| Timeline of the 2011 Atlantic hurricane season | |||||
|---|---|---|---|---|---|
 Season summary map | |||||
| Season boundaries | |||||
| First system formed | June 28, 2011 | ||||
| Last system dissipated | November 11, 2011 | ||||
| Strongest system | |||||
| Name | Ophelia | ||||
| Maximum winds | 140 mph (220 km/h) (1-minute sustained) | ||||
| Lowest pressure | 940 mbar (hPa; 27.76 inHg) | ||||
| Longest lasting system | |||||
| Name | Philippe | ||||
| Duration | 14 days | ||||
| |||||
The 2011 Atlantic hurricane season was an event in the annual hurricane season in the north Atlantic Ocean. It was well above average, with 19 tropical storms forming.[nb 1] Even so, it was the first season on record in which the first eight storms failed to attain hurricane strength. The season officially began on June 1, 2011, and ended on November 30, 2011, dates that conventionally delimit the period of each year when most tropical cyclones develop in the Atlantic basin.[2] The season's first storm, Tropical Storm Arlene did not form until June 28. The final storm to develop, Tropical Storm Sean, dissipated on November 11.
There were 19 named storms altogether during the season, including seven hurricanes of which three intensified into major hurricanes.[nb 2] The two most significant storms, in terms of loss of life and damage, were Hurricane Irene and Tropical Storm Lee. Hurricane Irene was a powerful and unusually large storm that made several landfalls along the East Coast of the United States after peaking with maximum sustained winds of 120 mph (195 km/h).[4] Tropical Storm Lee was a disorganized tropical cyclone that moved ashore into Louisiana before producing historic flooding in the Northeast United States as an extratropical cyclone.[5]
This timeline includes information that was not operationally released, meaning that data from post-storm reviews by the National Hurricane Center, such as a storm that was not operationally warned upon, has been included. This timeline documents tropical cyclone formations, strengthening, weakening, landfalls, extratropical transitions, and dissipations during the season.
By convention, meteorologists use one time zone when issuing forecasts and making observations: Coordinated Universal Time (UTC), and also use the 24-hour clock (where 00:00 = midnight UTC).[6] The National Hurricane Center uses both UTC and the time zone where the center of the tropical cyclone is currently located. The time zones utilized (east to west) prior to 2020 were: Atlantic, Eastern, and Central.[7] In this timeline, all information is listed by UTC first with the respective regional time included in parentheses. Additionally, figures for maximum sustained winds and position estimates are rounded to the nearest 5 units (knots, miles, or kilometers), following the convention used in the National Hurricane Center's products. Direct wind observations are rounded to the nearest whole number. Atmospheric pressures are listed to the nearest millibar and nearest hundredth of an inch of mercury.
