caribbean Sea.

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Rafael is expected to slam Cuba as a hurricane and then emerge into the Gulf of Mexico. From there, the storm’s ultimate path and intensity in the Gulf and potentially along the U.S. Gulf Coast is difficult to pinpoint with confidence because the system has just formed and is still several days away from reaching the area.

“It is too soon to determine what, if any, impacts could occur,” the National Hurricane Center said. Anyone from the U.S. Gulf Coast and the northeastern Mexico coast will need to monitor updates closely.

Early forecasts from the hurricane centre show the system’s centre reaching the U.S. Gulf Coast later this weekend anywhere from the Florida-Alabama border to Louisiana. But this area could shift dramatically in the coming days while the system tracks through the Caribbean.

The drastic differences between two major forecast models on the storm’s track once it enters the Gulf of Mexico highlight the forecast uncertainty. One depicts Rafael making landfall in western Cuba then tracking generally to the northwest before making landfall somewhere between Louisiana and the Florida Panhandle. The hurricane centre’s forecast looks rather similar to this scenario.

But another model is showing the potential for Rafael to make an abrupt left turn once it gets into the open Gulf. From there it tracks generally to the west and could fall apart entirely or make landfall in northeastern Mexico or the western Gulf Coast instead.

Any shifts will have a significant impact on the flood threat from the storm in Florida and other parts of the Southeast. The storm is enhancing rainfall ahead in these areas ahead of its potential arrival there. This means any areas that do get rain from the storm later this week or weekend will face an increased flood threat.

Five hurricanes have made landfall on the Gulf Coast this year, but this storm seems unlikely to be as severe as hurricanes Helene and Milton because its strength could be hampered by the terrain of Cuba and hostile storm-disrupting winds over the Gulf.

Tropical activity typically winds down in November, but the month still occasionally produces a storm. However, U.S. landfalls are exceptionally rare as 98 per cent of named storms make landfall in the U.S. before November, according to hurricane expert Michael Lowry. The Atlantic hurricane season ends Nov. 30.

While the threat the system poses to the US is still uncertain, its threats early this week in the Caribbean are much clearer.

Hurricane and tropical storm alerts are already in effect early Monday for Cuba, Jamaica and the Cayman Islands. Additional alerts will likely be issued in the coming days as the confidence in the system’s ultimate strength and track grows.

The bulk of the system’s storminess was over the Caribbean Sea early Monday, but drenching rain had already begun in parts of Hispaniola and Jamaica.

The system could bring torrential rainfall and flash flooding to more of the western Caribbean over the next few days. This heavy rainfall could also lead to mudslides, especially in the mountainous terrain of Jamaica and southern Cuba.

Rainfall totals of three to six inches are expected for Cuba, the Cayman Islands and Haiti. Parts of Jamaica could flirt with double-digit rainfall totals.

The system could also deliver strong winds, especially if it reaches hurricane-strength late Tuesday or early Wednesday. Dangerous storm surge could also inundate parts of the Cayman Islands and western Cuba.

CNN Meteorologist Robert Shackelford contributed to this report.