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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Quoting SevereHurricane:


I find that interesting because I initially thought it would start off as a reflection of the Cut-Off Low.


That's my interpretation from the latest NAM 18z.
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A cool upper atmosphere is ideal for bringing down the lifted condensation level.
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The "Front" Player is ON the Move..

..come on Down Babe.


Wunderground Frontal Map with Radar
Member Since: July 3, 2005 Posts: 414 Comments: 125421
Quoting Drakoen:


That upper level low has cut-off from an upper level trough over the SE CONUS. They are separate entities until they interact in the GOM. If you notice the low begins to develop without the help of a mid to upper level low south of Cuba.


I find that interesting because I initially thought it would start off as a reflection of the Cut-Off Low.
Member Since: September 7, 2008 Posts: 17 Comments: 1604
Quoting IKE:


You're right. I hadn't noticed that til I looped it.


If you go to this great site Adrian showed can see it a bit clearer:
Link

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Quoting SevereHurricane:


The ULL would just keep the System Sub-Tropical/Cold-Core. If its Sub-Tropical in nature then sheer aloft will be used to build more convection. Correct?


In some cases, an ULL can destroy a storm.
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Quoting IKE:


You're right. I hadn't noticed that til I looped it.


Yea. Even if it goes over South Florida there's a pretty decent chance of it heading back west as the ridge axis expands eastward.
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Quoting SevereHurricane:


The ULL would just keep the System Sub-Tropical/Cold-Core. If its Sub-Tropical in nature then sheer aloft will be used to build more convection. Correct?
Wha


That upper level low has cut-off from an upper level trough over the SE CONUS. They are separate entities until they interact in the GOM. If you notice the low begins to develop without the help of an upper level low south of Cuba.
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Link to Image Above
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177. IKE
Quoting Drakoen:


Yea. It still looks like it would have a chance to head back west though. From frame 78hr to 84hr is north northwest movement.


You're right. I hadn't noticed that til I looped it.
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Quoting Drakoen:


That's correct. The 850mb ridge moves eastward over the CONUS. The problem when it gets into the GOM is a cut-off upper level low at 300mb. Link


The ULL would just keep the System Sub-Tropical/Cold-Core. If its Sub-Tropical in nature then sheer aloft will be used to build more convection. Correct?
Member Since: September 7, 2008 Posts: 17 Comments: 1604
Quoting cchsweatherman:
After reading through beell's graphics and doing my own analysis, I'm starting to believe the way may have a situation similar to Tropical Storm Fay from last hurricane season developing. Seems like Florida may get the much-needed drought relief that it has been so desperately needing for quite some this upcoming week. By the way, this doesn't mean that I'm expecting a tropical storm, but I'm now expecting very heavy rainfall each day this upcoming week for Southern and Central Florida, especially Southeastern Florida where convergence will be greatest.


Woo hoo!! I wouldn't mind a tropical storm though, a little wind won't hurt anybody.
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EMC Cyclogenesis Tracking Page

Model Cycle: 2009051618


NAM



SREF Ensemble
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173. beell
Quoting Drakoen:
That's what I was looking at too Beell. That's how Fay got to be pull up to the NE instead of going into the panhandle. We'll see what happens.


Consensus is good!
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Can this probably Sub-tropical storm Ana taken as a Season forescst in terms of # of TC?
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Quoting Drakoen:
The focus looks to be south of Cuba.


I was looking at the same area thing are starting to realize the models forescast.
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After reading through beell's graphics and doing my own analysis, I'm starting to believe the way may have a situation similar to Tropical Storm Fay from last hurricane season developing. Seems like Florida may get the much-needed drought relief that it has been so desperately needing for quite some this upcoming week. By the way, this doesn't mean that I'm expecting a tropical storm, but I'm now expecting very heavy rainfall each day this upcoming week for Southern and Central Florida, especially Southeastern Florida where convergence will be greatest.
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Quoting SevereHurricane:


It would not be able to go any farther North after that image because of the High Pressure to the North.


That's correct. The 850mb ridge moves eastward over the CONUS. The problem when it gets into the GOM is a cut-off upper level low at 300mb. Link
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Well Paloma closed the 2008 Season by practically going right over us here in The Caymans, damaged the sister islands significantly, don't tell me we're gonna start off the 2009 season practically right over us too.Kinda depressing already.
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Quoting Drakoen:
18z NAM:


It would not be able to go any farther North after that image because of the High Pressure to the North.
Member Since: September 7, 2008 Posts: 17 Comments: 1604
Shear is now under 30 knots over most of the disturbance.. it's decreasing
Source-

http://cimss.ssec.wisc.edu/tropic/real-time/atlantic/winds/wg8shr.html

However shear is increasing 10 knots over Cuba right now.. Basically all that 5-10 knots in the USA will slide down south as the cold front pushes south.
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That's what I was looking at too Beell. That's how Fay got to be pull up to the NE instead of going into the panhandle. We'll see what happens.
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163. beell
Quoting hurricane23:
Developes it futher south and takes it NNE.


N or NNE would make sense-up the ridge weakness/trough. Then more west as this gap closes.

12Z 850mb GFS at 48 hours
Photobucket
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The focus looks to be south of Cuba.
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Member Since: May 14, 2006 Posts: 8 Comments: 13594
Quoting hurricane23:
Developes futher south and takes it NNE.


Yea. It still looks like it would have a chance to head back west though. From frame 78hr to 84hr is north northwest movement.
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I remember Andrew. I was visiting my grandparents in Vero Beach the day it hit. All we had was a few rain squalls there. My family had The Weather Channel on for about a day straight watching what was happening in Miami. I was only 15 at the time.
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157. IKE
Quoting nrtiwlnvragn:


Big change, from west to east. Will it swing back next run?


I noticed it shifted well east. NAM is notorious for doing that. See what the 18Z GFS does.
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Most of the Last 24 Hr runs..have a error with the initialization Point.

Time will bring about a SFC Low,then the input to solution will be better resolved.
Member Since: July 3, 2005 Posts: 414 Comments: 125421
Quoting cchsweatherman:


Been starting to notice what appears to be low-level circulation developing around 19N and 79W.
been shifting around all afternoon cchs this may all disappear once the sun goes down and we lose the daytime heating effect
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Developes it futher south and takes it NNE.
Member Since: May 14, 2006 Posts: 8 Comments: 13594
18Z NAM at 84 Hours
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thanks guys
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Quoting Drakoen:
The NAM is much further east on this run.


Right now thats more believable to me. (I say right now because the entire runs not out and for all we know the nam could make it dive south. LOL) The front grabs it and pulls it north east then leaves it for the high to build in and push it back west to northwest.
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18z NAM:
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Quoting KEEPEROFTHEGATE:
AOI
mark
19.3n/78.2w


Been starting to notice what appears to be low-level circulation developing around 19N and 79W.
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18Z SREF Ensemble

Member Since: July 3, 2005 Posts: 414 Comments: 125421
Quoting K8eCane:
dum question #1 this year (there will be more)

Where are the florida "straits?"


The water between Florida Keys and Cuba.
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Member Since: May 14, 2006 Posts: 8 Comments: 13594
Well I'm out for a while. Happy blob watching.
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The NAM is much further east on this run. A lot more moisture too.
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Quoting IKE:
18Z NAM @ 60 hours...



Big change, from west to east. Will it swing back next run?
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dum question #1 this year (there will be more)

Where are the florida "straits?"
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AOI
mark
19.3n/78.2w
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About JeffMasters

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.