On September 11, a non-tropical low formed along a frontal boundary situated over the north central Atlantic, well west of the Azores. The low drifted generally southward or southwestward over the next day. By September 12, it was producing gale force winds and displayed some organized convective banding. However, the surface low was still colocated with an upper-level low, not the high found for tropical cyclones, so it was designated Subtropical Storm Joyce. Existing contemporaneously with Florence, Helene, and Isaac, the new system was one of four named storms simultaneously occupying the Atlantic basin. This was the first time this had occurred since 2008. Also, Joyce was the fifth subtropical cyclone of the season, the first time that had happened since 1969.
Shortly after formation, the cyclone felt the influence of the much larger Tropical Storm Helene to its southeast. Steered around the periphery of its circulation, Joyce moved west-southwest and then turned south around Helene's left side as it reached the same latitude. Meanwhile, on September 13, Joyce transitioned into a tropical storm. The next day, it strengthened slightly to a moderate tropical storm and turned eastward in the wake of Helene. This intensification was short-lived, however, as increasing wind shear out of the southwest stripped away the little convection that formed in bursts near the center of circulation. On September 16, Joyce weakened to a tropical depression.
The shallow system was left behind by now ex-Helene and instead followed the boundary of a mid-level high located in the subtropical Atlantic. This caused the depression to turn south of due east by September 17 and then south by the 18th. Late on September 18, Joyce had ceased to produce deep convection and was finally downgraded to a remnant low. The low moved slowly southwestward until dissipation.
The above image shows the small Tropical Storm Joyce as well as the edge of the larger Tropical Storm Helene to the east, which greatly influenced Joyce's motion.
Joyce did not affect any landmasses during its journey through the northeast Atlantic.
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