Upon producing a well-defined center and persistent deep convection, became Tropical Depression Eight at 15:00 UTC on September 20.[139] The depression strengthened into Tropical Storm Gaston six hours later while it was located about 990 mi (1595 km) west of the Azores.[140] Gaston quickly intensified, attaining peak sustained winds of 65 mph (105 km/h) the following day, just 18 hours after formation.[141] However, additional strengthening was prevented as dry air became entrained into the eastern portion of the circulation.[142] Gaston then maintained its intensity for two days as it accelerated northeastward toward the western Azores despite being in an environment of moderate to strong shear, relatively dry air, and cool sea surface temperatures.[143] On September 23, Gaston began to interact with a shortwave trough/baroclinic zone, which shunted all of its the deep convection to the northeastern portion of the storm and it weakened slightly as it slowed down and began an anticyclonic loop through the central Azores along the southern side of a mid-level ridge.[144][145] However, Gaston restrenghtened later that day as convection reformed over northern and western sides of its circulation and it reached its peak intensity with sustained winds of 65 mph (100 km/h) and a minimum barometric pressure of 995 mbar (29.38 inHg) at 15:00 UTC.[146][147] Relentless wind shear then stripped Gaston of its deep convection and the storm began to weaken again early the next morning as it continued its loop, which it completed later that day as it passed just west of the central Azores.[148][149] Now moving westward away from the Azores, Gaston dropped to minimal tropical storm strength, but restrengthened for a third time as a large burst of convection developed over the northern portion of the circulation as it interacted with an upper-level trough.[150] Its winds increased to 50 mph (80 km/h) on the morning of September 25 and it maintained this intensity for most of the day as it center reformed under the convective mass.[151][152] However, Gaston soon moved away from the trough and wind shear quickly removed the remaining deep convection from the storm late that afternoon.[153] Convection did not reform over Gaston and it weakened for the final time before being declared a post-tropical cyclone at 03:00 UTC on September 26.[154]