Image source, Reuters

Here's our guide about all you need to know about the storm.

Image source, Getty Images

In Miami, Florida - where evacuation orders are in effect - residents have been stocking up on wooden boards, which they are using to protect windows from Irma's record-breaking wind speeds.

Fuel and drinking water are also in short supply in some parts of the state, as panicked residents stockpile essential goods.

Image source, Getty Images

Image source, Getty Images

Image source, Getty Images

The sheriff of Polk County, Florida has published tweets that some online users are finding offensive.

The office of Sheriff Grady Judd warned criminals that law enforcement officers (LEOs) will be checking IDs at all shelters for displaced Florida residents.

Several Twitter users questioned the sheriff's commitment to public safety.

Here's a graphic showing areas at risk from the storm surge.

Here are the latest pictures from some of the storm-hit islands in the Caribbean and also from other regions which are still bracing for Irma.

Image source, Royal Netherlands Navy

Image source, Reuters

Image source, AFP/Getty Images

Image source, Reuters

Image source, Getty Images

Winds and rain are now bearing down on the British and US Virgin Islands.

Puerto Rico is also expected to feel the brunt of the storm in the next several hours.

Radio 4 PM

A British Royal Navy ship is on standby to help in the aftermath of Hurricane Irma. RFA Mounts Bay is described as one of the most capable disaster response vessels anywhere in the world.

Captain Steve Norris, the Commanding Officer, told Radio 4's PM "we are preparing and planning for the worst".

He added that their primary role was "to save life" and that they were "waiting for our tasking" to assist.

Will Grant
BBC News, Havana

While islands across the Caribbean are used to dealing with powerful storms, Cuba has a particularly good track record in terms of hurricane preparedness.

In fact, even during times of hostile bilateral relations with the United States, it has been one area in which the old enemies have traditionally worked well together.

In essence, people in Cuba tend to obey the evacuation orders issued by the state. If told to abandon their homes and seek refuge with families or in shelters, the chances are they will do so - indeed there can be consequences for ignoring government instructions.

But the situation in Cuba is also complicated by other factors, especially the decades-long US economic embargo which makes it hard for people to find basic goods or construction materials with which to board up their homes.

The south of the US was rocked by Hurricane Harvey less than two weeks ago. Now we have Irma, and following shortly behind is Jose, which looks set to be upgraded from a tropical storm to a hurricane later today.

Is it weird to have so many, so close? We consulted an expert.

Meteorologist Emma Boorman said:

“Seeing multiple storms developing in the same area of the Atlantic in close succession is not really a rare occurrence. The atmospheric conditions are suitable for development, with warm sea surface temperatures and favourable winds, so having two or three storms developing within this time is not uncommon.”

But she added: “Rarer, though, is the strength of the hurricanes.”

Irma is expected to make landfall in the US as a category four. Since records began, there have never been two category four storms making landfall on the US mainland within the same season.

Royal Netherlands Navy have shared images from the island of Sint Eustatius.

They write that there is "relative calm" on the island, and add that the Marines are ready to respond to further emergencies.

Here are key points from BBC Weather on the storm sweeping the Caribbean:

• This is only the fifth Atlantic hurricane with a peak wind speed of 184mph or higher

• The others are Allen (1980), the Labor Day Hurricane of 1935, Gilbert (1988) and Wilma (2005)

• The most intense Atlantic hurricane on record (across all the regional basins of the Atlantic) was Wilma in 2005 - this storm had a central pressure of 882mb and sustained winds of 185mph, and also delivered the highest 24-hour rainfall total ever recorded in the northern hemisphere in Mexico (1576.1mm in 24 hours)

• Harvey was a category four storm when it made landfall in Texas in August

Image source, Getty Images

Image source, Getty Images

According to FlightRadar24.com, a plane from New York is still en route to San Juan, despite the potential for Hurricane Irma to smash into the island of Puerto Rico in the next few hours.

The Delta Air Lines flight is expected to land in the next 30 minutes.

Image source, Getty Images

The BBC's Reality Check team have spoken to emergency and insurance experts to determine how those huge figures are determined.

To estimate the cost of a disaster like Harvey or Irma, sophisticated economic models take into account data from past extreme weather events and incorporate thousands of different scale storms to predict the financial impact on a local area.

The costliest hurricane in US history was Katrina in 2005, estimated at $156bn (£119bn).

Read more here:

Reality Check: Paying for a hurricane

Dramatic footage has now emerged of gales and flooded cars in St. Martin

Will Grant
BBC News, Havana

The weather is currently calm in Havana, the BBC's Will Grant, external reports from the Cuban capital.

But as Hurricane Irma's predicted path lies over the island, local residents are already preparing, our correspondent says.

People have been stocking up on tinned food, fresh water and fuel, but so far there are no scenes of desperate shopping or boarding up homes in Havana, he adds.