Bonnie Regains Tropical Depression Status Near Cape Hatteras

One time Tropical Storm Bonnie regained tropical depression status near Cape Hatteras on Thursday morning.  The National Hurricane Center (NHC) will resume issuing advisories on Tropical Depression Bonnie at 11:00 a.m. EDT on Thursday.  At 5:00 a.m. EDT on Thursday the center of Tropical Depression Bonnie was located at latitude 35.0°N and longitude 75.7°W which put it about 15 miles (25 km) south of Hatteras,, North Carolina.  Bonnie was moving toward the east-northeast at 9 m.p.h. (15 km/h).  The maximum sustained wind speed was 25 m.p.h. (40 km/h) and there were wind gusts to 35 m.p.h. (55 km/h).  The minimum surface pressure was 1010 mb.

After making landfall in South Carolina during the weekend, the center of Bonnie made a counterclockwise loop over land and then drifted east of Charleston.   The center drifted back over water on Tuesday and more thunderstorms formed near the center of circulation.  However, the vertical wind shear was still significant and the tops of the thunderstorms were periodically blown away from the lower part of the circulation.  As a result the circulation of Post Tropical Depression Bonnie was relatively shallow and existed primarily in the lower troposphere below 700 mb (about 3 km above the surface).  The low level circulation of Bonnie has move slowly east-northeast since that time and more thunderstorms developed in several spiral bands around the circulation.

During the past 24 hours Bonnie drifted under the axis of an upper level trough where the upper level winds are lighter.  As a result thunderstorms have persisted and a well formed band wraps around the northern and western sides of the center of circulation.  The circulation also extends higher into the atmosphere and a small area of upper level divergence has developed over the center of circulation.  Bonnie again has the appearance of a tropical cyclone on both satellite and radar images, which is why NHC is resuming advisories on the system.

Tropical Depression Bonnie could intensify further in the short term.  The Sea Surface Temperature (SST) reported by a buoy at Diamond Shoals, which is near the center of Bonnie, is near 26°C.  So, there is enough energy in the upper ocean to support some strengthening.  The upper level winds are light and vertical wind shear is not significant at this time.  If the surface pressures start to decrease, then Bonnie has a chance to become a tropical storm again.  Eventually, Bonnie will move into an environment where the SSTs are cooler and there is more vertical wind shear.

Tropical Depression Bonnie is between a subtropical high pressure system to its southeast and mid-latitude westerly flow to its north.  That combination is steering Bonnie slowly toward the east-northeast.  A general easterly motion is expected to continue during the next few days.  On its anticipated track Bonnie will gradually move away from the east coast of the U.S.