Hurricane Irma caused devastation in low-lying Caribbean islands, made landfall in Cuba as the first category 5 hurricane since 1924 and made landfall again in Florida, USA, on 10 September as a very dangerous category 4 hurricane on the Saffir-Simpson windscale.
The US National Weather Service and US National Hurricane Center warned of life-threatening storm surge, floods, tropical storm force winds, torrential rain and tornadoes as large parts of Florida were paralysed by the storm.
Irma made landfall Sunday morning in the Florida Keys – a string of tropical islands just off the Florida and then made a second landfall on the Southwest Florida coastline Sunday afternoon. Both landfall areas are especially vulnerable to storm surge. By Monday 11 September it had weakened to a tropical storm, though life-threatening hazards continued.Casualty figures and economic losses are not immediately known, however in terms of economic losses, Irma is expected to rival Hurricane Harvey, which hit Texas in late August, as one of the most expensive tropical cyclones in history.
Irma was the first Category 4 hurricane to make landfall in Florida since Charley (2004) and major hurricane to make landfall in Florida since Wilma (2005). Hurricanes Irma and Harvey mark the first time that two Category 4 storms have made landfall in the United States in the same year.
Some notable records and facts about Irma (according to Colorado State University).
- Irma has now generated enough Accumulated Cyclone Energy (ACE) by itself to meet the NOAA ACE definition of an average full Atlantic hurricane season,
- Generated the most Accumulated Cyclone Energy by a tropical cyclone on record in the tropical Atlantic (7.5-20°N, 60-20°W). Generated more Accumulated Cyclone Energy than the first eight named storms of the Atlantic hurricane season (Arlene-Harvey) combined
- Maximum winds of 185 mph (300 km/h) for 37 hours – the longest any cyclone around the globe has maintained that intensity on record. The previous record was Haiyan which caused devastation in the Philippines in the Northwest Pacific at 24 hours in November 2013.
- Three consecutive days as a Category 5 hurricane – the longest in the satellite era (since 1966).
- Strongest storm on record to impact the Leeward Islands defined as 15-19°N, 65-60°W for this calculation, with max winds of 185 mph. Closest approach of a Category 5 hurricane on record to Turks and Caicos. First Category 5 hurricane to make landfall in the Bahamas since Andrew (1992). First Category 5 hurricane to make landfall since the Cuba Hurricane of 1924
Other notable facts include:
- On 9 September, there were three hurricanes active in the Caribbean Sea, Gulf of Mexico and North Atlantic at the same time. Irma, Jose and Katia. It is rare but not unprecedented to have three hurricanes here were also three hurricanes in 1967, 1980, 1995, 1998 and, most recently, 2010 (Igor, Julia and Karl. The last time there were 3 hurricanes of category 2 or above in the basin was in 1893.
- It is the first time on record that the Atlantic basin had two simultaneous storms with winds of more than 150 miles per hour (240 km/h). Hurricane Katia, which peaked as a category 2 storm, was on 9 September downgraded to a tropical depression after making landfall in Mexico.
- Hurricane Jose, which was a category 4 hurricane and prompted fears that it would cause even more devastation on islands battered by Irma, but by 11 September it weakened and was tracking away from the Turks and Caicos islands. It is expected to linger over the western Atlantic for several more days.
The relationship between possible linkages between hurricanes and anthropogenic climate change.
WMO Expert Team on Climate Impacts on Tropical Cyclones issued a statement on possible linkages between Hurricane Harvey and anthropogenic climate change on 2 September 2017.
Some of the messages are also pertinent to Hurricane Irma.
Model simulations also indicate that hurricanes in a warmer climate are likely to become more intense, and that it is more likely than not that the frequency of category 4 hurricanes … willincrease over the 21st century, even if overall tropical cyclone numbers do not increase, or even decrease. Such changes are not yet clearly detectable in observed data due in part to limitations of existing datasets.
Ongoing sea-level rise, attributable in part to anthropogenic climate change, also exacerbates storm surge for land-falling hurricanes such as Harvey. Damage resulting from the geophysical event itself will be influenced by the vulnerability of the affected region, which is increased by factors such as population and infrastructure growth, and potentially decreased by mitigation measures such as flood control systems. Extensive coastal development has generally led to large increases in hurricane damage in U.S. coastal communities over the past century.
In a previous statement issued in 2010, the expert group said
“Whether the characteristics of tropical cyclones have changed or will change in a warming climate — and if so, how — has been the subject of considerable investigation, often with conflicting results. Large amplitude fluctuations in the frequency and intensity of tropical cyclones greatly complicate both the detection of long-term trends and their attribution to rising levels of atmospheric greenhouse gases. Trend detection is further impeded by substantial limitations in the availability and quality of global historical records of tropical cyclones. Therefore, it remains uncertain whether past changes in tropical cyclone activity have exceeded the variability expected from natural causes.
However, future projections based on theory and high-resolution dynamical models consistently indicate that greenhouse warming will cause the globally averaged intensity of tropical cyclones to shift towards stronger storms, with intensity increases of 2–11% by 2100. Existing modelling studies also consistently project decreases in the globally averaged frequency of tropical cyclones, by 6–34%. Balanced against this, higher resolution modelling studies typically project substantial increases in the frequency of the most intense cyclones, and increases of the order of 20% in the precipitation rate within 100 km of the storm centre. For all cyclone parameters, projected changes for individual basins show large variations between different modelling studies.”
On the web www.hurricanes.gov