Nicole to race by D.C. region Friday, with rain and possibly tornadoes


Unseasonably warm and moist air is moving back into the mid-Atlantic ahead of the remnants of Tropical Storm Nicole, which will pass through the area on Friday. While Thursday is calm, Friday will show a chance of showers through the morning with intermittent showers throughout the day.

Major impacts in the DC area will include on and off periods of heavy rain that could lead to isolated flash flooding, and gusty winds from the south and southeast.

Given the high atmospheric spin associated with Nicole’s remnants, a tornado threat may also develop. Twister odds are somewhat higher south and southeast of Washington, toward southern Maryland, Richmond, and Virginia Tidewater.

Tropical Storm Nicole slams into Florida, poised to drench eastern US

The National Weather Service Storm Prediction Center placed the DC area at a level 1 of 5 risk for tornadoes, while areas to the south are at a level 2 of 5.

Additionally, the weather service has placed the region in Level 1 of 4 for extreme rainfall. Chances of heavy rain will increase west and northwest of the DC area.

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Time: Rain chances increase during the early morning hours on Friday, especially in the southwest of the area, and become possible by sunrise. Additional waves of rain pass through during the day. The rain should end late Friday night.

Coverage: Expect on and off rain, passing waves and maybe some thunder. The rain will move quickly but may be heavy at times.

Risks: The primary concerns are the risk for heavy rain, gusty winds and an isolated tornado or damaging wind gusts. The probability of flooding is quite low as the area has been dry recently.

Rain Forecasts: A wider 1 to 1.5 inches is most likely. Towards the mountains, 2 to 3 inches could fall. Southern Maryland and the Delmarva Peninsula may see half an inch to closer to an inch.

How Nicole will influence the region

By Friday morning, a weakening Nicole will be centered over central Georgia, as shown below, as the rain works its way north through the mid-Atlantic.

A hurricane has very large wind circulation. High pressure retreating northward will help tighten the pressure gradient in the mid-Atlantic, thus keeping wind speeds high. Expect winds of 20 to 30-plus mph Friday and potentially higher in any storm.

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As Nicole transitions from a tropical to a mid-latitude storm, a warm front will form (red scallop lines above) that could become a focus for any tornadic activity. Meanwhile, a strong cold front and a deep dip in the jet stream will reach the East Coast from the Ohio Valley.

Nicole’s remnant center will merge with that front, perhaps near the spine of the Appalachians, as a plume of deep tropical moisture moves northward to the east of the storm. Strong upwelling on the western side of Nicole’s remnants will interact with tropical moisture and produce very heavy precipitation over the Appalachians, along with more wet weather to the east.

By Friday evening, Nicole’s remnants will quickly move northeast, and skies may begin to really clear by midnight.

Why are strong winds and tornadoes a threat?

While the fuel for the types of storms that can produce hurricanes will be limited in the DC area, wind forcing (the variation in wind direction and or speed with height) will be significant. That combination of ingredients could set the stage for a low-top rotating storm. Those cells, in turn, can bring damaging (50-60 mph) wind gusts to two locations at the surface, as well as produce brief tornadoes.

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Inland tornadoes spawned by tropical debris are short-lived and weak, but those characteristics also make them difficult to detect by radar, thus hindering the issuance of timely warnings.

At this point, the Storm Prediction Center thinks the highest tornado threat will be just south of DC, however, we warn that this zone could extend further north if the air mass remains unstable through the late afternoon and early evening hours.

Rainfall totals will be highly track dependent. A total of around an inch seems reasonable in Washington right now. A shift in the forecast track to the east will bring higher totals closer to the area. The region has been quite dry recently, so the threshold rainfall for triggering flash floods at the local level is high.

Overall, the predicted track of Nicole’s remnants has moved westward, somewhat reducing possible precipitation in the immediate area.

Here are the estimated amounts by various models:

  • European (ECMWF): 0.50-1 inch+
  • American (GFS): 0.75-1.5 inches
  • American (NAM): 0.50-1 inch
  • Canadian (GEM): 0.75-1.5 inches
  • Icon: 0.75-1.5 inches

Additional track shifts are possible, which will affect the rainfall forecast. But we don’t expect big changes, now that we’re within a day of the event.


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