Tropical Storm Chantal: a Likely Harbinger of an Active Atlantic Hurricane Season

By: Dr. Jeff Masters , 2:02 PM GMT on July 08, 2013

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Tropical Storm Chantal is speeding westwards at 26 mph towards a Tuesday encounter with the Lesser Antilles Islands. Satellite loops show that Chantal has plenty of spin, with several well-developed low-level spiral bands that have gradually increased their heavy thunderstorm activity this morning. However, Chantal is fighting dry air associated with the Saharan Air Layer (SAL). The heavy thunderstorm activity near Chantal's center is rather thin, and there are virtually no heavy thunderstorms on the storm's north side, where upper-level northwesterly winds are creating light to moderate wind shear of 5 - 15 knots, and driving dry air into the storm. This dry air is readily apparent on water vapor satellite loops. Ocean temperatures are fairly warm, though, at 27.5 - 28°C. There have not been any hurricane hunter missions into Chantal yet, but an Air Force hurricane hunter aircraft deployed to St. Croix on Sunday, and is scheduled to investigate Chantal on Monday afternoon.


Figure 1. MODIS image of Chantal taken at approximately 10 am EDT Monday, July 8, 2013. At the time, Chantal had top winds of 45 mph. Image credit: NASA.


Figure 2. U.S. Air Force Master Sgt. Levi Denham, a WC-130J Hercules aircraft weather reconnaissance loadmaster assigned to the 53rd Reconnaissance Squadron (the Hurricane Hunters), performs pre-engine start-up inspections in St. Croix, Virgin Islands, on Sept. 16, 2010. DoD photo by Staff Sgt. Manuel J. Martinez, U.S. Air Force. Thanks go to wunderground member Patrap for pointing out this photo.

Forecast for Chantal
The 8 am EDT Monday forecast from the SHIPS model predicts that Chantal will experience low to moderate shear through Tuesday afternoon as it heads west-northwest at 25 mph towards Hispaniola. With ocean temperatures expected to warm to 28°C during that time, Chantal has the potential to intensify to a 65 mph tropical storm before hitting Hispaniola. Working against intensification will be the fast forward speed of the storm--tropical storms moving faster than 20 mph in the deep tropics usually have trouble intensifying. In addition, the Eastern Caribbean is an area where the trade winds accelerate, helping drive sinking air that discourages tropical storm intensification. Dry air will also slow down the intensification process, and I don't see Chantal making it to hurricane strength before interacting with the mountains of Hispaniola and/or Cuba on Tuesday night and Wednesday. This interaction may be able to destroy the storm, since wind shear is also expected to rise to the high range, 20 - 30 knots, Tuesday night through Thursday. Chantal has the potential to cause big problems for Haiti, which is highly vulnerable to flash flooding due to the lack of vegetation on the deforested mountains. However, there is a lot of dry air to the west of Chantal, which may act to keep rainfall totals in Haiti down to a manageable 2 - 4". Over 300,000 people are still homeless and living in makeshift tent camps in Haiti, three years after the great 2010 earthquake.

Once Chantal crosses Hispaniola and enters the Bahamas late this week, the trough of low pressure pulling the storm to the northwest is expected to lift out. It is unclear at this point whether or not this trough will be strong enough to pull Chantal out to sea, or whether the storm might be forced back to the northwest into the U.S. East Coast by high pressure building in.


Figure 3. There have been only thirteen tropical depressions or tropical storms that have formed July 15 or earlier that have passed through the Lesser Antilles since 1851, an average of one such tropical cyclone every thirteen years. Note that two of these storms, Dennis and Emily, occurred during the notorious Hurricane Season of 2005. There were five other pre-July 16 storms that formed east of the Lesser Antilles Islands, but did not pass through the islands (Bertha of 2009, Barry of 1989, and unnamed tropical depressions in 1967, 1978, and 2001.) Image credit: NOAA's Historical Hurricane Tracks website.

Chantal: an uncommon early-season Cape Verde-type tropical storm
Formation of a tropical storm east of the Lesser Antilles Islands in early July from an African tropical wave is an uncommon occurrence. Since Atlantic hurricane records began in 1851, there have been only thirteen tropical depressions or tropical storms that have formed July 15 or earlier that have passed through the Lesser Antilles, an average of one early-season tropical cyclone every thirteen years. Note that two of these storms, Dennis and Emily, occurred during the notorious Hurricane Season of 2005. There were five other pre-July 16 storms that formed east of the Lesser Antilles Islands, but did not pass through the islands (Bertha of 2009, Barry of 1989, and tropical depressions in 1967, 1978, and 2001 that did not become named storms.)

Chantal: a likely harbinger of an active Atlantic hurricane season
Chantal's formation on July 8 is an usually early date for formation of the season's third storm, which usually occurs on August 13. A large number of early-season named storms is not necessarily a harbinger of an active season, unless one or more of these storms form in the deep tropics, south of 23.5°N. According to Phil Klotzbach and Bill Gray, leaders of Colorado State's seasonal hurricane forecasting team,

"Most years do not have named storm formations in June and July in the tropical Atlantic (south of 23.5°N); however, if tropical formations do occur, it indicates that a very active hurricane season is likely. For example, the seven years with the most named storm days in the deep tropics in June and July (since 1949) are 1966, 1969, 1995, 1996, 1998, 2005, and 2008. All seven of these seasons were very active. When storms form in the deep tropics in the early part of the hurricane season, it indicates that conditions are already very favorable for TC development. In general, the start of the hurricane season is restricted by thermodynamics (warm SSTs, unstable lapse rates), and therefore deep tropical activity early in the hurricane season implies that the thermodynamics are already quite favorable for tropical cyclone (TC) development."

Two of this season's three storms have formed in the deep tropics--Tropical Storm Barry, which formed in the Gulf of Mexico's Bay of Campeche at a latitude of 19.6°N, and now Tropical Storm Chantal, which formed at a latitude of 9.8°N. With recent runs of the GFS model predicting formation of yet another tropical storm southwest of the Cape Verde Islands early next week, it appears that the Atlantic is primed for an active hurricane season in 2013.

Jeff Masters

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Quoting 3352. CybrTeddy:
This storm annoys me. Yesterday it had a visual presentation of a 60mph storm, yet the recon only found a 50mph storm with 1010mph pressures. Today it has the visual presentation of a 45mph storm, and the recon is finding a 60mph TS with 1003mb pressures.

satellite images are often misleading Ernesto last year looked well but was a mess underneath and many non tropical systems look like hurricanes
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3382. Grothar
The intensity models look a lot like my last EKG.


Member Since: July 17, 2009 Posts: 69 Comments: 25394
ok so I wake up to all the models not only shifting to the WEST, but all the reliable ones show Chantel taking a pretty good LEFT TURN.... that might even put her in the east gulf eventually?!?!? BIG CHANGES... I would suspect the next NHC will put her landfalling along the Florida coast...
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3380. 7544
looks like our ull didnt give in and did well at dmax is it still moving to the west
Member Since: May 6, 2007 Posts: 0 Comments: 6693
Good Morning/Evening

All the amazing animations, clean radar, and model tracking on here has me SPOILED to the core.
Let me just say thank you to all the people that make this happen so consistently, constantly, and nicely so that I CAN just take it for granted.
You have given me clear new eyes to see the world and weather and to blind them now would be a bighting pain.
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Quoting 3370. islander101010:
dead zone does not exist for developed systems

That's right. The "rule" is, if it is developed before it enters the Hebert Box it stays developed, if it is not a cyclone, i.e. wave, it wont develop. Usually
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3377. SLU
I'm located in the SW quadrant of Chantal about 20miles SW of the center and the winds are westerly at only 5 - 8 mph. Weak circulation caused by the rapid movement.
Member Since: July 13, 2006 Posts: 12 Comments: 4889
Quoting 3355. Levi32:
See this. The intensity models are now starting to make Chantal's strongest days occur after Hispaniola, not before. If she survives the mountains intact, the environment there is conducive to make her a problem afterwards.



NHC remains at the bottom of the guidance. I can't wait to see what the NHC does intensity wise and track wise with their cone.
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Quoting 3363. Hurricanes305:
Hey guys look at this for the first time Chantal has some good convergence going to equal the already decent divergence flow. Satellite may not support a 60mph storm yet but it is finally starting to get some surface lift. Something to watch for as it continues WNW today. Hurricane is very possible and I would not be surprised if the NHC show it becoming a Hurricane before DR.



Balanced by divergence:



We have a strengthening TS.


What I find interesting here also is the convergence and divergence shown in the AOI over the bahamas....
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We 've got strong wind in Martinique FWI , 40 to 50nds with rain !!!

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Recon is climbing...
Acft. Geopotential Hgt: 361 meters (~ 1,184 feet)
to
Acft. Geopotential Hgt: 953 meters (~ 3,127 feet)
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Nice to see you again TampaSpin. We need Ike to show up as well.
The more input, the better.
Good discussions this morning.
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You all see the 06z runs of the GFDL and HWRF? They both are now showing intensification in the Bahamas and a sharp left. That realistic?
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dead zone does not exist for developed systems john hope rules states if the system is not developed it wont until at least the western carib. remember gilbert. he flourished in the eastern carib.
Member Since: September 11, 2010 Posts: 1 Comments: 4353
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Quoting 3335. Murko:
Here at 25.46N 76.62W, North Eleuthera, Bahamas, we're getting some very heavy rain and winds of 30mph+, gusts to 40mph from the south to east.
Hey, Murko... wondered if I would see u in today... looks like the NW Bahamas is going to get the worst of this ULL... I'm not liking the idea of rain upon rain [w/ whatever comes of Chantal in our neck of the woods by the weekend]. And as I feared, it looks like whatever Independence festivities are likely to be rained out :o(
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Quoting 3356. TampaSpin:
Morning!!!! The Models are all over the place with the Intensity Forecast and track of Chantal. They are all related. Simply put, if Chantal is weaker she moves South all the way thru the Caribbean. If she stays as is (around 50mph), then she moves the Forecast Current Track. But, if she gets much stronger then she moves further north and miss the big mountains entering further East of the Bahamas into the Atlantic before making a left hand turn and possibly becoming a very Strong Hurricane.
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3365. hydrus
Quoting 3335. Murko:
Here at 25.46N 76.62W, North Eleuthera, Bahamas, we're getting some very heavy rain and winds of 30mph+, gusts to 40mph from the south to east.
I would say there is something trying to form under your blob..Keep us posted if possible.
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Hey guys look at this for the first time Chantal has some good convergence going to equal the already decent divergence flow. Satellite may not support a 60mph storm yet but it is finally starting to get some surface lift. Something to watch for as it continues WNW today. Hurricane is very possible and I would not be surprised if the NHC show it becoming a Hurricane before DR.



Balanced by divergence:



We have a strengthening TS.
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Quoting 3352. CybrTeddy:
This storm annoys me. Yesterday it had a visual presentation of a 60mph storm, yet the recon only found a 50mph storm with 1010mph pressures. Today it has the visual presentation of a 45mph storm, and the recon is finding a 60mph TS with 1003mb pressures.


Wow that's strong ;)
But I agree, like everyone was sayin the other day, this is gonna be one of those tricky storms to forecast.
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I think Chanty is coming for West Palm Beach, FL
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The end of the GFDL run...
Member Since: September 22, 2005 Posts: 18 Comments: 2316
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3358. Grothar
Quoting 3339. washingtonian115:
Gro is that Chantal or Dorian?.Is this still the GFS model?.sorry for the questions.


It would be the next storm. I can't say Dorian, because something else could form somewhere before that.
Member Since: July 17, 2009 Posts: 69 Comments: 25394
Morning!!!! The Models are all over the place with the Intensity Forecast and track of Chantal. They are all related. Simply put, if Chantal is weaker she moves South all the way thru the Caribbean. If she stays as is (around 50mph), then she moves the Forecast Current Track. But, if she gets much stronger then she moves further north and miss the big mountains entering further East of the Bahamas into the Atlantic before making a left hand turn and possibly becoming a very Strong Hurricane.
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3355. Levi32
See this. The intensity models are now starting to make Chantal's strongest days occur after Hispaniola, not before. If she survives the mountains intact, the environment there is conducive to make her a problem afterwards.

Member Since: November 24, 2005 Posts: 635 Comments: 26556
Well to answer my own question I think that's Chantal..but is it the new run of the GFS because it dropped her last model run.
Member Since: August 14, 2010 Posts: 10 Comments: 16434
Webcam at Le Lorrain, on the Northeast coast of Martinique.

Member Since: September 22, 2005 Posts: 18 Comments: 2316
This storm annoys me. Yesterday it had a visual presentation of a 60mph storm, yet the recon only found a 50mph storm with 1010mb pressures. Today it has the visual presentation of a 45mph storm, and the recon is finding a 60mph TS with 1003mb pressures.
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Looks like a pretty significant southward shift in the latest model suites. Will be interesting to see whether or not the NHC moves along with this significant southward shift. Also, am impressed by the Hurricane Hunter data showing a stronger tropical storm.
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Quoting 3347. bigtp3:
The 8AM models show Chantal turning west into South/Central Florida, i'm wondering why the official track has it nowhere near there...
NHC is still waiting for more consistency another shift west on the 11am cone is likely.
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Quoting 3343. Levi32:
Martinique is the place to be watching for high winds at the surface. Chantal's tight vortex is passing just south of there. So far nothing TS force yet.
Very tight compact winds.
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Quoting 3341. Grothar:


They've been shifting since last night



That shows Chantal going right over "my house"!
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3347. bigtp3
The 8AM models show Chantal turning west into South/Central Florida, i'm wondering why the official track has it nowhere near there...
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Member Since: September 22, 2005 Posts: 18 Comments: 2316
Quoting 3332. Grothar:


perkin'

That's good news. So glad you are doing better.
So everyone, gut feelings on Chantal. I'm seeing a brush with several islands, north along Florida and the hook towards the west somewhere near Jacksonville. I look forward to blogging with you all
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Well, it's that time of year already. I have to go up to my classroom and set it up. Everyone have a great day and I look forward to see what's happening when I get back this afternoon.
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3343. Levi32
Martinique is the place to be watching for high winds at the surface. Chantal's tight vortex is passing just south of there. So far nothing TS force yet.
Member Since: November 24, 2005 Posts: 635 Comments: 26556

Quoting 3331. Grothar:
126 hours


Oh no just like I said worse scenario it push Cat. 2 in the Bahamas If it become 60 mph at 11pm hurricane watches will likely go up for DR.
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3341. Grothar
Quoting 3327. FIUStormChaser:
8am Models are in...... Models shifted a little south... Bringing Chantal in near Stuart....


They've been shifting since last night

Member Since: July 17, 2009 Posts: 69 Comments: 25394
Another good set of readings just in from recon, still showing support for a 60mph intensity at 11.
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Quoting 3331. Grothar:
126 hours


Gro is that Chantal or Dorian?.Is this still the GFS model?.sorry for the questions.
Member Since: August 14, 2010 Posts: 10 Comments: 16434
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Quoting 3315. MAweatherboy1:
This could change, but right now shear is low and decreasing off the east coast of FL in the Bahamas region, that could allow for some pretty fast strengthening in that area if it survives to get there. The farther north it goes, the better it should do:

Shear is too bad in the East Caribbean especially if the storm remains in the good bubble of low shear it has a good chance to hit cane status if this continues but the Bahamas looks really ripe and some RI could not be out the question if it does interact with land too much and hold it winds too. We shall see.  
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Quoting 3307. GeoffreyWPB:
Are the models still spinning up a future Dorian?

grothars blob from yesterday off florid as east coast looks like it split in two. The bigger piece seems to be firing more convection. Anyone else see that?
Member Since: March 16, 2006 Posts: 0 Comments: 69
3335. Murko
Here at 25.46N 76.62W, North Eleuthera, Bahamas, we're getting some very heavy rain and winds of 30mph+, gusts to 40mph from the south to east.
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Quoting 3330. bwi:
Barbados radar presentation impressive. No eyewall, but you can see the outlines of where it would like to set up -- cruising along 14n


Chantal has slowed down?
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Recon is going in for another center fix.
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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.