Preliminary Report
Hurricane Bonnie
17 September - 02 October 1992

1992 PRELIMINARY REPORTS

Hurricane Andrew (5)
Hurricane Bonnie (2)
Hurricane Charley (2)
Tropical Storm Danielle (TS)
Tropical Storm Earl (TS)
Hurricane Frances (1)

Hurricane Bonnie formed at rather high latitudes and moved very slowly for a large part of its lifetime. It affected the Azores with tropical storm conditions, shortly before it became extratropical.

 

a. Synoptic History

Bonnie had its origins in a non-tropical weather system. A cold front moved off the east coast of the United States on September 11. The front continued moving southeast and then became stationary, with its western end in the vicinity of Bermuda by September 15. Surface pressures fell over an area a few hundred miles east-northeast of Bermuda the following day, and satellite pictures on the 17th showed that an area of clousiness and become detached and isolated from the frontal cloud band. The cloud pattern quickly became organized, exhibiting cyclonically curved bands and a small circularly-shaped overcast feature. The tropical depression stage of Bonnie began at 1800 UTC September 17.

The depression strengthened fairly rapidly, and became Tropical Storm Bonnie around 0600 UTC on the 18th. As is frequently the case in non-tropical-type developments, Bonnie was initially embedded within a larger-scale deep-layer cyclonic circulation. This provided an an environment of relatively weak vertical shear and also controlled the steering of Bonnie during the easrly stages. Bonnie moved slowly along counterclockwise path before strengthening into a hurricane at 1800 UTC September 18. The hurricane commenced an east-northeast to northeast motion on the 19th while exhibiting a fairly well-defined eye. The eye became indistinct at times on the 20th but on the 21st, satellite images showed that it had again become rather sharp in appearance. At 1800 UTC on September 21, Bonnie reached its peak intensity with estimated maximum winds of 109 mph. The forward motion, which was also slow, decreased even further on the 22nd. Bonnie was practically stationary from 1800 UTC on the 22nd until 1200 UTC on the 23rd, when it began drifting west-southwest. Bonnie weakened considerably as satellite imagery showed that the low-level center became exposed from the associated deep convection. Its winds had been reduced to tropical storm strength on the 24th. By the 25th, Bonnie had lost most of its deep convection and by 0000 UTC September 26 Bonnie weakened briefly to a tropical depression. However tropical storm strength was regained a little later on that same day as deep convection returned.

Bonnie began a southward motion on September 24th which continued until the 26th at which time Bonnie turned southeast and then east, while picking up some forward speed. The stalling and southwestward drift of Bonnie were caused by the northward retreat of deep layer westerlies over the west-central Atlantic area and the formation of a blocking-type pattern in the steering currents. A building mid-tropospheric high to the northwest of Bonnie forced the tropical cyclone southwestward. Subsequently, a broad deep-layer trough developed over the Atlantic to the east of Bonnie. The combined effects of the trough and high guided Bonnie southward for a while. Later on, as the influence of the trough became dominant, Bonnie was steered southeastward and eastward.

Although Bonnie had restrengthened back to a tropical storm, it remained in a westerly shearing environment on the 26th and 27th. The circulation center was generally near the western edge of the deep convective overcast. However on the 27th, Bonnie's cloud pattern took on a non-tropical comma shape and the deep convection was confined to an area several degrees east of the center. By the 28th, convection had returned near the center and Bonnie looked more like a tropical storm again. The system was then moving toward the east-northeast and it maintained that course for the next couple of days with some increase in forward speed. The center of the storm, moving near 23 mph, passed through the Azores island group on September 30th. Not much deep convection was associated with the system and, shortly after passing through the Azores, Bonnie became an extratropical low. The low then decelerated and looped clockwise, eventually moving back towards the Azores while dissipating.

b. Meteorological Statistics

c. Casualty and Damage Statistics

Apparently, Bonnie did not have serious effects on the Azores. No reports of casualties or damage due to Bonnie have been received.