Toward the end of September 2001, a poorly-defined tropical wave moved westward across the tropical Atlantic Ocean, through an area of hostile wind shear, which was caused by a large upper-level low within a trough, to the northeast of the Lesser Antilles.
A few days later, the upper-level low detached from the trough and moved southwestward over the Caribbean Sea, allowing for an upper-level ridge, or high-pressure area, to form over the tropical wave.
The change provided a favorable environment for tropical development, and an area of convection soon blossomed along the wave's axis.
As the tropical wave approached the Lesser Antilles, a mid-level wind circulation formed within the deepest part of the convection, and a low-level circulation became gradually more pronounced on satellite imagery.
Although its low-level circulation was small and poorly defined, the system increased in organization enough to be classified as Tropical Depression Eleven at 12:00 UTC on October 4, located about 100 mi (160 km) southeast of Barbados.
Operationally, however, Hurricane Hunters did not confirm the depression's formation until nine hours later.

In its early stages, the depression moved west-northwestward between the islands of St. Vincent and St. Lucia under the influence of a strong ridge to its north.
Compared to its appearance 24 hours before forming, the depression exhibited improved outflow and more distinct convection, although its lower circulation remained very poorly organized.
This was confirmed by a Hurricane Hunters flight into the system, which failed to report a closed circulation despite the depression's well-organized appearance on satellite imagery.
At 21:00 UTC on October 5, they reported a strengthening circulation with flight-level winds of 74 mph (119 km/h), corresponding to a surface wind intensity of 60 mph (95 km/h).
Based on these data, the depression was upgraded to Tropical Storm Iris, situated about 155 mi (250 km) south of the southern coast of Puerto Rico.
In post-season analysis, the National Hurricane Center (NHC) estimated that Iris had attained tropical storm status about nine hours earlier.

Despite the storm's intensification and well-organized satellite appearance, the circulation failed to become better defined.
In their first discussion on Iris, the NHC mentioned the potential for the system to degenerate into a tropical wave if it maintained its fast forward speed.
One forecaster noted that the center was fragile and that the cyclone could dissipate quickly if it encountered stronger wind shear to its south.
Although its overall appearance did not change significantly, the Hurricane Hunters reported a closed eye with a diameter 23 mi (37 km) and a stadium effect (eyewall curvature) on October 6.
Later that day, Iris reached hurricane strength just southwest of the southern tip of the Dominican Republic, and the NHC remarked that land interaction with the Greater Antilles was the only factor impeding further development.
After Iris reached winds of 85 mph (140 km/h) early on October 7, its intensity remained steady for about 24 hours.
During that time, the satellite appearance became slightly ragged as its outflow became restricted, possibly due to an upper-level low.
By late on October 7, the area of hurricane force winds associated with Iris extended only 25 mi (35 km) from its 16 mi (22 km) wide eye.

Early on October 8, after turning west-southwestward away from the Greater Antilles, Iris began strengthening again, with warm waters and an absence of significant wind shear.
The NHC predicted peak winds of 105 mph (165 km/h) before the storm would hit Belize.
It rapidly intensified with the favorable conditions, intensifying from 95 mph (150 km/h) to 140 mph (225 km/h) in a 12-hour period on October 8, making Iris a Category 4 hurricane on the Saffir-Simpson scale; in the same duration, the minimum central pressure dropped 38 mbar (1.12 inHg).
While intensifying, the hurricane developed concentric eyewalls, with an innermost eye having a diameter of 7 mi (11 km).
For comparison, the smallest k
Toward the end of September 2001, a poorly-defined tropical wave moved westward across the tropical Atlantic Ocean, through an area of hostile wind shear, which was caused by a large upper-level low within a trough, to the northeast of the Lesser Antilles. A few days later, the upper-level low detached from the trough and moved southwestward over the Caribbean Sea, allowing for an upper-level ridge, or high-pressure area, to form over the tropical wave. The change provided a favorable environment for tropical development, and an area of convection soon blossomed along the wave's axis. As the tropical wave approached the Lesser Antilles, a mid-level wind circulation formed within the deepest part of the convection, and a low-level circulation became gradually more pronounced on satellite imagery. Although its low-level circulation was small and poorly defined, the system increased in organization enough to be classified as Tropical Depression Eleven at 12:00 UTC on October 4, located about 100 mi (160 km) southeast of Barbados. Operationally, however, Hurricane Hunters did not confirm the depression's formation until nine hours later.
In its early stages, the depression moved west-northwestward between the islands of St. Vincent and St. Lucia under the influence of a strong ridge to its north. Compared to its appearance 24 hours before forming, the depression exhibited improved outflow and more distinct convection, although its lower circulation remained very poorly organized. This was confirmed by a Hurricane Hunters flight into the system, which failed to report a closed circulation despite the depression's well-organized appearance on satellite imagery. At 21:00 UTC on October 5, they reported a strengthening circulation with flight-level winds of 74 mph (119 km/h), corresponding to a surface wind intensity of 60 mph (95 km/h). Based on these data, the depression was upgraded to Tropical Storm Iris, situated about 155 mi (250 km) south of the southern coast of Puerto Rico. In post-season analysis, the National Hurricane Center (NHC) estimated that Iris had attained tropical storm status about nine hours earlier.
Despite the storm's intensification and well-organized satellite appearance, the circulation failed to become better defined. In their first discussion on Iris, the NHC mentioned the potential for the system to degenerate into a tropical wave if it maintained its fast forward speed. One forecaster noted that the center was fragile and that the cyclone could dissipate quickly if it encountered stronger wind shear to its south. Although its overall appearance did not change significantly, the Hurricane Hunters reported a closed eye with a diameter 23 mi (37 km) and a stadium effect (eyewall curvature) on October 6. Later that day, Iris reached hurricane strength just southwest of the southern tip of the Dominican Republic, and the NHC remarked that land interaction with the Greater Antilles was the only factor impeding further development. After Iris reached winds of 85 mph (140 km/h) early on October 7, its intensity remained steady for about 24 hours. During that time, the satellite appearance became slightly ragged as its outflow became restricted, possibly due to an upper-level low. By late on October 7, the area of hurricane force winds associated with Iris extended only 25 mi (35 km) from its 16 mi (22 km) wide eye.
Early on October 8, after turning west-southwestward away from the Greater Antilles, Iris began strengthening again, with warm waters and an absence of significant wind shear. The NHC predicted peak winds of 105 mph (165 km/h) before the storm would hit Belize. It rapidly intensified with the favorable conditions, intensifying from 95 mph (150 km/h) to 140 mph (225 km/h) in a 12-hour period on October 8, making Iris a Category 4 hurricane on the Saffir-Simpson scale; in the same duration, the minimum central pressure dropped 38 mbar (1.12 inHg). While intensifying, the hurricane developed concentric eyewalls, with an innermost eye having a diameter of 7 mi (11 km). For comparison, the smallest k
Hurricane Iris