(This article, originally posted at 11:38 a.m. Wednesday, was updated at 3:00 p.m. to incorporate the high wind watch issued by the National Weather Service.)

* High wind watch issued for entire region from 1 a.m. Friday to 6 a.m. Saturday *

A powerful nor’easter will rapidly intensify off the Mid-Atlantic and Northeast coasts Friday, generating a significant high-wind event in the Washington and Baltimore regions.

“Our confidence is increasing in a prolonged period of strong to damaging winds late Thursday night through Friday evening,” the National Weather Service office serving the Washington and Baltimore region tweeted Wednesday morning.

It added that this could be one of the strongest wind storms in the region in at least three years.

On Wednesday afternoon, the Weather Service issued a high wind watch for the period spanning Friday and Saturday morning meaning there is potential for  a “hazardous high wind event.” The watch is likely to transition to a warning or advisory on Thursday.

Exactly how strong the winds become will depend on how much the storm strengthens and its position relative to the coast, but gusts to at least 50 mph are likely along with sustained winds of at least 30 mph. It’s not out of the question that sustained winds could reach 40 mph with gusts exceeding 60 mph — which is equivalent to tropical storm strength — especially in the mountains and near the Chesapeake Bay.

Because the ground will become soggy from rain falling Thursday into Friday, the wind may more easily take down trees, raising the specter of scattered power outages. While widespread power outages cannot be ruled out in a worst-case scenario, the lack of foliage on trees and recent tree mitigation from power companies should reduce the risk.

The winds may also be strong enough to cause minor structural damage. Air travel delays are likely.

Between Wednesday and Thursday evening, it would be a good idea to secure loose outdoor objects or bring them inside. To prepare for the possibility of power outages, charge your mobile devices and have flashlights at the ready.

Wind timing and intensity

While subject to change, models tend to show winds rapidly increasing between midnight and sunrise Friday. Gusts could increase from 30 to 50 mph during this time. The strongest winds are likely between about 10 a.m. and 7 p.m. Friday, when gusts could reach 50 to 60 mph or so.

This will be a long-duration high-wind event, with gusts to 50 mph possible through Friday night and up to 40 mph through Saturday afternoon. On Sunday, while it will remain breezy, peak wind gusts should ease to around 20 to 25 mph.

Why are the winds expected to be so strong?

The rapid intensification of the storm off the coasts will really get the winds howling as its counterclockwise circulation drives wind from the Northeast along much of the Eastern Seaboard.

But the winds will be particularly strong in this storm because of the massive change in air pressure over a relatively small region; this change is known as the pressure gradient and what really drives wind speed. The greater the pressure gradient, the stronger the winds.

The nor’easter and its center of low pressure (colored in blue and purple in the graphic below) will be surrounded by abnormally high pressure both to its northwest over the Great Lakes and to its north, over Greenland (colored in red). Recall the “Greenland Block” we wrote about?

The difference in pressure between this beast of a storm and the enormous high-pressure zones surrounding it will set the stage for a memorable wind event not just in the D.C. area but also over the entire Mid-Atlantic and Northeast zones. Because of the configuration of weather systems, this zone is essentially going to turn into a raging wind tunnel.