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 63. flcanes:

First of all, i had no mean to doomcast. 2nd I believe you. My scenario was hypothetical. 3rd, do you think this will make landfall in south florida?
I know flcanes I just felt like teasing you. As of right now I really can't make a call until it gets into the E Carib. Just judging by past storms around the same position and the conditions around them I would say Chantal will have moments where the convection pulsates and the convection wane. It will also be interesting to see what Hispaniola does to the circulation, rip it apart, bounce off and around it, or just tracks through it intact. Then once it emerge on the other side how will the wind shear be like from the approaching trough along the east coast or will that trough lift out and a high settles in above it which is a nice recipe for strengthening. Lots of questions that are yet to be answered. The verdict is still out on this one.
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Quoting 53. flcanes:

Well, no models (besides yesterdays absurd CMC run) develop it


It does not have to be developed to be dangerous or of concern. Systems moving that slowly have often brought flooding rains and some dangerous winds in thunderstorms. When something that large is off a coast and moving in the direction of land and over the Bahamas, it should be watched very closely. Even if only for maritime interests.
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we need to watch the next tropical wave back of invest 95L
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80. 7544
Quoting 68. Grothar:
Still at BlobCon 1.



may have to upgrade to a 2 gro

maybe get a tag 96l by the nhc only because its getting very close to fl and not moving too much imo
Member Since: May 6, 2007 Posts: 0 Comments: 6874
Quoting 68. Grothar:
Still at BlobCon 1.

didn't someone post yesterday that the CMC sandwiched Florida with 2 storms.
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Quoting 72. Waltanater:
Quoting 2963. Hurricane1956:
Impressive feature East of Florida over the Bahamas,it really pick-up steam in the last few hours!! it seems to be trying to organize more,just wondering if the upper level low will transfer to the surface before it reach Florida?,but this morning looks very different than yesterday,I believe at one point the CMC model have this a Tropical Depression over Florida.
Any thoughts or information about this feature?.
This is approximately where Katrina first formed.... :)

Lol but no.
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Quoting 67. wunderkidcayman:

nah, plus convection isn't getting blown at all it was convection weakening, but new burst of convection now building and moved a bit N thats all. so its not giving the impression that its moving W, it is moving W.


At 1200 UTC, 08 July 2013, TROPICAL STORM CHANTAL (AL03) was located in the North Atlantic basin at 10.6°N and 50.6°W. The current intensity was 40 kt and the center was moving at 23 kt at a bearing of 280 degrees. The minimum central pressure was 1005 mb.
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CLIMATOLOGY SUGGESTS THAT TROPICAL
CYCLONES THAT MOVE RAPIDLY WESTWARD OR WEST-NORTHWESTWARD IN THE
DEEP TROPICS HAVE DIFFICULTY STRENGTHENING

The little rascals effectively "shear" themselves by means of their faster forward speed....
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Quoting 69. flcanes:

Ya, but last nights absurd CMC run disagreed. 2 storms making landfall in the CONUS? I think not.
Lol.The CMC tends to throw doom around with every little storm that's out there.It showed Chantal as a strong cat 1/weak cat 2.I'm surprised it hasn't latched on to that wave over africa.
Member Since: August 14, 2010 Posts: 10 Comments: 17661
I'm not Westcasting or Wishcasting I'm just stating whats there

anyway Hurricane Hunters should give us a better idea
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Quoting 2963. Hurricane1956:
Impressive feature East of Florida over the Bahamas,it really pick-up steam in the last few hours!! it seems to be trying to organize more,just wondering if the upper level low will transfer to the surface before it reach Florida?,but this morning looks very different than yesterday,I believe at one point the CMC model have this a Tropical Depression over Florida.
Any thoughts or information about this feature?.
This is approximately where Katrina first formed.... :)
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Quoting 68. Grothar:
Still at BlobCon 1.


When will it upgrade?
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Quoting 65. washingtonian115:
That upper level low will continue to stay in the upper levels.It will bring increase rain fall into Florida and perhaps the eastern gulf later on.I don't see it being much more than a gusty rain maker.

Ya, but last nights absurd CMC run disagreed. 2 storms making landfall in the CONUS? I think not.
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Still at BlobCon 1.

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Quoting 55. Relix:


Its clearly moving at 280 degrees. The convection getting blown to the south gives the impression of a westward moving system but the LLC seems on track with the NHC.

nah, plus convection isn't getting blown at all it was convection weakening, but new burst of convection now building and moved a bit N thats all. so its not giving the impression that its moving W, it is moving W.
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Quoting 62. Tropicsweatherpr:
SLU, Dr Masters nalied 100% the discsion about what Chantals presence means for the rest of the season which is not good at all for us who are in hurricane alley.

Yep. Stay safe!
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That upper level low will continue to stay in the upper levels.It will bring increase rain fall into Florida and perhaps the eastern gulf later on.I don't see it being much more than a gusty rain maker.
Member Since: August 14, 2010 Posts: 10 Comments: 17661
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Quoting 58. GTstormChaserCaleb:
Westcaster

Doomcaster...Kori wrote a good blog as to why this probably won't make it into the Western Caribbean or GOM. Says an ULL will be in the Gulf acting as a block and the Subtropical Ridge will weaken which will turn it more towards the north. The bend back in the models towards the East Coast caught my attention last night starting with the GFS and then the CMC. I know see most if not all the models showing this bend back to the East Coast.

First of all, i had no mean to doomcast. 2nd I believe you. My scenario was hypothetical. 3rd, do you think this will make landfall in south florida?
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SLU, Dr Masters nalied 100% the discussion about what Chantals presence means for the rest of the season which is not good at all for us who are in hurricane alley.
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Quoting 53. flcanes:

Well, no models (besides yesterdays absurd CMC run) develop it
Well there you go, It won't develop.
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I know all the talk this morning is about Chantal, but that mid-level feature over the Bahamas looks interesting. If nothing else, it should gives the Bahamas and SE Florida some windy and squally weather.
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Thoughts on the ULL heading towards FL? Strength/timing/rainfall?


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Quoting 51. wunderkidcayman:
hey guys after analyzing hi res vis of Chantal it had spit out a low level spin which quickly became a part of a new spin which is located 10.7N 51.1W moving W or just N of W 270 degrees
Westcaster ;)

Quoting 46. flcanes:

Worst case scenario: degenerates into open wave, goes to the west caribbean, and BOOM!!!
Doomcaster ;)...Kori wrote a good blog as to why this probably won't make it into the Western Caribbean or GOM. Says an ULL will be in the Gulf acting as a block and the Subtropical Ridge will weaken which will turn it more towards the north. The bend back in the models towards the East Coast caught my attention last night starting with the GFS and then the CMC. I know see most if not all the models showing this bend back to the East Coast.
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Jim Edds ‏@ExtremeStorms 20s
#Chantal doesn't worry me so much but forming far out in the Atlantic in early July is a bad sign for the rest of the season.



In other news....


@astro_luca Luca Parmitano 5m
Smoke on the water: forests fires in #Canada ... Foreste in fiamme in Canada #Volare
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Quoting 44. SLU:


At 1200 UTC, 08 July 2013, TROPICAL STORM CHANTAL (AL03) was located in the North Atlantic basin at 10.6°N and 50.6°W. The current intensity was 40 kt and the center was moving at 23 kt at a bearing of 280 degrees. The minimum central pressure was 1005 mb.


Okay, alright, I hadn't checked the ATCF before I made that post. 45mph now, still no real difference.
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Quoting 51. wunderkidcayman:
hey guys after analyzing hi res vis of Chantal it had spit out a low level spin which quickly became a part of a new spin which is located 10.7N 51.1W moving W or just N of W 270 degrees


Its clearly moving at 280 degrees. The convection getting blown to the south gives the impression of a westward moving system but the LLC seems on track with the NHC.
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.
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Quoting 52. zampaz:

I guess folks are too busy with Chantal to talk about the ULL at 25N 75W. I find it interesting and wonder what will happen though...will it push dry air into the gulf? Will it suck up energy and moisture?

As least it's been blessed by Gro with a Blob designator.

Click image for animated loop:


Well, no models (besides yesterdays absurd CMC run) develop it
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Quoting 10. 7544:
time to repost the ull is looking best it ever has at this hour could it pull a fast one ?

I guess folks are too busy with Chantal to talk about the ULL at 25N 75W. I find it interesting and wonder what will happen though...will it push dry air into the gulf? Will it suck up energy and moisture?

As least it's been blessed by Gro with a Blob designator.

Click image for animated loop:

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hey guys after analyzing hi res vis of Chantal it had spit out a low level spin which quickly became a part of a new spin which is located 10.7N 51.1W moving W or just N of W 270 degrees
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Quoting 48. biff4ugo:
So the wide dry SAL isn't strong enough or permanent enough to dampen the season, long term? Is the SAL a relatively minor generation factor compared to SST and Shear, or only come into play when looking at intensification?

SAL can still affect things
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Quoting 44. SLU:


At 1200 UTC, 08 July 2013, TROPICAL STORM CHANTAL (AL03) was located in the North Atlantic basin at 10.6°N and 50.6°W. The current intensity was 40 kt and the center was moving at 23 kt at a bearing of 280 degrees. The minimum central pressure was 1005 mb.

Indicative of at least 45 mph storm.
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So the wide dry SAL isn't strong enough or permanent enough to dampen the season, long term? Is the SAL a relatively minor generation factor compared to SST and Shear, or only come into play when looking at intensification?
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Quoting 46. flcanes:

Worst case scenario: degenerates into open wave, goes to the west caribbean, and BOOM!!!

WCS: It decreases its forward speed, conditions become more favorable, and it becomes a hurricane.
Member Since: June 14, 2013 Posts: 2 Comments: 1972
Quoting 42. hydrus:
It is only my opinion, but if Chantal would strengthen a bit, it would be better in the long run. If she is weak, the further south and west, putting her in an area where she could become dangerous.

Worst case scenario: degenerates into open wave, goes to the west caribbean, and BOOM!!!
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Chantal is not gaining mush latitude at this time, which may help it survive the dry air, and rapid forward motion. She is still tapping into the moisture in the ITCZ. Motion still remains nearly due west. IMO the comparisons to Isaac and Ernesto are spot on ATT.
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44. SLU
Quoting 29. CybrTeddy:
Getting that squashed look Emily in 2011 had. This won't get beyond 40mph today.


At 1200 UTC, 08 July 2013, TROPICAL STORM CHANTAL (AL03) was located in the North Atlantic basin at 10.6°N and 50.6°W. The current intensity was 40 kt and the center was moving at 23 kt at a bearing of 280 degrees. The minimum central pressure was 1005 mb.
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welcome cape verdes :D
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Quoting 29. CybrTeddy:
Getting that squashed look Emily in 2011 had. This won't get beyond 40mph today.
It is only my opinion, but if Chantal would strengthen a bit, it would be better in the long run. If she is weak, the further south and west, putting her in an area where she could become dangerous.
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Quoting 38. allancalderini:
ATCF say 45mph lets see what the NHC decide about it.


Ah yes, you're quite correct.
AL, 03, 2013070812, , BEST, 0, 106N, 506W, 40, 1005, TS

Won't get beyond 45* mph today then.
Member Since: July 8, 2005 Posts: 259 Comments: 24553
Outside of the ridiculous forward speed, Chantal is right on track.

No way that intensity forecast is verifying, though.
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Quoting 35. washingtonian115:
Here is another example of a distraction.



I call that "The end of the world"
Member Since: June 14, 2013 Posts: 2 Comments: 1972
Quoting 29. CybrTeddy:
Getting that squashed look Emily in 2011 had. This won't get beyond 40mph today.
ATCF say 45mph lets see what the NHC decide about it.
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Quoting 35. washingtonian115:
Here is another example of a distraction.
http://www.noaanews.noaa.gov/stories2004/images/f rances090504-1515z2.jpg

Hmm.
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Quoting 28. Hurricane1956:
I has been saying that we have to just keep a eye on this Upper level low,Chantel is having all the attention and it's so far away!!.This tropical feature is very close to the Florida Peninsula and I believe there are some mid level circulation with it,don't know if this will transfer to the surface?,it's sailing now through very warm waters,so will see what happens with it,but it looks rather impressive this morning.

Lets wait a bit. NHC may give 0% at next TWO
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Here is another example of a distraction.


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Quoting 23. washingtonian115:
Here was Ernesto in the central caribbean as a open wave.



when it slowed down it was able to build a nice center.



ernesto had plenty of bloggers popping antacids..it was a hard one to forecast..
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Thanks Doc.
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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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