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General Discussion >> 2018 Forecast Lounge

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cieldumortModerator
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98L Lounge
      #99653 - Thu Sep 20 2018 02:40 AM

Below: GFS Surface (10m wind and MSLP) analysis Sep 20 0z


Florence is no longer, having transitioned into an elongated trough of low pressure, and ultimately merging with a mid-latitude system and becoming part of the reason for frontogenesis while exiting the east coast. This merged system, with scant Florence DNA left in it, is now well offshore of the east coast and has a couple of lows developing within it.

For a few days, several models have had runs pinching off the southern extent/s of this system, with one or two synoptic-scale lows taking off on their own with subtropical or even tropical development. The NHC has outlined in this morning's TWO the region they consider the most promising for development within the next 5 days, and have placed a broad 40% oval around 34N 46W.

From this tonight's TWO
Quote:

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
200 AM EDT Thu Sep 20 2018
A non-tropical low pressure system is forecast to develop by Friday night over the central subtropical Atlantic Ocean between Bermuda and the Azores. Conditions are expected to be conducive for the low to acquire some subtropical or tropical characteristics, and a subtropical or tropical cyclone could form over the weekend or early next week while the low meanders over the central Atlantic Ocean.
* Formation chance through 48 hours...low...near 0 percent.
* Formation chance through 5 days...medium...40 percent.



Another region not currently mentioned by the NHC, but which is closer to land, has some models showing a bit of run-to-run consistency for development occurring between Bermuda and the South Atlantic states.

If one or both of these modeled Lows gets Invest tagged, which looks very possible, the title of this thread will be changed with whichever one picks up a tag first. If the second is also tagged, it will be placed in its own Lounge.

*The formerly non-tropical gale center located near Bermuda has just been tagged Invest 98L and the title of this thread has been changed accordingly. This system is already producing sustained winds to tropical storm force and watches/warnings may be issued as soon as today. - Ciel

Edited by cieldumort (Thu Sep 20 2018 02:50 PM)


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cieldumortModerator
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Re: Sub/Trop Development Possible [Re: cieldumort]
      #99654 - Thu Sep 20 2018 03:07 AM

The feature just northwest of Bermuda is already looking more interesting this late night.
(Bermuda is the oblong dot on the map below located near 32.5N 65W


Image cr: Weathernerds.org


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cieldumortModerator
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Re: Sub/Trop Development Possible [Re: cieldumort]
      #99655 - Thu Sep 20 2018 01:30 PM




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cieldumortModerator
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Re: Sub/Trop Development Possible [Re: cieldumort]
      #99656 - Thu Sep 20 2018 02:21 PM

NHC has just outlined the gale cyclone located north-northwest of Bermuda in the 2pm TWO and put a starting bid of 20% development odds on it, which could be very conservative. Most likely this system gets Invest tagged 98L shortly, and if current trends continue it would not be surprising to see "code yellow" ramp up to orange or even red in short order.

This system has some Florence DNA it it, but maybe not enough to technically be considered Florence 2.0 More accurately it might best be described as 'remnants of Florence merged with a mid-latitude, non-tropical low undergoing tropical transition,' and as such, if named, doubtful that it retains the Florence moniker. But this would be an interesting footnote in the history of that devastating hurricane.


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cieldumortModerator
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Re: 98L Lounge [Re: cieldumort]
      #99657 - Thu Sep 20 2018 02:57 PM

Solid ASCAT from 1445z today showing an area of strong winds up to Tropical Storm force located southeast of the center of 98L. While still a little oblong and a touch involved with its associated trof, only a slight increase in organization from this morning would likely qualify the cyclone for a name. The next name on the list in the Atlantic is Kyle.



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cieldumortModerator
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Re: 98L Lounge [Re: cieldumort]
      #99660 - Fri Sep 21 2018 02:41 AM

An update on 98L before a look at the models.

Some general surveying of a number of tropical experts today found no consensus on some key things. No consensus as to whether or not 98L should be considered a continuation of Florence, or an all-new cyclone if named, as well as no consensus as to whether or not 98L was on Thursday sufficiently put-together to be classified tropical storm, subtropical storm, or just still an extra-tropical storm (extra-tropical = non-tropical, despite the confusing jargon).

There was broad consensus that 98L had been producing winds to gale and tropical storm force for most if not all of the day and night, and that if it was determined by NHC to be either subtropical or tropical its status would go straight to getting a name (Kirk or Florence, depending on ones read of the matter).

It was and remains my personal "read" that 98L by early evening had become a tropical storm, and probably not Florence 2.0, but maybe.

Outside of the unsettling idea that maybe 98L retain the same name sadly so fresh in everyone's mind, this is really all kind of academic. What is more important right now is, what's it gonna do from here?

98L looks tonight to be a classic case of tropical cyclone been decapitated. North to northwesterly shear on the order of 25 - 50 KTS has pushed away almost all of the organized convection, replacing it with dry air. If deep convection does not return within the next few hours, and there is every reason to believe it won't, not in that environment, it may be that 98L is just one for review post-season the way some other after-the-season additions are.

However, models, and indeed the NHC, anticipate that conditions for development may become more favorable by early next week, and thus especially given that there is actually some consensus of the future track of 98L (a loop back around towards the east coast) it behooves us to know if it is going to be capable of bringing inclement weather. The states recently flooded by Florence do not have the ability yet to take on any more rain. Not one drop.

Run-down of 09/21/0z models so far:

ECMWF: Rounds the building High to the northwest clockwise and crosses coastal North Carolina as a closing off wave between 0z Wednesday the 26th and 0z Thursday the 27th. Likely a coastal rain-maker for 12-24 hours.

GFS: Rounds the building High to the northwest clockwise and comes just ashore in the Carolinas as an open-wave around 06Z Wednesday the 26th. Likely a coastal and inland rain-maker for 18-30 hours before zipping off with a front.

GFS FV3: Rounds the building High to the northwest clockwise and comes ashore near GA/SC as a closing-off wave around 12Z Wednesday the 26th and zipping off with a front. Likely a coastal and inland rain-maker for 18-30 hours.

CMC: Rounds the building High to the northwest clockwise and brushes the Carolinas as a closing off Low around 06Z Wednesday the 26th before being swept up and out by a front. Likely a coastal rain-maker for 12-24 hours.

ICON: Rounds the building High to the northwest clockwise and passes within a few hundred miles at most of the OBX as a reestablished 1012 MB depression by 12Z Wednesday the 26th. Likely a coastal rain-maker for 18-24 hours.

HMON: Rounds the building High to the northwest clockwise, maintaining 98L as a closed but often sloppy Low. End of run on 06Z Wednesday the 26th as a 1015 MB sloppy closed Low - possibly a TD - centered roughly 150 miles east-southeast of Savannah, Ga.

HWRF: Rounds the building High to the northwest clockwise, maintaining 98L as a closed but often sloppy Low. End of run on 06Z Wednesday the 26th as a 1012 MB sloppy closed Low - possibly a low-end Trop Storm - centered roughly 300 miles southeast of Myrtle Beach, SC.


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cieldumortModerator
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Re: 98L Lounge [Re: cieldumort]
      #99668 - Mon Sep 24 2018 11:32 AM


Above satellite image courtesy Weathernerds.org

98L is much improved this morning, with billowing convection atop and although mostly north of of an apparent well-defined LLC (I've circled this LLC in the image above), despite being squeezed upon by outside winds and battling dry air.

If the incipient tropical cyclone does not get pinched or sheared too much today, or chokes on too much dry air, and thus provided this convective trend lasts a few more hours, we could see Advisories by tonight. Steering currents favor a track towards the Carolinas - but probably limited odds to really ramp up

A few models' runs have taken 98L further inland to merge with an approaching front/trof, but most runs suggest it gets swept out to sea ahead of the trof, just brushing N.C.

While having some x-Florence DNA in it, meteorologically it is highly unlikely that 98L would be given that name if tropical storm force winds resume. The next name on the list this year in the Atlantic is Michael.


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danielwAdministrator
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Re: 98L Lounge [Re: cieldumort]
      #99669 - Mon Sep 24 2018 05:32 PM

98L continues just off of the Southeast and Mid-Atlantic Coasts.
Forecasts are Off and on presently. Will the system will intensify and which direction will it track?



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