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 2270. taco2me61:

Hi a Zoo long time no see :o) how are you doing...
And you are right it will never change :o) just saying

Taco :o)


Hey Taco:

Doing good -- not liking what they are saying about the early development and the way things are lining up. Certainly would not want a repeat of 04/05/06. That wasn't fun.

On a more serious note -- so many new people have come into South Florida in the 7 or 8 years since all the storms that people will not have the same level of preparedness, they don't have the memory of what it was like before.
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If it really wants to get it's act together it really needs to miss Hispaniola to the north or South....Cuba won't be too bad on it
Member Since: September 8, 2010 Posts: 0 Comments: 2069
Quoting 2269. stormpetrol:
Link

See that bright little red, I think that is Chantal center.

I have it 0.1 N of that
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2279. Patrap
Member Since: July 3, 2005 Posts: 421 Comments: 127566
Quoting 2267. Grothar:


So is mine, I was hoping someone would tell me.
Who said that?
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2277. Thrawst
I just realized, Levi didn't post a video today! Ahhh that's unfortunate I was ready to learn!! :)
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2276. Patrap
Member Since: July 3, 2005 Posts: 421 Comments: 127566
Quoting 2243. DataNerd:



You do realize those overlays tend to lag and not update often or properly right?

The floater and goes wind overlays are only good for getting a general idea of the situation not for hourly developmental analysis.


I take that into consideration, and I never use the overlays as gospels or something.

I just don't see your outflow, because the entire NW quadrant of the storm is missing.
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Quoting 2253. stormpetrol:
Barbados will have a very squally early morning as I suspect the center will pass just south of there.

Quoting 2257. wunderkidcayman:

I think it might as well either that or right over the island that radar in Barbados will be a great help


We in Barbados are being informed that the eye is forecast to pass about 50 miles to the north of us.
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2273. will40
Quoting 2258. weatherlover94:
I think we can expect quite a change at 11:00 with both path and Intensity ....anyone else agree ?


prob not a track change untill Sunday time frame.

NHC is already close on intensity but we shall see
Member Since: September 19, 2005 Posts: 2 Comments: 4110
2272. Grothar
Quoting 2255. JLPR2:


One of several links I have saved from you guys during the past 5 years. :D


I know I gave you a couple a long time ago, but I don't remember that one. It has a nice presentation.
Member Since: July 17, 2009 Posts: 69 Comments: 25369
Quoting 2268. TropicalAnalystwx13:

Up. It looks like Chantal might take a little longer to get into the Bahamas and then make landfall than originally thought, giving ample time for the ULL to back away and provide a favorable outflow pattern for the storm. This is depicted well by the intensity forecasts from the statistical models and the GFS.

oh gosh don't say that...
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Quoting 2265. zoomiami:
No matter how many years you watch the blog, and who comes and goes, it stays the same:

good outflow

no outflow

anticyclone over entire area

no --anticyclone is imaginary

convection shows deepening storm

convection shows little development

If anyone wanted to watch a ping pong match, this place is it.

Hi a Zoo long time no see :o) how are you doing...
And you are right it will never change :o) just saying

Taco :o)
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Link

See that bright little red, I think that is Chantal center.
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Quoting 2222. CybrTeddy:


In which manner do you think?
Quoting 2226. Jwd41190:


Adjusting up or down?

Up. It looks like Chantal might take a little longer to get into the Bahamas and then make landfall than originally thought, giving ample time for the ULL to back away and provide a favorable outflow pattern for the storm. This is depicted well by the intensity forecasts from the statistical models and the GFS.
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2267. Grothar
Quoting 2260. FOREX:


My vision is very poor. What change has occurred?


So is mine, I was hoping someone would tell me.
Member Since: July 17, 2009 Posts: 69 Comments: 25369
2266. Grothar
Member Since: July 17, 2009 Posts: 69 Comments: 25369
No matter how many years you watch the blog, and who comes and goes, it stays the same:

good outflow

no outflow

anticyclone over entire area

no --anticyclone is imaginary

convection shows deepening storm

convection shows little development

If anyone wanted to watch a ping pong match, this place is it.
Member Since: Posts: Comments:
2264. Relix
Quoting 2258. weatherlover94:
I think we can expect quite a change at 11:00 with both path and Intensity ....anyone else agree ?


I say they bump the intensity to 70mph south of PR and then lower it because of shear. May even emit a Hurricane watch for PR and Hispaniola. I also expect another eastward adjustment in the short term and a hook to the west at the end. In fact, I think 50 miles off the south coast of PR is a safe bet.
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Quoting 2258. weatherlover94:
I think we can expect quite a change at 11:00 with both path and Intensity ....anyone else agree ?


Not with track until about 15/16n. Then, yes.
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Looks like blob-con 3 out there if you include the Bahamian ULL and the dude behind chantal.
Looks like Chantal is going to fizzle out by the time she gets off the east coast of Florida.
And we'll probably have to worry about the wave behind her imo.
Anyway, it's going to be a long season!
Night all.
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2261. Patrap
Miami
NEXRAD Radar

Base Radial Velocity 0.50° Elevation
Range 124 NMI

Member Since: July 3, 2005 Posts: 421 Comments: 127566
2260. FOREX
Quoting 2236. Grothar:
Interesting switch in the models




My vision is very poor. What change has occurred?
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2259. Grothar
Member Since: July 17, 2009 Posts: 69 Comments: 25369
I think we can expect quite a change at 11:00 with both path and Intensity ....anyone else agree ?
Member Since: September 8, 2010 Posts: 0 Comments: 2069
Quoting 2253. stormpetrol:
Barbados will have a very squally early morning as I suspect the center will pass just south of there.

I think it might as well either that or right over the island that radar in Barbados will be a great help
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2256. Patrap
Member Since: July 3, 2005 Posts: 421 Comments: 127566
2255. JLPR2
Quoting 2249. Grothar:


That is a nice image.


One of several links I have saved from you guys during the past 5 years. :D
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Quoting ProgressivePulse:
As soon as Chantal can throw up some tall tops the outflow will be "Highlighted". Pretty shallow convection overall at the moment.


The LLC is still poorly defined per recon.

Plus the cloud pattern (bursting ahead of the main convection) indicates that the LLC may be partially exposed.
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Barbados will have a very squally early morning as I suspect the center will pass just south of there.
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Quoting 2240. hurricane23:
Fast-moving systems (> 20 kt) like Chantal have great difficulty closing off a surface circulation.


Yup, but I'll amend that by saying weak and undeveloped cyclones like Chantal have difficulty with it. If the GFS is right, the storm that develops behind it will have no such troubles (lower trade winds, much stronger by the time it reaches Chantal's longitude).

We all can agree if this happens, this will be trouble. GFS hi-res 144 hours out.
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Typhoon Soulik



The scary thing is, is that it's going to intensify quite a bit more before making landfall...
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My cousin got married and just scheduled for their honeymoon to be in the Turks & Caicos...Bad timing. Combine the ULL and Chantal.
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2249. Grothar
Quoting 2245. JLPR2:
TW behind Chantal is getting an interesting look.



That is a nice image.
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2248. Grothar
Quoting 2237. MiamiHurricanes09:
The ULL over the Bahamas looks like a greater threat to us tbh lol. But we'll see.


I'll monitor is closely.
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2247. Grothar
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Quoting 2245. JLPR2:
TW behind Chantal is getting an interesting look.

Has reasonable lower-level vorticity.

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2245. JLPR2
TW behind Chantal is getting an interesting look.

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Quoting 2232. Hurricanes305:


That is the trade winds which is causing it to make at around 20-25 mph and the LLC out racing its convection.
Latest shears map no wind shear:



You can't explain away why the upper level winds are the wrong direction.

WTF.
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Quoting 2193. RTSplayer:



The upper level wind overlay shows CYCLONIC winds above the storm in 3 quadrants.

There's not much outflow on this storm at all right now.

When you see outflow, it shoots straight out and then turns clockwise.



You do realize those overlays tend to lag and not update often or properly right?

The floater and goes wind overlays are only good for getting a general idea of the situation not for hourly developmental analysis.
Member Since: June 24, 2012 Posts: 0 Comments: 1534
Quoting 2235. hurricane23:


This storm remains poorly organized at the surface.



yep
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Quoting 2222. CybrTeddy:


In which manner do you think?
You're talking to the #1 wishcaster on the site, which way do you think?

;)

I kid.
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Fast-moving systems (> 20 kt) like Chantal have great difficulty closing off a surface circulation.
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Quoting 2222. CybrTeddy:


In which manner do you think?


Tonights intensity consensus is weakening to a 40 mph tropical storm as it crosses the Islands then strengthening quite a bit after it crosses the water....some models tonight bring it close to Cat 1 hurricane status now in 5 days as it heads for Florida. Im sure the NHC will catch onto this soon.
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Quoting 2228. ackee:
Did any of the model forecast the formation of chantal ?

nope not till 95L formed
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Quoting 2218. hurricane23:


Pulse i think we are ok here in sfl with chantal. If you take a look at the 18z GFS run the 200mb winds remain somewhat favorable until it enters the eastern Caribbean. Interaction w/upper-level trough increases substantially near DR. PLenty of hurdles land interaction-forward speed etc before its even a threat.
The ULL over the Bahamas looks like a greater threat to us tbh lol. But we'll see.
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2236. Grothar
Interesting switch in the models


Member Since: July 17, 2009 Posts: 69 Comments: 25369
Quoting ProgressivePulse:
As soon as Chantal can throw up some tall tops the outflow will be "Highlighted". Pretty shallow convection overall at the moment.


This storm remains poorly organized at the surface.


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Quoting 2227. SSideBrac:


Seconded

third

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Quoting 2218. hurricane23:


Pulse i think we are ok here in sfl with chantal. If you take a look at the 18z GFS run the 200mb winds remain somewhat favorable until it enters the eastern Caribbean. Interaction w/upper-level trough increases substantially near DR. PLenty of hurdles land interaction-forward speed etc before its even a threat.


Evening Adrian. I think so too personally, good practice though. I don't think this will be the last to enter our domain.
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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.

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