Hurricane Idalia is barrelling towards the Florida coast, with authorities urging residents in the northern part of that state's west coast to evacuate.

But the current Category 2 hurricane, which has already brought flooding rains to Cuba, is not the only hurricane in US waters, with Hurricane Franklin also clearly visible in the Atlantic, as you can see on the satellite image taken Wednesday morning (AEST).

Image: Two hurricanes but fortunately not double trouble, as Hurricane Franklin looks likely to miss populated areas. Source: RAAMB-Cira.

At this stage, Idalia is the one causing concern. It is set to impact the American coastline, and with potentially devastating impacts.

"There is great potential for death and catastrophic devastation. Storm surge on the coastal regions are projected as non-survivable," was the extremely blunt warning from the Sheriff's Office in Taylor County, on Florida's northwest coast, near the state capital of Tallahassee.

"This is a storm surge that, if you're there while that hits, it's going to be very difficult to survive," Florida Governor Ron DeSantis said in a news conference.

Image: Hurricane Idalia on Tuesday night, US time. Source: NOAA.

For an indication of how storm surge can inundate low-lying areas of Florida, take a look at this timelapse vision of the storm surge generated by Hurricane Ian in September 2022 on Sanibel Island on Florida's west coast.

Here is a time-lapse of the #StormSurge coming in on Sanibel Island, #Florida caught on a live traffic cam. This was only 30mins condensed down, it deteriorated quickly. 😬 #HurricaneIan #Hurricane #Ian pic.twitter.com/JKuNROvMm4

— BirdingPeepWx (@BirdingPeepWx) September 28, 2022

Meanwhile Taylor County is one of just 28 Florida counties where evacuation orders are in place before the rapidly intensifying Idalia makes landfall as a Category 4 storm on Wednesday morning local time (Wednesday evening AEST).

In addition to winds in the range of 178-208 km/h, the storm surge is predicted to be as high as three to five metres, which CNN described as "high enough to stack a wall of seawater halfway up the second floor of an average building".

If you click on a topographic map of Taylor County, you can see that large parts of it are below five metres in elevation, hence the urgency.

After crossing the Florida coastline, Idalia is expected to track in a generally northeasterly direction, crossing southern Georgia and hugging the coast of both South and North Carolina before moving out into the Atlantic.

There is the risk of flash-flooding, urban flooding, and riverine flooding in those three states.

Image: Forecast wind speeds for both hurricanes. Bear in mind that these are in mp/h. 100 mph = approx 161 km/h. Source: NOAA.

As for Hurricane Franklin, it is also expected to move in a northeasterly direction from its current position in the Atlantic, which means it will track away from the US coastline. It is currently located close to the British territory of Bermuda, where a tropical storm warning is in place, however it is not expected to pass over the islands.

The US hurricane season runs from June 1 to November 30. Unlike in Australia where only cyclones are named (a cyclone and hurricane are the same thing), US authorities name both severe tropical storms and hurricanes.

• In an average year, there are 10 severe tropical storms and 6 hurricanes.
• As of today, which is almost exactly halfway through the season, there have been 10 severe tropical storms and three hurricanes in US waters.