Hurricane Isaac formed off the coast of Africa on September 18. Intensification was partly suppressed by high wind shear and by cool sea surface temperatures in the wake of Hurricanes Gordon and Helene. Isaac reached tropical storm strength on September 28 and entered an area of low wind shear, allowing it to strengthen into an 85 mph (137 km/h) hurricane. Its intensity nearly matched forecasts made with the Statistical Hurricane Intensity Prediction Scheme (SHIPS).