The Azores and beyond

The Portuguese Institute for Sea and the Atmosphere has issued a hurricane warning for the central and western Azores, where winds could gust upward of 100 mph as Lorenzo passes near or just west of Flores Island on Tuesday night.

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A tropical storm warning is posted for the eastern islands, including Sao Miguel and Santa Maria, which will also become wrapped up in Lorenzo’s impressive wind field.

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Lorenzo’s hurricane-force winds extend outward up to 90 miles from the center, with tropical storm-force gusts spreading some 255 miles from the center.

Because of its fast forward speed, rainfall probably won’t be the worst aspect of this system for the islands. Two to four inches of rain is likely for the western Azores, although some places may see a bit more.

Dangerous surf and destructive waves are another story.

Portuguese government meteorologists are forecasting a southwesterly swell with 30 to 40 foot seas and occasional waves up to 72 feet. Over the open ocean, individual wave heights may, in the most extreme cases, approach 90 to 100 feet. A number of major transatlantic shipping routes are set to be affected.

After passing the Azores, Lorenzo will probably begin its transition to an “extratropical” storm, becoming more reminiscent of a nontropical storm over land or a nor’easter as its wind field expands and weakens.

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By Friday and into the weekend, Lorenzo’s remnant circulation will pass between Scotland and Iceland before it dissipates near the Faroe Islands to the north of Scotland.

A storm unlike any other on record

During its lifetime, Lorenzo has set a slew of records, each bearing the fingerprint of Earth’s changing climate.

Lorenzo rapidly intensified — not once, but twice. The first time occurred within a window last Wednesday to Thursday morning, when Lorenzo surged from an 80 mph storm to a 130 mph monster. That brought it to Category 4 status.

After some gradual weakening, Lorenzo did it again, strengthening from 115 mph Saturday morning to 160 mph by 11 p.m. It was a wild move by the storm, one not anticipated by the National Hurricane Center or meteorologists across other sectors.

At 10:10 p.m. Saturday, the National Hurricane Center announced Lorenzo became a Category 5 storm, which it then described as “the strongest hurricane this far north and east in the Atlantic basin.”

At that time, Lorenzo was located more than 600 miles east-northeast of where any other Category 5 hurricane on record had tracked before, per Sam Lillo, a graduate student at the University of Oklahoma.

Philip Klotzbach, a hurricane researcher at Colorado State University, tweeted a map of all recorded Category 5 origin points. As you can see in the image above, Lorenzo stands alone.

The climate context

While it’s impossible to attribute a single storm to climate change, it’s safe to say the trends exhibited by Lorenzo fit into an overall pattern favoring stronger, and potentially more errant, tropical cyclones.

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According to NOAA’s Geophysical Fluid Dynamics Laboratory, “the global proportion of tropical cyclones that reach very intense (Category 4 and 5) levels will likely increase due to anthropogenic warming.” A summary of available research suggests “rainfall rates will likely increase” as well; warmer atmosphere’s capacity to hold — and release — water is rising disproportionately faster than temperatures. Rising sea levels also favor more destructive storm surge threats.

This projected increase in storm intensity may already be underway.

The past four seasons, each of which have featured at least one Category 5 hurricane in the Atlantic, lend credence to this likelihood. It’s been a wild and unprecedented four years of hurricane activity, with Matthew, Irma, Maria, Michael, Dorian and now Lorenzo all achieving this elusive — and terrifying — status.

Research conducted by James Elsner, a professor of meteorology at Florida State University, illustrates that the past four years fit into a much broader increasing trend in Atlantic tropical cyclone strength.

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Lorenzo also rapidly intensified twice, presenting a forecast challenge to meteorologists in a field where models often fail to adequately predict such dramatic fluctuations in strength. Over the open ocean, it can be chalked up to an imperfect forecast, but rapid intensification can have enormous implications for storms close to shore. Rapid intensification was a key ingredient before landfall in both Harvey and Michael, which caused devastating damage in coastal Texas and Florida respectively.

Kerry Emanuel, a hurricane researcher and atmospheric scientist at MIT, wrote a 2017 paper in which he finds “the incidence of storms that intensify rapidly just before landfall increases substantially as a result of global warming.” Even more alarming is Emanuel’s simulation that storms intensifying 70 mph or more within 24 hours — which he ascribes as “occurring on average once per century” during the climate of the late 20th century — may now occur “every 5-10 years by the end of this century.”

A link between rapid intensification and climate change is well-established across the literature.

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Meanwhile, Lorenzo’s peculiar location is significant as well. Lorenzo’s leap to Category 5 strength occurred well outside the historical norm for storms of such strength, coming just two years after Ophelia became the Atlantic’s northeasternmost Category 3 on record.

A 2014 study by several atmospheric scientists found the latitude belt at which hurricanes achieve their maximum strength is slowly shifting poleward, at the rate of 35 to 40 miles per decade. It is unclear whether a link exists between how far east a storm develops and climate change, though of note is the anomalously warm water present in the eastern Atlantic during the time of Lorenzo’s passage.