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 2128. sporteguy03:

The models might be seeing a lighter shear environment and perhaps as suggested maybe the ULL enchances the outflow of Chantal. I am not sure it is a matter of who to believe, intensity forecasts are not all they great. Have you looked at the LGEM it seems to do a reasonable job at intensity.Link



That could indeed happen because more models than not are seeing a less hostile environment. Maybe the NHC will change there forecast by tomorrow
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2132. JRRP
mmm less dry air now...
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Member Since: September 2, 2009 Posts: 130 Comments: 21032
2130. GetReal
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Over all I guess Chantal is doing a lot better than you'd expect given the dry air and the complete lack of an anti-cyclone to ventilate it. The 5mp intensity gain every 6 to 12 hours really is pretty decent given that scenario.
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Quoting 2122. weatherlover94:


why do almost all of the models predict the storm will re-strengthen after it leaves Cuba and Hispaniola ? but the NHC says it's pretty much doomed ? who do we believe here ?

The models might be seeing a lighter shear environment and perhaps as suggested maybe the ULL enchances the outflow of Chantal. I am not sure it is a matter of who to believe, intensity forecasts are not all they great. Have you looked at the LGEM it seems to do a reasonable job at intensity.Link
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We are so desperate for rain in Texas, (North, West, South, Central), etc. We unfortunately need one or even two of these types of storms. Our lakes are anywhere from 5 to 20 feet below normal.

I know things tend to even out...the SE has gotten a LOT of rain recently...we need that!

Send it our way....

be safe
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Barbados radar

Now tell me where the west north west movement is?
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looks like W-WNW track at least up to 70W/75W

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2124. Patrap
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2123. will40
Quoting 2122. weatherlover94:


why do almost all of the models predict the storm will re-strengthen after it leaves Cuba and Hispaniola ? but the NHC says it's pretty much doomed ? who do we believe here ?



the NHC
Member Since: September 19, 2005 Posts: 2 Comments: 4066
Quoting 2060. TropicalAnalystwx13:

...without land interaction.

Given its interaction with Hispaniola, the SHIPS forecasts a 59 kt (68 mph) tropical storm.


why do almost all of the models predict the storm will re-strengthen after it leaves Cuba and Hispaniola ? but the NHC says it's pretty much doomed ? who do we believe here ?
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Quoting 2108. GTstormChaserCaleb:
Should be expected as that is the current steering right now will move even more north later on in the track.



Once it gets west of the lesser Antilles It may slow down to 15-20 mph and hold around that area as it crosses into the Bahamas.
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Going to make a new blog soon. :P
Member Since: June 2, 2013 Posts: 4 Comments: 711
Pardon me, but why is a floater called a floater?
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Quoting 2098. wunderkidcayman:

Nah if anything just a wobble
I'm expecting a more W-WNW movement soon

More and more models moved west. Freeport is still my prediction.
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2117. FOREX
Quoting 2108. GTstormChaserCaleb:
Should be expected as that is the current steering right now will move even more north later on in the track.



Any chance of this missing all of the Islands with a NW then Northernly component, or is their a high in place to keep it at lower latitudes?
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Guess it was a sign to start fresh? I don't know... I've only been using this handle for a month.
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2115. GetReal



All the players lining up for the show, and their turns of WU hysterics over the coming days.
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Quoting 2107. wunderkidcayman:

Are you sure because am on that and it says other wise


Link
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Quoting 2105. midgulfmom:

indeed pressure affects the storm velocity.

btw.. velocity is speed and direction.
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Quoting 2092. MiamiHurricanes09:
Models becoming far more consistent with it. Doesn't appear like it'll go out to sea after moving over the Bahamas.


It still needs some more HH data before I start to feel confident. But it has been usually very consistent and in good agreement.
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Wow! My account Was literally reset! There is no longer anyone on my ignore list, when I had 16. :P ... This sucks.
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2109. will40
Quoting 2105. midgulfmom:


yes usually shallow tracks west but not always the case
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Quoting 2089. FOREX:


Seems to be moving more NW now.
Should be expected as that is the current steering right now will move even more north later on in the track.

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Quoting 2096. nrtiwlnvragn:


It is listed under:

For Today (text issued yesterday)

Are you sure because am on that and it says other wise
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Quoting 2079. trHUrrIXC5MMX:
hey folks... just tuning in..

was the discussion of why such a high pressure (1010 mb) for a 50 mph storm already had?...

this storm is very shallow

Shallow affects steering....? Know it does, can't remember. Anyone? Thanks!
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Its looking more and more like a FL storm
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2103. will40
Quoting 2096. nrtiwlnvragn:


It is listed under:

For Today (text issued yesterday)


well thats strange sounding but i got it ty
Member Since: September 19, 2005 Posts: 2 Comments: 4066
Large area of convection over west Africa is going to fester along the coast and stir up some vorticity over the next 48 hours

Once the strong wave axis comes along, we could see our next system form rather quickly.



Wave axis is at about 2W right now...

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Quoting 2074. GetReal:



Very impressive expansion in size over the past 12 hours. Chantal is putting the weight on!!!


It sure has getting round too. Big burst of convection is imminent and look at the spiral bands to it west getting primed for DMAX.
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Evening to all...

Amazing... 2100 posts and I didn't make one! lol

Quoting 2077. RTSplayer:



The two historical analogs which initially turned north then turned west and hit the east coast.


The one that hit FL looks like the Nassau hurricane of 1926...

I'm also wondering what happens to TD Chantal if a N track over the Gulf stream occurs...

Now I gotta go read all the old posts... and I'm tired after a long day... so I dunno how much more post-wise I'll be doing....
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2099. will40
Quoting 2085. nrtiwlnvragn:


FLIGHT TWO -- TEAL 71
A. 09/1200Z,1800Z
B. AFXXX 0203A CYCLONE
C. 09/1030Z
D. 14.0N 60.8W
E. 09/1130Z TO 09/1800Z


Next flight is tomorrow morning, 6:30 AM EDT takeoff.


Link


this shows an entirely different PLOD
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Quoting 2089. FOREX:


Seems to be moving more NW now.

Nah if anything just a wobble
I'm expecting a more W-WNW movement soon
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Quoting 2095. airmet3:


Part of the 50kts wind is due to the 23 kts forward speed?


first... it's 50 mph....
second... speed is not a factor here
and third... you are way far from answering my question, clearly!

and no, storm winds are not in relation to the storm movement
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Quoting 2088. will40:


ty looks like they changed the one i have


It is listed under:

For Today (text issued yesterday)
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2095. airmet3
Quoting 2079. trHUrrIXC5MMX:
hey folks... just tuning in..

was the discussion of why such a high pressure (1010 mb) for a 50 mph storm already had?...

this storm is very shallow


Part of the 50kts wind is due to the 23 kts forward speed?
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Quoting 2057. GeoffreyWPB:
Updated...



After Recon find the center a little further South and West of the 5pm advisory the LLC is moving WNW maybe even N of due WNW at times. The Ships model really bring the intensity for the storm. The ULL may actually ventilate the storm once it gets into the Bahamas rather than shearing it like the NHC is thinking. We shall see In any case it will be moving slowly over the Bahamas and will likely cause torrential rains for Hispaniola & the bahamas. Before responding to the High and bend back to Florida.
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2093. skook

Haiti – With the 2013 hurricane season officially starting tomorrow (1/6) and already predicted to be “active or extremely active,” IOM Haiti is preparing its emergency response by stockpiling non-food items, including water purification tablets and other supplies to combat waterborne diseases.

It is also working closely with government and local authorities, partners and vulnerable populations to undertake flood mitigation work and prepare for possible evacuations.

With more than 320,000 internally displaced Haitians still living in 385 camps, of which about 100 remain at particular risk of flooding, landslides or other environmental challenges, Haiti remains particularly vulnerable to extreme climatic events.


Link
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Quoting 2078. nrtiwlnvragn:


NHC has not gone with the left hand turn..... yet.
Models becoming far more consistent with it. Doesn't appear like it'll go out to sea after moving over the Bahamas.
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I have noticed a very large layer of low clouds off NW Africa for a few days and I wonder what is causing that to persist. What that is doing is cooling the waters bigtime in that area.

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2090. GetReal
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2089. FOREX
Quoting 2084. wunderkidcayman:

odd


Seems to be moving more NW now.
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2088. will40
Quoting 2085. nrtiwlnvragn:


FLIGHT TWO -- TEAL 71
A. 09/1200Z,1800Z
B. AFXXX 0203A CYCLONE
C. 09/1030Z
D. 14.0N 60.8W
E. 09/1130Z TO 09/1800Z


Next flight is tomorrow morning, 6:30 AM EDT takeoff.


ty looks like they changed the one i have
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Quoting 2067. HurricaneAndre:
what time.


you're the "expert" should already know this information
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Quoting 2076. will40:


look at C the date it leaves


FLIGHT TWO -- TEAL 71
A. 09/1200Z,1800Z
B. AFXXX 0203A CYCLONE
C. 09/1030Z
D. 14.0N 60.8W
E. 09/1130Z TO 09/1800Z


Next flight is tomorrow morning, 6:30 AM EDT takeoff.
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Quoting 2061. Gearsts:
More north

odd
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2083. hu2007
well well we have a tropical warning,but my forecast is calling for 2 scenario.(1) if get above 60 mph a more wnw to nw should resume as early overnight during dmax (2) if get weaker should then continue a more west and even wsw and should die cause of the expected upper wsw shear from the upper low over bahamas, the most likely at this moment is the #1. i will keep my update from puerto rico and weather observation
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About JeffMasters

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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