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What Hurricane Joaquin might mean for the Washington, D.C., region

A serious weather event may unfold over the Washington, D.C., area Friday and into this weekend. Hurricane Joaquin is forecast to come very close to the Mid-Atl (Video: Monica Akhtar/The Washington Post)
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A serious weather event may unfold over the Washington, D.C., area Friday and into this weekend. Hurricane Joaquin is forecast to come very close to the Mid-Atlantic coast, and possibly move inland. At the very least, a period of heavy rain is likely. In a worst-case scenario, the region could contend with a dangerous, long-duration flooding event, widespread damaging winds and a significant surge of water up the Chesapeake Bay and Potomac River.

It is important to recognize that a worst-case scenario is one of several possibilities, so there’s no need to panic, but simply to begin thinking about hurricane and flooding preparedness and remaining tuned to the forecast, as it is likely to evolve substantially over the next 72 hours.

There is a good deal of uncertainty pertaining to the exact track of Joaquin, which currently possesses maximum sustained winds of 80 mph and is forecast to strengthen. The majority of computer models forecast it to make landfall between the North Carolina Outer Banks and the southern Delmarva peninsula late Saturday or Sunday. But a few models predict it to remain offshore, parallel to the mid-Atlantic coastline.

[Hurricane Joaquin current status and official forecast track]

Whether or not Joaquin comes ashore, at least one period of very heavy rain is likely in the D.C. area as a deep plume of tropical moisture ahead of the storm is absorbed by a front draped over the Eastern U.S. on Friday into Saturday. Meteorologists call this a PRE, short for “predecessor rain event,” and models indicate the potential for 2 to 6 inches of rain from this first phase of the storm. This, by itself, would likely lead to areas of flooding, especially after the 1 to 6 inches of rain which fell across the region Tuesday night.

[Tuesday night storm dumped 1-6 inches of rain across D.C. region: How it happened]

“The big forecast dilemma remains whether Joaquin will react to the high altitude atmospheric steering currents like Sandy did and make a sharp turn towards the Mid-Atlantic or whether it will stay far enough away to meander off to the north and east,” says Wes Junker, Capital Weather Gang storm expert.

“Many of the the models have Joaquin near or into the Mid-Atlantic coast by Sunday evening,” Junker adds. “But last night’s European model never lets Joaquin get captured by an area of low pressure over the eastern U.S. and consequently keeps the storm well out to sea.  Such a solution would offer the D.C. area another bout of heavy rain but would spare us from having to worry about tropical storm force winds and a serious storm surge in the Chesapeake Bay and Tidal Potomac.”

If Joaquin makes landfall in the Mid-Atlantic

If Joaquin makes landfall along the Mid-Atlantic coast Saturday into Sunday and moves inland, the potential for hazardous impacts across the region increases markedly.

[Interactive infographic: Billion-dollar weather disasters since 1980]

Depending on Joaquin’s exact track, rain associated with Joaquin’s core could push totals to 6 to 12 inches, with locally higher amounts possible, leading to widespread flooding of creeks, streams, rivers, poor drainage areas and low-lying areas. It is not out of the question that such a scenario could produce flooding on the scale of some of the greatest storms to ever affect the region, like Agnes in 1972.

Strong, even damaging winds would also be a serious concern if the storm moves inland towards the metro area. There is some potential for Joaquin to achieve major hurricane status, with maximum sustained winds of 111 mph over the ocean in the next 72 hours. As Joaquin moves north into cooler water and then potentially inland, those winds would weaken, but tropical storm-force winds in the 50-70 mph range (stronger in coastal areas) would certainly be possible in the D.C. area and, coupled with  saturated ground, could lead to downed trees and power lines, and outages.

Finally, several models forecast the storm to track inland just west of the Chesapeake Bay. Such a track would funnel a surge of water up the Chesapeake Bay and into the Potomac, presenting a tidal flooding threat in areas like Annapolis, Old Town, Va., Georgetown and Southwest D.C., in a similar fashion to Hurricane Isabel in 2003 — although it’s unclear whether surge heights would be as extreme.

In a Mid-Atlantic landfall scenario, the Virginia, Maryland and Delaware Atlantic beaches would be hammered by the combination of rain, hurricane-force winds, rising seas (storm surge) and tremendous wave action. Significant and costly coastal flooding could occur depending on the exact storm track. Even if Joaquin does not make landfall, minor to moderate coastal flooding and beach erosion are likely at the beaches.

“From the Carolinas into the Northeast, people should be monitoring their forecasts closely over the next several days as this storm has the potential to cause a lot of problems if it indeed is captured by the upper level flow and is pulled into the coast,” Junker said.