Hurricane Iris (1995) - Meteorological History

Meteorological History

A tropical wave exited western Africa on August 16, with a circulation emerging just south of Dakar, Senegal. It was the first of four consecutive waves that would later develop into tropical cyclones. As the system moved westward, thunderstorms diminished on August 18, before they gradually redeveloped. At around 1200 UTC, the National Hurricane Center (NHC) classified the system as Tropical Depression Ten about 690 mi (1,110 km) east of the Lesser Antilles. Around that time, the depression had a well-organized area of convection and evident circulation, as confirmed by a nearby ship. Within six hours of developing, the depression had intensified into a tropical storm. Initially, tropical cyclone forecast models had difficulty predicting the future of the storm, due to uncertain interaction between it and Tropical Storm Humberto to its northeast. In real-time, the NHC upgraded the depression to Tropical Storm Iris at 1500 UTC on August 23, or about 21 hours later than assessed in post-analysis. The intensity was based on satellite intensity estimates. At that time, the storm had a ragged central dense overcast—a uniformly circular area of thunderstorms—as well as rainbands to the north and south. A hurricane hunters flight late on August 23 indicated that Iris was significantly stronger, reporting 10–second sustained winds of 106 mph (170 km/h) at flight-level. Based on the reading, it is estimated Iris attained hurricane status around 1800 UTC that day, or about three hours after it was named.

After Iris strengthened into a hurricane, it turned to the west-southwest due to interaction with Hurricane Humberto. An upper-level low north of Puerto Rico increased wind shear over the hurricane, which dislocated the center from the deep convection. As a result, Iris weakened to tropical storm status on August 24 after being a hurricane for about 24 hours. As the storm approached the Lesser Antilles, the thunderstorms decreased markedly and the cloud pattern became disorganized. As late as August 25, there was uncertainty whether Iris would continue toward the islands or turn to the north. A new circulation became the dominant center as the storm continued westward, and Iris brushed Saint Lucia early on August 26. An approaching trough turned the storm to the northwest, bringing it near most of the Lesser Antilles. Early on August 27, Iris weakened to an intensity of 40 mph (64 km/h), although it immediately began restrengthening. Later that day, the center made landfall on Montserrat, Anguilla, and Barbuda with winds of over 60 mph (95 km/h). By that time, an eye began reforming, and the structure became better organized as wind shear decreased.

On August 28, Iris moved away from the Lesser Antilles, and at 1800 UTC re-attained hurricane status as it began a steady motion to the north-northwest. By that time, there was uncertainty in its future track due to the possible interactions among Iris, Humberto to the northeast, Tropical Storm Karen to the southeast, and the remnants of Tropical Storm Jerry to the west. In addition, after Tropical Storm Luis formed on August 27, there were four active tropical cyclones in the Atlantic. A few days later, there were three simultaneous hurricanes, which is a rare event, when Luis attained hurricane status. On August 30, Iris turned to the northeast while it began interacting directly with Tropical Storm Karen. Over the next few days, the smaller tropical storm moved around the larger circulation of Iris, potentially causing the hurricane to move erratically. Iris's intensity did not change significantly during that time, and it maintained strong outflow but a weak eyewall. An eastward-moving trough bypassed the storm to the north, causing the motion to become nearly stationary. A building ridge to the northeast caused Iris to turn to a northwest drift on September 1. By that time, the eye had become distinct and well-organized, and at 0600 UTC that day, Iris attained peak winds of 110 mph (175 km/h) to the southeast of Bermuda.

After reaching peak intensity, the hurricane began weakening due to increasing shear and cooler waters. An approaching trough turned Iris to the north, and early on September 3 the hurricane passed about 350 mi (560 km) east of Bermuda. That day, Iris absorbed the dissipating Tropical Depression Karen. It accelerated to the northeast as it lost tropical characteristics, and after weakening to a tropical storm, Iris transitioned into an extratropical cyclone on September 4 to the southeast of Newfoundland. The remnants turned to the east, moving in tandem with an extratropical storm to its north. On September 5, the barometric pressure dropped by more than 24 millibars (0.71 inHg), which qualified as being classified as a meteorological bomb. The next day, the winds strengthened to hurricane-status, and the storm maintained a track to the east due to a ridge weakening to the north. The pressure reached a minimum of 957 mb (28.3 inHg) early on September 7, lower than while Iris was tropical. That day, the storm weakened as it entered the English Channel, and the extratropical remnants continued across western Europe.