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Tropical Storm Henri was the eighth named tropical cyclone in the 2009 Atlantic hurricane season. A weak and disorganized cyclone, Henri formed on October 6 from a tropical wave and moved northwestward for most of its life. Persistent wind shear prevented it from intensifying beyond a weak tropical storm. After peaking in strength on October 7 it began to deteriorate, and weakened to a remnant low on October 8. Henri remained over open waters and did not affect any land areas, although the storm is noted for its sudden formation from a disturbance that was initially not expected to develop.
Template:Storm path Henri's origins are traced back to a tropical wave which emerged from the western coast of Africa on October 1, 2009. As it tracked westward across the Atlantic Ocean, it produced intermittent showers and thunderstorms. By October 4, the system had become accompanied by a large area of disorganized convective activity, and the National Hurricane Center remarked upon the possibility for tropical cyclone development. While located about 950 mi (Template:Convert/km) east of the Windward Islands on October 5, the system became better organized and more well-defined as it continued generally towards the west. Later that day, a broad area of low pressure formed in association with the wave. Although the strong thunderstorm activity was displaced to the east of the center of circulation, the disturbance had become a tropical depression around 0000 UTC on October 6 while located about 775 mi (Template:Convert/km) east of the Lesser Antilles. Operationally, however, the storm was not designated a tropical cyclone until later that day, when it was immediately declared a tropical storm.
Affected by strong southwesterly wind shear, Henri remained weak and disorganized, and its center continued was still located on the western edge of the main area of convection. Moving northwestward under the steering currents of a mid-level subtropical ridge to the north, the cyclone strengthened slightly late on October 6, but it was still anticipated to dissipate within 48 hours. By early the next morning, convection increased in intensity and coverage around the center, and Henri reached its peak intensity with winds of 50 mph (85 km/h) and a minimum central pressure of 1005 mbar (hPa; 29.68 inHg) at around 0600 UTC.
The period of development was short-lived, however: the cyclone quickly began to deteriorate once again as the vertical wind shear grew stronger, and the center of circulation had become further detached from the strongest thunderstorm activity. The storm continued to weaken, and on October 8, it was downgraded to a tropical depression. The depression remained disarranged, and satellite imagery suggested that multiple low-level vortices were present within the more broad circulation. Just 12 hours after degenerating into a depression, the cyclone decreased to a remnant area of low pressure. The storm's remnants continued northwestward for the next day, until high pressure over the western Atlantic turned the system southwestward; the remains of Henri dissipated near Hispaniola several days later.
Impact and forecasting
As a tropical cyclone, Henri remained over open waters of the Atlantic and did not impact any land areas. As a result, no deaths or damages occurred in association with the storm, and no tropical cyclone watches and warnings were issued. Additionally, no ships recorded tropical storm-force winds from the storm. In general, the storm's formation was poorly forecast. Although the possibility of tropical development was mentioned 36 hours prior to Henri's designation, it was initially assessed as having less than a 30% of strengthening into a depression.
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