Tragic loss of life and property is the news after Hurricane Dorian’s devastating path over the Bahamas. This record-breaking hurricane has been a powerful, slow-moving storm and now emergency response to damage is underway in the Bahamas, US Virgin Islands, and Puerto Rico while the governors from Florida, Georgia, South Carolina, North Carolina, and Virginia have all signed states of emergency.
Here are five striking facts about this historic storm to date:
Dorian is now the fifth hurricane to reach category five—the highest level possible on the Saffir-Simpson Hurricane Wind Scale—over the past four hurricane seasons in the North Atlantic.
Between 1924 and 2019 there have been only 35 category 5 hurricanes in the North Atlantic. Having five such storms form over just the past four hurricane seasons is way beyond the average occurrence rate.
Even more remarkable is that Dorian broke the record for the strongest storm so far north in the Atlantic east of Florida. Historically, the farther north a hurricane moves in the Atlantic the cooler the sea surface temperatures it encounters, which typically causes the storm to weaken. This time, however, the sea surface temperatures were warm enough to add energy and power to the hurricane. Having sea surface temperatures above what hurricanes need to be fueled, combined with slow-moving speed, can allow a storm to maintain major hurricane status (category 3 or above) for a longer time period.
What’s contributing to these warmer sea surface temperatures? Over the past half century, the ocean has absorbed more than 90 percent of the excess warming caused by burning fossil fuels and overloading the atmosphere with carbon. In keeping with this trend, the globally-averaged ocean temperature for July 2019 was the highest departure from average (+0.84 degrees Celsius; +1.51 degrees Fahrenheit) for July over the entire period of record (1880-2019).
At times, Dorian moved slower than most people walk along its devastating path over the Bahamas.
A nightmare for any person, property, or living creatures and plants along a hurricane path is a slowly churning major category hurricane. The risk of damage increases substantially with sustained major hurricane winds and intense rainfall over many hours.
While over the Bahamas, Dorian not only had sustained winds reaching 185 miles per hour, wind gusts were reported to be over 220 miles per hour. Let’s pause a moment here. Those wind gusts also fall within the highest category for tornadoes on the Enhanced F-Scale for Tornado Damage (over 200 miles per hour for a 3 second gust; note that since 2007 this scale is an update to the original Fujita scale that is based not on direct wind measurements, but rather wind gusts based on damage levels).
After a powerful landfall on Great Abaco Island, Dorian basically stopped over Grand Bahama Island for more than 24 hours, likely breaking records for the most powerful prolonged exposure in Atlantic hurricane history, comparable to Hurricane Mitch of 1998 over Honduras—which did not have a hurricane eye over land for so long as Hurricane Dorian.
Recent research finds that North Atlantic hurricanes have slowed in the speed of translation and are more likely to “stall” near a coast thereby increasing rainfall at those regions.
Dorian went through not just one, but two rapid intensifications (i.e. greater than 35 miles per hour increase in wind speed in less than 24 hours).
Before Dorian, it was unprecedented for rapid intensification to occur from an initial wind intensity greater than or equal to 130 knots (around 150 miles per hour) in the Atlantic. Historically a rare behavior, rapid intensifications of storms have become a dangerous feature of recent Atlantic hurricane seasons. This is why researchers are working hard to increase understanding to better predict rapid intensification and give earlier warning to those along the likely path of the storm. Research links rapid intensification with climate change.
In the last 24 hour, Hurricane #Dorian intensified from 130kt to 160kt … in fact it did this in under 9 hours.
Rapid intensification is an impressive enough feat, but becomes extremely rare from high initial intensities. From 130kt, it is unprecedented in the Atlantic. pic.twitter.com/Fi2e0y7EJo
— Sam Lillo (@splillo) September 1, 2019
Dorian generated massive storm surge in the Bahamas.
The forecasted storm surge for the Bahamas was between 18 and 23 feet. On-the-ground witnesses reported that the Grand Bahama International Airport in Freeport was submerged by Dorian storm surge. The reported elevation of the airport is around 6-8 feet above mean sea level, and the water level was several more feet above ground level. Early satellite imagery suggests around 60 percent submerged land during the catastrophic storm surge for Grand Bahama Island.
More storm surge and intense rainfall are in the forecast as Hurricane Dorian now moves north along Florida toward Georgia and the Carolinas.
Dorian’s forecast is similar to recent major damaging hurricanes Matthew and Florence.
Dorian is eerily similar to Hurricane Matthew (2016), which caused more than $10 billion in damages. Hurricane Dorian is about the same size as Matthew, forecast to be slower moving near Florida, and then moving at a similar speed near the Carolinas.
Dorian is likely to be similar or stronger than Matthew over the Florida to Carolina sections of the path. This spells trouble for the “Space Coast” section of Florida, with water surging over several tidal cycles. It’s also not good news for the Carolinas, which extend further out into the Atlantic and are more likely to intersect with Dorian’s path. The advisory from the National Hurricane Center at 5 PM EDT on September 3 depicts potential landfall in South Carolina on Thursday, September 5.
Hurricane Florence (2018) also underwent rapid intensification to a category 4, then weakened, then grew again to a major category hurricane before ultimately making landfall as a category 1 storm. Florence was the wettest on record for the Carolinas, dropping 20 to 30 inches of rain and causing life-threatening flooding, wind damage, and record-breaking storm surge of 9 to 13 feet.
The climate connection
Why is Hurricane Dorian behaving this way? Some of the key reasons can be found in the recent post, Hurricane Dorian: What Presidential Candidates—and All of Us—Need to Know, by my colleague Kristy Dahl. As she details, scientists expected several of the changes we’re seeing, as warmer oceans help intensify tropical storms, higher sea levels worsen storm surge, and a warmer atmosphere brings greater rainfall intensity.
More disturbing, however, is the fact that scientists are now working hard to better understand some of the more fundamental surprises over recent years: rapid intensifications with recent Atlantic hurricanes and a tendency toward slow-moving storms than can transfer and absorb more water and energy from the ocean and bring that to land in tragic and devastating ways.
If you are at risk from Hurricane Dorian, local authorities have the latest details for staying safe in the regions where you or your family or friends may be. Be sure to sign up for your community’s warning system; the Emergency Alert System (EAS) and National Oceanic and Atmospheric Administration (NOAA) Weather Radio also provide emergency alerts. Please be careful while preparing for Dorian and seek help if necessary. Keep tracking any changes in information with Dorian and, if necessary, prepare earlier rather than later.
Support from UCS members make work like this possible. Will you join us? Help UCS advance independent science for a healthy environment and a safer world.
Originally posted by Union of Concerned Scientists on 2019-09-04 05:24:30