Still watching for a potential early-season Atlantic subtropical storm

By: Dr. Jeff Masters , 7:10 PM GMT on May 16, 2009

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The latest 00Z and 12Z runs of the GFS, UKMET, NOGAPS, and ECMWF global dynamical computer models continue to indicate the possibility of an early season subtropical storm forming in the Gulf of Mexico 3 - 7 days from now. A modest area of low shear air is expected to open up between the polar jet stream to the north and the subtropical jet stream to the south, between Cuba and the northern Gulf of Mexico. The models have not been consistent with the timing or the size of this low shear area, and I wouldn't be surprised to see them back off again from this forecast with Sunday's set of runs. Nevertheless, I'll call once again for a 10% chance of development of a subtropical depression in the eastern Gulf of Mexico, 4 - 7 days from now. There isn't much of a disturbance at present to look at--there are some scattered showers between Cuba and Jamaica, but they are under a hefty 30 knots of wind shear. These showers should gradually increase in intensity and areal coverage over the next two days, and phase space diagrams from Florida State University indicate that an extratropical low may form near the western tip of Cuba 2 - 3 days from now. The storm may then gradually transition to a subtropical or tropical system later in the week, if the shear is low enough. Even if the shear is high and the storm remains extratropical, it could be a substantial rain-maker where it comes ashore. The models target the northern Gulf Coast between Louisiana and the Florida Panhandle as the most likely landfall location, but it is too early to place any confidence in this track.

There is also about a 10% chance a subtropical storm may form in the mid-Atlantic a few hundred miles east of Bermuda. There, a large upper-level cold low has cut off from the jet stream, and it may spin in place long enough over the next week to develop a warm core and be classified as a subtropical storm. It is unlikely that a subtropical storm forming that far out in the Atlantic this early in the year would pose a threat to any land areas, with the possible exception of Bermuda.

Climatology of early-season Atlantic tropical cyclones
Tropical storms are uncommon in the Atlantic before June 1, with only 26 named storms on record between 1851 - 2008. Five of these have made it to hurricane strength, and only one--Hurricane Able of 1951--made it to major hurricane status. Last year's Tropical Storm Arthur may be the deadliest May tropical cyclone on record. Though only a 40 mph tropical storm at landfall, Arthur killed five people in Belize and caused $78 million in damage. Three early-season storms have brought hurricane-force winds to land. The March 1908 hurricane swept through the northern Lesser Antilles Islands as a Category 1 or 2 hurricane, destroying at least 24 boats and causing damage to buildings on St. Bartholomew. Hurricane Able of 1951 brought sustained winds of 90 - 95 mph to the northern Bahama Islands, but caused little damage. Hurricane 2 of May 1908 hit North Carolina's Outer Banks as a Category 1 hurricane, but also caused little damage.


Figure 1. Tracking map for the earliest hurricane to make landfall, the March 1908 hurricane in the northern Lesser Antilles Islands.

List of all early season (formed in January - May) Atlantic named storms
May 31, 2008: Tropical Storm Arthur
May 6, 2007: Subtropical Storm Andrea
April 18, 2003: Tropical Storm Ana
April 21, 1992: Subtropical Storm 1
May 6, 1981: Tropical Storm Arlene
January 18, 1978: Subtropical Storm 1
May 21, 1976: Subtropical Storm 1
May 23, 1972: Subtropical Storm Alpha
May 17, 1970: Hurricane Alma (Category 1)
May 28, 1959: Tropical Storm Arlene
February 2, 1953: Tropical Storm Alice
May 25, 1952: Tropical Storm 1
May 15, 1951: Hurricane Able (Category 3)
May 22, 1948: Tropical Storm 1
May 19, 1940: Tropical Storm 1
May 27, 1934: Tropical Storm 1
May 14, 1933: Tropical Storm 1
May 5, 1932: Tropical Storm 1
May 13, 1916: Tropical Storm 1
May 24, 1908: Hurricane 2 (Category 1)
March 6, 1908: Hurricane 1 (Category 2)
May 27, 1890: Tropical Storm 1
May 16, 1889: Hurricane 1 (Category 1)
May 17, 1887: Tropical Storm 2
May 15, 1887: Tropical Storm 1
May 30, 1865: Tropical Storm 1

I'll have an update Sunday.

Jeff Masters

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937. IKE
Morning everybody...

Ah...first sip of freshly brewed coffee...

6Z NAM looks close to that 00Z ECMWF.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
No invest yet...light rain on PC Beach now, w/90 per cent chance of more. Yee haw!

Mornin' Ike
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Morning

Subtropical Sandwich Anyone?

It will be updated should any new information becomes available.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
934. IKE
TAMPA... LONG TERM (TUESDAY NIGHT-SATURDAY)...INTERESTING WEATHER SCENARIO
TO SAY THE LEAST AS MODELS IN AGREEMENT ON A CUTOFF LOW SETTLING
INTO THE EASTERN GULF. MOISTURE AND INSTABILITY ON THE EAST SIDE OF
THE LOW WILL PROVIDE GOOD RAIN CHANCES...BUT EXACTLY WHERE WILL THE
LOW SETTLE DOWN? NAM/GFS/ECMWF ALL HAVE A SURFACE REFLECTION OF THIS
LOW SOMEWHERE ACROSS THE SOUTHERN HALF OF THE STATE TUESDAY NIGHT.

CUTOFF LOWS TEND TO SIT IN PLACE FOR SOME TIME...SO THIS ONE WILL
DOMINATE OUR WEATHER LIKELY FOR THE ENTIRE LONG TERM PERIOD. GIVEN
MODEL CONSENSUS THAT IT WILL STAY TO OUR WEST WILL LEAN TOWARD THE
ABOVE NORMAL SIDE FOR POPS AND KEEP AT LEAST CHANCE SHOWERS IN FOR
EACH PERIOD. WILL NOT GO AS HIGH ON POPS AS THE GUIDANCE THROUGH
THURSDAY...THEN WILL GO CLOSE TO FOR FRIDAY AND SATURDAY GIVEN THE
BEND BACK TOWARD CLIMATOLOGY.

WITH THE INCREASE IN RAIN CHANCES...EXPECT TEMPERATURES TO BE OR
BELOW NORMAL WHEREAS MORNING LOWS WILL BE ABOVE.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
933. IKE
00Z ECMWF seems quite believable.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
932. IKE
Morning long-term discussion from Tallahassee...

"LONG TERM (TUE NIGHT-SUN)...THERE CONTINUES TO BE GOOD AGREEMENT
THAT A BROAD AREA OF SURFACE LOW PRESSURE OVER THE NWRN CARIBBEAN
WILL DRIFT NWWD WITH TIME INTO THE CNTRL/ERN GOMEX UNDER A MID/UPPER
CLOSED LOW OVER THE ERN GOMEX. A LARGE SPRAWLING AREA OF LOWER
HEIGHTS/PRESSURES IS FCST BY ALL OF THE MODELS...WITH THE 00Z GFS
SLIGHTLY DEEPER/FURTHER NORTH WITH ITS LOW CENTER THAN THE
ECMWF/UKMET/CANADIAN MODELS. BASED ON THE AVAILABLE MODEL
TRENDS...WILL COMPROMISE BETWEEN THE 12Z ECMWF AND 00Z GFS
SOLUTIONS. THIS SYSTEM WILL HAVE SEVERAL IMPLICATIONS ON THE
EXTENDED FCST. TIGHTENING PRESSURE GRADIENT NORTH AND EAST OF LOW`S
FCST TRACK WILL INCREASE SURFACE WINDS TO SMALL CRAFT ADVISORY
LEVELS...WITH GALE FORCE WINDS A DISTINCT POSSIBILITY. FOR
NOW...WILL CAP SUSTAINED WINDS AT 30 KT AND GUSTS AT 35 KT EARLY IN
THE EXTENDED PERIOD. THESE WIND CAPS MAY NEED TO BE RAISED BY LATER
SHIFTS AS CONFIDENCE INCREASES. AS THE GULF LOW PRESSURE SYSTEM
TRACKS TO THE NW...E-SE FLOW WILL DRAW ATLANTIC AND GOMEX MOISTURE
INTO THE REGION. THE RESULT WILL BE INCREASING POPS FOR THE WED-FRI
TIME FRAME. ALSO...THIS SYSTEM HAS THE POTENTIAL TO ACQUIRE
SUBTROPICAL CHARACTERISTICS OVER THE CNTRL/ERN GOMEX DURING THIS
TIME...AND WILL BE MONITORED CLOSELY DURING THE NEXT SEVERAL DAYS."
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Morning all from Spain,

Are a low developing under the deep convection close to Cuba? Too soon to know it perhaps.
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Come and join my 2009 AHS prediction contest! It is due when the first tropical depression forms.
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929. ackee
we are geting lot of rain here in jamaica now
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gnight all
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Hi all. I see that there's not a lot of users up right now.

I've tracked the discussion on this page, and I see that there is a possible invest near Cuba and/or in the mid-Atlantic. I give 20~40% chance of it each forming. How about you guys?
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did you go to PCHS?
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yep, grew up in pc, but living in lehigh for another 2.weeks then I'm moving to cape coral lol
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Seems to be quite a few west coast FL users, even many from Ft Myers - Sarasota.
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Lehigh, but I work in port Charlotte
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Quoting TampaSpin:


Did you look at My own model that i put together....

No, I didn't see it on there, where is it?
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hey charlotte, where do you live, im in Englewood
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Hmmm.. I think it's gonna be an interesting year in the tropics
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Quoting GatorWX:
Looks good, what do you think of Atlantic low? Keeps trying to wrap convection, then sheds it off. Shear is somewhat favorable at least on the northern portion.


Did you look at My own model that i put together....
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Looks good, what do you think of Atlantic low? Keeps trying to wrap convection, then sheds it off. Shear is somewhat favorable at least on the northern portion.
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Sweet, I'll check it out.
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Quoting GatorWX:
hey Tampa, decided to start posting now that things are at least somewhat interesting.


i did my first update today....Link
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hey Tampa, decided to start posting now that things are at least somewhat interesting.
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Hi Gator
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At best we'll see 20-25 kts, MAYBE 15-20 which is decent, but probably not decent enough considering it isn't organized at all at this point.
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There's 30-50 kts of shear across the entire eastern gulf. These winds will die down a bit with the approaching front, but I doubt they will really be "favorable" enough to allow a TD.
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the ULL will pull it north and then the trof will absorb it later on.
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Quoting GatorWX:
Still 30-35 kts of shear on top of carib disturbance. I don't think it'll be an invest until at least Monday. It certainly is holding its own against the shear, but it'll be pretty tough to build up with that wind there. LLC is possible, but strengthening not so much until the vertical winds die down at least 10-15 kts. Atlantic disturbance is under much less shear and in the short term, has a better chance, but it seems every time it tries to build around the center, the storms collapse and it has to start over. Really doesn't look any better than Fri evening and yesterday. Something to look at at least for this early in the season.



The low shear environment is starting to materialize with our Cuban Project, we'll see. Seems to be organizing in the face of hardship, hate to see what it does if it finds a sweet spot, models have been gun hoe.
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Looks like a good soaker for Florida, not much more. Whether it's an invest, TD, etc, it's not going to amount to anything but rain. TS seems very unlikely. Their is the possibility of a very narrow window of favorable upper level winds, and whether or not it encounters this area, it simply doesn't have the time to become much of anything.
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Still 30-35 kts of shear on top of carib disturbance. I don't think it'll be an invest until at least Monday. It certainly is holding its own against the shear, but it'll be pretty tough to build up with that wind there. LLC is possible, but strengthening not so much until the vertical winds die down at least 10-15 kts. Atlantic disturbance is under much less shear and in the short term, has a better chance, but it seems every time it tries to build around the center, the storms collapse and it has to start over. Really doesn't look any better than Fri evening and yesterday. Something to look at at least for this early in the season.
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Quoting hurricanealley:


Will that help the system develop?


The now visual ULL is why I think the GFS and UKMET are doing well with all of this. The surface low will follow the counterclockwise flow of the ULL and get kicked out further east.
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Quoting Patrap:

CMC 00Z


Based on my obs of satellite img, I think the 00ZGFS and the 00ZUKMET have a good solution. This trough coming down is rather strong for May. I think the CMC is underestimating this trough. "Correction" Not picking up on the ULL in the straights.
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Eastern North America (last 4 cycles, NPS)

Member Since: July 3, 2005 Posts: 426 Comments: 128654
Quoting TheCaneWhisperer:
ULL at 24N 84W


Will that help the system develop?
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CMC 00Z
Member Since: July 3, 2005 Posts: 426 Comments: 128654
Caribbean Sector,IR Imagery, Loop






-- EMC Cyclogenesis Tracking Page --

Model Cycle: 2009051700

North America: Model Tracks for Mid-Latitude Cyclones



Multi-Model
Member Since: July 3, 2005 Posts: 426 Comments: 128654
ULL at 24N 84W
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Vortex, ROFL! I had to read it three times! Too funny!

Goodnight everyone - see ya tomorrow!
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Vortex Thats funny LOL
nite all
i assume i'm going to court UH i mean BED now
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Quoting Vortex95:
assuming the assumptions of assumption are being assumed then assuming about the assumption of a criteria of an invest, assuming that there one is somthing that has been explained by Orca assuming that what he typed was turthful assuming that he is a credible person, assumingly.


ROFLMAO, I want a double of what ever your drinking :)
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Quoting TheCaneWhisperer:


If convection / circulation persists overnight and model support continues, you'll have your invest AM tomorrow for the Caribbean AOI. IMO, all criteria have been met to declare an invest.


Let's Nip This In The Bud.

If convection / circulation persists overnight and model support continues, you'll have your invest AM tomorrow for the Caribbean AOI. IMO, all my personal criteria would be met to declare an invest.

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G'nite Keeper! See you tomorrow:o)
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Orca, big fish don't have the things umptions make out of you. :o)
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well iam off to bed see whayt happens in the day time heat tomorrow later all
Member Since: July 15, 2006 Posts: 174 Comments: 54368
Quoting Orcasystems:


Umm your going to say I use assume to much :) and we all know what assumptions make me?
Quoting K8eCane:
look up at 887


I think I would reword the second part.
There is a definition of an what an invest is... but not a definition of that the criteria is to declare an Invest.
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I think we'll be looking at a different animal in the Carib tomorrow. AOI has a strong hold on the low cloud deck now, we should have a surface low soon.
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look up at 887
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Quoting K8eCane:
I assume you are aware there is really no such thing as "Criteria" to be meet to be declared an Invest?

I would assume that someone must have a definition of the criteria... but I have never been able to find one.. I know.. I have looked around for one a lot.


Umm your going to say I use assume to much :) and we all know what assumptions make me?
:P
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a good attorney or a not so good one would tear you up in court with statements like these
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.