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Here Comes Cindy!

Josh Larson @ 11:30 PM

Cindy for beginners

Perhaps the past two weeks' worth of tropical humidity and active thunderstorms should have presaged the fact that we can't keep our eyes of the Tropics this time of year. Indeed, the remnants of Tropical Storm Cindy (which I'll dub Cindy 2.0) are poised to bring heavy rain, thunderstorms, and potential flooding to the Washington, DC metro area during a short window from approximately 4-8pm today through 8pm to midnight Friday.

If you've kept up with the recent posts on, you'll see that there's the typical disagreement between major computer models, and therefore the meteorological community, regarding exactly how Cindy 2.0 will impact the DC Metro area. One major model camp (the GFS) suggests very high amounts of precipitation (on the order of 4-6" or more), while another major model camp (the NAM) suggests much lower amounts (on the order of 1-2").

While the National Weather Service has issued a Flash Flood Watch highlighting rainfall amounts of 3-6" with locally higher amounts, believes that these totals are somewhat overdone. (For those who speak meteorologese, I believe the GFS is having feedback problems, and has overdone precipitation amounts.) That being said, there is no doubt that Cindy 2.0 will have a significant impact on the entire region -- including flooding rain, gusty thunderstorms, localized flash flooding, a slight threat of tornadoes -- so be prepared for storm-related disruptions.

The Basics
  • Start-time: ~4-8pm today
  • End-time: around midnight Friday
  • Most likely amounts: 2-3" immediate metro area
  • Where might there be more western suburbs (3-5"+ possible)
  • Where might there be less southeast suburbs (~1")
Look out for:
  • Embedded thunderstorms which may cause torrential rain, flash floods
  • A slight chance of tornadoes from embedded supercell thunderstorms
  • Highly localized nature of precipitation amounts
  • A few locations, especially west of town, may see 6"+
Approximate Timeline
  • 4pm-12am: scattered showers, thunderstorms
  • 12am-8am: steadier rain; thunderstorms
  • 8am-2pm: moderate to heavy rain at times
  • 2pm-6pm: periodic rain, thunderstorms; stray tornado?
  • 6pm-12am: scattered showers, thunderstorms taper off
Accumulation probabilities (see image for accumulation potential)
  • >1": 75%chance/coverage
  • 2-4": 50% chance/coverage
  • 4-6": 25% chance/coverage
  • >6": 10% chance/coverage
  • The computer models have shown significant disagreement. A slight wobble in the track of Cindy 2.0, and the precipitation amounts could change considerably.
  • Note, again, that there will be highly localized rainfall amunts due to the location of embedded thunderstorms; hypothetically, you might receive 1 inch, while your friend only 10 miles away might see over 4 inches.
  • I'm going out on a limb in suggesting the potential for tornado development; the NWS has ignored this potential component of Cindy 2.0. Don't be alarmed, however, as the threat is still low.

Dennis is now a Category 1 Hurricane, located more than 200 miles ESE of Kingston, Jamaica. Sea surface temperatures (SSTs) in its path are at above-normal levels (supplying significant heat and energy) and wind shear (which can significantly weaken hurricanes) is minimal. As it continues on its trek west-northwest, it will likely strengthen considerably. The latest model guidance suggests that it will continue to move northwest and strengthen to a dangerous Category 3 or greater hurricane by the time it makes landfall somewhere, most likely, along the Louisiana, Mississippi, or Alabama coasts on Monday. However, due to a different pattern aloft than in the wake of Cindy, the remnants of Dennis will likely not affect our area; instead, it looks like they may bring much-needed rain to the south-central part of the nation.

Nationals vs. Mets, 1:05pm, RFK
Variably cloudy skies, with some peaks of sun possible, with humid conditions but pleasant temperatures near 80°. There is a slight (<20%) chance of a stray shower towards the end of the game, though it likely will remain dry. Update: Rain showers will likely move in earlier than anticipated, increasing the chances of a rain delay. Be prepared with rain gear.

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