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 kmanislander:
Hey Adrian, any chance of a "still" image ?



Hey Kman,

Of course here you go.

Member Since: May 14, 2006 Posts: 8 Comments: 13804
As for precentages,
I really want the rain, my yard looks like Mars. So, I'll be less conservitive and say 50% chance of it.

The whole state needs it badly as usual. Need a fay to fix things up.
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80. extreme236 8:11 PM GMT on May 16, 2009

Absolutely, like bears coming out of hibernation LOL
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Quoting Weather456:


was it a normal afternoon dropped or a 24 hr tendency, that is a drop compared to this time yesterday.


Definitely lower than yesterday.
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Quoting CaneWarning:


Yeah, I was in Homestead for that one.


My aunts house was on US1 and 312 street in florida city.
Member Since: May 14, 2006 Posts: 8 Comments: 13804
Hey Adrian, any chance of a "still" image ?

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Interesting that the NCEP Ensemble 24 hrs ago was on it,and remains.

But looks like the initialization Point is OFF



Member Since: July 3, 2005 Posts: 426 Comments: 128630
Quoting kmanislander:
Hi there 236

Yep, one by one we all show up again LOL

As for the "blob" near the Caymans we could sure use the rain.


Guess my tropical weather senses drew me back maybe? lol
Member Since: August 2, 2007 Posts: 19 Comments: 19234
Quoting hurricane23:


Its an animated gif of the last radar image taken from NHC before the WSR-57 radar was blown off the roof. My experience with 160+mph winds in florida city.


Yeah, I was in Homestead for that one.
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Quoting extreme236:
Nice to see all the regulars from last year around again :)


Hey Extreme! Been awhile! The ole' crews back for yet another season.
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Quoting extreme236:
Well long time no see...looks like maybe something interesting to watch out in the Atlantic now.


Welcome back Extreme. Glad to have you back. Hope all has been well.

Quoting stormpetrol:
Good Afternoon to all, pressure here in Grand Cayman has dropped 2 mb since this morning down to 1012 now, not that low but worth watching.


Thats an interesting observation right there. Keep us updated as it may suggest something could be happening.
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Quoting CaneWarning:


Nice avatar...is that Andrew?


Its an animated gif of the last radar image taken from NHC before the WSR-57 radar was blown off the roof. My experience with 160+mph winds in florida city.
Member Since: May 14, 2006 Posts: 8 Comments: 13804
Hi there 236

Yep, one by one we all show up again LOL

As for the "blob" near the Caymans we could sure use the rain.
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at 1015.5mb..
Member Since: October 5, 2007 Posts: 20 Comments: 4970

GFS, NOGAPS, UKMET, ECMWF, and a few other lesser known ones all on for Development.
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Nice to see all the regulars from last year around again :)

And that I wasnt forgotten lol
Member Since: August 2, 2007 Posts: 19 Comments: 19234
pressure down here in swfl as well over the last 24hrs...
Member Since: October 5, 2007 Posts: 20 Comments: 4970
Quoting Patrap:


Not if ya cant see it, Squeaky Hint..LOL


Ahem !!
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Even if the shear is high and the storm remains extratropical, it could be a substantial rain-maker where it comes ashore.

Thanks, Doc! Shear may prohibit development of a totally tropical system but it will do its part to add deep layer support for convection.

All the while this thing drifts NW-ish waiting for some lee troughing to develop over the central CONUS while high pressure over the NE drifts slowly eastward- Plenty rain over the coast as it approaches the weakness between these features.

A central gulf coast landfall would seem to split the difference between developing troughiness to the west and the departing high to the NE of the surface low.

Then some interaction as it gets absorbed by the next eastward moving system over the US. Who the heck knows when that will be. Note the long extended off-days for Vortex2! Could be Monday-a-week from now!

This system and its effects may be quite surprising.
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Quoting stormpetrol:
Good Afternoon to all, pressure here in Grand Cayman has dropped 2 mb since this morning down to 1012 now, not that low but worth watching.


was it a normal afternoon dropped or a 24 hr tendency, that is a drop compared to this time yesterday.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting CaneWarning:


What is your take on the blob?


I was just about to check that out...I got a new computer so I don't have any of my cool satellite and model links from last year.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
Good to see ya Extreme!
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Quoting kmanislander:


Distracting though LOL


Not if ya cant see it, Squeaky Hint..LOL
Member Since: July 3, 2005 Posts: 426 Comments: 128630
Quoting kmanislander:


Distracting though LOL


Yeah, I keep watching it.
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63. IKE
Quoting extreme236:
Well long time no see...looks like maybe something interesting to watch out in the Atlantic now.


Hey extreme.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting CaneWarning:


Nice avatar...is that Andrew?


Distracting though LOL
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Quoting extreme236:
Yup I'm back...figured I should get back to the tropics now that the season starts up in less than a month.


What is your take on the blob?
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Good Afternoon to all, pressure here in Grand Cayman has dropped 2 mb since this morning down to 1012 now, not that low but worth watching.
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Yup I'm back...figured I should get back to the tropics now that the season starts up in less than a month.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
Quoting hurricane23:
Nevere mind.


Nice avatar...is that Andrew?
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Hi extreme, I just came back this morning!

LOL
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good to see ya 236
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Nevere mind.
Member Since: May 14, 2006 Posts: 8 Comments: 13804
Hey, extreme. I just came back to Wunderground about 1-2 weeks ago, myself.
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The gulf is warm.
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Here is the GOM May 15 TCHP 08-09 Comparison though.

Gulf of Mexico (Updated every ~10-15 mins.)

More TCHP this year than last at this time,easily.

Tropical Cyclone Heat Potential

Gulf of Mexico Fields
Date: May 15 2009


15 May 2009


15 May 2008
Member Since: July 3, 2005 Posts: 426 Comments: 128630
Quoting extreme236:
Well long time no see...looks like maybe something interesting to watch out in the Atlantic now.


Welcome back!
Member Since: July 24, 2005 Posts: 407 Comments: 19076
extreme236 is back...!
Member Since: October 28, 2006 Posts: 57 Comments: 30559
Well long time no see...looks like maybe something interesting to watch out in the Atlantic now.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
interesting, as of yesterday the northern gomex was almost entirely devoid of yellows, save for right up against the coast. BTW, ty buddy.
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Not that Im aware of..but im sure there is an archive somewhere.
Member Since: July 3, 2005 Posts: 426 Comments: 128630
10%? NO way, Higher than that, at least 25-30%.
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How do i change the image next to my posts? Forgot
Member Since: May 14, 2006 Posts: 8 Comments: 13804
Patrap, do they have links that show the potential compared to last year?
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Maximum Potential Hurricane Intensity


The maps display potential minimum pressure and maximum winds, calculated according to a method developed by Dr. Kerry Emanuel. Dissipative heating is handled according to a method described in Bister and Emanuel (1998). The maps are based on data from the 00Z global operational analysis from NCEP for the date shown on the plot. The top panel shows the potential minimum central pressure for a hurricane at any given location (in millibars). Only values less than 1000mb are shaded. Cyan squares indicate grid points where the algorithm failed to converge. Also shown are the sea surface temperatures (°C). The bottom panel shows the potential maximum wind speed expressed in terms of the type and severity of storm they would represent (TD = Tropical Depression, TS = Tropical Storm, H1-H5 = Hurricanes of category 1-5 on the Saffir-Simpson scale).
Member Since: July 3, 2005 Posts: 426 Comments: 128630
Quoting WeatherStudent:
bloggers any heads up of what i migth anticipate here in fort laddy-dady coming up next week?


Sun, clouds, rain, wind.
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Quoting cchsweatherman:
ECMWF Joins The Fray


Looks like it has it hitting South Florida then heading into the GOM.
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Hey patrap, if you're around, do you have a link to that max intensity chart? I seem to have misplaced it =(
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Going to wait for tomorrow morning's computer models runs before I create my forecasts for the upcoming week on the CCHS Weather Center site. Even though I'm quite impressed by the model consensus on development near Florida, I really want to wait for better model consensus in terms of strength, track, and timing. No matter what, this will be a very difficult forecast to create, even for the NWS Local Offices in Florida and on the Gulf Coast.
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Quoting IKE:
I think 10% is too low.

I think it will get designated at least a TD or STD...


If the Doc goes on holiday, we have Ana... given the track record!
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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.