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Posted at 11:00 AM ET, 09/29/2010

Tropical storm Nicole not so tropical

By Greg Postel

An inside look at this rainmaker's dynamics

* When/how will TD16 impact the DC area?: Full Forecast | NatCast *
* Around midday: Updated rain and wind projections for DC area *

11 a.m. update (originally posted at 10:15 a.m.): Tropical depression 16 has strengthened just enough to be named Tropical Storm Nicole. Nicole is a minimal tropical storm with sustained winds to 40 mph and it is not expected to appreciably strengthen - though it will be a very significant rainmaker for the East Coast, including the D.C. metro region.

Tropical storm Nicole, previously Tropical Depression 16 (TD16) has failed to significantly intensify since forming yesterday in the Caribbean Sea, a little more than 100 miles south of Havana Cuba. The center of circulation is believed to be located roughly 120 miles east southeast of Havana. TD16's Nicole's maximum sustained winds are now estimated at 35 mph 40 mph, four shy of what it needs to be named tropical storm Nicole.

The poorly organized circulation is expected to continue a northeast movement at roughly 10 mph for the next day or so, with an increase in forward speed thereafter.

Keep reading for more on this tropical storm...

td16-sat-092910.gif
Visible satellite image of TD16 this morning. Source: NOAA.

The strongest winds and most intense thunderstorm activity are dislocated from the center by several hundred miles to the southeast. From our distant glance, it's difficult to identify classic features of a tropical cyclone.

There is no long-lived complex of intense thunderstorms near the primary low-level vortex. There is no evidence of a high pressure system (clockwise circulation) above the main low-level swirl. And the list goes on.

The thunderstorm activity that gave birth to TD16 appears to be part of a much broader concentration of disturbed weather that has settled over the Caribbean Sea in the past week.

Since tropical storm Matthew moved though several days ago, showers and thunderstorms have erupted repeatedly in this part of the world and, consequently, have given rise to a large-scale low pressure system over these very warm waters.

When TD16 formed yesterday - the latest such low pressure system - it was best described as a "monsoon depression" by Weather Underground meteorologist Jeff Masters, who wrote:

TD 16 resembles the "monsoon depressions" common in India's Bay of Bengal or the Western Pacific. A monsoon depression is similar to a regular tropical depression in the winds that it generates--about 30 - 35 mph near the outer edges (and usually stronger on the eastern side of the circulation.) Monsoon depressions have large, calm centers, and can evolve into regular tropical storms, if given enough time over water to develop a tight, closed circulation.

In some circumstances, especially earlier in hurricane season when wind shear is typically less of a factor, an atmospheric regime like this could produce tropical cyclones galore. After all, a warm and humid atmosphere that is capable of sustaining thunderstorm clusters, that overlies bath-like ocean water, and that slowly rotates in a counterclockwise fashion, is an ideal place for tropical cyclone development.

But that is not quite what we have this time around.

With dry and windy conditions aloft expected to continue to reside over much of the Southeast and Gulf of Mexico in the wake of a strong cold front that recently penetrated all the way to the Yucatan Peninsula and Northwest Caribbean Sea, TD16 Nicole should devolve into a non-tropical/hybrid system fairly quickly in this extremely hostile environment.

td-16-ulwinds.gif
Upper level winds. Longer arrows indicate stronger winds. Source: University of Wyoming.

As shown in the image to the right, strong winds on the southern periphery of an 'upper trough' (low pressure at high altitudes) currently extend well south of Cuba. As TD16 Nicole moves northward, it will begin to encounter these stronger winds aloft and disintegrate fairly rapidly. Wind shear (changing of the wind with height) of this magnitude, especially when it is associated with a strong frontal zone from the continental U.S. as it is now, is a tropical cyclone assassin.

As TD16 Nicole more closely interacts with the upper trough, the strong winds it encounters will tear apart any thunderstorm groups that try to isolate a warm and humid inner core -which is something it would require to intensify further.

And once TD16 Nicole ingests some of the dry continental air brought to the region by northerly flow on the backside of the upper trough -with surface dew points in the 50s currently observed over the Northern Gulf of Mexico- its chances of maturing as a tropical cyclone will surely be choked.

However, this is not to imply that the East Coast will escape impacts from what is left of TD16 Nicole as it moves northward along or near the Coast. Upward motion (that produces clouds and rain) on a larger, non tropical-cyclone scale, is expected to accompany the remnants of TD16 Nicole as it moves northward in tandem with the upper trough during the next couple of days.

With a tropical pedigree, this hybrid weather system carries the potential for generating heavy rainfall across many locations in the mid Atlantic States. Accumulations upwards of four inches are quite possible along the heavy rain path. Yet by that time, I would prefer to think of this system as a rain-maker from the Caribbean, rather than attach any meaningful tropical aspects to it.

By Greg Postel  | September 29, 2010; 11:00 AM ET
Categories:  Tropical Weather  
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Next: Moisture from tropics to feed D.C. rainmaker

Comments

First. AND Tropical Storm Nicole has been born! See http://www.nhc.noaa.gov/

Posted by: snowedin85 | September 29, 2010 11:02 AM | Report abuse

Nice write up on the rainmaker. Interesting that you posted just before the nws announcement of a change of name to TS Nicole.

"...DEPRESSION BECOMES A TROPICAL STORM...CENTER STILL NEAR CENTRAL CUBA... "

Posted by: dqreads | September 29, 2010 11:04 AM | Report abuse

The track of Nicole seems to be further east with the latest map produced by the NHC. However, they do not track it as long as in previous estimates. Not sure why.

Posted by: rocotten | September 29, 2010 11:04 AM | Report abuse

@rocotton - Nic is expected to be fully post-tropical before it gets north of Florida, thus the end of tropical tracking at that latitude...bascially this will be a 'Nic'Easter" for us.

Posted by: DullesARC | September 29, 2010 11:15 AM | Report abuse

Hi guys - can someone please explain how a storm like Nicole technically becomes post-tropical, while still at a relatively low latitude. Thanks.

Posted by: dhb2 | September 29, 2010 11:22 AM | Report abuse

New track is definitely to the east, watches & warnings dropped in Florida. Does this mean we may not get the rain after all?

Posted by: kathyb39 | September 29, 2010 11:28 AM | Report abuse

Hi dhb2

It's not the latitude that matters (whether a system is "tropical" or not). It's the storm structure and its relationship with the surrounding environment. In this case, we have an extratropical upper trough that has penetrated south of 30N and introduced the kind of wind shear and humidity levels in places that don't normally see them this early in the Fall. Nicole is becoming overwhelmed by unseasonably strong winds and cooler air.

Technically, the transition occurs as the vertical structure of the vortex becomes tilted/diffused in a way that destroys the mechanism by which it once maintained itself ... which is via a complex self-induced exhange and ingestion of moist enthalpy from the ocean surface.

greg

Posted by: gregpostel | September 29, 2010 11:37 AM | Report abuse

@kathyb39, this is from the National Hurricane Center and it explains Nicole's shift to the east and why we'll still get a lot of rain:

THE GLOBAL
MODELS SUGGEST THAT EXTRATROPICAL DEVELOPMENT WILL OCCUR ALONG THE
NORTHERN EXTENT OF THE TROUGH OFF THE EAST COAST OF CENTRAL OR
NORTH FLORIDA LATER TODAY. THE EXTRATROPICAL LOW IS THEN FORECAST
TO MOVE NORTHWARD ALONG THE U.S. EAST COAST DURING THE NEXT COUPLE
OF DAYS. NICOLE IS FORECAST TO MOVE NORTHEASTWARD ACROSS CUBA AND
THE NORTHWESTERN BAHAMAS...AND IS LIKELY TO DISSIPATE AS THE
EXTRATROPICAL DEVELOPMENT BECOMES THE DOMINANT EVENT. THE NEW NHC
TRACK IS A LITTLE EAST OF THE PREVIOUS ADVISORY AND SHOWS
DISSIPATION OF THE TROPICAL CYCLONE MUCH SOONER THAN PREVIOUSLY
PREDICTED. GIVEN THE COMPLEXITY OF THE SCENARIO...HOWEVER...
UNCERTAINTY IN THIS FORECAST IS HIGHER THAN NORMAL.

Posted by: snowedin85 | September 29, 2010 11:38 AM | Report abuse

"The Perfect Storm" in 1991 wasn't tropical by the time it hit NEngland but it was still a very bad scene up there.

Posted by: JerryFloyd1 | September 29, 2010 11:48 AM | Report abuse

Hi JerryFloyd1

Absolutely ! But the un-named tropical system that conspired to create those conditions in 1991 was quite a bit stronger ... at minimal category 1 intensity.

greg

Posted by: gregpostel | September 29, 2010 11:58 AM | Report abuse

CWG - the models are notoriously slow to break out precip far enough north in these tropical moisture setups. based on radar, it certainly seems prudent to raise the rain probabilties for the afternoon.

Posted by: foul_throw | September 29, 2010 12:37 PM | Report abuse

Thanks, snowedin85. Not long after I posted my question, it started to drizzle here in Bethesda. I know we need the rain, I'm just hoping we don't get the flooding.

Posted by: kathyb39 | September 29, 2010 1:03 PM | Report abuse

I don't pretend to be a meteorologist, so I was hoping someone could explain the 2 different precipitation maps at this link:

http://www.hpc.ncep.noaa.gov/qpf/day1-5.shtml

They show notably different rain totals for the DC area, and I was wondering how to interpret this?

Posted by: FH59312 | September 29, 2010 1:11 PM | Report abuse

Hi FH59312

Sure thing ... the plot on the left is the latest forecast made this morning, and the plot on the right is a forecast made by the same model from last evening (12 hours earlier).

Hope that helps

greg

Posted by: gregpostel | September 29, 2010 1:19 PM | Report abuse

Hi FH59312

Sure thing ... the plot on the left is the latest forecast made this morning, and the plot on the right is a forecast made by the same model from last evening (12 hours earlier).

Hope that helps

greg

Posted by: gregpostel | September 29, 2010 1:20 PM | Report abuse

Getting a little drizzle in Laytonsville. On radar it looks like the rain intensity is diminishing as the system moves North.

Posted by: dprats21 | September 29, 2010 1:22 PM | Report abuse

I would just note those are not model outputs in the HPC images, but rather what they think will happen.

Posted by: Ian-CapitalWeatherGang | September 29, 2010 1:25 PM | Report abuse

This system should most likely be labeled as Subtropical Storm Nicole...especially at our latitude.

The comparison with the 1991 "Perfect Storm" is apt, considering, as mentioned, that this system is quite a bit weaker, though still potentially nasty. It seems to be behaving as a strong out-of-season nor'easter.

Posted by: Bombo47jea | September 29, 2010 1:29 PM | Report abuse

Looking at the National Mosaic http://radar.weather.gov/ridge/Conus/full_loop.php the volume of precip from the mid-Atlantic states down to the Keys (just north of what appears to be Nicole's center) is amazing.

Depending on how things evolve, this storm could give our thirsty soil a serious quench, and more.

Posted by: JerryFloyd1 | September 29, 2010 1:30 PM | Report abuse

Any idea how Nicole will impact air travel at DCA tomorrow?

Posted by: dbokie1 | September 29, 2010 1:32 PM | Report abuse

@dbokie1

We have the answer to your question in our latest post, just published: http://voices.washingtonpost.com/capitalweathergang/2010/09/tropical_storm_nicole_remnants.html

Posted by: Jason-CapitalWeatherGang | September 29, 2010 1:44 PM | Report abuse

The comments to this entry are closed.

 
 
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