Sunday, August 29, 2021

Tropical Storm Julian (2021)

Storm Active: August 28-29

Another tropical wave was crossing the Atlantic in mid-August when a broad area of low pressure formed along it. Atmospheric conditions didn't support development, however, and the disturbance tracked slowly northwest for several days. The Northern Atlantic Oscillation (NAO) was in negative phase, meaning that the Bermuda-Azores high pressure system was weaker than usual. This gave the system a window to gain latitude before reaching the Caribbean islands. Because it did so, it encountered cooler waters for a while, and organization was again put on hold. Around August 27, the system was at the latitude of Bermuda (though well to the east), and turned eastward. Finally, late on August 28, after tracking across the Atlantic for more than ten days, the disturbance was classified Tropical Depression Eleven.

By that time, the cyclone was already accelerating northeastward in the mid-latitude flow, pushed onward by an approaching cold front. Interaction with this front also drove some intensification and the system became Tropical Storm Julian on August 29. Though it was the eleventh cyclone of the season, it took the "J" name because it reached tropical storm strength while Tropical Depression Ten was still below this threshold. The cyclone reached an intensity of 60 mph winds and a pressure of 995 mb that evening just before transitioning to an extratropical low. It continued across the north Atlantic for a few more days before being absorbed.



Julian had the typical appearance of a cyclone moving northeastward in the subtropics, with an asymmetric, "comma-like" satellite presentation.


A vast majority of the track above shows the system that became Julian before and after its short stint as a tropical cyclone (the four circular dots in the middle).

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