Hurricane Isaac strengthened to Category 2 on the Saffir-Simpson Scale over the North Atlantic Ocean west of the Azores on Saturday.  At 11:00 a.m. EDT on Saturday the center of Hurricane Isaac was located at latitude 40.2°N and longitude 39.7°W which put the center about 695 miles (1120 km) west-northwest of the Azores.  Isaac was moving toward the east-northeast at 20 m.p.h. (32 km/h).  The maximum sustained wind speed was 105 m.p.h. (165 km/h) and there were wind gusts to 125 m.p.h. (200 km/h).  The minimum surface pressure was 968 mb.

Even though Hurricane Isaac was at latitude 40°N, it intensified to a Category 2 hurricane on the Saffir-Simpson Scale on Saturday morning.  A circular eye was present at the center of Isaac’s circulation.  The eye was surrounded by a ring of thunderstorms and the strongest winds were occurring in that ring of storms.  Bands of showers and thunderstorms were revolving around the core of Hurricane Isaac.  Storms near the core of Isaac generated upper level divergence that pumped mass away from the hurricane.

The circulation around Hurricane Isaac was reasonably symmetrical given it high latitude.  Winds to hurricane force extended out 45 miles (75 km) from the center of Isaac’s circulation.  Winds to tropical storm force extended out 200 miles (320 km) from the center of Hurricane Isaac.

Hurricane Isaac will move through an environment unfavorable for intensification during the next 24 hours.  Isaac will move over water where the Sea Surface Temperatures are near 24°C.  It will move under the eastern side of an upper level trough that is southeast of Greenland.  The upper level trough will produce strong southwesterly winds that will blow toward the top of Isaac’s circulation.  Those winds will cause the vertical wind shear to increase.  The combination of cooler water and stronger vertical wind shear will cause Hurricane Isaac to weaken during the next 24 hours.

The upper level trough southeast of Greenland will steer Hurricane Isaac toward the east-northeast during the next 24 hours.  On its anticipated track, Hurricane Isaac will pass northwest of the Azores on Sunday.

Elsewhere, the circulation of former Hurricane Helene was spinning down south of the Ohio River and Tropical Storm Joyce was churning east of the Northern Leeward Islands.

At 11:00 a.m. EDT on Saturday the center of Tropical Depression Helene was located at latitude 36.6°N and longitude 86.4°W which put the center about 50 miles (80 km) northwest of Nashville, Tennessee.  Helene was moving toward the east at 3 m.p.h. (5 km/h).  The maximum sustained wind speed was 15 m.p.h. (25 km/h) and there were wind gusts to 25 m.p.h. (40 km/h).  The minimum surface pressure was 968 mb.

At 11:00 a.m. EDT on Saturday the center of Tropical Storm Joyce was located at latitude 20.0°N and longitude 46.0°W which put the center about 1120 miles (1805 km) east of the Northern Leeward Islands.  Joyce was moving toward the northwest at 10 m.p.h. (16 km/h).  The maximum sustained wind speed was 50 m.p.h. (80 km/h) and there were wind gusts to 65 m.p.h. (105 km/h).  The minimum surface pressure was 1004 mb.