A potential tropical storm has emerged just off the US Gulf Coast as flood alerts have already been issued to millions across three states just miles away.

Forecasters warn that there is a high likelihood a large, low pressure area just south of Texas will organize into Tropical Storm Isaias this week.

According to AccuWeather, the storm is expected to impact the Gulf states, including Louisiana, Alabama, Mississippi and Florida, while also spreading heavy rain, thunderstorms and floods into Georgia, the Carolinas and points farther north.

Tropical moisture moving up from the Gulf of America has already been feeding storms over the US, triggering flood watches from the National Weather Service (NWS) on Monday.

Over four million Americans across the Florida Panhandle, southern Alabama and Georgia have been warned to expect several inches of rain through Monday evening, potentially leading to dangerous flash floods.

Up to eight inches of rain are expected to fall across all of northern Florida between Monday and Wednesday - followed by the potential eruption of Isaias as a tropical storm in the Gulf.

Currently, the National Hurricane Center (NHC) says there is a 70 percent chance a tropical cyclone will form this week, with AccuWeather expecting this to take place between Wednesday and Friday.

This would be the first tropical system to impact the US mainland since Edouard made landfall along the Gulf Coast on September 1.

Urgent alerts to boats traveling along the Florida coast near Tallahassee have also been issued Monday morning, warning of tornado-like waterspouts forming in the Gulf during the severe storms expected throughout the day.

NWS warned in a statement: 'Thunderstorms can produce sudden waterspouts. Waterspouts can easily overturn boats and create locally hazardous seas. Seek safe harbor immediately.'

To this point, a hurricane has not formed in the Atlantic Ocean or in the Gulf this year. If Isaias were to grow into a hurricane, it would set a new record for the latest date the first hurricane of the year formed.

However, forecasters believe it is highly unlikely the cyclone will strengthen to that point.

AccuWeather Senior Meteorologist Dan Pydynowski said in a statement: 'The waters across the Gulf of America are very warm, but stronger wind shear farther north across the Gulf may limit development potential.'

AccuWeather Lead Hurricane expert Alex DaSilva added on Monday that the strongest impacts as Isaias moves toward landfall in the US will likely come in Louisiana, Alabama, Mississippi and along the Florida Panhandle.

Up to eight inches of rain is predicted to fall between Saturday and Sunday, with the worst-case scenario projecting as much as 14 inches.

The weather service noted that even if a name tropical storm does not form, the approaching Gulf system will likely spread flooding downpours all the way to the Ohio Valley, the Mid-Atlantic and parts of the Northeast, including Pennsylvania and New Jersey.

AccuWeather expects that the storm will wreak havoc on travel across Louisiana, Mississippi, Alabama, Florida, Georgia, the Carolinas, Tennessee, Kentucky, West Virginia, Virginia, Maryland, Delaware, Ohio, Pennsylvania, and southern New Jersey between Saturday and next Monday.

There are only two years on record in which a hurricane failed to develop in the Atlantic, 1907 and 1914.

The historic downturn in hurricane activity in the Atlantic this year has been fueled by the impact of a 'super El Niño' on the other side of the US.

El Niño is the widely used name for a natural weather phenomenon where sea surface temperatures in the Pacific Ocean become abnormally warm. The current El Niño is expected to be one of the warmest in recorded history.

This flips weather patterns around the globe, causing the normally chaotic hurricane season along the US East Coast to fizzle before storms have a chance to grow.

Tropical cyclones need two major factors to play in their favor in order to grow from tropical depressions to tropical storms to hurricanes - warm water for fuel and less wind shear cutting apart their structures.

Although there have been eight cyclones which made it tropical storm status this year, meaning their winds were between 39 and 73mph, strong wind shear aided by El Niño hindered all of these storms from becoming hurricanes.