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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Hello all back on from earlier.

Was very surprised after the initial fix of the center and the patch of dead winds being found that they were able to find 64 mph winds in the NE quadrant, I didn't see anything like that intensity coming so that is significant.

Also was interesting to note the motion and the convective restructuring that is underway right now. I would expect that the pressure is just a bit high right now probably due to that very same thing, the convective restructuring, and that is why we were seeing a pressure of 1010 mb despite much higher winds.

I would expect that unless the system goes back into degradation we will see a much lower pressure show itself during the day tomorrow.


In the meantime highest winds so far found by recon:

Time: 22:40:00Z
Coordinates: 12.1167N 54.1333W
Acft. Static Air Press: 967.2 mb (~ 28.56 inHg)
Acft. Geopotential Hgt: 383 meters (~ 1,257 feet)
Extrap. Sfc. Press: 1011.2 mb (~ 29.86 inHg)
D-value: -
Flt. Lvl. Wind (30s): From 156° at 55 knots (From the SSE at ~ 63.2 mph)
Air Temp: 19.9°C (~ 67.8°F)
Dew Pt: 19.9°C (~ 67.8°F)
Peak (10s) Flt. Lvl. Wind: 56 knots (~ 64.4 mph)
SFMR Peak (10s) Sfc. Wind: 59 knots (~ 67.8 mph)
SFMR Rain Rate: 32 mm/hr (~ 1.26 in/hr)
(*) Denotes suspect data
Member Since: Posts: Comments:
Quoting 1864. RTSplayer:


It moved due west over the past 3 hours, so it's back on track to be a bit more southerly than expected, as I thought it might.

Ok let's see if I can clear this up the steering should continue on a w/wnw path with some jogs to the nw at times until it gets towards the vicinity of Puerto Rico. Then a gradual turn more towards the nw crossing over Hispaniola.

The ULL over the Bahamas is creating a weakness in the Subtropical Ridge on the Southwestern Flank and it is evident over Cuba that area of weakness is shifting eastward and will allow for this turn to occur.

Now look up over North Dakota and Minnesota notice the short wave digging there that will also come down and take a jab at the Subtropical Ridge on the Western and Northern Flank which will turn the system even more towards the North,

After that it remains to be seen if the Short Wave leaves quickly or hangs around. If it leaves quickly the Ridge builds back in and closes the weakness thus shunting the storm back towards the West, if it hangs around the storm continues its northward movement towards the Carolinas.

Member Since: June 30, 2013 Posts: 12 Comments: 8187
The Gulf of Mexico looks VERY favorable right now
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Quoting 1908. Relix:
Its not moving WSW or due west. Come on. The center just wasn't were we thought it was. It was to the SW. What it does is pose a bigger threat to Haiti and the Bahamas. Probably won't even leave me much rain here in PR.

You're under a Tropical Storm Warning.
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1929. Patrap
At 00:17:30Z (last observation), the observation was 298 miles (479 km) to the ESE (107°) from Bridgetown, Barbados.

Product: Air Force High Density (HDOB) Message (URNT15 KNHC)
Transmitted: 9th day of the month at 00:16Z
Date: July 9, 2013
Aircraft: Air Force Aircraft (Last 3 digits of the tail number are 302)
Storm Number: 03
Storm Name: Chantal (flight in the North Atlantic basin)
Mission Number: 1
Observation Number: 36

00:17:30Z 11.867N 55.383W 966.8 mb
(~ 28.55 inHg) 403 meters
(~ 1,322 feet) 1012.3 mb
(~ 29.89 inHg) - From 45° at 5 knots
(From the NE at ~ 5.8 mph) 22.5°C
(~ 72.5°F) 19.9°C
(~ 67.8°F) 6 knots
(~ 6.9 mph) 12 knots
(~ 13.8 mph) 1 mm/hr
(~ 0.04 in/hr) 10.0 knots (~ 11.5 mph)
200.0%
Time Coordinates Aircraft
Static Air Pressure Aircraft
Geopotential Height Extrapolated
Surface Pressure D-value Flight Level Wind (30 sec. Avg.) Air Temp. Dew Point Peak (10 sec. Avg.)
Flight Level Wind SFMR
Peak (10s Avg.) Sfc. Wind SFMR
Rain Rate Estimated Surface Wind (30 sec. Avg.)
Using Estimated Reduction Factor Peak Wind at Flight Level to
Est. Surface Reduction Factor
HDOB Observations
Member Since: July 3, 2005 Posts: 423 Comments: 128228
1928. Grothar
Quoting 1910. Doppler22:

Hey Gro, are you going to issue a Blob alert for the storm coming off of Africa that may turn into Dorian?


I posted in two days ago. Where were you? I pulled out the globe and everything.
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If they shift farther South and left then the storm could miss Hispaniola and just cross Cuba
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never mind that I think they found it and pressure still aroun 1011mb
Member Since: June 13, 2009 Posts: 2 Comments: 11948
1925. Relix
Quoting 1919. Grothar:


That's with the new info?
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Looking at trajectories based on current forecasts, Chantal is about 423 miles away from St Lucia. If it keeps moving at its current speed of 26 mph and doesn't wobble its track, it will take around 16 hours to make landfall there after sliding by or hitting Barbados at in about 12 hours.

Given the current, fairly generous windfield distances of 90 miles from the center, tropical storm-force winds could be felt as soon as in 8 or 9 hours in Barbados and in about 12 hours in St Lucia.



St Lucia is also where the 1016mb isobar is positioned and where I am speculating that we'll see Chantal slow down somewhat and move perhaps a bit further west unless it has substantially increased intensity by that time (doubtful).

And, please, check my math - I'm using formulas.
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Looks like the cone will need to be shifted southward to reconcile with the new position.

Member Since: September 2, 2009 Posts: 130 Comments: 21193

Quoting 1908. Relix:
Its not moving WSW or due west. Come on. The center just wasn't were we thought it was. It was to the SW. What it does is pose a bigger threat to Haiti and the Bahamas. Probably won't even leave me much rain here in PR.
I dont see anything for PR right now But anytime TCs enter the Eastern Caribbean moving wnw they usually do it anyways all the real action is right near the COC.
Member Since: May 25, 2012 Posts: 0 Comments: 2043
1921. Patrap
Quoting 1907. evilpenguinshan:
Does anyone know where to find the microwave pass imagery? I haven't seen one since last night, and I'm curious to see how Chantal's core has held up since then.



AMSU Microwave 89GHz Imagery (4 km Mercator)


AL032013 - Tropical Storm CHANTAL
Member Since: July 3, 2005 Posts: 423 Comments: 128228
1920. hydrus
Quoting 1897. washingtonian115:
What does it show for future "Dorian".
It actually has that system hanging back. Doesnt do much of anything.
Member Since: September 27, 2007 Posts: 1 Comments: 21173
1919. Grothar
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Quoting 1815. Stormchaser121:
That's quite the left turn
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1917. ncstorm
18z GFS Ensembles Spread..

240 hours


264 hours


276 hours
Member Since: August 19, 2006 Posts: 13 Comments: 15277
1916. hydrus
Quoting 1899. 7544:


looks like the ull is pulling it al together the las couple of hours hmmmmm
That run is at 126 hours out..
Member Since: September 27, 2007 Posts: 1 Comments: 21173
I think next vortex they will find 1009mb or at least a low 1010mb
Member Since: June 13, 2009 Posts: 2 Comments: 11948
So I take it the wave the GFS develops has now officially emerge off of Africa?.
Member Since: August 14, 2010 Posts: 10 Comments: 16964
1913. Patrap
Itsa making good time too.


Approx 200 miles in 8 hours

Member Since: July 3, 2005 Posts: 423 Comments: 128228

Quoting 1901. Patrap:
Guidance seems to be converging with the new Heading, extrapolated, should bring a shift left next output.
Very much agreed may show a scenario of it passing through the windward passage. I always though the models were too north and left that why I don't trust them till Recon data can be implemented. Now we should see more accurate runs from now on. 
Member Since: May 25, 2012 Posts: 0 Comments: 2043
1911. gator23
Lots and lots of wishcasting going on in here tonight. And by people who usually dont... Seems like folks missed the season a whole lot.
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Quoting 1906. Grothar:


and they removed my BlobCon.

Hey Gro, are you going to issue a Blob alert for the storm coming off of Africa that may turn into Dorian?
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1909. Patrap
Quoting 1906. Grothar:


and they removed my BlobCon.


Da Nerve I tell ya'

;0
Member Since: July 3, 2005 Posts: 423 Comments: 128228
1908. Relix
Its not moving WSW or due west. Come on. The center just wasn't were we thought it was. It was to the SW. What it does is pose a bigger threat to Haiti and the Bahamas. Probably won't even leave me much rain here in PR.
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Does anyone know where to find the microwave pass imagery? I haven't seen one since last night, and I'm curious to see how Chantal's core has held up since then.
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1906. Grothar
Quoting 1833. Patrap:
,,"there's something a happening here, what it is, aint zactly clear"..



and they removed my BlobCon.
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1905. hydrus
Member Since: September 27, 2007 Posts: 1 Comments: 21173
Quoting 1877. Neapolitan:
waves

I know this has been said several times, but damn that's impressive for early July.
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Quoting 1900. TropicalAnalystwx13:

Definitely going to be interesting to see what happens
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1902. wpb
vortex weak winds not finding anything strong in any clusters.1011mb
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1901. Patrap
Guidance seems to be converging with the new Heading, extrapolated, should bring a shift left next output.
Member Since: July 3, 2005 Posts: 423 Comments: 128228
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1899. 7544
Quoting 1892. hydrus:

HWRF.


looks like the ull is pulling it al together the las couple of hours hmmmmm
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Quoting 1884. weatherlover94:
Good evening everybody, I have been on my I Pod all day talking to you guys on and off.....if somebody has already answered this question I apologize I did not see the reply. The Ships Intensity model on this page

http://www.tropicalatlantic.com/models/data.cgi?ba sin=al&year=2013&storm=03&display=goog lemap&latest run=1

Is now showing a Cat 1 Hurricane hitting Florida. Help me out people. Did I miss something or is this model just drunk or something ?

It is just seeing some favorable conditions for Chantal should it still be in tact. Check back after its interaction with Hispaniola.
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Quoting 1892. hydrus:

HWRF.
What does it show for future "Dorian".
Member Since: August 14, 2010 Posts: 10 Comments: 16964

Quoting 1879. CaribBoy:


It's a little dive to the SW... I wasn't expecting this based on Visible sat this afternoon. Though the convective mass has continued its WNW movement.

The center that recon found was further sw of the 5:00pm estimate its still moving WNW
Member Since: May 25, 2012 Posts: 0 Comments: 2043
1895. Patrap
Member Since: July 3, 2005 Posts: 423 Comments: 128228
Quoting 1864. RTSplayer:


It moved due west over the past 3 hours, so it's back on track to be a bit more southerly than expected, as I thought it might.



Not really back on track the track is now more W and S
Member Since: June 13, 2009 Posts: 2 Comments: 11948
1893. Patrap
At 00:07:30Z (last observation), the observation was 293 miles (471 km) to the ESE (103°) from Bridgetown, Barbados.

Product: Air Force High Density (HDOB) Message (URNT15 KNHC)
Transmitted: 9th day of the month at 00:06Z
Date: July 8, 2013
Aircraft: Air Force Aircraft (Last 3 digits of the tail number are 302)
Storm Number: 03
Storm Name: Chantal (flight in the North Atlantic basin)
Mission Number: 1
Observation Number: 35


00:07:30Z 12.150N 55.383W 966.1 mb
(~ 28.53 inHg) 402 meters
(~ 1,319 feet) 1011.5 mb
(~ 29.87 inHg) - From 11° at 12 knots
(From between the N and NNE at ~ 13.8 mph) 22.0°C
(~ 71.6°F) 21.5°C
(~ 70.7°F) 14 knots
(~ 16.1 mph) 19 knots
(~ 21.8 mph) 1 mm/hr
(~ 0.04 in/hr) 16.3 knots (~ 18.7 mph)
135.7%
Time Coordinates Aircraft
Static Air Pressure Aircraft
Geopotential Height Extrapolated
Surface Pressure D-value Flight Level Wind (30 sec. Avg.) Air Temp. Dew Point Peak (10 sec. Avg.)
Flight Level Wind SFMR
Peak (10s Avg.) Sfc. Wind SFMR
Rain Rate Estimated Surface Wind (30 sec. Avg.)
Using Estimated Reduction Factor Peak Wind at Flight Level to
Est. Surface Reduction Factor
HDOB Observations
Member Since: July 3, 2005 Posts: 423 Comments: 128228
1892. hydrus

HWRF.
Member Since: September 27, 2007 Posts: 1 Comments: 21173
1891. Patrap
Tropical Atlantic - Rainbow Loop

ZOOM here
Member Since: July 3, 2005 Posts: 423 Comments: 128228
Quoting 1877. Neapolitan:
waves
Wave is already looking impressive.It may be one of those waves that develop immediately.
Member Since: August 14, 2010 Posts: 10 Comments: 16964
WOW look at that!
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Chantal has moved due west since 5. 11.8 at both advisories.
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1887. Patrap
T-storms from the ULL

..interesting'





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1886. skook
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Is the wave coming off Africa the one the GFS is forcasting to become a hurricane?
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Good evening everybody, I have been on my I Pod all day talking to you guys on and off.....if somebody has already answered this question I apologize I did not see the reply. The Ships Intensity model on this page

http://www.tropicalatlantic.com/models/data.cgi?ba sin=al&year=2013&storm=03&display=googlemap&latest run=1

Is now showing a Cat 1 Hurricane hitting Florida. Help me out people. Did I miss something or is this model just drunk or something ?
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Quoting 1863. wunderkidcayman:

I think when Recon fly back to the center they will find it lower



nah no relocation they just being cautious


You don't know.
Member Since: October 6, 2007 Posts: 0 Comments: 6166

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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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