25th Anniversary of Hurricane Bob

Hurricane Bob races toward New England on Aug. 19, 1991 (NOAA)

Hurricane Bob races toward New England on Aug. 19, 1991
(NOAA)

On August 19, 1991, Hurricane Bob brushed the tip of Long Island and came ashore in Rhode Island.  Although only a Category 2 hurricane at that time, Bob managed to rack up a sizable damage bill to become one of the costliest New England hurricanes.

Flight track of NOAA 42 on Aug. 17th, 1991, Synoptic Flow mission

Flight track of NOAA 42 on Aug. 17th, 1991, Synoptic Flow mission

Bob formed from a disturbance that split from a frontal zone south of Bermuda, which drifted southwestward.  By Aug. 16th, the disturbance formed a low-level circulation center east of the Bahamas and became a tropical depression.  Within a day, the depression had strengthened enough to become a tropical storm and was named.  It drifted slowly to the northwest but began to turn northward as a trough approached from the west.  It began to strengthen to hurricane force and accelerate forward. To help define the currents pushing Bob northward, NOAA 42 flew a Synopic Flow mission, where they dropped sondes around the hurricane to define the upper-level winds used by the computer models.

As it passed by the Outer Banks, Bob strengthened to its peak level of 115 mph (185 km/hr) winds.  It also began to race toward New England at 25 mph (35 km/hr).  NOAA 42 flew a buoy comparison mission into Bob.  The aircraft overflew several ocean buoys east of North Carolina in the hurricane-force winds to provide corresponding flight-level winds.  The purpose was to refine the equations used to reduce flight-level winds to the surface.

Track of Hurricane Bob 1991 (Unisys)

Track of Hurricane Bob 1991
(Unisys)

On the evening of Aug. 19th, Bob crossed the eastern tip of Long Island, before passing over Block Island, and making landfall at Newport, RI.  Its winds were estimated at 100 mph (155 km/hr) and quickly diminished.  But the major damage was done by Bob’s rainfall, as much as 8″ (203 mm) in parts of New England and the Canadian Maritimes.  Eventually the remnants of Bob were tracked out into the Atlantic and all the way to Portugal.  Along its way, Bob was responsible for 15 direct deaths and US$1.5 billion in damages.

Papers using data from Hurricane Bob written by HRD scientists:

Burpee, R. W., S. D. Aberson, J. L. Franklin, S. J. Lord, and R. E. Tuleya, 1996:  The impact of omega dropwindsondes on operational hurricane track forecast models.  Bull. Amer. Met. Soc., 77, 925-933.

DeMaria, M., J. Kaplan, and J.-J. Baik, 1993:  Upper-level eddy angular momentum fluxes and tropical cyclone intensity change.  J. Atmos. Sci., 60, 1133-1147.

Franklin, J. L., S. E. Feuer, J. Kaplan, and S. D. Aberson, 1996: Tropical cyclone motion and surrounding flow relationships:  Searching for beta gyres in omega dropwindsonde datasets.  Mon. Wea. Rev., 124, 64-84.

Houston, S. H., W. A. Shaffer, M. D. Powell, and J. Chen, 1999: Comparisons of HRD and SLOSH surface wind fields in hurricanes: Implications for storm surge modeling.  Wea. Forecast., 14, 671-686.

Kaplan, J., and M. DeMaria, 2001:  On the decay of tropical cyclone winds after landfall in the New England area.  J. Appl. Meteor. Clim., 40, 280-286.

Powell, M. D., 1993:  Wind measurement and archival under the Automated Surface Observing System (ASOS):  User concerns and opportunity for improvement.  Bull. Amer. Met. Soc., 74, 615-623.