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SNE "Tropical" Season Discussion 2021


WxWatcher007
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Almost lost count of the use of "hone in on" in this discussion.

Confidence still highest in heavy rainfall with tropical downpours
associated with Elsa as it moves through. PWAT values will get up to
2-2.25 inches, which is around the maximum for this time of year per
SPC Sounding Climatology for CHH. Unsurprisingly, will have warm
cloud layer depths between 3.5-4.5 km, so will have very efficient
rainfall processes going on. Still some uncertainty on the track,
which will delineate where the heaviest QPF is located and where the
wind risk will be. Right now the greatest probabilities of 24 hr QPF
AOA 1 inch are highest across the interior per the EPS/GEFS
guidance, which falls in line with a more inland track as shown by
the latest ECMWF. Will really need to hone in on this track for
determining where the highest rainfall amounts are anticipated. This
is somewhat in contrast to some of the latest deterministic guidance
showing the highest swath from eastern CT/RI into eastern MA. So,
will need to really hone in on the track to determine where the
heaviest rain will fall and where there could potentially be a flood
threat especially given the recent rains we`ve received. Went with
the latest WPC guidance for QPF. Agree with the WPC latest Day 3
Excessive Rainfall Outlook.

As stated in the previous section, will really need to hone in on
the track of Elsa to determine not only the heavy rainfall risk, but
also where the damaging wind risk will be highest. The latest
ECWMF/NAM guidance are concerning given we have a 60-70+ kt
southerly 925 hPa jet associated with Elsa crossing eastern portions
of the CWA. Other pieces of deterministic guidance are a bit more
muted with the strength of this jet, but have really just thrown out
the GFS in the latest update as it appears to keep the core too far
offshore, which is counter to the ECMWF/UKMET/ICON/NAM and GEM
guidance. Will need to watch this closely. Once again will refer
folks to the official NHC page for the official track/timing of Elsa
as it moves through the region.

 

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I'm not sure I understand ( Meteorologically ) what the mechanisms are these guidance are "honing in on" to maintain that type of system structure/identity/and power this far N over cold water/land interface, after already having traversed total land for some 500 miles. 

wtf man -

no one is question how these guidance are doing that, - they are just programmed to discuss what it impacts the surface as though there is not other option?  I guess that's what we've become. 

wholly reliant

But you know, if they're right they're right...  But then I have to question if that disk of wind is anywhere less than 1500 meters

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6 minutes ago, Typhoon Tip said:

I'm not sure I understand ( Meteorologically ) what the mechanisms are these guidance are "honing in on" to maintain that type of system structure/identity/and power this far N over cold water/land interface, after already having traversed total land for some 500 miles. 

wtf man -

no one is question how these guidance are doing that, - they are just programmed to discuss what it impacts the surface as though there is not other option?  I guess that's what we've become. 

wholly reliant

But you know, if they're right they're right...  But then I have to question if that disk of wind is anywhere less than 1500 meters

I hope that the models are picking up on some kind of baroclinic transition, as I can see those winds being probable in a transitioning hybrid system, certainly not anything fully tropical.

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2 minutes ago, tiger_deF said:

I hope that the models are picking up on some kind of baroclinic transition, as I can see those winds being probable in a transitioning hybrid system, certainly not anything fully tropical.

I've seen mets discuss the 1938 hurricane, and while it has been a Cat 5 in the Bahamas, it still had Cat 3 winds because of baroclinic forcing.  Almost no rain West of the center.  I'd guess that is what the ensembles are seeing.

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20 minutes ago, Typhoon Tip said:

I'm not sure I understand ( Meteorologically ) what the mechanisms are these guidance are "honing in on" to maintain that type of system structure/identity/and power this far N over cold water/land interface, after already having traversed total land for some 500 miles. 

wtf man -

no one is question how these guidance are doing that, - they are just programmed to discuss what it impacts the surface as though there is not other option?  I guess that's what we've become. 

wholly reliant

But you know, if they're right they're right...  But then I have to question if that disk of wind is anywhere less than 1500 meters

925 LL jet Baroclinic enhancement. See Isaias 

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Tropical Storm Elsa Discussion Number  31
NWS National Hurricane Center Miami FL       AL052021
500 PM EDT Wed Jul 07 2021

Surface synoptic data indicate that the center of Elsa has moved 
into extreme southern Georgia and, assuming continued weakening 
since earlier today, the maximum winds are estimated to be 40 kt. 
This may be a generous estimate of the current intensity since no 
surface observations of sustained tropical-storm-force winds have 
been recently received.  Elsa should weaken into a tropical 
depression on Thursday.  By early Friday, the dynamical models show 
some restrengthening of the cyclone as it moves along the 
Mid-Atlantic coastline.  However, the simulated satellite imagery 
from the global models at that time depict the system resembling a 
frontal cyclone, so it is dubious as to whether Elsa will be 
completely tropical in 48 hours.  Due to the uncertainty as to when 
extratropical transition will occur, tropical storm watches have 
been issued for Long Island and portions of southern New England at 
this time.

The initial motion is northward, or 010/12 kt.  Elsa is forecast to 
turn north-northeastward overnight as it moves around the 
northwestern periphery of an Atlantic subtropical ridge while 
accelerating northeastward ahead of a broad mid-level trough over 
the eastern United States and Canada on Thursday.  The official 
forecast is about the same as the previous one and closely follows 
the multi-model consensus.


Key Messages:

1. Heavy rainfall may result in considerable flash, urban, and
isolated moderate river flooding over northern Florida.  Heavy
rainfall across southeast Georgia, South Carolina, North Carolina,
and southeastern Virginia may result inconsiderable flash and urban
flooding across southeast Georgia and the Lowcountry of South
Carolina.  Heavy rainfall across the Northeast and New England
Thursday and Friday could lead to isolated flash and urban flooding.

2. Although the center of Elsa is expected to remain inland of the
coastline from Georgia through the Carolinas during the next day
or two, tropical storm conditions are expected along portions of the
coasts of Georgia and South Carolina tonight.  Tropical storm
conditions are also possible along the coast of the mid-Atlantic
and southern New England states by Thursday night or Friday.


FORECAST POSITIONS AND MAX WINDS

INIT  07/2100Z 30.8N  83.4W   40 KT  45 MPH...INLAND
 12H  08/0600Z 32.8N  82.1W   35 KT  40 MPH...INLAND
 24H  08/1800Z 35.6N  79.4W   30 KT  35 MPH...INLAND
 36H  09/0600Z 38.8N  75.4W   35 KT  40 MPH...INLAND
 48H  09/1800Z 42.0N  70.5W   35 KT  40 MPH...INLAND
 60H  10/0600Z 46.0N  64.5W   40 KT  45 MPH...POST-TROP/EXTRATROP
 72H  10/1800Z 50.0N  57.0W   40 KT  45 MPH...POST-TROP/EXTRATROP
 96H  11/1800Z...DISSIPATED

$$
Forecaster Pasch

 

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