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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1833. Patrap
,,"there's something a happening here, what it is, aint zactly clear"..

Member Since: July 3, 2005 Posts: 423 Comments: 128231
Quoting 1824. CybrTeddy:
Seems to me that the area of lowest pressure is incredibly small, so small that the recon has yet to sample it.
That would make sense.

It's usually a low pressure with low winds, not the other way around.
Member Since: September 2, 2009 Posts: 130 Comments: 21193
Quoting 1828. wunderkidcayman:

That should change further S and W

Agreed
Member Since: September 2, 2011 Posts: 0 Comments: 1148
Very odd weather here in MA/RI at the moment.

Look at this (real) feature retrograding from the cape westward towards RI - it's sprinkling at my house (+) at the northwest tip.

At the current time points, look at the storms popping near Providence 90 degrees offset from the onshore flow.

Amazing.

Member Since: Posts: Comments:
1829. 7544
Quoting 1821. 7544:
somethings hapening with the ull its either dying or workin down to the surface anyone know ? tia i do see lot of new conv ball building east tho ???
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Quoting 1815. Stormchaser121:

That should change further S and W
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Quoting Tropicsweatherpr:


Will it race like Chantal over 25 mph?


From what I can tell, it shouldn't struggle nearly as much as 95L/Chantal did.

If it takes place, it's going to be an extremely interesting tropical cyclone to track.
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1826. Patrap

Member Since: July 3, 2005 Posts: 423 Comments: 128231
1825. ncstorm
120 hours


132 hours


138 hours
Member Since: August 19, 2006 Posts: 13 Comments: 15276
Seems to me that the area of lowest pressure is incredibly small, so small that the recon has yet to sample it.
Member Since: July 8, 2005 Posts: 259 Comments: 24016
18z GFS Ensembles really like this one

72 hours



120

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Quoting 1819. Stormchaser2007:
I'm definitely going to be interested in our next tropical wave as the steering pattern in place will not allow for a system to go out to sea.

Should exit on Wednesday and possibly develop in as little as 36 or 48 hours (and that's conservative)

42 hours



72 hours (Tropical Storm)



120 hours



Will it race like Chantal over 25 mph?
Member Since: Posts: Comments:
1821. 7544
somethings hapening with the ull its either dying or workin down to the surface anyone know ? tia i do see lot of new conv ball building east tho ???
Member Since: Posts: Comments:
1820. Patrap
At 23:37:30Z (last observation), the observation was 278 miles (447 km) to the E (94°) from Bridgetown, Barbados

Product: Air Force High Density (HDOB) Message (URNT15 KNHC)
Transmitted: 8th day of the month at 23:37Z
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: 32

23:37:30Z 12.833N 55.500W 966.2 mb
(~ 28.53 inHg) 412 meters
(~ 1,352 feet) 1012.7 mb
(~ 29.91 inHg) - From 60° at 40 knots
(From the ENE at ~ 46.0 mph) 23.0°C
(~ 73.4°F) 20.5°C
(~ 68.9°F) 44 knots
(~ 50.6 mph) 36 knots
(~ 41.4 mph) 0 mm/hr
(~ 0 in/hr) 32.7 knots (~ 37.6 mph)
81.8%
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: 128231
I'm definitely going to be interested in our next tropical wave as the steering pattern in place will not allow for a system to go out to sea.

Should exit on Wednesday and possibly develop in as little as 36 or 48 hours after it leaves the continent (and that's conservative)

42 hours



72 hours (Tropical Storm)



120 hours

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1817. Patrap
click Tropical FORECAST points to see the Forecast Points

Tropical Atlantic - Rainbow Loop
Member Since: July 3, 2005 Posts: 423 Comments: 128231
Member Since: September 2, 2011 Posts: 0 Comments: 1148
Quoting 1788. Saltydogbwi1:


Hey Levi thanks for your input...quick question for you would the percentage you subtract from the flight level winds change depending on aircraft altitude? or is it a general rule of thumb to always use 20%...Thanks in advanced


There is a table in this pdf.


NHC's Use of Aircraft Data
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it seems like since 2008, the Greater Antilles has been a magnet for a lot of storms, hindering the potential of several. Chantal may be another example. Just imagine if it had not been for these islands.
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1812. Patrap
Member Since: July 3, 2005 Posts: 423 Comments: 128231
1811. Patrap
Member Since: July 3, 2005 Posts: 423 Comments: 128231
1810. hydrus
Quoting 1805. GTstormChaserCaleb:
The latest GFS run has landfall on the FL/GA border. I am not discounting the Southeastern states just yet. I would say from NC south is fair game.
The Carolinas are always fair game, even when its not cane season....always somethin goin on there with weather.
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Quoting 1803. RTSplayer:
I say this every time, but I think it's stupid that NHC doesn't use 55mph in official forecasts.


It's practical reasons. NHC mainly uses knots...45 knots = ~50 mph, 50 knots = ~60 mph (rounded). To use 55 mph, the NHC would have to say 48 knots, which gives the false impression that wind speeds are precise.
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1808. ncstorm
18z GFS Ensembles Spread is running now..

108 hours
Member Since: August 19, 2006 Posts: 13 Comments: 15276
Some more 50kt flight-level winds being reported.

http://www.tropicalatlantic.com/recon/URNT15/KNHC /
Member Since: September 2, 2009 Posts: 130 Comments: 21193
Quoting 1798. Tazmanian:
TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
800 PM EDT MON JUL 8 2013

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

THE NATIONAL HURRICANE CENTER IS ISSUING ADVISORIES ON TROPICAL
STORM CHANTAL...LOCATED SEVERAL HUNDRED MILES EAST OF THE WINDWARD
ISLANDS.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.

$$
FORECASTER KIMBERLAIN

Bahamas ULL is gone
Member Since: Posts: Comments:
Quoting 1800. ProgressivePulse:
Regardless of the prior path it looks like there is a ceiling modeled at 27N, West Palm Beach.
The latest GFS run has landfall on the FL/GA border. I am not discounting the Southeastern states just yet. I would say from NC south is fair game.
Member Since: June 30, 2013 Posts: 12 Comments: 8187
Quoting 1803. RTSplayer:
I say this every time, but I think it's stupid that NHC doesn't use 55mph in official forecasts.


It is, but that's big government and I will leave it at that. At the end of the day 5mph isn't a very big difference.
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I say this every time, but I think it's stupid that NHC doesn't use 55mph in official forecasts.
Member Since: Posts: Comments:
1802. Patrap
At 23:27:30Z (last observation), the observation was 321 miles (517 km) to the E (93°) from Bridgetown, Barbados.

Product: Air Force High Density (HDOB) Message (URNT15 KNHC)
Transmitted: 8th day of the month at 23:26Z
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: 31

23:27:30Z 12.883N 54.850W 966.5 mb
(~ 28.54 inHg) 406 meters
(~ 1,332 feet) 1012.5 mb
(~ 29.90 inHg) - From 91° at 43 knots
(From the E at ~ 49.4 mph) 22.1°C
(~ 71.8°F) 20.2°C
(~ 68.4°F) 46 knots
(~ 52.9 mph) 40 knots
(~ 46.0 mph) 1 mm/hr
(~ 0.04 in/hr) 37.4 knots (~ 43.0 mph)
Tropical Storm 87.0%
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: 128231
Quoting 1794. all4hurricanes:

Oops my bad
that is really weird why did they start with an N storm?

Back then, there was one naming list. The 1963 PHS ended with the M storm, and thus the 1964 PHS began with the N storm.
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Regardless of the prior path it looks like there is a ceiling modeled at 27N, West Palm Beach.
Member Since: August 19, 2005 Posts: 5 Comments: 5395
1799. ncstorm
Quoting 1795. whitewabit:


During a named storm post not related to the storm should be kept on ones own blog ..


I see..thanks
Member Since: August 19, 2006 Posts: 13 Comments: 15276
TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
800 PM EDT MON JUL 8 2013

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

THE NATIONAL HURRICANE CENTER IS ISSUING ADVISORIES ON TROPICAL
STORM CHANTAL...LOCATED SEVERAL HUNDRED MILES EAST OF THE WINDWARD
ISLANDS.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.

$$
FORECASTER KIMBERLAIN
Member Since: May 21, 2006 Posts: 5091 Comments: 115072
Quoting 1777. MrstormX:


http://en.wikipedia.org/wiki/1964_Pacific_hurrica ne_season#Hurricane_Natalie

EPAC!


also states the pacific database never showed the storm above 50mph

highly unlikely it was a hurricane
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Quoting 1743. wunderkidcayman:
hey guy which one should I use first or second

B. Center Fix Coordinates: 11°38'N 54°34'W (11.6333N 54.5667W


They are the same, just different units.

1st is Deg. then min.
2nd is Degrees in decimal

It's just math
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1795. whitewabit (Mod)
Quoting 1787. ncstorm:


Hi,

So posting crow pics which has been a tradition here at WU not allowed anymore??..I want to be able to post so I want to make sure I understand new rules of the blog..TIA


During a named storm post not related to the storm should be kept on ones own blog ..
Member Since: Posts: Comments:



http://en.wikipedia.org/wiki/1964_Pacific_hurrica ne_season#Hurricane_Natalie

EPAC!

Oops my bad
that is really weird why did they start with an N storm?
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1793. nigel20
Quoting Envoirment:
Typhoon Soulik




Typhoon Soulik would not only cause quite a bit of wind damage, but wide spread flash flooding...especially if it was affecting land at the moment.
Member Since: November 6, 2010 Posts: 11 Comments: 7997
Funny how people attack and then run like cowards :).
Anywho I wouldn't be surprised if Chantal becomes a hurricane before Hispaniola now.Looks like she's going to follow the NHC forecast almost exactly.
Member Since: August 14, 2010 Posts: 10 Comments: 16964
I tell ya what is decreasing with the slight shifts east is the amount of land interaction. Hispaniola is no joke but the eastern half is much less disruptive than the western half.

Member Since: August 19, 2005 Posts: 5 Comments: 5395
1790. ncstorm
Quoting 1779. GTstormChaserCaleb:
LOL well I had mine yesterday for being wrong about not having a storm in July. So I will pass on seconds. :-P

By the way in case you guys were wondering this was the FIM-9 at 126hrs.



I knew we were missing a model run..forgot all about the FIM..
Member Since: August 19, 2006 Posts: 13 Comments: 15276
I am not in my computer now so I don't have access to sat images. How does the wave the models develop looks like now?
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Quoting 1767. Levi32:
This 60kt wind spike on SFMR isn't really real. It's clearly rain-contaminated, whether it was marked as such or not on the raw data.



The best estimate is and always will be the flight-level wind minus ~20%, which puts us at 50-55 mph.



Hey Levi thanks for your input...quick question for you would the percentage you subtract from the flight level winds change depending on aircraft altitude? or is it a general rule of thumb to always use 20%...Thanks in advanced
Member Since: Posts: Comments:
1787. ncstorm
Quoting 1776. whitewabit:
It would be a shame to not be able to post in the middle of a storm ..


Hi,

So posting crow pics which has been a tradition here at WU not allowed anymore??..I want to be able to post so I want to make sure I understand new rules of the blog..TIA
Member Since: August 19, 2006 Posts: 13 Comments: 15276
Soulik is looking great:

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1785. barbamz
Quoting 1770. all4hurricanes:

This is just not true, an N named storm in July?
there was never a Hurricane or Tropical Storm Natalie according to wikipedia


Look here (Epac storm):
Hurricane Natalie
Category 1 hurricane (SSHS)
Duration July 6 – July 7
Peak intensity 80 mph (130 km/h) (1-min) 1001 mbar (hPa)

On July 5, the ship California Star recorded winds of 35 mph (55 km/h) and a barometric pressure of 1,005.8 mb (30 inHg);[5] consequently, the storm was upgraded into Tropical Storm Nataline.[3] After passing through the Tres Marinas Islands just offshore, Nateline attained its peak intensity of 80 mph (130 km/h) (making Nataline a Category 1 hurricane on the present-day Saffir-Simpson Hurricane Wind Scale) and a peak pressure of 1,001 mb (29.6 inHg), though the Pacific hurricane database does not show the storm getting any stronger than 50 mph (80 km/h).[5] The next day, July 7, the NFWC reported that Nataline made landfall near Mazatlan with winds of 50 mph (80 km/h) just before dissipating.[3] No known impact was recorded.[5]
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Quoting 1776. whitewabit:
It would be a shame to not be able to post in the middle of a storm ..


Duly noted...
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Quoting 1772. washingtonian115:
Looking good Chantal looking good.Can't wait to see what she looks like in the morning.
Yea! last night DMAX did wonders for it know as the sunset a deep convection is starting to fire with really impressive TS winds. Cant wait for morning.
Member Since: May 25, 2012 Posts: 0 Comments: 2043

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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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