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 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.
Member Since: August 19, 2005 Posts: 5 Comments: 4863
Quoting 2216. RTSplayer:



The storm has always had upper level winds blowing across it either NE to SW or E to W.

At one time a few days ago there was actually an upper level low on top of it, which tends to inhibit TC formation, so I don't know where this "always had outflow" thing is coming from.
Quoting 2216. RTSplayer:



The storm has always had upper level winds blowing across it either NE to SW or E to W.

At one time a few days ago there was actually an upper level low on top of it, which tends to inhibit TC formation, so I don't know where this "always had outflow" thing is coming from.


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:

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2231. HadesGodWyvern (Mod)
TY 07W
2013JUL09 010100

CI: T4.7
962.6 hPa 82.2 knots
T4.0 (Initial) 3.9 (Adjusted) 3.8 (Raw)
UNIFRM
19.6N 140.1E

75 knots estimated from JTWC

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Quoting 2198. interstatelover7166:
To sum it up, Chantal could really do anything at this point. Unfortunately, it's a wait-and-see situation right now.

isn't that always the case
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Quoting 2221. Jwd41190:


Yeah I am watching this because I live in SC and we really do not need anymore rain right now...


Hello from WV. We have seen nothing but rain this summer. If whats left of it comes up this way we are going to flood out bad
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2228. ackee
Did any of the model forecast the formation of chantal ?
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Quoting 2215. stormwatcherCI:
I am glad you said SOME.


Seconded
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Quoting 2213. TropicalAnalystwx13:
Probably gonna need some adjusting...



Adjusting up or down?
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As soon as Chantal can throw up some tall tops the outflow will be "Highlighted". Pretty shallow convection overall at the moment.
Member Since: August 19, 2005 Posts: 5 Comments: 4863
Quoting 2213. TropicalAnalystwx13:
Probably gonna need some adjusting...



OFCL by far below the intensity consensus.
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2223. Grothar
Member Since: July 17, 2009 Posts: 63 Comments: 23740
Quoting 2213. TropicalAnalystwx13:
Probably gonna need some adjusting...



In which manner do you think?
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Quoting 2204. weatherlover94:
A lot of spread in the GFS ensembles. Several take it to the Carolina's and several take it through Florida and to Texas. A lot to figure out in the coming days


Yeah I am watching this because I live in SC and we really do not need anymore rain right now...
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Quoting 2214. Hurricane1956:
Relix don't get frustrated,it's the same story every year!!!,some of the Caymans people in this Blog wishing every storm to go over their Island real sad!! and you right there is a lot of people coming to this blog to get accurate information about the Tropics.One thing that I learned through out the year the National Hurricane Center is superb!!! tracking this storms for us,they are not perfect but very very good!!.

not true its just that we know when storms are coming we get hit so many times that its just instincts
and another think if you were implying me I am not wishing
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Quoting 2196. will40:


tomorrow morning at 6:30 AM


Ok thanks...I will be on the way to work then...guess I can check it afterwards then.
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Quoting ProgressivePulse:
Chantal ought to put on a decent boost of rpm tonight. Long way to go till Dmin and as some have said, outflow is recently expanding. Chantal was looking a bit disheveled this afternoon in satellite presentation. The convergence map should reflect this in the next hour or so when it updates, not so great here.





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.
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Quoting 2213. TropicalAnalystwx13:
Probably gonna need some adjusting...




Quite a bit of adjusting
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Quoting 2208. Hurricanes305:


This storm always had outflow which is why it stay alive in the dry air and remain in an excellent moisture bubble. I dont which satellite you are looking at.



The storm has always had upper level winds blowing across it either NE to SW or E to W.

At one time a few days ago there was actually an upper level low on top of it, which tends to inhibit TC formation, so I don't know where this "always had outflow" thing is coming from.
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Quoting 2214. Hurricane1956:
Relix don't get frustrated,it's the same story every year!!!,some of the Caymans people in this Blog wishing every storm to go over their Island real sad!! and you right there is a lot of people coming to this blog to get accurate information about the Tropics.One thing that I learned through out the year the National Hurricane Center is superb!!! tracking this storms for us,they are not perfect but very very good!!.
I am glad you said SOME.
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Quoting 2190. Relix:

No.... its not getting to the Caymans. There is no WSW movement. Stop mis-informing people who come here to get some information. Its clearly moving WNW right now, maybe a hint of NW
Relix don't get frustrated,it's the same story every year!!!,some of the Caymans people in this Blog wishing every storm to go over their Island real sad!! and you right there is a lot of people coming to this blog to get accurate information about the Tropics.One thing that I learned through out the year the National Hurricane Center is superb!!! tracking this storms for us,they are not perfect but very very good!!.
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Probably gonna need some adjusting...

Member Since: July 6, 2010 Posts: 109 Comments: 30282
Quoting 2201. TropicalAnalystwx13:

"VISIBLE AND WATER VAPOR IMAGERY CONTINUE TO INDICATE AN INCREASE IN
THE UPPER-LEVEL ANTICYCLONIC OUTFLOW PATTERN." - NHC @ 5pm AST


If you can show me actual outflow on this system, I'd be happy to concede, because I don't see it, and I've watched hundreds of these things.

There's a couple faint puffs around 55 to 56W, and that's it. then if you look a half degree to either side of that line, the wind is contrary to that again, so it's not convincing me of anything at all.
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2211. JRRP
Quoting AllStar17:


It is too early to say that IMO.

yeah you are right.. i meant with the NHC track
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Quoting 2206. canehater1:
Do the latest model runs indicate more uncertainty in

trough strength and subsequent rebuilding of the

Atlantic Ridge?



There is some spread,yes
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Quoting 2188. Hurricanes305:


That does not make any sense you are just confusing yourself this likey to stay east of Jamaica but you never now the high could suddenly build back as it has been dominant but the models are showing it building over it once it turns NW/NNW into the Bahamas.

I ain't confusing anything


Quoting 2190. Relix:

No.... its not getting to the Caymans. There is no WSW movement. Stop mis-informing people who come here to get some information. Its clearly moving WNW right now, maybe a hint of NW


come on stop that cayman bull now

I did not say WSW so stop that putting words in my mouth bull

I not misleading info

Its moving W-WNW with just a slight wobble to the WNW-NW here and there
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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.


This storm always had outflow which is why it stay alive in the dry air and remain in an excellent moisture bubble. I dont which satellite you are looking at.
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Quoting 2159. Patrap:
Miami
NEXRAD Radar

Base Reflectivity 0.50° Elevation
Range 248 NMI



"And so it begins..."

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Do the latest model runs indicate more uncertainty in

trough strength and subsequent rebuilding of the

Atlantic Ridge?
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2205. JLPR2
Quoting 2169. Gearsts:
Popcorn convection in front meaning moist environment for deeper convection.


You think it might pop? So far it's been going through cycles of decent convection strengthening and weakening, maybe the environment it's heading into could help it keep it together all day, therefore strengthening.

Despite its fast pace it is a small cyclone and when those find a favorable spot they tend to strengthen quickly.
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A lot of spread in the GFS ensembles. Several take it to the Carolina's and several take it through Florida and to Texas. A lot to figure out in the coming days
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Quoting 2186. weatherlover94:
Does it appear to be slowing down any?




Slightly but nothing big still moving around 20-25mph
But I expect a slow down to 15-20 mph around 62-65W. After 65W it could have a chance to really strengthen if conditions warrant.
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Chantal ought to put on a decent boost of rpm tonight. Long way to go till Dmin and as some have said, outflow is recently expanding. Chantal was looking a bit disheveled this afternoon in satellite presentation. The convergence map should reflect this in the next hour or so when it updates, not so great here.



Member Since: August 19, 2005 Posts: 5 Comments: 4863
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.

"VISIBLE AND WATER VAPOR IMAGERY CONTINUE TO INDICATE AN INCREASE IN
THE UPPER-LEVEL ANTICYCLONIC OUTFLOW PATTERN." - NHC @ 5pm AST
Member Since: July 6, 2010 Posts: 109 Comments: 30282
2200. Patrap
Member Since: July 3, 2005 Posts: 415 Comments: 125681
2199. ncstorm
Member Since: August 19, 2006 Posts: 13 Comments: 13476
To sum it up, Chantal could really do anything at this point. Unfortunately, it's a wait-and-see situation right now.
Member Since: October 15, 2012 Posts: 0 Comments: 290
2197. Gearsts
Quoting 2190. Relix:

No.... its not getting to the Caymans. There is no WSW movement. Stop mis-informing people who come here to get some information. Its clearly moving WNW right now, maybe a hint of NW
lol
Member Since: August 2, 2010 Posts: 0 Comments: 1035
2196. will40
Quoting 2184. Jwd41190:
When is the next recon?


tomorrow morning at 6:30 AM
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what are the chances it carrys this Upper level anti-cyclone all the way to Florida ?
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Chantal is moving way too fast for any rapid intensification. May peak at 60mph by mid day tmrw. But unless the system slows down before the wind shear gets to it I think that will be about it for chantal
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Quoting 2143. TropicalAnalystwx13:

Anticyclonic flow is evident atop Chantal. Recently developed.

Quoting 2157. TropicalAnalystwx13:

Expanding outflow in all quadrants except the northwest isn't indicative of a developed/developing anticyclone aloft? Color me surprised.



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.
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2192. Patrap
Member Since: July 3, 2005 Posts: 415 Comments: 125681
Quoting 2166. ncstorm:
Challenge: Pick one and follow it the whole way.
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2190. Relix
Quoting 2167. wunderkidcayman:
looking at shortwave loop it kinda looks like chantal was moving WNW but now coming out of it into a more W movement so more W-S of due WNW

No.... its not getting to the Caymans. There is no WSW movement. Stop mis-informing people who come here to get some information. Its clearly moving WNW right now, maybe a hint of NW
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2189. GetReal
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Quoting 2167. wunderkidcayman:
looking at shortwave loop it kinda looks like chantal was moving WNW but now coming out of it into a more W movement so more W-S of due WNW


That does not make any sense you are just confusing yourself this likey to stay east of Jamaica but you never now the high could suddenly build back as it has been dominant but the models are showing it building over it once it turns NW/NNW into the Bahamas.
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I think LLCOC is now near 12.1N 55.6W
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Does it appear to be slowing down any ?
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2185. Relix
Darn! Girl looking very good for the picture right now. Definitely moving at 285-290 degrees as well. I am thinking it may even shoot for the mona passage.
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When is the next recon?
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2183. Patrap
Member Since: July 3, 2005 Posts: 415 Comments: 125681

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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.