Tuesday, August 23, 2011

Hurricane Isabel: 
What are the lessons learned?

Image from Bowley's Quarters in Baltimore County. 

Text of this report from the Sterling VA NWS Hurricane History pageIsabel was one of the most significant tropical cyclones to affect the Chesapeake Bay region since Hurricane Hazel in 1954 and the Chesapeake - Potomac Hurricane of 1933. Isabel made landfall near Drum Point on the NC Outer Banks on the 18th as a strong category 2 hurricane with maximum sustained winds of 105 mph. Isabel then traveled north northwestward losing its tropical characteristics on the 19th over western Pennsylvania. 

2. Impacts Isabel will be remembered for the very large field of tropical storm force winds which caused a great deal of tree damage, the extensive flash flooding  in the Shenandoah Valley, and the unusually high storm surge in the Chesapeake Bay and the Potomac River Basin. Fallen trees and limbs were the overwhelming reason for widespread power failures and damage and destruction to nearly 8,000 homes, which will likely made Isabel as one of the most expensive storms. At the peak of the storm, well over 2 million people were without power.  Isabel is a reminder that if the impacts of a Category 2 hurricane can be so extensive, the impact of Category 3 or higher could be devastating. 

3. Rainfall Rainfall totals were generally in the 6 to 12 inches in the Shenandoah Valley of Virginia, 2 to 6 inches across western Maryland and eastern West Virginia, and 1 to 3 inches across Baltimore and Washington metro areas. Upper Sherando (Augusta County) reported a storm total of 20.20 inches. Moderate to Major River flooding occurred in the Potomac, Shenandoah, Rapidan and Rappahannock rivers. In the city of Waynesboro, 300 people were evacuated and about $250,000 damage was caused to public property.  Flood caused 2 to 3 feet of water in downtown Waynesboro. Four people lost their lives mainly  due to drowning. See rainfall map for Isabel.

4. Storm Surge Isabel also caused an unusually high storm surge (6-8 feet above normal) in the Chesapeake Bay and Potomac River Basin. Storm surge in the Chesapeake Bay and the Potomac River reached the highest levels since the Chesapeake/Potomac Hurricane of 1933. Substantial flooding from storm surge was experienced by residents and businesses in Baltimore, Annapolis, northern Virginia and Washington DC. In Annapolis, the peak water level reached 6.44 feet above mean sea level and caused extensive damage at the Naval Academy. In Baltimore, the peak water level reached 7.35 feet mean sea level.  Link to the animation graphic

The most extensive flooding occurred at Fell's Point and at the Inner Harbor, near downtown. Several feet of water inundated streets and alleys there. Significant also occurred in low-lying areas of Old Town Alexandria. Portions of King Street were under as much as 5 to 6 feet of water. In Washington, DC (Georgetown at the foot of Wisconsin Ave.), the water level reached 8.72 feet. The headquarters of the police and fire harbor patrol at Water Street were also flooded.

A question from Foot's Forecast to state and county officials, school superintendents and parents alike: Have we learned our lessons from Isabel? As stated in the 1993 National Geographic Special about a simulated hurricane impact on New Orleans: "Mother Nature has given us fair warning."

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