Felix was the second major hurricane (category 3 on the Saffir-Simpson Hurricane Scale) of the season. It remained over the open waters of the eastern Atlantic Ocean, but briefly threatened the Azores Islands.
a. Synoptic History
Felix developed from a tropical wave and associated weak surface low that crossed the African coast on 5 September. The wave and low pressure area tracked westward for the next two days. On 6 September, QuikSCAT satellite wind data indicated that a surface circulation near the wave axis had become better defined. Deep convection continued to increase and weak banding features developed later that day as the system tracked a few hundred miles south of the Cape Verde Islands. By early 7 September, QuikSCAT satellite wind data and nearby ship observations indicated the low pressure system had become better defined with westerly winds of 12 to 17 mph noted about 120 nautical miles southwest of the low-level center. Deep convection became more centralized and banding features became more pronounced in visible satellite imagery. Dvorak satellite intensity estimates indicated the system had developed into Tropical Depression Seven at 1200 UTC that same day about 360 nautical miles southwest of the Cape Verde Islands.
Tropical Depression Seven tracked rapidly westward between 21 to 23 mph for the next day or so. Despite the otherwise favorable upper-level ridging across the system, the depression failed to develop any further. It is surmised that the rapid westward motion may have been associated with a low-level shear condition, which resulted in the deep convection becoming displaced farther to the east of the low-level center. Another possibility, based on satellite water vapor and AMSU (Advanced Microwave Sounding Unit) temperature data, is that the surrounding environment was more stable than usual, which could also have been an inhibiting factor to maintaining persistent deep convection near the center. By 1800 UTC on 8 September, convection became disorganized and QuikSCAT surface wind data, plus a few ship reports, indicated that Tropical Depression Seven had degenerated into a northeast-to-southwest oriented open wave about 650 nautical miles west-southwest of the Cape Verde Islands.
The wave tracked westward at around 17 mph for the next 36 hours. An unfavorable vertical shear pattern developed across the system when an upper-level trough amplified southward into the deep tropics to the west of the wave. Eventually, the southwesterly upper-level shear relaxed enough to allow for the redevelopment of deep convection near the mid-level vorticity center late on 9 September. By 0600 UTC 10 September, conventional satellite data suggested that a closed surface circulation had reformed and the system became again Tropical Depression Seven. A QuikSCAT overpass at 0816 UTC confirmed the existence of a broad cyclonic circulation in the surface wind field.
Tropical Depression Seven tracked west-northwestward and maintained a steady intensity of 35 mph for the next 24 hours. By 1200 UTC 11 September, the depression had acquired more convective banding features and satellite intensity estimates indicated the system had become Tropical Storm Felix.
The cyclone gradually turned northwestward and slowly intensified, reaching hurricane strength around 0000 UTC on 13 September. Shortly after reaching hurricane status, Felix underwent a period of rapid intensification (RI) in which the cyclone strengthened 35 mph in an 18 h period. It is estimated that Felix reached a peak intensity of 115 mph around 0000 UTC 14 September, when it was situated about 1400 miles southwest of the Azores Islands. It maintained that intensity until 0600 UTC, after which it began to recurve to the northeast and gradually turned more eastward ahead of an approaching mid-latitude trough.
Shortly after reaching its peak intensity, Felix began to weaken at a slow but steady pace as upper-level westerly shear began to increase. Late on 16 September, Felix turned northeastward and began moving over much cooler water. The cyclone weakened to tropical storm status at 1200 UTC 17 September, when it stalled about 350 miles southwest of the Azores. Increasing upper-level northwesterly shear and cold upwelling (as indicated by sea-surface temperature reports from nearby buoys and ships) caused Felix to weaken more rapidly as it drifted southward over its cold wake. It weakened to a depression at 1800 UTC 18 September and dissipated at 0000 UTC on 19 September, when it was about 400 miles southwest of the Azores Islands.
b. Meteorological Statistics
The period of rapid intensification that occurred is not unusual for a tropical cyclone that moves through a weakness in the subtropical ridge. Once on or just north of the ridge axis, the upper-level shear is usually at a minimum, which allows for the inner-core circulations to become more vertically aligned. As often is the case during RI periods, the eye diameter of Felix at the end of the RI cycle had contracted down to nearly half its original size. It also worth noting that the first indication of an eye in the microwave data became evident several hours before it appeared in conventional satellite imagery.
Pressure reports from drifting buoys 41644 and 44765 were critical in determining the strength of Felix since satellite intensity estimates became less reliable once the cyclone began to lose its central deep convection and overall convective organization.
There were no reports of tropical storm force winds in the Azores Islands because Felix rapidly weakened and eventually turned southwestward away from the islands.
c. Casualty and Damage Statistics
No reports of damage or casualties associated with Hurricane Felix were received by the National Hurricane Center.
Intensity For Hurricane Felix