Coastal Flood — Lower Mobile, Alabama

2011-09-03 · Lower Mobile, Alabama

Event narrative

The public reported 1 to 2 feet of water covering the parking lot at Hoppies Boat Launch...2 miles northeast of Hollingers island. The water was rising at time of observation.

Wider weather episode

Tropical Storm Lee began as a tropical wave in the Caribbean Sea during the last week of August. By the evening of Thursday, 1 September 2011, the tropical wave further developed into Tropical Depression 13. By 1 PM the following Friday afternoon, Tropical Depression Lee had formed. Lee slowly moved northward towards the south central Louisiana coastline by Saturday afternoon 3 September, while continuing to produce extremely heavy rainfall over portions of southern Louisiana, southern Mississippi, southern Alabama and the northwest Florida Panhandle.

The outer rain-bands of Lee produced near-continuous heavy rainfall over portions of southern Alabama, southeastern Mississippi and the northwestern Florida Panhandle by early Saturday morning and that endured through early Sunday before dry air aloft wrapped into Lee's western side. The center of Lee moved over land around sunrise Sunday, 4 September. However, it would be a while before Lee would weaken to a depression because it remained nearly stationary while the southern half of the circulation was over water where it could continue to derive additional energy from the warm ocean. The next day, Lee was eventually picked up by an upper air trough, turned northeastward and resumed a faster forward speed late in the day on Sunday, 4 September as it began its welcome exit to the northeast late Sunday through late Monday.

Lee's impacts were far reaching across our region. Although the continuous rains became somewhat intermittent as dry air wrapped into Lee from the west, this created a situation from Sunday afternoon through midday Monday whereby individual thunderstorms became more intense due to increasing levels of atmospheric instability. Stronger thunderstorms and isolated tornadoes affected the North Central Gulf Coast Region, as they formed within the detached outer spiral rain-bands well to the east of Lee's center on Sunday and finally to the southeast on Monday. The highest total storm tide levels (astronomical plus surge effects) ranged from approximately 3.5 to just barely over 5 feet.

While Lee was in the process of being picked up by a fast moving upper air trough, a series of squall lines that produced moderately widespread thunderstorm wind damage along and ahead of the surface cold front, as well as more isolated tornadoes, affected the area through late Monday afternoon. In all, some 10 to 15 inches of rain fell along coastal sections of Alabama and northwest Florida. Additionally, several weak tornadoes occurred producing modest structural and tree damage. There was also moderate beach erosion and the rip currents endured over a multi-day period. Inland flooding was exacerbated along the immediate coastal zone by higher tide levels due to Lee's surge effects which created poor to no drainage of area coastal rivers, bays and sounds on during astronomical high tide cycles from 3-5 September (late night hours each day).

Source: NOAA Storm Events Database, event_id 347149. Narrative written by the NWS forecast office that issued the report.