First named storm in the Atlantic possible this week :Is 91L

[KatDaddy]

From this morning's Jeff Master's post at the WeatherUnderground tropical page:

First named storm in the Atlantic possible next week

Both the GFS and ECMWF models are predicting that an extratropical "cut-off" low will separate from the jet stream early next week several hundred miles east of Bermuda, and linger for several days over subtropical waters with temperatures in the 22 - 24°C range. These ocean temperatures may be warm enough to allow the storm to organize into a named subtropical storm. However, climatology argues against such an occurrence; there has been only one named April storm in the Atlantic since 1851. If a subtropical storm does form next week, it would probably not affect any land areas.

Jeff Masters

[cycloneye]

ECMWF in it's 12z run continues to have the development scenario for the low pressure.

[wxman57]

This is the reason it's very hard to have fewer than 10 named storms these days. Prior to the past decade, there would not even have been the consideration of naming such a system.

[RL3AO]

This is the reason it's very hard to have fewer than 10 named storms these days. Prior to the past decade, there would not even have been the consideration of naming such a system.

Every year now seems to be good for at least two of these cutoff lows developing in the open Atlantic with another two or three getting close enough where they go code red in the TWO.

[Chacor]

This seems as good a time as any to point out the following recommendation the NHC is putting forward at the ongoing RA IV Hurricane Committee meeting regarding the definition of a subtropical system:

Update definition of subtropical cyclone
RSMC Miami
April 2012
-The current definition of subtropical cyclone is too vague. It defines a subtropical cyclone as having characteristics of both tropical and extratropical cyclones, but doesn’t indicate what those specific defining characteristics are. Adding specificity to the definition would promote greater consistency among forecasters in its application, and promote better understanding with users.
- Adopt the following definition for subtropical cyclone:
A non-frontal low-pressure system that has characteristics of both tropical and extratropical cyclones. Like tropical cyclones, they are non-frontal, synoptic-scale cyclones that originate over tropical or subtropical waters, and have a closed surface wind circulation about a well-defined center. In addition, they have organized moderate to deep convection, but lack a central dense overcast. Unlike tropical cyclones, subtropical cyclones derive a significant proportion of their energy from baroclinic sources, and are generally cold-core in the upper troposphere, often being associated with an upper-level low or trough. In comparison to tropical cyclones, these systems generally have a radius of maximum winds occurring relatively far from the center (usually greater than 60 n mi), and generally have a less symmetric wind field and distribution of convection.

[cycloneye]

12z Euro continues to develop the low,now only three days out.

[NDG]

It will be tough for that cutoff ULL to gain any subtropical charecteristics.
Euro and GFS show that it will stay north of the 30th latitude between the 50th & 60th longitude Sunday night through Wednesday night, where SSTs are near or slightly below 70 degrees F.

[AJC3]

Just a reminder for folks that the 26C/80F SST threshold assumes sort of a "standard deep tropical atmosphere". In other words, if mid/upper level tropospheric temperatures are typical of what you would find in or near the MDR, then it's safe to use that number. In this case, it's not, since the surface low is being forecast to develop beneath a cold core 500MB cutoff low. Systems that have their origins in higher latitudes, and/or beneath cutoff cold core lows have a lower SST threshold for central convection to develop or maintain itself since the lower SST's are offset by cooler mid level temperatures.

That being said, a lot has to go right for a deep layer cold core cutoff to acquire sufficient quasi-tropical characteristics to be subjectively called a TC or even an STC for that matter.

Generally, I bet against these types of cyclones becoming STCs/TCs, given the time of year, shear/stability issues, etc. However, you'll probably eventually see an invest out of this, and possibly a Special TWO or two. Happy bear watching.

[cycloneye]

TAFB has it in 24 hours as a frontal low. Let's see if it detaches from it or not.

[AJC3]

TAFB has it in 24 hours as a frontal low. Let's see if it detaches from it or not.

Interesting to see that the low is forecast to intensify into a 48kt+ storm as opposed to remaining a 34-47kt gale center.

[NDG]

GFS has been persistent in keeping the storm as an asymmetric cold core system with a large swath of gale force winds creating some large waves that may reach the eastern US coast later in the week.

[MGC]

The low is attached to a front this morning.....weather (pun intended) or not if it can detach from the front is one thing....cool SST are another. Small chance of become a SST right now.....MGC

[Kingarabian]

It's wrapping up pretty nicely this morning.

[cycloneye]

This area is now invest 91L,so the thread is locked. Go to ActiveStorms/invests forum to get all the information and to make comments.