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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VDM out.

Doesn't include the intense winds outside of the remarks section.

New HDOB showing more 45kt+ winds.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
Quoting 1644. jeffreeysweetypie:
the track has chantal hittimg us in florida should we start to board up yet and get our emergency gear ready to hunker down?


Use it as a good opportunity to make sure your ready for Hurricane Season. Chantal "should" be no more than a weak TS if it were to make Landfall in FL. Obviously that can change in a heartbeat though so stay tuned to the latest NHC advisories in the meantime.

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I think the surface level winds are a bit high (it is VERY unlikely the surface has higher winds than flight level, especially considering Chantal's current level of organization).

It IS, however, possible that the surface winds could be the result of a downdraft from the aforementioned dry air.

As for track, the 3-day NHC track is reasonable and appropriate, as is the intensity forecast. Beyond three days... too many variables between forward speed, land interaction, trough off the east coast, and strength. Trying to prognosticate where Chantal will go beyond that is akin to reading tea leaves or tossing chicken bones to determine the future.
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Quoting 1657. SLU:
Amazing .. such a poor circulation with near hurricane strength winds and no pressures lower than 1010mb.

Quoting 1657. SLU:
Amazing .. such a poor circulation with near hurricane strength winds and no pressures lower than 1010mb.

Danny was a hurricane with a pressure of 1000 in 2003.
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The center of Chantal should pass just south of Barbados , they should be in for some nasty weather soon!
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Quoting 1652. stormgirI:

i luv how you worded that...."just as I predicted, and "as many of you were anticipating". are you always right and everyone else wrong.


When you put it in that light, I feel arrogant! Nah, I never claim to be right or wrong, I just put a prediction out there and wait to see if it gets shoved in my face. I do know however how this blog works after observing for nearly a decade. The mood changes with the organization of the cyclone.
Member Since: July 8, 2005 Posts: 259 Comments: 24161
Everyone including me.We need to apologize to ScottTracker2K.He almost hit the nail with a 60mph tropical storm.
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Quoting 1652. stormgirI:

i luv how you worded that...."just as I predicted, and "as many of you were anticipating". are you always right and everyone else wrong.

He did state it awhile back, and no, He doesn't state that he's right all the time, actually he rarely does. He was just pointing out that some of us skipped to conclusions too early. Now get back under your bridge and stop trying to start things and state things that aren't true.
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1674. sar2401
Quoting JrWeathermanFL:
Time: 22:40:30Z
Coordinates: 12.1333N 54.1167W
Acft. Static Air Press: 964.6 mb (~ 28.48 inHg)
Acft. Geopotential Hgt: 414 meters (~ 1,358 feet)
Extrap. Sfc. Press: 1011.8 mb (~ 29.88 inHg)
D-value: -
Flt. Lvl. Wind (30s): From 159° at 54 knots (From the SSE at ~ 62.1 mph)
Air Temp: 19.6°C (~ 67.3°F)
Dew Pt: 19.6°C (~ 67.3°F)
Peak (10s) Flt. Lvl. Wind: 55 knots (~ 63.2 mph)
SFMR Peak (10s) Sfc. Wind: 60 knots (~ 69.0 mph)
SFMR Rain Rate: 28 mm/hr (~ 1.10 in/hr)
(*) Denotes suspect data

Hmmm...1011mb and surface winds higher than flight level winds...looks like more analysis will be required.
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1673. Patrap
At 22:57:30Z (last observation), the observation was 417 miles (671 km) to the E (93°) from Bridgetown, Barbados.


Product: Air Force High Density (HDOB) Message (URNT15 KNHC)
Transmitted: 8th day of the month at 22:56Z
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: 28

22:57:30Z 12.750N 53.433W 966.4 mb
(~ 28.54 inHg) 423 meters
(~ 1,388 feet) 1014.4 mb
(~ 29.96 inHg) - From 150° at 41 knots
(From the SSE at ~ 47.1 mph) 21.7°C
(~ 71.1°F) 19.4°C
(~ 66.9°F) 43 knots
(~ 49.4 mph) 34 knots
(~ 39.1 mph) 2 mm/hr
(~ 0.08 in/hr) 32.4 knots (~ 37.3 mph)
79.1%
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: 426 Comments: 128632
1672. Thrawst
Quoting 1656. Grothar:
Ominous. I would move this to 1%.




Personally I'd go for 0.1% but take it as a grain of salt.
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1671. will40
Quoting 1657. SLU:
Amazing .. such a poor circulation with near hurricane strength winds and no pressures lower than 1010mb.



yes the pressure vs the winds is very rare with a system this small
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1668. LBAR
She's moving way too fast for any sort of well-defined system to form. I'm still surprised "Chantal" was named at all. But what do I know? I'm just a rank amateur.
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Quoting 1645. Dakster:
This could be an interesting 8pm and definitely 11pm update.

I agree Dakster :o) With all this Data I'm sure even this "Blog" will go crazy Too :o)

Taco :o)
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Quoting 1651. Tazmanian:
updated wind shear map




Look at the SE Caribbean shear is about 15-20kts conditions shear-wise is getting interesting.
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Chantal is Charley's angel. Tight pressure gradient and small storm.
Member Since: June 30, 2013 Posts: 12 Comments: 8418
1614. Saltydogbwi1

Not flagged either.
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Quoting 1611. MiamiHurricanes09:
LMAO.

Plenty of 50kt flight-level winds.

Highest were 56kt flight-level winds.

From 149 at 56 knots
(From the SSE at ~ 64.4 mph)


SFMR winds in the 45-50kt range.

Chantal's a damn good troll.

It's a 55 Mph TS... NHC may bring it up to 60 Mph, but for Now im sticking with 50 mph until they find higher winds to support 60. They still need a formidable and identifiable center, which they have yet to really do...
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1662. Gearsts
Quoting 1643. JRRP:
where is the RIP CHANTAL ?
That's why some on here need to learn patience, is actually a little annoying lol
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1635.

I was saying yesterday that she'd be 60mph after the HH got out and I might be close to right :/
Member Since: July 19, 2011 Posts: 12 Comments: 2447
1659. Patrap
RainBow Top Loop

Member Since: July 3, 2005 Posts: 426 Comments: 128632
1658. sar2401
Quoting SouthernIllinois:

Has the name Natalie ever been used??

Yep. TS Natalie, July, 1964. No hurricane though.
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1657. SLU
Amazing .. such a poor circulation with near hurricane strength winds and no pressures lower than 1010mb.

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1656. Grothar
Ominous. I would move this to 1%.


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Quoting 1643. JRRP:
where is the RIP CHANTAL ?

Technically an open wave could still produce those kinds of winds... :)
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Quoting 1642. MiamiHurricanes09:
Hey Nigel!

Yeah, I was quite the downer myself though, didn't expect that they'd find these winds by any means.

Chantal definitely has some surprises.
This storm continues to defy odds it turning me into a believer. The first recon pass was a test. 
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Keep ignoring me,way to jump to conclusion.I said not to dismiss this system.
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updated wind shear map




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1650. ncstorm
if this blog would LEARN to be patient before jumping to conclusions, it would flow so nicely..the LMAO, the LOL, the Im speechless, the satellite estimates are not good to determine a storm on..etc..just watch and wait before determining the final end to things..will go a long way in life's lessons
Member Since: August 19, 2006 Posts: 13 Comments: 15663
hope you all are ready islanders barbados first heavy winds moving in good luck
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1648. Thrawst
Chantroll.
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Quoting 1631. nigel20:

Hey MH09! I guess that people will now say that Chantal will become an hurricane...not open wave anymore. :)

Too late. StormTrackScott beat you too it. He was betting on crow that it would make it there... All I want to do it laugh.
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Surface shouldn't be higher than flight level winds on that 69mph reading. Take the flt level winds down 5-10kts.
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1645. Dakster
This could be an interesting 8pm and definitely 11pm update.
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1643. JRRP
where is the RIP CHANTAL ?
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Quoting 1631. nigel20:

Hey MH09! I guess that people will now say that Chantal will become an hurricane...not open wave anymore. :)
Hey Nigel!

Yeah, I was quite the downer myself though, didn't expect that they'd find these winds by any means.

Chantal definitely has some surprises.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
Time: 22:40:30Z
Coordinates: 12.1333N 54.1167W
Acft. Static Air Press: 964.6 mb (~ 28.48 inHg)
Acft. Geopotential Hgt: 414 meters (~ 1,358 feet)
Extrap. Sfc. Press: 1011.8 mb (~ 29.88 inHg)
D-value: -
Flt. Lvl. Wind (30s): From 159° at 54 knots (From the SSE at ~ 62.1 mph)
Air Temp: 19.6°C (~ 67.3°F)
Dew Pt: 19.6°C (~ 67.3°F)
Peak (10s) Flt. Lvl. Wind: 55 knots (~ 63.2 mph)
SFMR Peak (10s) Sfc. Wind: 60 knots (~ 69.0 mph)
SFMR Rain Rate: 28 mm/hr (~ 1.10 in/hr)
(*) Denotes suspect data
Member Since: July 19, 2011 Posts: 12 Comments: 2447
She continues to play with us.
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1639. Patrap
Tropical Storm 03L

UW-CIMSS Automated Satellite-Based
Advanced Dvorak Technique (ADT)
Version 8.1.4
Tropical Cyclone Intensity Estimation Algorithm

Current Intensity Analysis



UW - CIMSS
ADVANCED DVORAK TECHNIQUE
ADT-Version 8.1.4
Tropical Cyclone Intensity Algorithm

----- Current Analysis -----
Date : 08 JUL 2013 Time : 214500 UTC
Lat : 11:54:00 N Lon : 54:10:47 W


CI# /Pressure/ Vmax
3.5 / 999.3mb/ 55.0kt


Final T# Adj T# Raw T#
3.1 3.1 3.1

Center Temp : -7.4C Cloud Region Temp : -43.2C

Scene Type : CURVED BAND with 0.58 ARC in LT GRAY
Maximum CURVED BAND with 0.60 ARC in LT GRAY
at Lat: 11:41:59 N Lon: 54:22:11 W

Positioning Method : FORECAST INTERPOLATION

Ocean Basin : ATLANTIC
Dvorak CI > MSLP Conversion Used : ATLANTIC

Tno/CI Rules : Constraint Limits : NO LIMIT
Weakening Flag : ON
Rapid Dissipation Flag : FLAG

C/K/Z MSLP Estimate Inputs :
- Average 34 knot radii : 46km
- Environmental MSLP : 1014mb

Satellite Name : GOES13
Satellite Viewing Angle : 27.9 degrees



Member Since: July 3, 2005 Posts: 426 Comments: 128632
1638. will40
Quoting 1626. MAweatherboy1:

High rain rate though. I think the strongest from that data set with a rain rate under the generally accepted 0.75 inches per hour was 54mph.


no (*) tho
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A whole slough of 50 Mph winds in Chantal's NE quad, there is just trying to find and pin down the center.
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Lmfao this almost everyone on here dazed and confused. Plenty of TS winds going on that is why I love Recon some goo data to go into the models now.

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And just as I predicted, the recon found a lot higher winds than many of you were anticipating.

Pressures are high still, but that just means Chantal has a lot tighter of a pressure gradient then you'd might think.
Member Since: July 8, 2005 Posts: 259 Comments: 24161
Quoting 1626. MAweatherboy1:

High rain rate though. I think the strongest from that data set with a rain rate under the generally accepted 0.75 inches per hour was 54mph.


Just learned something new... Thanks for that.
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1633. Dakster
Quoting 1601. Sfloridacat5:
Chance of a system making landfall on the N.E. Fl. coast is rather low.
It can and does happen, but the probability is quite low.
Much better chance of the system making landfall up the coast in the Carolinas or further South in Fl.


I don't know why - but that seems to be the case.
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About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.