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Hurricane Irma causes devastation, breaks records

11-09-2017Source:WMO

Hurricane Irma has caused devastation in low-lying Caribbean islands, made landfall in Cuba as the first category 5 hurricane since 1924 and made landfall again in the Florida Keys, USA, on 10 September as a very dangerous category 4 hurricane on the Saffir-Simpson wind scale. The US National Weather Service is warning of life-threatening storm surge, floods, tropical storm force winds and tornadoes.

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)

Irma made landfall in the Florida Keys-a string of tropical islands just off the Florida coastline. They are especially vulnerable to storm surge. At 1100 AM EDT (1500 UTC), the center of Hurricane Irma is moving toward the north near 9 mph (15 km/h. On the forecast track, the eye of Irma should move over the Lower Florida Keys shortly, and then move near or over the west coast of the Florida Peninsula later through Sunday. Irma should then move inland over northern Florida and southwestern Georgia Monday afternoon. Maximum sustained winds are near 130 mph (215 km/h) with higher gusts. Irma is a category 4 hurricane on the Saffir-Simpson Hurricane Wind Scale. While weakening is forecast, Irma is expected to remain a powerful hurricane while it moves near or along the west coast of Florida. Hurricane-force winds extend outward up to 80 miles (130 km) from the center and tropical-storm-force winds extend outward up to 220 miles (350 km).

The combination of a dangerous storm surge and the tide will cause normally dry areas near the coast to be flooded by rising waters moving inland from the shoreline.

The US National Weather Service warned of an imminent danger of life-threatening storm surge flooding along much of the Florida west coast. The threat of catastrophic storm surge flooding is highest along the southwest coast of Florida where 10 to 15 feet of inunduation is expected. This is a life threatening situation.

It is vital that everyone within the affected area follow advice from national and local disaster management authorities and meteorological services.

Hurricane Jose remains a category 4 hurricane. There had been fears it would cause even more devastation on islands battered by Irma, but on Sunday it was tracking north west of Costa Rica.

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.

It is rare but not unprecedented to have three hurricanes are in the Caribbean Sea, Gulf of Mexico and North Atlantic at the same time. There 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, according to Colorado State University. 

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.”

Source: WMO

Editor: Wu Peng