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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Member Since: Posts: Comments:
Quoting 711. floridaboy14:
what will recon find?
A: wave
B:40-45mph storm
c 50mph storm
d 60mph storm


I too agree with 50-55 MPH

Taco :o)
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Quoting 725. wxchaser97:

...except 55mph isn't used in the NHC advisories since it has no good knot conversion.


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Quoting 711. floridaboy14:
what will recon find?
A: wave
B:40-45mph storm
c 50mph storm
d 60mph storm
D, (im thinking 58 mph)
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Chantal definitely has room to make some northward wobbles relative to the forecast track. If you look at the bigger picture, Chantal's circulation is still embedded in a larger wave "pocket," for which I have highlighted the inverted-V signature below. Chantal's center is locked to the western edge of the wave structure, positioned well to the south of the northern peak of the wave, and this setup means that Chantal has some wiggle room to make NW wobbles despite the predominantly westerly or WNW trade wind flow, as long as her center is south of the peak of the wave. If you are wondering how Cape Verde storms can move north in a westerly trade wind flow, this is how.

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Quoting 724. TropicalAnalystwx13:

That's it?

You're so conservative sheesh.
Avila's getting into my head. :(
Member Since: September 2, 2009 Posts: 130 Comments: 21194
first thing they will look for west winds????
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I want to take a minute in a single post to say "KUDOS" to the bloggers here today. :) Good information, good graphics, and good prognostications! All very helpful and very civil to boot.

I'm out until later, have to go chase a few bucks! :) Enjoy! Chantal now and Dorian possibly on the way! Whew! Fast start to a long season ahead. Thanks, everyone!
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Quoting 718. stormchaser19:


50-55 mph

...except 55mph isn't used in the NHC advisories since it has no good knot conversion.

Oh and I think 50mph storm.
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Quoting 715. MiamiHurricanes09:
A category 12.

That's it?

You're so conservative sheesh.
Member Since: July 6, 2010 Posts: 113 Comments: 32283
Quoting 701. Waltanater:
Chantal is about 20 miles west of where it should be at this time. I think by 5pm tomorrow we may see a shift to the left in the models, IMO.


Dont worry in the next hour or so it will be 5 miles ahead of it.
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Quoting 711. floridaboy14:
what will recon find?
A: wave
B:40-45mph storm
c 50mph storm
d 60mph storm
winds 50 mph
Member Since: Posts: Comments:
Member Since: Posts: Comments:
Quoting 711. floridaboy14:
what will recon find?
A: wave
B:40-45mph storm
c 50mph storm
d 60mph storm
I think it will be at "c."
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Quoting 711. floridaboy14:
what will recon find?
A: wave
B:40-45mph storm
c 50mph storm
d 60mph storm
I don't poll on Mondays try again tomorrow when the polls are actually open ;)
Member Since: June 30, 2013 Posts: 12 Comments: 8437
Quoting 711. floridaboy14:
what will recon find?
A: wave
B:40-45mph storm
c 50mph storm
d 60mph storm


50-55 mph
Member Since: Posts: Comments:
Member Since: Posts: Comments:
Quoting 711. floridaboy14:
what will recon find?
A: wave
B:40-45mph storm
c 50mph storm
d 60mph storm


I think 50mph at least
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Quoting 711. floridaboy14:
what will recon find?
A: wave
B:40-45mph storm
c 50mph storm
d 60mph storm
A category 12.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
I see we have our third storm of the season.

I don't think we can rule out it becoming a hurricane just yet.
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daddy already had northeast winds reported by a blogger in the bahamas.
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712. JRRP
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what will recon find?
A: wave
B:40-45mph storm
c 50mph storm
d 60mph storm
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12Z WCOSS GFS likes South Carolina.....


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Quoting 703. yonzabam:


Seems outwith the centre of rotation. Looks like just a dry spot to me.

Member Since: July 6, 2010 Posts: 113 Comments: 32283
Quoting 698. Clearwater1:

Looks to me as though she is right on nhc track. Appears to be a more northerly movement, but I think that is just the ne quadrant expanding, it's cloud field.
I think she is right on target for the lattitude but more westerly on the longitude, based on predictions from 12 hours ago.
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Quoting 691. MiamiHurricanes09:


One thing to note the storm has its outflow channel out on all side feeding into the storm there is dry air but it not affecting the storm. It biggest problem is its forward speed at around 25 it needs to slow down and let air rise into its CDO for it the become really strong. but for now outflow is firing on all cylinders and the LLC is tuck under its CDO. If this slows down some it could intensify quite a bit.
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Recon reporting.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
705. JRRP
61knots
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18:30 UTC is Wheels up

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Quoting 693. Bluestorm5:
Look ready to make a next step... forming an eye.



Seems outwith the centre of rotation. Looks like just a dry spot to me.
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Quoting 649. moonlightcowboy:



Agreed. I've been suspect of it reaching the surface myself, and have been watching surface vorticity for the last three or four days - nothing has changed, although it does look to have good vorticity at the mid-levels and has been. It's also in an area of fairly dry air as well. At best, right now I think, it'll help to moisten the atmosphere for Chantal, and if it retrogrades westwards ahead of the storm, it may help to pull/tug the storm along behind it as well as help ventilate it. :)


absolutely nothing happening at the surface with the bahamas mid/ULL as mlc indicates:
Most recent ASCAT PAss:
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Chantal is about 20 miles west of where it should be at this time. I think by 5pm tomorrow we may see a shift to the left in the models, IMO.
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apparently RECON will leave the tarmac to mission are soon
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Quoting 676. Bluestorm5:
Honestly, the storm look like 50 mph. While visible satellite is impressive, I am having hard time seeing 60 mph or more on other satellites such as rainbow and AVN. Chantal just lost the red color on AVN for first time in awhile.


Let's see what Dmax do!!!
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Quoting 677. GTstormChaserCaleb:
It's really pulling north now into that breakage and feeling the Coriolis Effect of the Earth.
Quoting 677. GTstormChaserCaleb:
It's really pulling north now into that breakage and feeling the Coriolis Effect of the Earth.

Looks to me as though she is right on nhc track. Appears to be a more northerly movement, but I think that is just the ne quadrant expanding, it's cloud field.
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12Z GFDL finds the Windward Passage...........


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AL, 03, 2013070800, , BEST, 0, 97N, 461W, 35, 1008, TS, 34, NEQ, 50, 50, 0, 50, 1013, 150, 20, 45, 0, L, 0, , 0, 0, CHANTAL, M, 12, NEQ, 30, 0, 0, 0
AL, 03, 2013070806, , BEST, 0, 101N, 484W, 35, 1007, TS, 34, NEQ, 50, 50, 0, 50, 1012, 180, 20, 45, 0, L, 0, , 0, 0, CHANTAL, M, 12, NEQ, 30, 0, 0, 0
AL, 03, 2013070812, , BEST, 0, 107N, 506W, 40, 1005, TS, 34, NEQ, 50, 50, 0, 50, 1012, 180, 20, 50, 0, L, 0, , 0, 0, CHANTAL, M, 12, NEQ, 60, 0, 0, 50
AL, 03, 2013070818, , BEST, 0,114N, 528W, 40, 1005, TS, 34, NEQ, 50, 50, 0, 40, 1012, 180, 20, 0, 0, L, 0, , 0, 0, CHANTAL, M,
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I say
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Quoting 687. DocNDswamp:
Just a thought, and probably not alone pondering this... but Chantal's fast forward motion - which is anticipated to continue as crosses Hispaniola - might actually help limit disruption from land interaction, if takes track similar to latest 12Z GFS, getting back over water within around a 9-12 hr time frame... seems would have time to regenerate before affected by SWLY shear a day later or so.

Lot of "ifs", as usual... not even considering those long-range projections that raised my heart rate a little earlier... ;)




If that track occurs in the 12z GFS, I don't like an ULL backing away from it to the west like the GFS 500mb maps show. It also shows another ULL to the east of the Bahamas. Great ventilation setup in the Gulf.
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Quoting 688. MississippiWx:
WPac TCs are so legit.

Look ready to make a next step... forming an eye.

Member Since: August 1, 2011 Posts: 28 Comments: 8031
next big hurdle will west winds be found lots of nail biting ahead
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Member Since: September 2, 2009 Posts: 130 Comments: 21194
Chantal is probably a 50mph ts,I am happy this July hasn`t turn boring like the past previous the last July I love was 2008 with Bertha,Cristobal,and Dolly.
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Quoting Bluestorm5:
Honestly, the storm look like 50 mph. While visible satellite is impressive, I am having hard time seeing 60 mph or more on other satellites such as rainbow and AVN. Chantal just lost the red color on AVN for first time in awhile.


It's actually looking a little ragged over the last hour or so. Some of the outer rainbands, such as they are, are already moving onshore in Guyana, and the center is only about 300 miles from the coast. I wonder if some land interaction isn't having some effect, especially at her forward speed?
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WPac TCs are so legit.

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Just a thought, and probably not alone pondering this... but Chantal's fast forward motion - which is anticipated to continue as crosses Hispaniola - might actually help limit disruption from land interaction, if takes track similar to latest 12Z GFS, getting back over water within around a 9-12 hr time frame... seems would have time to regenerate before affected by SWLY shear a day later or so.

Lot of "ifs", as usual... not even considering those long-range projections that raised my heart rate a little earlier... ;)


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Quoting 677. GTstormChaserCaleb:
It's really pulling north now into that breakage and feeling the Coriolis Effect of the Earth.


Breaking away from the ITCZ, systems always seem to get a natural two-degree Coriolis bump more northwards. I think we'll still see more of a just better than westwards movement, west/westnorthwest, considering the strong low/mid level easterly flow. Imo, I think it's still too shallow and way too far away still to feel any weakness more northwards. Could be wrong, certainly wouldn't be the first time! ;)
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Quoting 681. Levi32:


The 45mph maximum winds in the NHC advisory are the Earth-relative winds. You do not add the forward storm motion vector.


Sorry Boss..................... :)
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Quoting 665. Tribucanes:



Not answering a question, just passing along what Skyepony had mentioned a few days ago. I'm an enthusiast not an expert. Nice very passive aggressive sarcasm though. The obvious rarity of ULL making it to the surface, land interaction, and less than rocket fuel SST's would be the answer. I make it a habit to let the experts, those in the field, and those well versed in the science of answer questions.


I meant no sarcasm, (but feel free to enjoy any unintended humor you might find in there.) It is difficult to discern any emotion with pure text. I was trying to point it out to the poster of #601 as additional information, that's all. No harm intended. I hope none taken.

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Quoting 610. moonlightcowboy:


ULL's rarely make it to the surface. They do, but it's not a common occurrence. To answer your question directly though, a storm must have fuel and that comes from the warm waters at the surface.

And, in this case, the ULL is also in a dry-air environment.

Thank you.
Quoting 649. moonlightcowboy:



Agreed. I've been suspect of it reaching the surface myself, and have been watching surface vorticity for the last three or four days - nothing has changed, although it does look to have good vorticity at the mid-levels and has been. It's also in an area of fairly dry air as well. At best, right now I think, it'll help to moisten the atmosphere for Chantal, and if it retrogrades westwards ahead of the storm, it may help to pull/tug the storm along behind it as well as help ventilate it. :)

Appreciate your sharing ideas in this and post 610 MLC.
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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.