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Posted at 1:30 PM ET, 09/29/2010

Moisture from tropics to feed D.C. rainmaker

By Jason Samenow

A general 1-4" of rain likely for metro region

* Outlook through the weekend: Full Forecast | NatCast *
* Nicole not so tropical | Hurricane Tracking Center *
* Flash flood watch into Thurs. | Wind Advisory eastern suburbs (map) *

Radar & lightning: Latest regional radar shows movement of precipitation and lightning strikes over past two hours. Refresh page to update. Click here or on image to enlarge. Or see radar bigger on our Weather Wall.

By the time tropical storm Nicole nears the mid-Atlantic coast, it will have transitioned into an entirely different kind of weather-maker more closely resembling a 'Noreaster than a tropical storm. Though the track of Nicole itself is now forecast to pass mainly east of Washington, its deep plume of moisture will be feeding a new low pressure system riding up a front draped across the mid-Atlantic. The end result will be generous rainfall amounts with localized flooding.


1 PM to 7 PM TODAY
Light to moderate rain at times. Temps 66-68.
Light to moderate rain. Temps 64-68.
Rain, becoming heavy at times. Temps 62-67.
Heavy rain & some gusty winds. Temps 64-72.
Rain tapers SW to NE. Temps 72-76.



When will conditions be the worst? The heaviest rain is anticipated late tonight and early tomorrow morning. Allow plenty of extra time for the a.m. commute.

When will it end? Per the timeline above, rain will start winding down in the early afternoon in the southwest suburbs (Prince William and Fauquier counties) and probably mid-to-late afternoon in the northeast suburbs (PG and Anne Arundel counties)

Will this be as bad as Isabel with downed trees and power lines? No way. No how. Though winds may be quite gusty at the Md./De./Va. beaches, winds in the immediate metro region will probably only be on the order of 10-20 mph (with some higher gusts possible during heavy rain bands). Widespread power outages are not anticipated locally. Some of the eastern suburbs, however, adjacent to the Chesapeake Bay could see gusts of 30-50 mph - perhaps enough to cause some isolated outages.

Keep reading for more FAQs

Does the drought mean less chance of flooding? Not entirely. The answer is yes for areas that only see around 1 to 2 inches. The ground is dry enough that it can probably handle that much unless it falls within a very short period of time like 1 to 3 hours. But if the potential for higher storm totals (around 3-4" or more) verifies, then flooding is a legitimate concern.

When there's enough rain over a short enough period of time, flooding can occur no matter how dry the ground is. Computer models indicate (through what's called Flash Flood Guidance) that given the current soil moisture conditions, flash flooding would be possible for areas that receive around 3-4 inches over a 6-12 hour period.

I have a flight tomorrow. Will there be delays? Yes...there will likely be flight delays, particularly in the morning due to the potential for heavy rain and low visibilities. Also, this storm will impact much of the East Coast, so delays at other airports will have ripple effects.

Will there be flooding along the tidal Potomac? There is a coastal flood watch for the potential for minor flooding from tides two to three feet above average late Thursday and Thursday night. Flooding along the lines of what was seen during Isabel or anything close to that is not expected.

What will impacts at the Va./Md./De. beaches be like? Heavy rain and gusty winds are likely, starting tonight in Va., and extending northward towards Md. and De. into tomorrow. Sustained winds of 25-35 mph are possible (higher gusts) and around 2-4" of rain. A high surf advisory has been issued with seas of eight to 13 feet possible. Minor to moderate coastal flooding is possible, as described by the National Weather Service in Wakefield, Va.:


How confident are you in your forecast? Except for a few isolated locations, the storm that came through earlier this week failed to produce the predicted amounts of precipitation, which ranged from 1-3" here at CWG to higher amounts (such as the National Weather Service's 2-4") from other outlets. As we explained in a post-mortem assessment, the tracking of that storm's low-pressure center too far west of the region subjected the metro area to the mercy of showery, hit-or-miss type precipitation, which for most locales turned out to be more miss than hit.

The chances of this latest storm fizzling appear to be lower as its low-pressure center is expected to track closer to the area, giving us a better chance at seeing a solid area of rain over the area for an extended stretch of time. But, while we're fairly confident we'll see significant rains near or over 1 inch, confidence is lower as to whether and where we'll see higher totals on the order of 2-4" or more.


National Radar
Regional Radar

(CWG's Dan Stillman contributed to this post)

By Jason Samenow  | September 29, 2010; 1:30 PM ET
Categories:  Floods, Tropical Weather  
Save & Share:  Send E-mail   Facebook   Twitter   Digg   Yahoo Buzz   StumbleUpon   Technorati   Google Buzz   Previous: Tropical storm Nicole not so tropical
Next: NOAA: Rainfall may be "very dangerous"


We're supposed to drive up to Long Island tomorrow morning. Should we plan to leave tonight?

Posted by: larryn703 | September 29, 2010 1:41 PM | Report abuse


I don't think driving to Long Island would be pleasant at all tomorrow. Tonight would be less inclement for sure, though showers are streaming north.

Posted by: Jason-CapitalWeatherGang | September 29, 2010 1:57 PM | Report abuse

Are we going to get another "D.C. split"? More rain to the east and west. Oh well, to the west needs it more.

Posted by: JerryFloyd1 | September 29, 2010 2:01 PM | Report abuse

Steady rain in Manassas.

Posted by: FIREDRAGON47 | September 29, 2010 2:02 PM | Report abuse


May see a split again-- as locations west benefit most from frontal rains, and locations east get more rain from the direct remnants of Nicole herself. There's still a lot of uncertainty, however.

Posted by: Jason-CapitalWeatherGang | September 29, 2010 2:09 PM | Report abuse

Power outages are not anticipated locally.

The author clearly isn't a Pepco subscriber ;)

Posted by: LongshoreCowboy | September 29, 2010 2:13 PM | Report abuse

LongshoreCowboy - I take it you have been having trouble with your Pepco power, eh? In what locale are you based? This time around we should be "ok" with power outages, but with all this rain, it might only take one gust of wind near the end of this event to topple a power line or two. CWG will monitor!

Posted by: Camden-CapitalWeatherGang | September 29, 2010 2:18 PM | Report abuse

I have to drive to Norfolk tomorrow afternoon - will the rain be letting up by then?

Posted by: badnewshound | September 29, 2010 2:23 PM | Report abuse



Posted by: Jason-CapitalWeatherGang | September 29, 2010 2:25 PM | Report abuse

Thanks, CWG, this is very helpful. I am in Falls Church with a creek that doesn't like tropical storms, so a "DC split" would be just fine by me. TS Hanna was 13 inches of water in my house with rainfall totals around 6-7 inches. Here's for three inches instead of four or five or six!

Posted by: erbele | September 29, 2010 2:28 PM | Report abuse

Will the Nationals game in D.C. tonight be rained out? What about tomorrow if they have to reschedule?

Posted by: fs228 | September 29, 2010 2:38 PM | Report abuse

If this were snow....

Posted by: newsregister | September 29, 2010 2:50 PM | Report abuse

newsregister sends a shudder up my spine ... CWG, does the amount of moisture we're seeing in our rain events lately suggest more huge snows ahead?

Posted by: mhardy1 | September 29, 2010 2:58 PM | Report abuse

is that "creek" holmes run?

my daughter and i go down there during/after heavy rain to watch the flooding and gauge how heavy the rain was based on how high that creek is.

Posted by: walter-in-fallschurch | September 29, 2010 2:59 PM | Report abuse


I think the Nats game will probably be canceled. We'll try to update NatCast if we hear anything.

Posted by: Jason-CapitalWeatherGang | September 29, 2010 3:00 PM | Report abuse

Can't wait! I enjoyed this last rain so much and will really enjoy another day of heavy rain. Its so relaxing. I just mowed my friend's lawn today and now I get to sit on the porch swing and watch it get even greener. Thank you rain Gods!

Posted by: SusanMarie2 | September 29, 2010 3:10 PM | Report abuse

@fs228 - I have Nats tickets also - but tonight's the last home game of the season and completely meaningless in the standings - there's a good chance that if it's rained out it won't be rescheduled :-(

Posted by: hohandy1 | September 29, 2010 3:40 PM | Report abuse

Is there someplace online that lists DCA hourly temps for today? Trying to determine if DCA has made it to 70 degrees since 12 midnight. thanks.

Posted by: JerryFloyd1 | September 29, 2010 3:42 PM | Report abuse

Posted by: mkbf26 | September 29, 2010 3:54 PM | Report abuse

@walter-in-falls-church. Yes, Holmes Run Creek. The lastest post makes me think I need to start moving furniture, ugh.

Posted by: erbele | September 29, 2010 3:54 PM | Report abuse

@mkbf26, thanks! this could be the first day since I suppose May that temps have failed to rise above 70 degrees.

Posted by: JerryFloyd1 | September 29, 2010 4:11 PM | Report abuse

So by "winding down" by afternoon tomorrow, do we mean "no more rain", "drizzling", "scattered showers", or "steady rain but not a downpour"? This may be an impossible q to answer. I'm located on Capitol Hill and had an outdoor activity scheduled for tomorrow around 4 and wondering if we should cancel; if it's one of the first two we can go ahead but not in steady rain...

Posted by: ikeforpres | September 29, 2010 4:32 PM | Report abuse

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