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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2183. Patrap
Member Since: July 3, 2005 Posts: 426 Comments: 129093
Quoting 2166. ncstorm:


Some of those GOM scenarios are disconcerting.
Member Since: June 29, 2009 Posts: 13 Comments: 5315
also outflow looks to be getting better
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2180. Patrap
Miami
NEXRAD Radar

Velocity Azimuth Display Wind Profile ° Elevation
Range 124 NMI

Member Since: July 3, 2005 Posts: 426 Comments: 129093
Quoting 2157. TropicalAnalystwx13:

Expanding outflow in all quadrants except the northwest isn't indicative of a developed/developing anticyclone aloft? Color me surprised.
Should I get the yellow/orange/red crayon out, sir?
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2178. noxshox
Quoting 2134. RkptMom:
My 15 year old daughter is visiting a friend in Fort Lauderdale, Fl. Should I be concerned, or just keep a watchful eye? The latest model trends are making me a little nervous.

If NHC's forecast holds up, it's no biggie, as it's predicted to only be a depression as it nears that location. To echo the other replies, though, always keep a watchful eye. These things can be very unpredictable and change course with little notice. Stay tuned and good luck to both you and her. :)
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Quoting 2158. caribbeantracker01:


exactly so when the center shows it self we shall see what is the motion

yep and it won't be too long now
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Quoting 2155. JRRP:

Chantal will pass over Sierra de Neiba
montains 2000 mt


It is too early to say that IMO.
Member Since: June 29, 2009 Posts: 13 Comments: 5315
2174. Patrap
Tropical Atlantic - Rainbow Loop

click the image to ZOOM
Member Since: July 3, 2005 Posts: 426 Comments: 129093
Quoting 2161. Patrap:


Gaining latitude now as it moves WNW about to find warmer waters and less dry air. This should really help it a lot to bulk up some more. Don't forget DMAX and what it was able to do for it last night.
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New model output raises more questions than it answers, and this is with the addition of recon.

The sharp left hand turn causes a massive spread in the models, with suggestions all the way from due north to south west across the GOM into Mexico, thats a horrible spread.

On the whole my opinion remains that there is not any reliable handling of this system beyond 3 days, and that even the 3 day handling is pretty abysmal.


Once again, points to this being a very tricky system to track.

Not really much you can do when you get a long tracker this early in the season and you have this bizarre jet+bermuda pattern on top of it. This thing ultimately could end up going anywhere. People need to keep an eye on this, because where it goes will govern intensity. If it made it through the straights or over the Florida mainland into the GOM on a western heading that would be a very bad thing and RI would be very distinct issue.
Member Since: June 24, 2012 Posts: 0 Comments: 1546
Quoting 2168. Patrap:


was noticing that, surface trough now along in the area where the ULL is

Member Since: March 10, 2010 Posts: 1 Comments: 7874
IM getting my shutters out tomorrow
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2169. Gearsts
Popcorn convection in front meaning moist environment for deeper convection.
Member Since: August 2, 2010 Posts: 0 Comments: 1960
2168. Patrap
Member Since: July 3, 2005 Posts: 426 Comments: 129093
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
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2166. ncstorm
Member Since: August 19, 2006 Posts: 13 Comments: 16041
Quoting 2154. RTSplayer:
Florida mas as well get ready. All the models are saying left hook now.


Get ready for what... A rainstorm?!?
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2164. RkptMom
Thanks all. That's why I follow the blog, because things are constantly changing and these things can be unpredictable. Back to lurking and keeping a watchful eye.
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2163. Kyon5
Quoting 2161. Patrap:
It's getting that shape. It will be interesting to see what it does tonight.
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Outflow is very good
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2161. Patrap
Member Since: July 3, 2005 Posts: 426 Comments: 129093
2160. Gearsts
Quoting 2154. RTSplayer:
Florida mas as well get ready. All the models are saying left hook now.

Holy GFS that's close
Member Since: August 2, 2010 Posts: 0 Comments: 1960
2159. Patrap
Miami
NEXRAD Radar

Base Reflectivity 0.50° Elevation
Range 248 NMI

Member Since: July 3, 2005 Posts: 426 Comments: 129093
Quoting 2152. wunderkidcayman:

well maybe more like W-WNW


exactly so when the center shows it self we shall see what is the motion
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Quoting 2150. RTSplayer:


No, only like one quadrant (SW) has anti-cyclonic flow, and that's more coincidence than anything.

Expanding outflow in all quadrants except the northwest isn't indicative of a developed/developing anticyclone aloft? Color me surprised.
Member Since: July 6, 2010 Posts: 113 Comments: 32528
Chantal is really starting to get its act together in the last few frames.. I think we might see some good strengthening tonight
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2155. JRRP
Quoting stormchaser19:
Topography map of Hispaniola

Chantal will pass over Sierra de Neiba
montains 2000 mt
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Florida may as well get ready. All the models are saying left hook now.

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Quoting 2118. Stormchaser121:

More and more models moved west. Freeport is still my prediction.



And here I thought trolls were too early today.
Member Since: June 24, 2012 Posts: 0 Comments: 1546
Quoting 2137. Hurricanes101:


you cant tell movement by looking at the radar from Barbados

The system is too far away. Also overall the average motion is still WNW

well maybe more like W-WNW
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Quoting 2143. TropicalAnalystwx13:

Anticyclonic flow is evident atop Chantal. Recently developed.



Outflow well established. Will be interesting to see how much land interaction the storm encounters down the road.
Member Since: June 29, 2009 Posts: 13 Comments: 5315
Quoting 2143. TropicalAnalystwx13:

Anticyclonic flow is evident atop Chantal. Recently developed.



No, only like one quadrant (SW) has anti-cyclonic flow, and that's more coincidence than anything.
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2149. will40
Quoting 2134. RkptMom:
My 15 year old daughter is visiting a friend in Fort Lauderdale, Fl. Should I be concerned, or just keep a watchful eye? The latest model trends are making me a little nervous.


right now i would keep a watchfull eye. things can change but looks like Firday Night and Saturaday would be worst times
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Quoting 2134. RkptMom:
My 15 year old daughter is visiting a friend in Fort Lauderdale, Fl. Should I be concerned, or just keep a watchful eye? The latest model trends are making me a little nervous.
There's an equal chance of being impacted then not, but stay tuned because it's a few days out and many things could change.
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I think the current modeling track forecasts are off, and this is why. And, please, never let it be said that I can't get unnecessarily long-winded! :)

First off, I'm really not going to take the upper CONUS trough into much consideration at this point. It's way too far away northwards, too shallow in longitude and too lateral across the CONUS.

But, let's consider the ULL which apparently is getting quite a bit of attention from the models and some of the bloggers. Look at surface vorticity. There's been some thought that this ULL may make its way down to the surface, become warm-core and an element of some concern. However, most of that thought has dissuaded, but still with thoughts of how it will affect Chantal's track. Right now, apparently, modeling is seeing this as a fairly particularly pulling/tugging force on Chantal that will draw it more northwards and perhaps just east of FL before running into the ridge and turning the system back westwards across the peninsula and possibly into the GoM.



Here's why I think the ULL now centered over the Bahamas will be less of a factor. :)
Again, look at the vorticity charts. It is quite the broad upper level low amidst a fair amount of dry air. And, although there is some very slight surface reflection at the 850mb layer and a tad more elongated reflection at the 700mb layer, most of the intensity is where it should be in the mid and upper levels, and which puts the strongest effects of the ULL between 18,000 and 34,000 feet (part of a Caribbean inverse trough tilted sw to ne). And, it seems to be retrograding west/northwest too, still adding distance between itself and Chantal.



So, if we consider the weakness as it is, mostly in the 500mb layer and up, and take into consideration that Chantal is still a moderate TS with vertical heights from the surface to just now becoming more substantial to the 500mb heights, imo, we can discern that the former should have less effect to the latter being in two different atmospheric layers: the ULL mostly in the upper levels with Chantal mostly in the lower levels still. Plus, consider that Chantal is currently about to encounter some mid-to-upper level shearing as it crosses yet another inverse upper level trough just east of the Antilles, and which should keep the storm's intensity somewhat limited still.

Are you still with me? LOL. Don't blame you if you're not, and certainly I make no premise of this being accurate. In fact, I have the most trouble prognosticating effects of troughing on tracks than I have with any of the things I've learned about the tropics over the years. So, I still ask questions, post wrong things sometimes, and have quite a bit to learn. And, these smarter, younger bloggers with so much more knowledge than me are quite impressive, and to them I say "awesome" you are, and to please keep the knowledge coming! :)

At about 15n, the moderate TS Chantal will come up against 1016mb of high pressure at the surface, the same layers its affecting. My experience has been that no storm, even the stronger ones can push through 1016mb of high pressure. They can bend it, push up against it, but ultimately have to find a way around it. And, I think this will be the case with Chantal along about the vicinity of St Lucia or possibly Guadaloupe (in that area), and that's when it will turn more west around the ridge looking for an escape route poleward.

Will the ULL, the CONUS trough weaken the ridge? Probably so, but not, imo, to the extent current modeling is processing. I think we will see Chantal move a bit further west still, around the edge of the 1016mb isobar which currently extends as far west as Texas. However, I am expecting the western tongue of the ridge to erode, and that line will move considerably further eastwards, perhaps to the Big Bend area of FL even. But, I don't think we'll see it retrograde out into the Atlantic, not without the CONUS trough becoming stronger and dipping further southwards.

Out on a limb now, if I had to take a WAG now, it would be that Chantal would cross over into the Caribbean at St Lucia or maybe slightly above, track more westwards to the west-central part of Cuba, cross over into the GoM just west of the Keys and up the peninsula towards Tampa and maybe the Big Bend or even the Apalachicola area. I suppose it could even track further west, but I'm not buying into that at this point either.

Hey, don't shoot me, I'm not even the piano player! :) But, maybe it's some tropical food for thought. I think I'm gonna give it a rest tonight and see how she looks in the morning. All reasonable contradictions and discerning thoughts otherwise respected, appreciated and, hopefully, I'll learn something more about the very interesting tropics weather! :)
Member Since: July 9, 2006 Posts: 184 Comments: 29610
2146. Gearsts
Should pass really close to the radar.Link
Member Since: August 2, 2010 Posts: 0 Comments: 1960
Quoting 2126. caribbeantracker01:
Barbados radar

Now tell me where the west north west movement is?


well radar dosen't extend out to 55W but everything in front suggest W movement maybe even a bit S of W
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My July Daily Update of the GOES East Infrared Hurricane Sector imagery is currently uploading to YouTube.

It will be ready to view in about an hour. Of particular interest in the animation is the trough that is runs along the Gulf Coast. What happens to the trough is supposed to have a big influence on where this system may go.

I found it very interesting.

Also, the music is not the "Jurassic Park" theme. It is another theme song that I played on the piano (with drums...because you gotta have drums with this tune.)

See you an about an hour! :)

Oz---
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Quoting 2129. RTSplayer:
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.

Anticyclonic flow is evident atop Chantal. Recently developed.

Member Since: July 6, 2010 Posts: 113 Comments: 32528
I think the models are slowly picking up on a slow down and eventual meander in and North of the Bahamas. Where she winds up looping back along the east coast is TBD.
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Quoting 2134. RkptMom:
My 15 year old daughter is visiting a friend in Fort Lauderdale, Fl. Should I be concerned, or just keep a watchful eye? The latest model trends are making me a little nervous.

Watchful eye and stay updated if any watches or warnings are issued. Still a good 5 days out, so by Thursday or Friday you will have a better idea.
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used the ruler again north of barbados headed to the butterfly island. shes no slouch good night
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2139. GetReal
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Topography map of Hispaniola
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Quoting 2135. FOREX:


It's moving Northwest now. Obvious.


you cant tell movement by looking at the radar from Barbados

The system is too far away. Also overall the average motion is still WNW
Member Since: March 10, 2010 Posts: 1 Comments: 7874


photo of the Oldsmar, FL water spout earlier today courtesy of @ericgreening on Twitter shot by his aunt from the bay as it passed over their house.
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2135. FOREX
Quoting 2126. caribbeantracker01:
Barbados radar

Now tell me where the west north west movement is?


It's moving Northwest now. Obvious.
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2134. RkptMom
My 15 year old daughter is visiting a friend in Fort Lauderdale, Fl. Should I be concerned, or just keep a watchful eye? The latest model trends are making me a little nervous.
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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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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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