Hurricane Irma has already caused severe damage and loss of life as it rips through the Caribbean – but worse things could follow
According to the National Hurricane Center, Irma is the strongest hurricane ever recorded in the Atlantic, outside of the Caribbean and Gulf of Mexico.
It is a Category 5 on the five-point Saffir-Simpson scale, but that does not convey the true magnitude of its power.
Its sustained winds reached 297 kilometres per hour (km/h) on Wednesday, gaining a wind speed close to the theoretical maximum speeds attainable for cyclones.
This ranks second only to 1980’s Hurricane Allen’s 305km/h.
In another respect, Irma is in a league of its own.
It is the longest lasting Category 5 system ever recorded in either the Atlantic or eastern Pacific, in records that stretch back to 1851 and include around 2,600 cyclones.
The source of Irma’s energy is the warm waters of the western Atlantic. The sea surface temperatures are around 29C to 30C, well in excess of the 26.5C minimum required for hurricane formation.
Worryingly, the waters ahead of Irma are at an exceptionally warm 31C, so there is plenty of potential energy to fuel Irma’s wind and rain.
Depending on its traction, the storm could hit the US states of Florida, Georgia or the Carolinas, or even head into the eastern Gulf of Mexico. Meanwhile, Tropical Storm Jose is also brewing in the Atlantic.
Irma is currently west-northwest of Puerto Rico. It is expected to run to the north of the island of Hispaniola. Nevertheless, heavy rainfall and a one-metre storm surge could cause significant problems across Haiti and the Dominican Republic.
In addition to winds, which will be “catastrophic” as defined by their strength, there will be a storm surge – an elevation of sea level as a result of the build-up of water caused by the wind.
Across all these islands that surge is expected to be between five and 6.5 metres. Such a surge is comparable to that which hit Tacloban in the Philippines, during Typhoon Haiyan.
Irma is expected to be over the Turks and Caicos around 00:00 GMT on Friday and the main islands of the Bahamas at 06:00 GMT on Saturday.
After that, the track of Irma is uncertain. Some computer models take it on to the northern coast of Cuba, while others continue its track across the Bahamas.