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 2525. will40:



yes see the break starting to form the weakness?


The low is to cut off and the high to build west with Chantal. Chantal will head west from that point forward.
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144 hrs. down to 992 mb.

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Quoting 2513. islander44:


Well, scupper my uppers.

Marshfield, class of '70. Sailed out of Cohasset when we bought our second sailboat. Thankfully we never turned her turtle.



Class of 70 also! Sailed Flying Scot. Only turtled once. Too cold to chance it again!!
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Quoting 2526. GTstormChaserCaleb:
Looks like it is heading towards the Cape on this run.


Seems like the Gfs shifted south a little, but a more eastern track.
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Quoting 2510. ProgressivePulse:
This is going to be a "B" of a forecast once it clears Hispaniola, lol. Faint of heart do not attempt....


0Z CMC has Chantel skirting Florida and the 0Z Gfs has Chantel all the way east of the Bahamas......

Thats a huge discrepancy
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Chantal makes landfall as, or very close to, a hurricane.

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Quoting 2519. SavannahStorm:
Westward, Ho!

Looks like it is heading towards the Cape on this run.
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2525. will40
Quoting 2516. ProgressivePulse:
ok so this run we get the block at 114, the cut off low progressive. As MH09 stated a more formidable storm here.




yes see the break starting to form the weakness?
Member Since: September 19, 2005 Posts: 2 Comments: 4266
Looks like the 12Z.
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Dorian forming over the central Atlantic while Chantal situating east of Florida at 126 hours on the 0z GFS run:

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Evening all. I hope everyone in Chantal's path takes care. And that she quickly passes over Hispaniola.
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2520. sar2401
Quoting AztecCe:
so, what's everybody's long-term guess on chantal's u.s. landfall?
i'm gonna say a georgia/s. carolina hit

Here's what I think. Chantal is going to make landfall in the Dominican Republic as a 60 mph TS. It's going to ingest a lot of dry air and get caught in increasing shear. The mountains in the DR are going to weaken Chantal, and she will then cross the Windward Passage as a 35 mph TD. The mountains in eastern Cuba are going to tear her up even more, and she will emerge into the Gulf as a remnant low. The low will then turn west because of the low over the SE US and be absorbed in the circulation of that low, giving those of us in the Southeast a whole bunch of rain from Thursday until Sunday, Chantal has until Friday to survive as any kind of TC. There's a reason why the NHC said this in the 11 pm discussion:

Although not explicitly shown in the forecast...Chantal could weaken below tropical storm force or perhaps even dissipate in the 3 to 4 day time period.
Member Since: October 2, 2004 Posts: 0 Comments: 16293
Westward, Ho!

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Close to a stall and then towards FL as a TS. Believable in the least. Can't wait to see if the CMC agrees. Also, Dorian looking healthy for the time of the year.

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0Z GFS 135 hour

Much further south, just hanging off the coast nearing hurricane status.

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ok so this run we get the block at 114, the cut off low progressive. As MH09 stated a more formidable storm here.

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Goodnight everyone!

114 hrs. down to 997 mb. turning back towards the west.

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Quoting 2508. Stormchaser2007:
The reason that "Dorian" is initially weaker is because it's actually quite larger than the 18z run.

It eventually becomes a large and impressive tropical cyclone by 132 hours

We'll see what happens tomorrow with this one.


Wave was introduced at 00z analysis.
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Quoting 2501. JustDucky251:


Cohasset. Sailed because it was less bone chilling than swimming. Turning turtle was a chilling event, however.


Well, scupper my uppers.

Marshfield, class of '70. Sailed out of Cohasset when we bought our second sailboat. Thankfully we never turned her turtle.

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GFS seems to think Chantal will slow down a lot through the Bahamas. Not good at all.
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Quoting 2492. HurricaneAndre:
The wave towards Africa.What percentage do you think they will give it.
A 0%
B 10%
C 20%
D 30%

I pick C or D.
ummm how about no mention at the TWO. At most B
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This is going to be a "B" of a forecast once it clears Hispaniola, lol. Faint of heart do not attempt....
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2509. HadesGodWyvern (Mod)
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The reason that "Dorian" is initially weaker is because it's actually quite larger than the 18z run.

It eventually becomes a large and impressive tropical cyclone by 132 hours

We'll see what happens tomorrow with this one.
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Chantal is more intense on this run tho lol.
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2506. will40
looks like she wobbles back west tho
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Quoting 2499. ProgressivePulse:
May get a full recurve on this run, lol.


Doubtful- the Bermuda High is quickly lumbering into the picture for the block.
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0Z GFS 120 hour

Commence turn a little further south?

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Quoting 2499. ProgressivePulse:
May get a full recurve on this run, lol.


Either that or a loop or two. 'Twill be interesting.
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2502. will40
Quoting 2499. ProgressivePulse:
May get a full recurve on this run, lol.


sure looks that way
Member Since: September 19, 2005 Posts: 2 Comments: 4266
Quoting 2495. islander44:


Hey, JustDucky, I grew up south of Boston in the 60's. What town?

And yes, I've noticed that the water here in Maine is MUCH warmer than normal this summer. Surprising, as we had such a cool spring.


Cohasset. Sailed because it was less bone chilling than swimming. Turning turtle was a chilling event, however.
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2500. HadesGodWyvern (Mod)
Japan Meteorological Agency
Tropical Cyclone Advisory #18
TYPHOON SOULIK (T1307)
12:00 PM JST July 9 2013
=============================

SUBJECT: Category Three Typhoon Named Cyclone In Sea East Of The Philippines

At 3:00 AM UTC, Typhoon Soulik (970 hPa) located at 19.6N 139.9E has 10 minute sustained winds of 65 knots with gusts of 95 knots. The cyclone is reported as moving west at 11 knots.

Storm Force Winds
==================
60 NM from the center

Gale Force Winds
===============
240 NM from the center

Dvorak Intensity: T4.0

Forecast and Intensity
=======================
24 HRS: 20.9N 135.1E - 80 knots (CAT 3/Strong Typhoon) South Of Japan
45 HRS: 22.4N 130.4E - 85 knots (CAT 4/Very Strong Typhoon) South Of Japan
69 HRS: 23.6N 125.3E - 90 knots (CAT 4/Very Strong Typhoon) South Of Okinawa
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May get a full recurve on this run, lol.
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The next two waves start to combine into a formidile looking mass on the 0Z GFS.





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Quoting 2492. HurricaneAndre:
The wave towards Africa.What percentage do you think they will give it.
A 0%
B 10%
C 20%
D 30%

I pick C or D.


Given their conservative nature that far out, I would expect an A or B.
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Quoting 2482. MiamiHurricanes09:
Future "Dorian" nowhere near as intense on the 00z compared to the 18z.


No surprise here.
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Quoting 2474. JustDucky251:


Yeah, I grew up south of Boston back in the 60's and the water temps in June were 40-50, July 50-60, and if you were lucky they might get to 65-70 by Labor Day. Tried to go swimming In Freeport, ME in August and nearly emerged a soprano.


Hey, JustDucky, I grew up south of Boston in the 60's. What town?

And yes, I've noticed that the water here in Maine is MUCH warmer than normal this summer. Surprising, as we had such a cool spring.
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It seems the models are more and more trying to close the ridge off and send Chantal into the mainland, I wouldn't be surprised if this trend continues to the point where we have a Florida landfall and a chance for it to come back out in the GOM if only for a short time.
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0Z GFS 102 hour

Slightly to the south and east vs. 18Z.

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The wave towards Africa.What percentage do you think they will give it.
A 0%
B 10%
C 20%
D 30%

I pick C or D.
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2491. LBAR
Here's to hoping Hispaniola does its job and rips Chantal to shreds.
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Quoting 2484. sar2401:
OK, here's what the local mets in Birmingham, AL are saying:

...yet another anomalous system expected Wednesday night/Thursday. This system will set up a touch further east than this current low that is finally leaving. So what does that mean. Well Thursday looks to be a washout. Confidence is high that most everyone will see
rain...but exact timing kept ME from going 80 or higher for the percentage of rain. Expect this to go higher over the next few days. It also means that highs will once again be in the upper 70s to low 80s from Thursday through Sunday and possibly into next week...depending on whether or not the system can actually leave.


This is the ULL that's supposed to cross Florida and then be in place right in south Alabama. At the same tme, Chantal is expected to make an easterly turn toward the Bahamas. Wouldn't Chantal, assuming it still exists, sense the weakess in the low over Alabama and start turning to the west? I don't understand this track thinking.


Another shortwave is forecast to move into the eastern United States by that time. The models show this feature lifting out and leaving Chantal behind, but not fast enough to cause an immediate westward turn.
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High entering stage right at 84, GFS 00Z



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Quoting 2482. MiamiHurricanes09:
Future "Dorian" nowhere near as intense on the 00z compared to the 18z.
every run is different so we shall see
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It's so well insulated, Bob Vila would be proud...
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Quoting 2482. MiamiHurricanes09:
Future "Dorian" nowhere near as intense on the 00z compared to the 18z.


Patience. Still develops it.
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Quoting 2483. MrstormX:
Although the circulation of Chantal is pushing the dry air forward, I can't help but feel the rapid pace of the LLC is causing the system to inhale a little of it.

true
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2484. sar2401
OK, here's what the local mets in Birmingham, AL are saying:

...yet another anomalous system expected Wednesday night/Thursday. This system will set up a touch further east than this current low that is finally leaving. So what does that mean. Well Thursday looks to be a washout. Confidence is high that most everyone will see
rain...but exact timing kept ME from going 80 or higher for the percentage of rain. Expect this to go higher over the next few days. It also means that highs will once again be in the upper 70s to low 80s from Thursday through Sunday and possibly into next week...depending on whether or not the system can actually leave.


This is the ULL that's supposed to cross Florida and then be in place right in south Alabama. At the same tme, Chantal is expected to make an easterly turn toward the Bahamas. Wouldn't Chantal, assuming it still exists, sense the weakess in the low over Alabama and start turning to the west? I don't understand this track thinking.
Member Since: October 2, 2004 Posts: 0 Comments: 16293
Although the circulation of Chantal is pushing the dry air forward, I can't help but feel the rapid pace of the LLC is causing the system to inhale a little of it.
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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.