Ed Dunham
Former Meteorologist & CFHC Forum Moderator (Ed Passed Away on May 14, 2017)
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A weak non-tropical low pressure area interacting with an upper-level trough has formed to the southeast of Myrtle Beach, South Carolina, and has issued a Special Tropical Weather Outlook. At 19/12Z, Invest 93L was located at 32.6N 77.3W with sustained winds of 30kts and a central pressure of 1009mb.
The system is drifting to the southwest and upper south southwesterly windshear has displaced most of the convection to the north of the low pressure center. This southwesterly shear is expected to abate over the next couple of days, however the SSTs are a chilly 25C. There is a 50/50 chance for additional tropical or subtropical development.
ED
ADDED: 93L upgraded to TS Alberto at 19/21Z.
Edited by Ed Dunham (Sat May 19 2012 10:43 PM)
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CoconutCandy
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Invest 93L strikes me as a rather interesting pre-season system, perhaps capable of spawning a sub-tropical cyclone. And just maybe we'll even have a named system before the official start of Hurricane Season, still a couple weeks away.
Although cloud top temps have warmed slightly these past few hours, this is the normal course of events during the so-called diurnal convective minimum cycle.
If the wind shear does not become prohibitive, I would expect a big increase in the amount of deep and sustained convection overnight, and we might have a named storm as early as tomorrow, as the system is currently only 5 kts. shy of the requisite 35 kt. threshold for a named system.
And being so close to land, the 'inner core' convection is already showing up quite nicely on the Wilmington, NC Doppler Radar. Of interest to note here are the cumulus 'streets' beginning to wrap tightly around the low level circulation center in the NW-ern semicircle.
Wilmington, NC Dopplar Radar Loop
Not only will this aid the forecasters in determining a more precise center fix for their advisories on this developing system (should they become necessary), but provides an excellent on-going assessment of the intensity of the convection, and the degree of convective organization.
It's always interesting to note the degree of correlation between the animated satellite loop signatures and the progressive Doppler radar reflectivities over time.
All in all, Invest 93L is certainly a system to keep an eye on, primarily for the Outer Banks of North Carolina and points northwards, as the consensus of the early model runs indicates that, once 93L finishes meandering towards the SW as it currently is doing, it should begin a path towards 'recurvature' as early as tonight or early tomorrow.
Should Invest 93L become a named storm, it will be given the name 'Alberto'. Stay tuned!
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"Don't Get Stuck on Stupid" - General Honore, following Hurricane Katrina
Edited by CoconutCandy (Sun May 20 2012 10:46 AM)
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Hurricane Fredrick 1979
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I see on the site it has it .01L waiting to see if the names it at 5:00PM
Any thoughts here???
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cieldumort
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Invest 93L is very likely to be officially upgraded to Tropical Storm Alberto by 5PM. Stay tuned.
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CoconutCandy
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You are correct! 'Alberto' it is. Likely to be designated as a subtropical system, at least initially, as I doubt true warm core transition has likely not yet been attained. It would be interesting to see a 'Phase State' Diagram on this developing cyclone.
Also, there has been a Tropical Cyclone Formation Alert posted on the website, so perhaps will begin issuing advisories on 'Alberto' as early as 5pm, as you suggest.
My! How quickly things can develop, right in your own backyard, as it were!
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"Don't Get Stuck on Stupid" - General Honore, following Hurricane Katrina
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cieldumort
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Main page is up on Tropical Storm Alberto.
Alberto is more tropical than subtropical, hence the use of the moniker, albeit qualified.
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MichaelA
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I think they'll go purely tropical on this since it's over the Gulf Stream and drawing energy from it.
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Michael
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CoconutCandy
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Yes, from reading the first Advisory just posted, it appears to be a fully qualified, pure warm core tropical system. Thus, Tropical Storm 'Alberto' has indeed formed, and a stone's throw from shore at that!
SATELLITE...RADAR...AND SURFACE DATA INDICATE THAT THE SMALL SURFACE LOW LOCATED OFF THE COAST OF SOUTH CAROLINA HAS ACQUIRED THE CHARACTERISTICS OF A TROPICAL CYCLONE.
And strengthening IS expected, at least in the near term ...
ALBERTO IS SITUATED IN A MARGINAL THERMODYNAMIC ENVIRONMENT FOR STRENGTHENING ...
It appears that the convection has not quite yet wrapped entirely around the LLCC, but continued returns from the Wilmington Doppler radar suggests this IS occurring, right before our eyes, and would eventually lead to the formation of a Central Dense Overcast (CDO) over the LLCC, nearly always a harbinger of further intensification.
THE LOW-LEVEL CIRCULATION IS A BIT TO THE EAST OF THE COLDEST CLOUD TOPS AND THE CIRCULATION CENTER SEEN ON RADAR.
A TROPICAL STORM WATCH COULD BE REQUIRED FOR A PORTION OF THE COAST OF THE CAROLINAS THIS EVENING.
Animated Doppler Radar Loop out of Wilmington, North Carolina:
Wilmington, NC Dopplar Radar Loop
Finally, of interest to note:
ALBERTO IS EARLIEST-FORMING TROPICAL STORM IN THE ATLANTIC BASIN SINCE ANA IN 2003. THIS IS ALSO THE FIRST TIME THAT A TROPICAL STORM HAS FORMED BEFORE THE OFFICIAL START OF THE HURRICANE SEASON IN BOTH THE ATLANTIC AND EAST PACIFIC BASINS.
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"Don't Get Stuck on Stupid" - General Honore, following Hurricane Katrina
Edited by CoconutCandy (Sat May 19 2012 05:18 PM)
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Ed Dunham
Former Meteorologist & CFHC Forum Moderator (Ed Passed Away on May 14, 2017)
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In the last couple of hours TS Alberto seems to have slowed down with perhaps a slight westward drift. At 20/04Z coordinates were 31.8N 78.6W and convection has been displaced to the northwest and west of the center. With the low-level center exposed, intensification has stopped and not much movement is expected on Sunday.
ED
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MichaelA
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Looking at the RGB Sat Loop this morning, it appears that Alberto struggled with shear over night, but has managed to overcome that a bit this morning. It will be interesting to see just how close to the coast he will get before the forecast reversal of direction takes place.
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Michael
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CoconutCandy
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It would appear that Tropical Storm Alberto is having to deal with several constraints this morning.
First and foremost, a good part of the low level circulation is exposed and is nearly totally lacking in any deep convection, albeit along a few cloud streets to the NE, where numerous towering cumulus and a smattering of weak thunderstorms are occurring in the convergent airflow into the cyclone.
The somewhat meager deep convection that does remain, as mentioned, is displaced to the West and NW of the LLCC, and isn't too impressive at that. I had surmised yesterday that deep and sustained 'bursting type' convection, with cloud top temps colder than -70 Celsius, might flare overnight during the convective max cycle.
But that never panned out, with overnight convection, as depicted on IR Satellite loops and excellent Doppler Radar coverage, remaining somewhat lackluster and, plausibly due to the ongoing wind shear, could not manage to wrap completely around the center of circulation, usually a requisite factor for significant intensification to occur.
In this passive microwave image from a polar orbiting satellite, you see the thunderstorms restricted to the Western quadrant only.
Although a Dense Overcast HAS formed over the remaining deep convection, one can't really call it a CENTRAL Dense Overcast (CDO), which is very often the harbinger of (sometimes rapid) intensification, as it does not overlay the LLCC, and the "thermodynamic throughput" of the convective mass that does remain has been insufficient to release the requisite amount of 'latent heat of condensation' required to further warm the nascent developing warm core, in turn, to lower the central pressure substantially, and for the winds to respond accordingly, as is the usual course of events in the typical disturbance --> depression --> tropical storm --> hurricane lifecycle.
The take away here is that Alberto, despite his 'best efforts', has to live with the synoptic deterrents (upper level wind shear and dry air entrainment) and various thermodynamic constrains that are impinging upon it and prohibiting further intensification at this time
I surmise, however, that should Alberto's LLCC remain well offshore and should it find itself squarely over the warm gulf stream again (think oceanic heat content!), AND the ongoing shear to relax just a tad, that the window of opportunity remains open for deep convection to fire and encompass the LLCC and a decent feature to form, that a fairly respectable looking tropical storm may very well blossom yet.
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"Don't Get Stuck on Stupid" - General Honore, following Hurricane Katrina
Edited by CoconutCandy (Sun May 20 2012 11:54 AM)
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MichaelA
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A very good and well thought analysis. Also, looking at the vis sat loop, it appears to me that the exposed CC may be broadening indicating that it may be filling in/spinning down some (at least in the short term). If the storm survives long enough to reposition over the warmer waters of the Gulf Stream, it may have a chance to hang together a while longer.
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Michael
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MichaelA
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Checking in and looking at the latest RGB and Water Vapor loops, there is a new flare up of convection near the CoC but just on the western side and the dry air has wrapped around nearly 3/4 of the way around the center. Also, cloud tops are being blown off to the west and NW. It wouldn't surprise me if Alberto simply died in place or actually moved onshore.
The 5PM discussion states that there are plenty of environmental concerns with Alberto's future development, if any. On the latest sat loops, the little bit of convection has moved to the center, but that is about the only convection associated with the storm. Water vapor still shows significant dry air all around Alberto. On another note, it does appear that the loop is beginning with Alberto drifting more southward in the later loop pics. With the really harsh environment, I don't see Alberto gaining any significant strength before he becomes post tropical in the next day or two.
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Michael
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Edited by MichaelA (Sun May 20 2012 06:13 PM)
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MichaelA
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The earlier convection near the center has dissipated with only one or two small cells remaining on the western side. Not much else going on there at all tonight. Alberto appears to be drifting nearly due South almost due East of Jacksonville, FL. We should see if the turn to the NE is happening by early tomorrow morning. I have to be at work at 7 AM, so it's sign off time for me.
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Michael
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