Hurricane Hunters fly right into centre of Irma

Next time you're fretting about stormy weather during a flight, remember this. There are people deliberately flying planes into hurricanes.

And video posted on Twitter by the National Oceanic and Atmospheric Administration (NOAA)'s Hurricane Hunters show just how scary it can be.

The Hurricane Hunters were flying directly into the centre of Irma to record valuable data about the intense storm which continues to gather power over the Caribbean.

"We're dropping dropsondes, which are instruments that fall by parachute, sort of the opposite of a weather balloon," flight director Richard Henning told Fox News.

"All that (data) gets fed into the computer models that help forecast the track of the storm."

The video shows the WP-3D Orion being battered by wind and rain with visibility at practically zero.

But it takes just seconds for the weather to change dramatically as they enter the eye of the storm.

All of a sudden, the wind stops, the clouds drop away and the sun comes out.

But the size of the hurricane's eye only belies the intensity of the storm.

Irma is now the most powerful Atlantic Ocean hurricane in recorded history, and is on trajectory to pass over Puerto Rico and hit Florida.

Residents in the populous Miami metropolitan area are now heading north and west in hopes of avoiding the storm.

Meteorologists said Irma could strike the Miami area by early Sunday, then rake the entire length of Florida's east coast and push into Georgia and the Carolinas.

"This thing is a buzz saw. I'm glad Floridians are taking it very seriously," said Colorado State University meteorology professor Phil Klotzbach.

"I don't see any way out of it."

Already two people have been killed on the islands of St Barts and St Martin, with the death toll likely to rise.

And there's little reprieve once Irma passes. Tropical storm Jose has just been upgraded to a hurricane.

Meanwhile, Hurricane Katia is also gathering strength.

Jose is only a category one storm at this stage, but is heading west to threaten the Lesser Antilles.