On September 22, a vigorous tropical wave over Africa emerged into the far east Atlantic. Immediately, it showed signs of organization, and was classified Tropical Depression Thirteen that night while located southeast of the Cabo Verde Islands. The next day, it developed spiral bands and steadily strengthened, earning the name Tropical Storm Lorenzo that afternoon. Upper-level winds, sea surface temperatures, and humidity were all in Lorenzo's favor as it continued to intensify. The cyclone turned west-northwest on September 24 as it followed the boundary of a mid-level ridge. Later that day, Lorenzo achieved hurricane status. The cyclone was also quite a large hurricane, with tropical storm force winds extending over 200 miles from the center of circulation.
On September 25, an eye feature began to form on satellite imagery. This led to more rapid strengthening shortly thereafter. Lorenzo was able to overcome a small dry air intrusion and stabilize its eyewall overnight. By mid-morning on the 26th, it had rocketed to major hurricane strength, becoming the 3rd of the 2019 season. Nor did the rapid increase in strength stop there. By later in the day, Lorenzo was a category 4 hurricane. At that point, it was the second easternmost forming category 4 on record, behind only Hurricane Julia of 2010. In fact, by that evening, the system was brushing up against the maximum theoretical intensity for a hurricane forming in that region, given the sea temperatures and atmospheric conditions. Overnight, it peaked with 145 mph winds and a pressure of 937 mb. Meanwhile, the cyclone followed a very well-forecast curve toward the north into a weakness in the aforementioned ridge.
An eyewall replacement cycle commenced on September 27, weakening the hurricane back to a category 3 as the inner eyewall convection became ragged and asymmetric but expanding its windfield. The eye itself also clouded over on visible imagery. This weakening may have been exacerbated by southwesterly shear, but Lorenzo came back with a vengeance on the 28th, completing the replacement and developing very cold cloud tops in the new eyewall. With this organization came a truly extraordinary burst of strengthening in which the cyclone's winds increased 40 kt in just 12 hours. At its peak that night, Lorenzo was a category 5 hurricane with sustained winds of 160 mph and a minimum pressure of 925 mb, making it, by far, the easternmost category 5 ever observed in the Atlantic.
By September 29, the storm was curving northward and then north-northeastward into cooler waters and a more stable atmosphere, causing a steady decline of the maximum winds. The large storm continued to grow in size, however, as it gained latitude. On the 30th, Lorenzo, now a category 2 storm, began to accelerate northeastward toward the Azores islands. Some signs of extratropical transition were evident by October 1, but the storm still had a vigorous core of convection. That night, the center passed near the western Azores, by which time the wind radii were huge: hurricane force winds extended up to 150 miles from the center and tropical storm force winds up to 390 miles. Several of the islands experienced damaging winds and very high surf from the massive circulation. After passing to the northeast, Lorenzo became extratropical. Late the next night, the storm slammed into Ireland, bringing hurricane force wind gusts. The storm later passed over the UK before finally dissipating.
The above image shows Lorenzo as a category 4 hurricane over the eastern Atlantic.
Lorenzo did not affect any land for most of its life, but ultimately became one of the most powerful cyclones on record to affect the Azores when it passed over the western islands as a large category 2 hurricane.
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