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 454. CycloneOz:
I can post a "Month of July 2013" GOES East Infrared Hurricane Sector animation UPDATED DAILY.

It might be cool to see Chantal move in unison with all the other weather in the sector.

Are you interested in me creating a new animation everyday for this system?


Oz.. good to see ya around brother!
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Quoting 473. Levi32:
It's too soon to know if the GFS depiction of Chantal bending all the way back into the GOM is realistic. However, a bend west late in the forecast period is no surprise, given the trough-split that occurs over the SE US and backs westward. That is a classic landfall pattern where the Bermuda ridge can build back westward towards the eastern seaboard and steer storms NW towards the coast.

I think Chantal, if she survives the greater Antilles, will affect the US. The million-dollar question for forecasters is will she still exist as a significant entity at that time, or will she die to high mountains and wind shear. That's what we have to wrestle with over the coming days.
Do you think she will slow down a bit as she gets close to us?
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Quoting 474. SLU:


You can see that a new burst of convection has began right over the previously partially exposed center and the quality of the convection looks better with more curvature.



And the WNW movement is clear.
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Quoting 470. ncstorm:
12z CMC..switched up..NHC got their work cut out for them..

new storm developing on the west coast of florida..Chantal heading west and then here comes the african wave..

Thanks Gro.

I see it has latched on the idea of "Dorian" being our first true cape verde storm.
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Quoting 468. southernema:


so what is everyone's opinion of this possibly happening

It's certainly plausible at this point, but it's not the most likely possibility in my opinion. Lots of time to sort it out though.
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Quoting 452. GTstormChaserCaleb:
I remember Katia. :D


Vee must find moose und skvirrel!
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Quoting 472. washingtonian115:
Remember the CFS had a hurricane in your vicinity on the 13th of July.Doesn't look so nutty now.
And i said poof to that, silly me.
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Quoting 452. GTstormChaserCaleb:
I remember Katia. :D


I remember Mary Alice.
Member Since: July 17, 2009 Posts: 71 Comments: 26958
Quoting 470. ncstorm:
12z CMC..switched up..

new storm developing on the west coast of florida..Chantal heading west and then here comes the african wave..



The storm in the GOM is the ULL. It passes over Florida and then into the GOM in the CMC's latest forecast. And, that doesn't look too farfetched given the current intensification of the ULL.
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474. SLU
Quoting 469. TylerStanfield:

Can I get your definition of Better Organized? Want to take note of this.


You can see that a new burst of convection has began right over the previously partially exposed center and the quality of the convection looks better with more curvature.

Member Since: July 13, 2006 Posts: 13 Comments: 5362
It's too soon to know if the GFS depiction of Chantal bending all the way back into the GOM is realistic. However, a bend west late in the forecast period is no surprise, given the trough-split that occurs over the SE US and backs westward. That is a classic landfall pattern where the Bermuda ridge can build back westward towards the eastern seaboard and steer storms NW towards the coast.

I think Chantal, if she survives the greater Antilles, will affect the US. The million-dollar question for forecasters is will she still exist as a significant entity at that time, or will she die to high mountains and wind shear? That's what we have to wrestle with over the coming days.

GFS Day 6 showing the trough split over the north gulf coast with Chantal's 500mb vorticity signature just east of Florida.

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Quoting 443. Gearsts:
Remember the CFS had a hurricane in your vicinity on the 13th of July.Doesn't look so nutty now.
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Where did the list of varying 'casters finally end up? fishcaster, doomcaster, etc etc... did someone post a final list or is it just buried in the blog somewhere?
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12z CMC..switched up..NHC got their work cut out for them..

new storm developing on the west coast of florida..Chantal heading west and then here comes the african wave..

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Quoting 464. SLU:
Chantal getting better organised.


Can I get your definition of Better Organized? Want to take note of this.
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Quoting 459. TropicalAnalystwx13:
The 12z GFS pushes Chantal, or what's left of it, into the Gulf of Mexico as the ridge to the northeast builds back in. A backing upper-level low allows for intensification.



so what is everyone's opinion of this possibly happening
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Quoting 424. washingtonian115:
Sorry to bother you with this Gro but again.Which one is the one the GFS develops?.


I believe the 2nd one, but at this rate all of them may have a chance to develop.
Member Since: July 17, 2009 Posts: 71 Comments: 26958
Quoting 445. washingtonian115:
Well can anybody answer?.


Answer what?
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465. JRRP
Quoting Stormchaser2007:

OH my God!! is a beast
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464. SLU
Chantal getting better organised.

Member Since: July 13, 2006 Posts: 13 Comments: 5362
Quoting 432. StormTrackerScott:


Hows Roxy?

Already done. :P
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DOOM!!!

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Quoting 459. TropicalAnalystwx13:
The 12z GFS pushes Chantal, or what's left of it, into the Gulf of Mexico as the ridge to the northeast builds back in. A backing upper-level low allows for intensification.



Which would send her to what part of Texas?
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i dont see no dorians yet.
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The 12z GFS pushes Chantal, or what's left of it, into the Gulf of Mexico as the ridge to the northeast builds back in. A backing upper-level low allows for intensification.

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Dorian:



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Quoting 432. StormTrackerScott:


Hows Roxy?


Roxy is well. Just working on her 50 shades of ASCAT.
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Quoting 454. CycloneOz:
I can post a "Month of July 2013" GOES East Infrared Hurricane Sector animation UPDATED DAILY.

It might be cool to see Chantal move in unison with all the other weather in the sector.

Are you interested in me creating a new animation everyday for this system?

Yes.
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Quoting 409. GTstormChaserCaleb:
Got another France/Jeanne like track showing up on the GFS:


Bite. Your. Tongue. - and knock on wood while you're doing it lol
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I can post a "Month of July 2013" GOES East Infrared Hurricane Sector animation UPDATED DAILY.

It might be cool to see Chantal move in unison with all the other weather in the sector.

Are you interested in me creating a new animation everyday for this system?
Member Since: August 26, 2006 Posts: 10 Comments: 3918
It appears the ULL over the Bahamas is working down to the mid levels, nevertheless it will provide a path for Chantel to follow
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Quoting 446. Mamasteph:
Then the NHC HAS named them after strippers for a reason..lol..
I remember Katia. :D
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Ameister12 and TropicalAnalystwx13 have forgotten the model depictions of Hurricane Irene in which the GFS runs depicted it as low as 922 and 919 mb.
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Quoting 423. ncstorm:
the 12z Navgem is strengthening Chantal now..currently running

If our little trough does not have enough influence and Chantel remains weak, she could feasibly make the gulf...
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Quoting 445. washingtonian115:
Well can anybody answer?.

To what?
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Quoting 416. mysticloud:
I so agree with this blog. We are looking at an active hurricane season. Am worried for so many Caribbean islands who have not yet recovered fully from sandy. Poor. Haiti and eastern Jamaica. If wind shear don't slow its chances of intensification then its flash flooding. I am also watching the wave behind chantal to see what's its spin


I'm just surprised at how early the CV door has opened up thus far. Let's hope a repeat of 2005 isn't in store. There's this unsettling feeling I have that Chantal could pull an Emily although it could dissipate just as quickly as it emerged. At any rate as it stands for now this may be a very active blob and blog season.
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Quoting 426. HCW:
NHC needs to stop naming storms after strippers :)
Quoting 427. TylerStanfield:
Seems like Chantal has a cycle it goes through every 24 hours with her CDO. She sheds off her convection, becoming partially exposed, and then refires a new CDO and hold onto that one for a 18-24 hours, then repeats. Has done this 2 times now, with her CDO.
Then the NHC HAS named them after strippers for a reason..lol..
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Well can anybody answer?.
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72 hours
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Not sure what to say about the PDO. Guess Neutral is best-fitted.



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Quoting 427. TylerStanfield:
Seems like Chantal has a cycle it goes through every 24 hours with her CDO. She sheds off her convection, becoming partially exposed, and then refires a new CDO and holds onto that one for a 18-24 hours, then repeats. Has done this 2 times now, with her CDO.
Girls I tell ya ;)
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Chantal in the Gulf in July means bad news guys! Wasn't there a Chantal that hit coastal TX about 10 years ago?



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Quoting 426. HCW:
NHC needs to stop naming storms after strippers :)
No they do not. In fact, they should post there pictures with every new advisory...Including intermediate.
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Quoting 434. txjac:
Collected .63 inch here in Houston!

yay...
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Quoting 420. StormTrackerScott:
Damm! This may have TX written all over it!


Its only one run that the GFS has shown this...
Don't get the Texans stirred up.
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434. txjac
Collected .63 inch here in Houston!
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Quoting 423. ncstorm:
the 12z Navgem is strengthening Chantal now..currently running

When the NOGAPS is showing a strong storm know that something is ah brewing.
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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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