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


Unseasonably warm and humid air is moving back into the Mid-Atlantic ahead of the remnants of Tropical Storm Nicole, which will make landfall in the region on Friday. While Thursday will be calm, Friday will feature a chance of rain in the morning, with scattered showers throughout the day.

Major impacts in the DC area include on-and-off periods of heavy rain that may lead to isolated flooding, and southerly and southeasterly winds.

Because of the high atmospheric spin associated with Nicole’s remnants, there may also be a tornado threat. The likelihood of twisters is somewhat higher south and southeast of Washington, toward Southern Maryland, Richmond and the Virginia Tidewater.

Tropical Storm Nicole is battering Florida, set to drench the eastern US

The National Weather Service Storm Prediction Center placed the DC area in a Level 1 of 5 risk for tornadoes, while areas to the south were in a Level 2 of 5 risk zone.

Additionally, the Weather Service placed the region at a Level 1 of 4 risk for excessive rainfall. Chances of heavy rain will increase west and northwest of the DC area.

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Timing: Rain chances increase early Friday morning, especially in the southwest of the area, and likely as the sun rises. Additional waves of rain followed during the day. The rain should end late Friday night.

Scope: Expect on-and-off showers, rip currents, and maybe a few thunderstorms. Showers will be fast moving but can be quite heavy at times.

Risks: The main concerns are heavy rain, gusty winds and a risk for an isolated tornado or damaging wind gust. The possibility of flooding is relatively low as the area has been relatively dry recently.

Rain projections: A width of 1 to 1.5 inches is likely. Towards the mountains, 2 to 3 inches could fall. Southern Maryland and the Delmarva Peninsula will likely get closer to a half inch to an inch.

How Nicole will influence the region

By Friday morning, the center of the weakening Nicole was over central Georgia, as shown below, with showers moving northward into the Mid-Atlantic.

The storm features massive air circulation. A high pressure depression to the north will help tighten the pressure gradient across the Mid-Atlantic, thus keeping wind speeds elevated. Expect winds to frequently gust from 20 to 30-plus mph Friday and possibly higher with any thunderstorms.

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As Nicole transitions from a tropical to more of a mid-latitude hurricane, a warm front (red scalloped lines above) will develop that could become a focus for any tornado activity. Meanwhile, a strong cold front and deep sinking jet stream is approaching the East Coast from the Ohio Valley.

The center of Nicole’s remnants will merge with that front, perhaps near the spine of the Appalachians, as a plume of deep tropical moisture moves northward to the storm’s east. Strong upwelling on the western side of Nicole’s remnants will interact with tropical moisture to produce a patch of potentially heavy rain over the Appalachians, with wetter weather to the east.

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

Why are strong winds and tornadoes a danger?

While fuel for the types of storms that can produce tornadoes will be limited to the DC area, wind shear (change in wind direction and or speed with altitude) will be significant. That combination of ingredients could set the stage for a low-top rotating storm. Those cells, in turn, can bring gusts of damaging (50-60 mph) surface winds in some spots, as well as form brief tornadoes.

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Inland tornadoes caused by tropical debris tend to be short-lived and weak, but those characteristics also make them difficult to detect with radar, thus preventing the issuance of timely warnings.

At this point, the Storm Prediction Center feels that the highest tornado threat is just south of D.C. However, we warn that this zone could extend farther north if the air mass remains unstable through the afternoon and early evening.

Rainfall totals will be highly track dependent. Right now, about an inch total in Washington seems reasonable. A change in the forecast track farther east will bring higher totals closer to the area. The region has been relatively dry recently, so the threshold rain was high which triggered flash flooding in some areas.

Overall, the predicted track of Nicole’s debris has moved to the west, somewhat reducing the rainfall potential in the immediate area.

Here are the values ​​expected by the different 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 changes are possible, which will affect the rain forecast. But we don’t expect much change, now that we’re a day into the event.


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