Summary of Huricane Isabel and its Effects on the DC Metro Area

Hurricane Isabel, the eighth storm of the 2003 urricane season, formed west of the Cape Verde Islands on September 6^th. By September 7^th, Isabel had strengthened into a hurricane.

Steady intensification was noted as Isabel tracked steadily in a west-northwest direction. By September 11, Isabel had reached Category 5 status, with peak winds of 160 mph. Fortunately, after September 14, Isabel weakened.

By the time Isabel made landfall on the North Carolina coast, between Cape Lookout and Cape Hatteras at about 1 p.m. on September 18, Isabel had weakened to a Category 2. The strongest winds recorded on land were slightly over 100 mph. The lowest pressure record at landfall was 957 millibars, or 28.26” of mercury.

The computer models did an extraordinary job handling the track of Isabel. Due to a persistent upper ridge and surface high pressure area east of New England, it became apparent several days before landfall that Isabel was not going to recurve to the north and northeast in the usual fasion. Instead, it was to be steered relentlessley on a northwest path toward the Carolina coast and beyond.

After its landfall during the early afternoon of September 18, Isabel continued on its northwest march at 20-25 mph, its center passing about 30 miles west of Richmond during the evening hours and over western Maryland before daybreak on September 19.

In the Washington area, there were several periods of strong winds between 5 p.m. and 1 a.m., interpersed with periods of lesser winds. The strongest wind recorde at a major station was 78 mph at Quantico, followed by 69 mph at Andrews AFB and Patuxent NAS. National Airport clocked a two minute sustained wind of 45 mph, with a peak gust of 58 mph.

Rainfall was generally two to three inches in the immediate D.C. area, but ranged as high as 6-12 inches in the Shenandoah Valley and Blue Ridge Mountains, where some flash flooding was noted.

From a historical prospective, Isabel was not nearly windy as Hazel in 1954 (winds reached 98 mph at National Airport), nor was it nearly as wet as Agnes in 1972 (6-12 inches of rain recorded across the metro area.) Nevertheless, Isabel will probably go down as the most destructive hurricane to ever hit the MD/VA/DC area.

The reason for such heavy destruction was in part due to a very wet summer that softened the soil in the local area and made for very dense leaf growth. Those factors made the trees extremely vulnerable to wind gusts of even 50 mph or less.

The result was thousands of trees being riped apart and toppled in the area, causing extensive property damage and unprecendented power outages.

Approximately 2 million area residents were put in the dark. It took over a week to restore power in all areas, despite crews being brought in from far away.

In the Fairfax area, the power outages at all four water treatment plants incapacitated the water filtration system, causing 1.2 million residents to be told to boil their drinking water.

In D.C. alone, 300 trees were reported downed, of which 23 fell on houses. In Prince Georges County, 450 downed trees were counted and 85 homes were significantly damaged, mostly by falling trees. In Montgomery County, 200 roads were closed due to fallen trees and powerlines. Over half of Montgomery County’s traffic signals were reported out of order.

The wind damage and treefall patterns were quite erratic, with some areas receiving extensive damage, while other areas got away with little or none.

The other factor which made Isabel so damaging was devastating tidal flooding, which was most severe in the Baltimore and Anne Arundel County area. In some areas, the high water marks along Chesapeake Bay and the Potomac River actually exceeded the records set during the Hurricane of 1933.

The tidal flooding was caused b a long fetch of southeast winds coming up the Chesapeake Bay and the Potomac River int the tight pressure gradient between Isabel to the southwest and a strong high pressure system to the northeast.

The record stages included 11.3 feet on the Potomac at Georgetown and 7.58 feet along the Chesapeake Bay in Annapolis, which broke the 1933 record of 6.35 feet.

Along the Potomac River, floodwater inundated properties along the river in Washington and Old Town Alexandria. Residents in Belle View community of Fairfax were forced to evacuate. Fortunately, the flood damage in the immediate D.C. area was restricted to a relatively small area along the waterfront.

The tidal surge was largely responsible for over 500 homes being destroyed in Maryland alone, with nearly 3,600 others being heavily damaged. Damage at the Naval Academy alone was estimated in the tens of millions of dollarss. Much of the historic waterfront area of Annapolis ws inundated.

In Baltimore, a ten foot wall of water pushed several blocks inland, destroying hundreds of cars and flooding out entire neighborhoods. Damage in Maryland was estimated at $1 billion.