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Posted at 12:45 PM ET, 09/28/2010

Tropical depression forms, eyes Florida, East Coast

By Jason Samenow

Heavy rain, wind possible in D.C. metro region by Thursday

* Rain possible by late Wed.: Full Forecast | Rain that wasn't | NatCast *

Satellite image of Tropical Depression 16, located south of Cuba. Image courtesy NASA.

A vigorous disturbance swirling in the Caribbean south of Cuba was classified a tropical depression late this morning by the National Hurricane Center.

The depression (TD16), the 16th of the season in the Atlantic basin, will be named tropical storm Nicole if it strengthens as forecast later today. Tropical storm warnings (map) have been posted for much of South Florida, the Florida Keys, the Cayman islands, Cuba, and the northwest and central Bahamas. After passing south Florida tomorrow, this system is then likely to race up the East Coast, potentially impacting large areas with wind and flooding rain - including the D.C. metro region.

At the moment, TD16 is not terribly well-organized. Lacking the hallmark symmetry of a hurricane with thunderstorms wrapping around a well-defined center, this lopsided storm has most of its thunderstorm activity concentrated on the system's southeast side.

Maximum sustained winds are 35 mph, well below hurricane strength of 74 mph, but only modest strengthening is necessary for it to reach tropical storm intensity with 39 mph sustained winds.

Despite moderate wind shear (turning of the wind with height which can impede storm development by ripping apart thunderstorms) TD16 is surrounded by very warm water which should provide it with enough fuel to reach tropical storm status.

It's unlikely TD16 or Nicole will reach hurricane intensity because it will not only battle with wind shear, but it will also encounter the landmasses of Cuba and South Florida and eventually cooler water as it heads northward.

Though winds upwards of 30-40 mph along the coast are nothing to sneeze at, torrential rain is likely to be the biggest impact from this storm. This system is associated with copious amounts of deep tropical moisture which will surge northward ahead of it. National Weather Service forecasters are predicting 3-5" or more of rain over South Florida and such amounts may well be commonplace further north as this system charges up the coast.

Tropical storm forecast model tracks as of 8 a.m. this morning. Source: Colorado State University

Track guidance is pretty consistent taking the storm's center across southeast Florida before paralleling the Southeast coast and then intersecting the North Carolina Outer Banks. After that point, the track scenarios widen with some computer models taking TD16 inland up the coastal plain towards the Chesapeake Bay, others even further inland, and some offshore. The exact track will determine where the most rain falls:

  • A track to the west of the D.C. metro region would result in lesser rain amounts (more showery rains, like we experienced Monday) but the slight possibility of severe thunderstorms and tornadoes.
  • A track over the region would increase the likelihood of flash flooding and rainfall totals of up to 3-5" or so. Wind gusts over 30 mph would also be possible
  • A track east of the D.C. metro region would result in lesser rain amounts (though still possibly substantial) and more severe impacts along the Delmarva peninsula, including coastal flooding and beach erosion.

At this point, the the D.C. region should be aware of the possibility of heavy, wind-swept rain as well as coastal flooding/erosion Wednesday night into Thursday (with some rain beginning as early as Wednesday afternoon). As the event draws closer, we will be able to hone in on exactly how much rain will fall and where and pinpoint some of the other potential impacts.

By Jason Samenow  | September 28, 2010; 12:45 PM ET
Categories:  Floods, Tropical Weather  
Save & Share:  Send E-mail   Facebook   Twitter   Digg   Yahoo Buzz   StumbleUpon   Technorati   Google Buzz   Previous: The rain that wasn't
Next: PM Update: Brief respite in stormy period


Assuming the system does track up the eastern seaboard, where is it apt to be Friday a.m.? Right now, the NHS is only showing a three-day cone, with the system off the Georgia coast Thursday a.m

Posted by: JerryFloyd1 | September 28, 2010 1:34 PM | Report abuse


Probably around New England.

Posted by: Jason-CapitalWeatherGang | September 28, 2010 1:37 PM | Report abuse

Saw this on the NWS site re. rainfall amounts from TD16:


Posted by: FH59312 | September 28, 2010 1:56 PM | Report abuse


I saw that too, but not sure if that will still be the case when the storm transitions from "tropical" to "extratropical" around our latitude

Posted by: Jason-CapitalWeatherGang | September 28, 2010 2:02 PM | Report abuse

I'm supposed to be driving from McLean to the Chesapeake Bay Club across the Bay Bridge early on Thursday morning (7am) for a work conference, should I even bother trying to attempt it?

Posted by: HokieTerp | September 28, 2010 2:13 PM | Report abuse

Jason, thanks, hopefully out of the NYC area with minimal, if any, damage to Amtrak's catenary/trackage between NYC and DC.

Posted by: JerryFloyd1 | September 28, 2010 2:25 PM | Report abuse

Hope I'm wrong, looks like a better chance of a miss than a hit 4 rain on Thurs. Most of the rain will b 2 the E again.
Looks like this will end up as the 4th warmest Sept. on record.

Posted by: VaTechBob | September 28, 2010 2:27 PM | Report abuse

I believe we should look at the middle of the road on the forecast.. there could be some rain, could be a bit of a breeze, but unlikely we stay dry --also unlikely we experience terrible flooding. I would not change plans yet this week or weekend.

Posted by: Camden-CapitalWeatherGang | September 28, 2010 2:30 PM | Report abuse

Jason, is everyone but you, Ian, and Matt on vacation? You seem to be pulling the yeoman's load as of late.

How are you holding up?

Mr. Q.

Posted by: Mr_Q | September 28, 2010 2:31 PM | Report abuse

Models are shifing west...just enough for us in Metro DC to best pay attention. I'll have my Jim Cantore rain pants on standby for Thursday...(no goggles). I remember what Hannah did...probably a decent comparison to what our high end potential is for Nicole.

Posted by: DullesARC | September 28, 2010 2:38 PM | Report abuse


I agree Hannah might be the best analog in the last few years-- probably less wind...


Wouldn't change plans until tomorrow when we'll have better info for you to base your decisions on

Posted by: Jason-CapitalWeatherGang | September 28, 2010 2:43 PM | Report abuse

@mr. q:

This has become my full-time gig so when there is "breaking" weather during the day, I'll be covering it most of the time. Otherwise, you'll see the same mix of writers for the most part. I used to be just part-time.

Posted by: Jason-CapitalWeatherGang | September 28, 2010 2:45 PM | Report abuse

I'm supposed to fly out of DCA on Thursday morning (8:30) for Chicago...connecting to China...are we looking at flight delays from this?

Posted by: dtdc1 | September 28, 2010 2:48 PM | Report abuse

I know Im not the only one thinking this, and I bet that it gets talked about a little more tomorrow, but its a good thing last night's rain was a bust. And if Nicole (they just found the 35 kt winds - updagrade at 5pm) tracks juuuust to our west then some "you know whats" may have a chance to spin up since we could be in the right front quadrant. Im guessing that the next run of models will really have a good handle on track, since the Hurricane Hunter data will be in there. The trough to the east may be slowing down a bit, thus the shift west in the models. Thursday is trending a bit damp around here.

Posted by: DullesARC | September 28, 2010 2:58 PM | Report abuse


Will depend on the storm track. Based on current info, chance of delays are highs. Stay tuned.

Posted by: Jason-CapitalWeatherGang | September 28, 2010 3:00 PM | Report abuse

Ugh...thanks, I guess. So if I had a choice to switch to flying out of Dulles rather than DCA, would that be recommended? (Farther west equals less impact?)

Posted by: dtdc1 | September 28, 2010 3:02 PM | Report abuse

OK, stand down for 5pm...ATCF might have had a typo since they changed their winds back to 30 kts - not guaranteed to be Nic at 5pm just yet. Obviously, negligable/semantics...but what in the name of the Western Pacific is happening in the NW Carrib? Monsoon low...

Posted by: DullesARC | September 28, 2010 3:04 PM | Report abuse

Track of the storm will dictate. Conditions could be worse further west. No way to tell right now and do not advise changing flight plans.

Posted by: Jason-CapitalWeatherGang | September 28, 2010 3:08 PM | Report abuse

Thanks, Jason. Will hold tight with fingers crossed for a while I guess!

Posted by: dtdc1 | September 28, 2010 3:09 PM | Report abuse

@Jason - Absolutely right about winds on the coast to 40mph. What I saw in Earl a few weeks ago pretty much blew my mind, and that was about 45-55mph sustained. I dont think that the general public understands (or has even come close to experiencing) strong TS winds during an event. Our gusts to 50 or so here after cold front passages in the winter are nasty enough. Try sustaining that speed for 30-40 minutes at a time. It caught me off guard...along with the sand and the sideways (upwards, even) rain.

Posted by: DullesARC | September 28, 2010 3:10 PM | Report abuse

When will it be time for all of us to toss our lawn furniture in the swimming pool?

Posted by: wiredog | September 28, 2010 3:10 PM | Report abuse


Thanks! I'll be watching this closely!

Posted by: HokieTerp | September 28, 2010 3:12 PM | Report abuse

So does 'extratropical' spell bad news for our region? As in, is this another Isabel?

Posted by: Akabang | September 28, 2010 4:07 PM | Report abuse

Naturally, since we've got some type of tropical weather heading our way, this is the weekend we're heading to the Outer Banks. We plan to leave Thursday, when would be the best time to travel?

Posted by: weathergrrl | September 28, 2010 4:12 PM | Report abuse


The storm is long gone by the weekend and somewhere near the Northeast coast Thursday night (well north of the Outer Banks). You could probably leave Thursday.

Posted by: Jason-CapitalWeatherGang | September 28, 2010 4:33 PM | Report abuse

This could be a nightmare forecast, whoever ends up near the frontal zone will cash out while places close by might not see much at all. Hopefully the 18z NAM is wrong... 7-9"+ right over the heart of the area might cause trouble!

Posted by: Ian-CapitalWeatherGang | September 28, 2010 4:51 PM | Report abuse

Thx, Jason!

Posted by: weathergrrl | September 28, 2010 5:21 PM | Report abuse


Here's to your success.

Mr. Q.

Posted by: Mr_Q | September 28, 2010 6:25 PM | Report abuse

@Ian ...for those of us who aren't hardcore weather folks, what's an 18z NAM? And is there really a chance we could get 7-9"+?

Numbers like that make my flood-prone-basement-owning heart quiver...

Posted by: SSFSCoWA | September 28, 2010 6:37 PM | Report abuse

The NAM is a weather forecasting model. 18Z is the time. That weather model is predicting a large amount of rainfall.

Posted by: MKadyman | September 28, 2010 7:04 PM | Report abuse

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