National Hurricane Center
Later on September 22, the National Hurricane Center began noting the possibility of increasing wind shear, due to a large upper trough. Despite this, the intensity predictions did not forecast weakening within the next three days. Isaac continued to strengthen and reached hurricane status at 1200 UTC on September 23. However, the National Hurricane Center did not operationally upgrade Isaac until 2100 UTC on September 23, at which time the storm was a Category 2 hurricane. Thereafter, Isaac significantly intensified, and on the following day, it reached an initial peak intensity with winds of 120 mph (205 km/h). The National Hurricane Center then predicted Isaac would become a Category 4 hurricane on September 25, though this did not materialize.