Hurricane Isaias is charging toward Florida as it threatens the entire East Coast. There is some potential for it to unload heavy rainfall in the D.C. region between late Monday and Tuesday.

How much rain will depend on exactly how close the storm tracks to the region. Track scenarios range from it staying just offshore the Delmarva coast, in which case little rain would fall, to the storm riding up the Chesapeake Bay, which would likely result in heavy rainfall.

As of Saturday morning, computer models tend to favor a track closer to the bay, and a heavy rainfall scenario.

In addition to heavy rain, parts of the region could also experience gusty winds over 30 mph on Tuesday, especially east of Interstate 95, if the storm center tracks near the bay or over the Delmarva. However, widespread damaging winds will be unlikely, as the storm will have transited over land through eastern North Carolina and southern Virginia, causing weakening.

How much rain are we talking about? The current the National Weather Service forecast projects a widespread 2 to 4 inches, with isolated amounts to half a foot. That would be enough to cause areas of flooding, especially of small streams and in poor drainage areas.

The heaviest amounts would likely occur east of I-95.

Here are amounts projected from different models for the District through Wednesday:

  • American: 3.4 inches
  • European: 3.1 inches
  • UKMet: 2.6 inches
  • Canadian: 1.2 inches

The exact timing of the rainfall is still coming into focus but showers could begin in the region on Monday morning or afternoon, arriving south to north, with the heaviest rain on Tuesday, tapering off by the evening.

The rain will come not only from Isaias itself but also from moisture surging out ahead of it, interacting with a front stalled over the region. This could result in enhanced rainfall late Monday into early Tuesday, well before the heavy rains from Isaias itself arrive.

Jeff Halverson, Capital Weather Gang’s severe weather expert, said upper level winds favor rains breaking out prior to Isaias’ arrival in the Mid-Atlantic, and they could be heavy at times.

“In addition to the frontal interaction, the moisture from Isaias may also interact with a pocket of upper level energy in the jet stream, causing the heavy rains to be fairly widespread over portions of the Mid Atlantic, and spread further inland from the Bay and coast,” he said via email.

Thunderstorms ahead of the storm on Monday afternoon and evening could produce isolated damaging wind gusts. Then some locally strong winds could occur within Isaias’s rain bands on Tuesday, especially east of Washington.

As the track of Isaias is expected to be along or just east of the Chesapeake, we do not expect a major storm surge (rising water for coastal areas) for the shores along the bay and Tidal Potomac. However, if the track shifts west of Washington (unlikely, but not impossible), minor to moderate coastal flooding could be possible.

Implications for coastal zones from Outer Banks to Jersey Shore

Many Washingtonians may be vacationing this week at the Mid-Atlantic beaches, from North Carolina’s Outer Banks through the Delmarva and into southern New Jersey. Heavy rain, coastal flooding and tropical-storm-force winds are possible in all of these areas between late Sunday night and early Wednesday.

The worst weather should only last 12 to 24 hours in these areas, so canceling trips is unnecessary unless the forecast changes. But be prepared to spend a day or so indoors and/or delay arrival until after the storm passes. It is important to monitor the forecast, heed the advice of local officials and avoid travel during the worst of the storm.

Of all the Mid-Atlantic beaches, conditions may be the worst along the Outer Banks. Dare County, N.C., is advising visitors to consider delaying arrival until after the storm passes and is considering whether it will require evacuations.

“Dare County is likely to experience impacts from the storm as early as Sunday evening, August 2,” said its emergency management director Drew Pearson in a news release. “Now is the time to assemble or restock your disaster supply kit with essentials to sustain your family and your pets for three to five days. Have your evacuation plan ready to execute.”