Hurricane Erin (2001) - Meteorological History

Meteorological History

A tropical wave moved off the coast of Africa on August 30. It almost immediately displayed signs of tropical cyclone formation with the development of deep convection and curved rainbands. Organization continued, and late on August 30 Dvorak classifications began on the system. On August 31, after passing well south of the Cape Verde islands, the system stopped its organization trend. Convection became sporadic, and the system became poorly organized as it moved westward at 20 mph (32 km). However, environmental conditions remained favorable. On September 1, the cloud pattern became better organized, and a low-level circulation quickly developed. Following an increase in convection and conformation of a low-level circulation by a buoy, it is estimated the system developed into Tropical Depression Six late on September 1 while located 1,600 miles (2,590 km) east of the Lesser Antilles.

Located to the south of a mid-level ridge, the depression moved to the west-northwest. With weak to moderate upper-level wind shear over the system, the depression gradually organized, and intensified into Tropical Storm Erin on September 2. Though Erin had favorable upper-level outflow and developing convection, the inner core of the storm remained disorganized. The storm slowly strengthened, and attained an initial peak intensity of 60 mph (95 km/h) while located about 1,150 miles (1,855 km) east of the Lesser Antilles. Favorable conditions were expected to allow Erin to continue to strengthen to reach winds of 85 mph (135 km/h). However, an upper-level low to the northwest of Erin produced strong vertical shear over the storm, and Erin quickly weakened as the low-level circulation became exposed to the southwest of the deep convection. The shear slightly abated on September 4, allowing Erin to briefly re-strengthen. However, the storm remained disorganized, and following an increase in southwesterly wind shear Erin began a weakening trend. On September 5, Erin weakened to a tropical depression, and hours later the low-level circulation dissipated.

The remnant low pressure area continued to the west-northwest, and on September 6 the system gradually produced deep convection. A surface circulation redeveloped in the northern portion of the remnants of Erin, and the system developed into a tropical depression again late on September 6 while located 365 miles (585 km) north-northwest of where it previously dissipated. The depression moved to the north-northeast, then turned to the north-northwest, and regained tropical storm status on September 7. Erin steadily intensified, and its convection and cloud pattern became much better organized on September 8. On September 9 Erin intensified into a hurricane while located 275 miles (440 km), and a 40 mile (65 km) wide eye developed. Erin quickly strengthened on September 9 to reach a peak intensity of 120 mph (195 km/h)., however some sources claim that Erin may have been a little stronger.

Shortly after reaching its peak intensity, Erin passed 105 miles (170 km) east-northeast of Bermuda, its closest approach to the island. The hurricane maintained peak strength for 18 hours before slowly weakening. Its weakening trend was slower than usual due to warmer than usual water temperatures, and by late on September 10 Erin weakenend to a Category 2 hurricane. Multiple short-wave troughs weakened the western portion of the subtropical ridge, and on September 11 Erin decelerated as it turned to the east. A strengthening mid- to upper-level trough over eastern Canada turned the hurricane to the northeast. It gradually accelerated its forward motion, and on September 15, after weakening to a strong tropical storm, Erin passed just east of Cape Race, Newfoundland. Convection gradually diminished as it moved through the north Atlantic Ocean, and later on September 15 Erin became extratropical. The extratropical storm continued northeastward, and after crossing over southern Greenland Erin merged with a high-latitude cyclonic flow to the east of Greenland on September 17.