29 September 2019

Amazing Lorenzo becomes season's 2nd Category 5 hurricane

Late Saturday night, Lorenzo beat the odds and was upgraded to a Category 5 hurricane... the second of the season. The last season with two Category 5s was 2017 (Irma and Maria), and then 2007 before that (Dean and Felix).  In my previous blog post on Thursday when Lorenzo was a Category 3 hurricane, I mentioned this possibility and included the historical odds: "It will almost certainly keep going into Category 4 status, and could even reach Category 5 intensity (160+ mph) at some point.  Only about 2% of Atlantic named storms ever achieve Category 5 status".

Enhanced infrared satellite image of Hurricane Lorzeno from around the time it was upgraded to Category 5 intensity. (NOAA)
Not only did it beat the odds, it did so extremely far east; in fact, as Phil Klotzbach at Colorado State University nicely illustrated on a map, it reached Category 5 status about 600 miles further east than the previous easternmost: Hugo (1989).  I added labels to point out the three frontrunners.

Locations where all known Category 5 hurricanes first reached that intensity. (Phil Klotzbach, CSU: https://twitter.com/philklotzbach/status/1178137123687284737)
While this seems quite far north to have such an intense hurricane, the ocean temperatures in that area are normally quite warm this time of the season, and this year they're even warmer.  The water under Lorenzo when it was a Category 5 hurricane is about 28°C (82.4), which is about 1°C (1.8°F) warmer than average... just enough to give it that extra jolt.

Sea surface temperatures (°C), with Lorenzo's Category 5 position marked by a black X. (NASA)
As of 5am EDT on Sunday, it has weakened just slightly to an upper-end Category 4 hurricane with 155 mph sustained winds. The large hurricane (tropical storm force winds extend an average of 205 miles from the center), is forecast to continue tracking to the north then turn northeast, which will bring it near the Azores early Wednesday.  Beyond that, it is expected to begin the transition to an extratropical cyclone, but it will remain quite strong as it heads toward the British Isles on Friday. Both areas could easily experience hurricane conditions including destructive winds and significant storm surge.

Looking back at the history of NHC intensity forecasts for Lorenzo and comparing them to the observed intensity, we can see that the first peak was fairly well-anticipated, but the second and even stronger peak was certainly not.

Elsewhere across the basin, things will remain quiet for the foreseeable future.

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