A WSR-88D Radar View of Tropical Cyclone Ed

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  • 1 WSR-88D Operational Support Facility—South, Norman, Oklahoma
  • | 2 National Hurricane Center, Miami, Florida
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Abstract

The Guam WSR-88D (Weather Surveillance Radar-1988 Doppler) Doppler radar collected reflectivity, Doppler radial velocity, and other information for Supertyphoon Ed as it traversed the northern sections of Guam as a minimal tropical storm on 30 September 1993. This was the first-ever recorded passage of a tropical cyclone over a Next Generation Weather Radar WSR-88D Doppler radar site. Reflectivity data provided valuable information about the location of a precipitation-free “eye,” while radial velocity data provided useful information about tropical cyclone wind center location and strength. The velocity data also provided a 3-h lead time to upgrade the tropical cyclone to tropical storm intensity prior to landfall. Forecasters at Andersen Air Force Base used this information to give what turned out to be a very accurate short-range forecast of a brief period of gales with maximum gusts to 26 m s−1. Land-based surface wind observations correlated extremely well with 75%–80% of the 1500-m radial velocity estimates, which is similar to findings made by Powell and Tanner et al. Additional radar signatures of interest include offsets between the reflectivity center and velocity circulation center, detection of tropical storm and typhoon/hurricane force winds, Doppler velocity maxima within the convective rainbands, and mesocyclonic circulations detected by the WSR-88D's mesocyclone algorithm.

Concerning mesocyclones, one was detected very close to the location of the actual wind center when Ed was developing an eye prior to landfall. Within approximately 1 h of initial mesocyclone occurrence, a cyclonic divergent velocity-couplet pattern formed, possibly due to the development of low-level supergradient winds. The observed Doppler velocity patterns were consistent with the lower-tropospheric horizontal wind and vertical motion patterns in and around the eye as described by Malkus, Kuo, and Gray and Shea. After clearing the west coast of Guam, two separate mesocyclones formed just inward of the eyewall and appeared to be ingested into the main eye circulation. Similar findings were obtained from airborne Doppler radar analyses made by Marks and Houze. Shortly thereafter, Ed underwent a period of rapid intensification. In both instances, the mesocyclones appeared to have played a role in eye development and intensification.

Abstract

The Guam WSR-88D (Weather Surveillance Radar-1988 Doppler) Doppler radar collected reflectivity, Doppler radial velocity, and other information for Supertyphoon Ed as it traversed the northern sections of Guam as a minimal tropical storm on 30 September 1993. This was the first-ever recorded passage of a tropical cyclone over a Next Generation Weather Radar WSR-88D Doppler radar site. Reflectivity data provided valuable information about the location of a precipitation-free “eye,” while radial velocity data provided useful information about tropical cyclone wind center location and strength. The velocity data also provided a 3-h lead time to upgrade the tropical cyclone to tropical storm intensity prior to landfall. Forecasters at Andersen Air Force Base used this information to give what turned out to be a very accurate short-range forecast of a brief period of gales with maximum gusts to 26 m s−1. Land-based surface wind observations correlated extremely well with 75%–80% of the 1500-m radial velocity estimates, which is similar to findings made by Powell and Tanner et al. Additional radar signatures of interest include offsets between the reflectivity center and velocity circulation center, detection of tropical storm and typhoon/hurricane force winds, Doppler velocity maxima within the convective rainbands, and mesocyclonic circulations detected by the WSR-88D's mesocyclone algorithm.

Concerning mesocyclones, one was detected very close to the location of the actual wind center when Ed was developing an eye prior to landfall. Within approximately 1 h of initial mesocyclone occurrence, a cyclonic divergent velocity-couplet pattern formed, possibly due to the development of low-level supergradient winds. The observed Doppler velocity patterns were consistent with the lower-tropospheric horizontal wind and vertical motion patterns in and around the eye as described by Malkus, Kuo, and Gray and Shea. After clearing the west coast of Guam, two separate mesocyclones formed just inward of the eyewall and appeared to be ingested into the main eye circulation. Similar findings were obtained from airborne Doppler radar analyses made by Marks and Houze. Shortly thereafter, Ed underwent a period of rapid intensification. In both instances, the mesocyclones appeared to have played a role in eye development and intensification.

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