and was upgraded to Tropical Storm Helene. Helene began to turn to the northwest on September 21 due to a major trough in the eastern Atlantic. Later on September 21, Helene intensified into a hurricane. Favorable conditions allowed the storm to continue strengthening, and on September 22, Helene became a major hurricane. Late on the following day, Helene attained its peak intensity; maximum sustained winds were at 145 mph (233 km/h) and the minimum pressure of . After reaching peak intensity, Helene weakened as it tracked generally northward through the open Atlantic. By early on September 29, Helene briefly restrengthened into a Category 2 hurricane and reached a secondary peak of 105 mph (169 km/h). However, later that day, Helene weakened back to a Category 1 hurricane while accelerating to the northeast. At 12:00 UTC on September 30, Helene transitioned into an extratropical cyclone while centered well south of Iceland. The precursor tropical wave produced thunderstorms and gusty winds ranging between 23 and 34 mph (37 and 55 km/h) in Cape Verde on September 17. Tropical Depression Fifteen While Hurricane Helene was spinning in the central Atlantic, a tropical wave that moved off the coast of Africa in late September rapidly organized. On September 27 the storm became the fifteenth tropical depression of the season while it was about south-southeast of Cape Verde. The depression tracked westward at 15 to but weakened rapidly. The next day it was downgraded to a tropical wave while still in the far eastern Atlantic, and never reformed in the Atlantic. Aside from a brief threat to the Cape Verde islands, the system remained far from any landmasses throughout its life. Tropical Storm Isaac A tropical wave moved off the coast of Africa on September 23. It traveled westward at a low latitude along the Intertropical Convergence Zone (or ITCZ), and its convection gradually grew more organized. On September 29 it was identified as Tropical Depression Sixteen about southeast of Barbados. The westward path of the storm shifted two degrees northward, possibly as a result of the formation of a new center. On September 30 the depression was upgraded when an Air Force reconnaissance plane discovered tropical storm-force winds. Westerly vertical wind shear prevented deep convection at the center of the storm. As Isaac approached the islands, northern parts of the Lesser Antilles were issued tropical storm warnings. Nevertheless, the storm lasted only a short