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TS Nicole Impact Thread for Friday into Saturday


yoda
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12 hours ago, toolsheds said:

Question about how Nicole formed.  If it started as a subtropical storm, doesn't that change where the wind field is located within the storm?  If it does, could that wind field shift as it strengthens and becomes a hurricane? 

Generally, yes. A subtropical storm almost always has a wind field that is lopsided, with the maximum winds as a result further from the low level center. You could see it very clearly in the early stages of subtropical development of Nicole, as maximum winds and convection were well east.

Since then, the wind field has tightened and become more symmetrical, as is necessary for a tropical cyclone—this organization allowed Nicole to become a hurricane. 

Hope that helps. 

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Well written AFD from LWX this afternoon 

 

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...

The remnants of Hurricane Nicole, now Tropical Storm Nicole,
will impact the area Friday into Friday night. Nicole will
continue to weaken as the storm approaches the Mid-Atlantic, bringing
the potential for multiple hazards to the region. With the
ensemble mean low track near or just west of the Allegheny
Front, the region will be in the warm sector of the decaying remnants.
A strong southerly flow of 40-55 kts right above the surface
will result in a rather dynamic wind field and advect Tds into
the mid to upper 60s with PWs 3-4 SA above normal. Given the
building instability and lift associated with the first quasi-
warm frontal band, rain showers will likely overspread the
region near or by daybreak Friday. Expect continued showers with
isolated thunderstorms through the day, though coverage likely
remains isolated to scattered in nature. By the afternoon once
the first source of synoptic lift moves through, there could be
a break of a few hours in the afternoon. By the evening, all
attention will focus to the remnant low and south/southeast
extending frontal feature which could be the focus for damaging
winds and perhaps tornadoes. The track and speed of the low will
ultimately determine how much instability rooted within the
boundary layer remains post sunset due to diurnal constraints
of instability this time of year. Given the strong wind field,
any instability may be sufficient for the production of isolated
severe thunderstorms. Will continue to monitor. Now for the
hazards

Heavy Rain Potential ...
With the persistent south/southeast flow and moisture advection
into the area, the Blue Ridge (southern Blue Ridge near
Wintergreen) will be the focus for the highest QPF amounts
(2-3", locally higher) through the event. With the persistent
south/southeast flow, the area to the northwest of the Blue
Ridge (Shenandoah Valley and the Hampshire to Hardy County area
into Washington County) could actually downslope resulting in
less QPF across that area. The secondary maximum in QPF is
likely across the eastern slopes of the Allegheny Front (1-3").
Along and east of I-95 much lower amounts of an inch or less are
expected. With the low tracking along or west of the
Alleghenies, the forcing will be better in that area. To the
east, the intermittent nature and lack of persistent forcing
will result in lower amounts. Believe the relative lack or
suppressed amounts of instability will help tamper the Flash
Flood threat even though PWs are near 1.75". FFG is also the
highest it has been in some time given the 2-3" departure from
normal precipitation over the region from the past 30 days. With
that being said, isolated to scattered instances of flooding
are possible Friday and Friday night along and west of the Blue
Ridge Mountains (especially in areas near higher terrain
susceptible to poor drainage). All ensembles and MARFC keep
rivers below any flood stages.

Severe Thunderstorm Potential ...
From an environmental standpoint, most ingredients will exist
Friday afternoon/evening. The shear (50-60+ kts), SRH (100-300
m2/s2), LCLs (<1000m at times), SPC/STP (>1), extra/sub-tropical
 rainbands all are worrisome. However, there is considerably
uncertainty regarding how much instability (CAPE) exists when
the aforementioned band moves through the region (generally
speaking near 7 PM through 1 AM) and remains rooted within the
boundary layer. Some guidance has the instability elevated by
the time this feature moves through. There could be discrete
low-topped supercells as indicated by some guidance and
supported by model soundings ahead of this feature during the
afternoon hours. Regardless, severe thunderstorms capable of
isolated damaging wind gusts and isolated tornadoes will be
possible Friday evening.

Damaging Wind Potential ...
With a dynamic wind field just above the surface (40-55kts), the
focus and tricky part of the forecast will be how much and if
any of this mixes down to the surface Friday evening into the
overnight. Model guidance diverges on if this makes it to the
surface, but given the bias of some guidance to bring down too
much rain on the backside of precipitation, have opted not to
pursue Wind Advisories at this time. There is likely a 1-3 hour
surge of enhanced winds (perhaps 30-45 mph) translating from
SSW to NNE through the center of the CWA Friday evening into the
overnight. Therefore, gusty winds may result in an isolated
wind damage threat Friday evening through Friday night. The
areas of greatest concern area especially along the higher
ridges of the Allegheny Front, Blue Ridge, and Catoctin
Mountains.
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