Hurricane Harvey – AL092017_Harvey.pdf

Hurricane Harvey 2Hurricane Harvey17 AUGUST – 1 SEPTEMBER 2017SYNOPTIC HISTORYThe wave that spawned Harvey moved off the west coast of Africa on 12 August with a large convective mass that had mostly dissipated by late the next day. Convection increased near the wave axis on 15 August, likely due to the passage of a convectively coupled Kelvin wave early that day (Fig. 1). A low pressure center formed early on 16 August, but easterly shear initially prevented any organization of the associated convection. The shear relaxed overnight, allowing deep convection to build near the center, and a tropical depression formed around 0600 UTC 17 August about 440 n mi east of Barbados. The depression became a tropical storm 12 h later. The “best track” chart of Harvey’s path is given in Fig. 2, with the wind and pressure histories shown in Figs. 3 and 4, respectively. The best track positions and intensities are listed in Table 11. Harvey moved quickly westward, south of a western Atlantic ridge, reaching an initial peak intensity of 40 kt early on 18 August. The storm’s center passed over Barbados at 1000 UTC that day and St. Vincent five hours later, although most of the strong winds occurred away from those islands to the north of the center. Increasing northerly wind shear caused Harvey to gradually weaken back to a depression early on 19 August and to degenerate into a tropical wave by 1800 UTC that day over the central Caribbean Sea. The remnants of Harvey moved rapidly to the west and west-northwest for the next couple of days, staying convectively active while they moved over the Yucatan Peninsula on 22 August. A low pressure area formed late that day in association with a short-lived burst of deep convection. The low moved west-northwestward into the Bay of Campeche early on 23 August and, shortly after 0600 UTC, more persistent deep convection increased near the low. By 1200 UTC, an Air Force Reserve reconnaissance aircraft found that the circulation of the low had become better-defined, indicating that Harvey had regenerated into a tropical depression when its center was located about 150 n mi west of Progreso, Mexico. Initially, the depression was poorly organized with a large radius-of-maximum winds(RMW). This structure did not last for long as a smaller RMW formed, possibly due to concentrated deep convection near the center. Harvey began to rapidly intensify late on 23 August in an environment of light shear, very warm water and high mid-level moisture. The storm turned northward, steered around the western edge of the distant subtropical ridge, and the track gradually bent toward the northwest during the next day or two. The cyclone’s rate of intensification increased early on 24 August as a large mass of deep convection formed over the center, and an eye was noted on reconnaissance observations by 1200 UTC that day. Harvey 1 A digital record of the complete best track, including wind radii, can be found on line at Data for the current year’s storms are located in the btk directory, while previous years’ data are located in the archivedirectory.



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