Disturbance 93L off South Carolina coast could become a tropical storm
A hybrid low pressure system with both tropical and extratropical characteristics has formed in the waters off the coast of South Carolina, about 120 miles southeast of Myrtle Beach--a little going-away present for outgoing NHC director Bill Read, who retires on June 1! Residents along the South Carolina and North Carolina coast should pay attention to 93L, as it has the potential to strengthen into a tropical storm and hit the coast on Sunday or Monday, with North Carolina at highest risk. NHC designated this system Invest 93L Saturday morning. Wind shear is a moderate 20 knots over 93L, and the storm is over the warm waters of Gulf Stream, which are 81°F (27°C), just above the 26°C threshold usually needed for a tropical storm to form. The system is tangled up with an upper level trough of low pressure, which is pumping cold, dry air into the storm, inhibiting development. Wind shear is expected to remain in the moderate range, 15 - 20 knots, through Monday, which is low enough that 93L has a decent chance of developing into the Atlantic's first tropical depression. Since 93L is very small, it is highly vulnerable to even a modest increase in wind shear or dry air, which could rapidly disrupt it. Conversely, the storm's small size and favorable positioning over the warm waters of the Gulf Stream mean it is also capable of suddenly organizing, and it would not be surprise to see 93L become Tropical Storm Alberto by Sunday. NHC is giving 92L a 50% chance of developing into a tropical depression or tropical storm by Monday. Since 93L is so small, the computer models are having trouble resolving it, and we don't have very good forecasts of the storm right now. Steering currents are weak, and I expect 93L will wander off the coast of South Carolina through Sunday, before getting caught up by a trough of low pressure on Monday which should lift it out to the northeast. Heavy rain showers from 93L are located about 50 miles offshore of the coast of South Carolina, as seen on Wilmington radar. These showers will probably move onshore between Charleston and Wilmington Saturday night and Sunday, bringing 1 - 3 inches of rain to portions of the coast. At times today, 93L has had a cloud-free center resembling an eye on radar, but this was not a true eye, and winds are probably near 35 - 40 mph in the heaviest rain squalls near the center.
Figure 1. Afternoon radar image of 93L from the Wilmington radar.
Jeff Masters
Reader Comments
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Could be AMM with the cooler coastal temps
Like all tropical cyclones...yeah there could be a slight tornado threat if the spiral rain bands would get on up into land. I believe when spiral rain bands from a tropical cyclone suddenly slam into the friction of land...it can cause weak tornadoes to spin up. I am not sure exactly why/how this happens...anyone else can elaborate?
Also...I don't think there is a strong understanding about tornadoes and tropical cyclones. Some cyclones produce a lot of tornadoes and others do not at all...
Larger Image Resolutions: http://lance-modis.eosdis.nasa.gov/cgi-bin/imagery /single.cgi?image=crefl1_143.A2012140161000-201214 0161500.2km.jpg
93 in the ATL.
It's still May, right ? Or did I miss something ???
The most impressive May system near the east coast was Category 3 (Major) Hurricane Able in 1951. Its the only major hurricane in the Atlantic in the month of May. I bet if there were Invests and satellites back then...it would have looked pretty cool too...
P.S. I am not saying this is going to be like Able ;)
Aletta is no more.
2012051912
32.4 282.3
-999.9-999.9
100
32.4 282.3
191800
1205191800
1
SUBJ/TROPICAL CYCLONE FORMATION ALERT//
WTNT21 KNGU 191800Z
RMKS/1. FORMATION OF A SIGNIFICANT TROPICAL CYCLONE IS POSSIBLE
WITHIN A 100 NM RADIUS OF 32.4N 77.7W WITHIN THE NEXT 24 HOURS.
AVAILABLE DATA DOES NOT JUSTIFY ISSUANCE OF A NUMBERED TROPICAL
CYCLONE WARNING AT THIS TIME. WINDS IN THE AREA ARE ESTIMATED
TO BE 30 TO 35 KNOTS. METSAT IMAGERY AT 191555Z INDICATES THAT A
CIRCULATION CENTER IS LOCATED NEAR 32.4N 77.7W. THE SYSTEM
DISPLAYS A WESTWARD DRIFT LESS THAN 05 KNOTS.
2. REMARKS: SATELLITE AND RADAR IMAGERY INDICATE THAT THE AREA OF
LOW PRESSURE LOCATED ABOUT 120 MILES SOUTHEAST OF MYRTLE BEACH
SOUTH CAROLINA HAS BEGUN TO ACQUIRE TROPICAL CHARACTERISTICS. MODEL
GUIDANCE DEPICTS THE AREA OF INTEREST DRIFTING WESTWARD WITH
SHOWERS AND THUNDERSTORMS PRESISTING NEAR THE CIRCULATION CENTER.
3. THIS ALERT WILL BE REISSUED, UPGRADED TO WARNING OR CANCELLED BY
201800Z.//
9312051912 324N 777W 30
AL 93 201205191745 DVTS 3210N 7780W SAB EG 1515 ///// T DT=2.5 BO CBND MET=1.5 PT=1.5 FTBO CON
AL 93 201205191745 DVTS 3220N 7770W TAFB SS 2020 ///// T DT 2.0 BO CURVED BAND
FM FWC-N
BT
UNCLAS
MSGID/NLMC/OVLY2/0087/MAY
OVLY/TCFA/191800Z9/MAY/1OF1/TCFA AL9312/METOC
ARC/0/G///322400N1/0774200W0/100NM
TEXT/20//G/294200N7/0774800W6/TCFA AL9312
TEXT/20//G/284200N6/0774800W6/VALID UNTIL 201800Z
TEXT/20//G/274200N5/0774800W6/WINDS: 30-35 KTS
TEXT/20//G/264200N4/0774800W6/MVG: WESTWARD LESS THAN 05 KNOTS
ENDAT
BT
#0001
NNNN
Alberto...
: )
Convection near to the center of GOH disturbance
You can see the transition away from baroclinic as the trough weakens and convection consolidates around the center. This should become Alberto very soon.
Who issues TCFAs (tropical cyclone formation alerts) for 93L?
By the way...you can read my 12th discussion this year and also my 1:45 PM EDT update if you want to know (in high detail) how this system originated and developed. I can understand this might seem like it "came out of thin air" for those who haven't been watching the tropics lately...
Tropical Cyclone Formation Alert (TCFA) 93L
May-19-12, 2:30:01 PM | Maritime.CDO@navy.mil (FWC-N CDO)
Issued: Sat 19 May 2012 18:00Z
Tropical Cyclone Formation Alert Graphic
Tropical Cyclone Formation Alert Text
Tropical Cyclone Formation Alert JMV data
Tropical Cyclone Formation Alert Gold Ovly
FNMOC Satellite Data Tropical Cyclone Page
Yesterday, nothing
Today, 93L at the verge of becoming a TS.
Not bad, 2012...
With all this latest data coming in as well as the issuance of a Tropical Cyclone Formation Alert, it appears we may just be a matter of hours from the birth of Tropical Storm Alberto. There is nothing that I have seen that would prevent this from becoming Tropical Storm Alberto given the current trends and satellite analysis.
This is correct..Its clearly atleast a TD or a weak TS. If it wasn't for those 20kt westerlies over it this could have very quickly intensified into a hurricane.
Link
TCFA is a Naval product
I'm right there with you...I've been saying 100% since 1:45 PM myself!
Wind shear is supposed to weaken today as the upper level low pulls away.
The last time we had a landfalling US Tropical Storm was Lee in early Sept of last year along the gulf coast. To have that happen during hurricane season is one thing but to have one in May in the "off season" is truly extraordinary.
Its about time its "tropical." My rule of thumb for caling something tropical in structure is to run a satellite animation and see anticycloinc cirrus streaming outward from its top. That anticyclonic cirrus indicates a warm core that reaches the storm top.
Why warm? Because an upper anticyclone is a thermal feature from warm air. An upper cyclone (the opposite) is a thermal feature from cold air.
Air mass modification
Or hurricane.
I think it is safe to say it could get stronger. Looks like shear was analyzed a tad bit too high.
Why would they bother with the special outlook again? Shouldn't they just go ahead and do the advisory?
I choose 93L
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