Tropical storm Nicole not so tropical
An inside look at this rainmaker's dynamics
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...
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.
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.
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.
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.
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