Is there a pattern to Historical Tropical Cyclones that have impacted the CB Watershed?

The majority of tropical cyclones that impact the CB originate in the Atlantic Ocean, and most frequently during the period of August through October; and, to a lesser extent, in the Carribean or eastern Pacific, and mainly during the period of June through August , where storms move into the Gulf of Mexico, make landfall along the northeastern Gulf Coast, and then head inland north towards the CB. For those storms that originate in the Atlantic Ocean, a common point of origin is just offshore of the Horn (or Sahel region) of Africa. They begin as low-pressure systems that develop from atmospheric disturbances that initially moved westward off the Sahel and African coast.  If drought conditions prevail in the Sahel region, however, as they did throughout most of this Summer, 2007, few of these disturbances develop, and the threat of tropical cyclones from this region is reduced (http://typhoon.atmos.colostate.edu/).

Once formed, the low-pressure system can gain strength by drawing energy from the warm ocean waters that prevail because of summer heating along the tropics, and typically moves westward as a result the Trade Winds, which also prevail in these same summer tropical waters.

The ultimate path and strength of the storm is determined by how long it remains steered by the westward Trades in warm waters. While it remains in the tropics and heading west towards the Caribbean, Gulf of Mexico, and lower eastern United States, and potentially gaining in strength, climactic and ocean conditions in the tropical Pacific Ocean can intervene. If an El Nino condition prevails in the tropical equatorial region of the Pacific Ocean it causes stronger westerly winds in the upper atmosphere over the lower latitudes of the United States.  These winds can shear tropical storms apart and help steer the Atlantic storm away from the mainland (http://www.pmel.noaa.gov/toga-tao/enso.html).  Initially, this summer there was no indication of a strong El Nino condition in the tropical Pacific Ocean, but in August, 2007, El Nino conditions strengthened, and sheering winds became a factor.

Meterological conditions prevailing over the United States and North Atlantic also can influence the direction and intensity of an approaching cyclonic storm.  If a trough of low pressure exists over the United States and simultaneously a high pressure system over the central North Atlantic Ocean, high steering winds, the "Prevailing Southwesterlies", created by this combination of low and high pressure systems can act to curve the storm increasingly to the north as it moves west. Thus the position and strength of the Ocean high pressure center and the US low-pressure trough, which can vary markedly on a weekly basis, play major steering roles that determine whether the storm curves quickly to the north, and eventually northeast into colder waters, and remains ocean bound, or curves only slowly and therefore maintains or increases in strength if it is steered into the the Gulf of Mexico, or the warm Gulf Stream along the Atlantic Coast, before it makes landfall as a tropical depression, storm, or hurricane.

Because of the complexity of factors that determine the fate of tropical depressions in the eastern Atlantic, and the changing nature of these factors, tropical depressions and their fate are continuously monitored by the NOAA National Weather Service's National Hurricane Center. They track and forecast storm strength and track. Depressions are numbered in sequential order through the hurricane season, generally June through October. When a tropical cyclone reaches tropical storm strength, it is named from an alphabetical list drawn up for the season (http://www.nhc.noaa.gov/aboutnames.shtml) for the list of hurricane names for the current (2007) season. Names of disastrous hurricanes like Andrew, Hugo, and Fran, are retired and their names are replaced on the six year list by an international committee.

If the National Hurricane Center's forecasted storm track indicates the storm will move inland and that storm track includes the Chesapeake Bay (CB) Watershed, or that the storm will remain ocean bound but pass near the Virginia, Maryland, and Delaware coasts, that should be of concern to all CB residents. Three examples of storms that did reach Hurricane strength in the Atlantic, and utlimately passed inland and northwest, directly through, and along the coast east of the CB are Isabel (2003), the 1993 Hurricane, and Floyd (1992). All caused significant damage and indicated the vulnerability of the CB to these types of storms.

The Chesapeake Inundation Prediction System (CIPS), is being developed, to provide a forecast capability to local National Weather Services (Wakefield, VA, Sterling, VA, and Mt.Holly, NJ) in the CB area to better predict the storm surge and inundation in the CB associated with these types of tropical storms.