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 628. SFLWeatherman:
Models do not have it going down to TD they have it at TS


The new ships model is projecting a cat 1 hurricane for the east coast of FL. Very interesting days ahead.
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NHC 2 p.m. advisory on Chantal is out.
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IMHO it really doesn't seem like dry air is as much of a problem at all for chantal compared to the LLC moving at great forward speed and periodically exposing itself. on water vapor, it really seems like the atmosphere around the storm is moist enough.
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Can an ULL venilate a TC??? Like right now theres an ULL in the bahamas, what if Chantal was able to catch up and be in range to benfit from it. Is that a possibility or will the ULL be long gone. Does this even make since? LOL..
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Skyepony said two days ago the ULL in question would cross Florida and have a chance to develop in the Gulf before ending up near the Louisiana coast. Would be a rare sight, but this a good looking ULL. Would be amazing, and as this is shaping up to be an amazing season; it'll probably happen.
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Models do not have it going down to TD they have it at TS
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Chantal is quickly gaining cloud cover in her NE quadrant, an area that has been mainly void of clouds throughout her lifetime. You can even see the hint of convective bands beginning to form there as well. Chantal is defying all odds and if this pace keeps up, a minimal hurricane is not too far fetched. She will be very susceptible to small changes in the environment, however, thanks to her rapid pace. We will just have to see what happens. Chantal is making a believer out of all of us, though.

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Quoting 615. TropicalAnalystwx13:
The GFS is hellbent on the next Cape Verde storm reaching 991 millibars and then weakening on its way to the Islands. Not sure why...it has a beautiful anticyclone, a very moist air bubble, and fast motion doesn't seem to be as big of an issue.

Should be fun to track.
I have been waiting for Dorian since ughhhh can`t remember I hope the don`t steal the name.
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I am willing to put my neck on the line and say Chantal will be a hurricane tomorrow.

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Quoting 618. MississippiWx:


Yeah, probably so. I think this is going to be a bad year for the islands as they take the brunt of strong CV storms.
Sadly for the greater antilles they will take the brunt of the storms and the US would probably recieve weaker systems thanks to the Islands.
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Morning all.

Great post by Dr. Masters and it really goes to heart of the situation we find ourselves in folks.

Our third storm is here and its only the 8th! Not a good sign at all. Whether this ultimately proves ill remains to be seen of course, but with GFS forecasting at least one if not two new additional storms in the next 160 hrs its fair to say we are in for it.

Whats even more disconcerting is the very odd ridging scenario in play over the U.S. and particularly the unusually strong Bermuda high this year, following on the back of a very strange winter which lasted longer than normal, only to be followed by consistent days of record temperatures worldwide.

Even more telling is that while active, the EPAC should have gone a bit faster if we were looking at an average season ahead, and it hasn't. Tells me that more energy is staying on the Atlantic side.


All in all chantal is also going to be a slippery fish to track, right now we have some model consensus, but the steering situation governing this storm is very dynamic as proven by early runs prior to classification. Data from this afternoons recon should provide the model runs later tonight with more accuracy, and I expect a westward or southward shift of the consensus.

Needless to say, the chances of chantal making it intact to the GOM, are low given the sheer present due to the earliness of the season.

One thing that is certainly noticeable is that chantal is improving its convective appearance, evident on RGB loops and in the latest forecast discussion.

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Quoting 621. MechEngMet:


That's a great question. I don't know why it couldn't. This time of year anything can happen in the GOM.

I'm just a bit surprised none of the better prognosticators haven't offered a more valuable opinion (more than mine) on the matter.


Mech, see post #610. I know, the blog is going by so fast it's difficult to keep up. :)
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Quoting 601. congaline:
Ok here's my question asked once again... the ULL which even if it wanted to has no time to develop, is showing signs of lower level circ now, and is showing more convection... Once it moves into the GOM what is to stop it from intensifying there?


That's a great question. I don't know why it couldn't. This time of year anything can happen in the GOM.

I'm just a bit surprised none of the better prognosticators haven't offered a more valuable opinion (more than mine) on the matter.
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This likely a 60 mph system here.

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Quoting 605. JLPR2:
So, was watching the RGB loop from the SSD site and it seems Chantal gained a bit of northward motion to her movement. At this rate it is going to cross 12N before 55W, which is the next point in the forecast track.

Notice that too, interesting
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Quoting 602. washingtonian115:
That's wishful thinking with that pattern in play.
Quoting 612. TylerStanfield:

Ha! That's a funny joke with the pattern it will be forming in there is almost a 0% chance of an escape out to sea.


Yeah, probably so. I think this is going to be a bad year for the islands as they take the brunt of strong CV storms.
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Quoting 598. bappit:

If the dry air is in the storm's circulation, the storm will have a hard time getting rid of the dry air. But it can be done. If the dry air is near the storm but not already drawn into the circulation then it might avoid it.

If a storm has a shallow circulation--Chantal probably does--then dry air that is nearby may not actually be drawn into the circulation but ride above it. It depends on how high up the dry air is.

MissWx pointed out that the low level circulation seems to be outrunning the higher level clouds. If might it can sneak away from the dry air then ... but it also might just end up being a naked swirl, too.


Excellent point. :) See post #587. Of course, you know this, Bappit.
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Seeing some circulation in that system near the Bahamas.
0% chance from the NHC. Fixing to bring some more rain to SoFla....
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The GFS is hellbent on the next Cape Verde storm reaching 991 millibars and then weakening on its way to the Islands. Not sure why...it has a beautiful anticyclone, a very moist air bubble, and fast motion doesn't seem to be as big of an issue.

Should be fun to track.
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Quoting 603. tornadodude:
The original had poor contrast, and when I enhanced the contrast, it looked pretty odd, so I went with black and white. 

Ahh, I see!
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GOM SST loop

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Quoting 600. MississippiWx:


I'm kind of pumped about that potential storm, SC. Could be a classic CV hurricane. Hopefully, it will dodge land and go harmlessly out to sea.

Ha! That's a funny joke with the pattern it will be forming in there is almost a 0% chance of an escape out to sea.
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Quoting 601. congaline:
Ok here's my question asked once again... the ULL which even if it wanted to has no time to develop, is showing signs of lower level circ now, and is showing more convection... Once it moves into the GOM what is to stop it from intensifying there?


ULL's rarely make it to the surface. They do, but it's not a common occurrence. To answer your question directly though, a storm must have fuel and that comes from the warm waters at the surface.

And, in this case, the ULL is also in a dry-air environment.
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Nice to see that NHC addressed the upper level low so folks in South Florida don't freak out just taking the satt loops at "face" value........... :)
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NEW CMC going into S FL
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Quoting 599. hericane96:
This is just my opinon and its to far out to know.
If Chantal stays weak, small and doesnt have a good depth then it would be hard for it to fill the trough and get pulled up the east coast before the high pressure builds back in. The latest GFS makes better since. It all about timing and strength like always....In a few days we will have a better handle on the situation.


If it goes Warm core, then it has all the available TCHP to take advantage of.

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Quoting 590. allancalderini:
I believe if the NHC when flying in the storm find a stronger system than already is she might become a hurricane after all.

Doesn't look too strong on satellite.
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605. JLPR2
So, was watching the RGB loop from the SSD site and it seems Chantal gained a bit of northward motion to her movement. At this rate it is going to cross 12N before 55W, which is the next point in the forecast track.

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Quoting 579. Camille33:

Ignored.


While I agree with you Camille33, worrying more about Dorian than Chantal right now seems highly unreasonable seeing the millions that could be affected by a strong TS or weak hurricane in Chantal; poofing him for an opinion seems just as highly unreasonable. Weatherlover is just an enthusiast like the rest of us, differing opinions make the world go round, be cool.
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The original had poor contrast, and when I enhanced the contrast, it looked pretty odd, so I went with black and white. 
Quoting Bluestorm5:
Wondering why black and white?

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Quoting 600. MississippiWx:


I'm kind of pumped about that potential storm, SC. Could be a classic CV hurricane. Hopefully, it will dodge land and go harmlessly out to sea.
That's wishful thinking with that pattern in play.
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Ok here's my question asked once again... the ULL which even if it wanted to has no time to develop, is showing signs of lower level circ now, and is showing more convection... Once it moves into the GOM what is to stop it from intensifying there?
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Quoting 545. Stormchaser2007:
GFS Ensembles are on board with EATL development



I'm kind of pumped about that potential storm, SC. Could be a classic CV hurricane. Hopefully, it will dodge land and go harmlessly out to sea.
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This is just my opinon and its to far out to know.
If Chantal stays weak, small and doesnt have a good depth then it would be hard for it to fill the trough and get pulled up the east coast before the high pressure builds back in. The latest GFS makes better since. It all about timing and strength like always....In a few days we will have a better handle on the situation.
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Quoting 492. BaltimoreBrian:



How does a storm 'outrun' the dry air around it? wouldn't they all be moving together?

If the dry air is in the storm's circulation, the storm will have a hard time getting rid of the dry air. But it can be done. If the dry air is near the storm but not already drawn into the circulation then it might avoid it.

If a storm has a shallow circulation--Chantal probably does--then dry air that is nearby may not actually be drawn into the circulation but ride above it. It depends on how high up the dry air is.

MissWx pointed out that the low level circulation seems to be outrunning the higher level clouds. If might it can sneak away from the dry air then ... but it also might just end up being a naked swirl, too.
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Quoting 566. hurricane23:


Dont see much relaxation in those winds if it ever makes it into the southern bahamas.
Quoting 570. hurricane23:
12z canadian is right into those cuban mountains then rides it up the florida eastocast. Sure


This is the Adrian we've all grown to know and love in previous years. Welcome back! LOL. :-)
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I believe TEAL 70 went Wheels up from St. Croix at 1800Z
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Quoting 564. tornadodude:
Since it didn't post before, here you go!





El Reno Tornado
Wondering why black and white?
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Quoting 582. Waltanater:
What about Chantal?


Chantel is going to be a tricky system to forecast especially for the US ...for those in the islands it could be a big system for some people ...Dorian has the potenti to be a stronger system even if it never hits land
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Quoting 592. flcanes:

Its possible...

Unlikely, but not impossible...
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Quoting 590. allancalderini:
I believe if the NHC when flying in the storm find a stronger system than already is she might become a hurricane after all.

Its possible...
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Quoting 588. Walshy:
Waters may be cooler over the Bahamas but if we look now it is supportive of all that convection. Chantal could do the same if it makes it there.

As long as there is no to little shear, chantal could survive
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I believe if the NHC when flying in the storm find a stronger system than already is she might become a hurricane after all.
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ZCZC MIATWOAT ALL
TTAA00 KNHC DDHHMM

TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
200 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 EAST OF THE WINDWARD ISLANDS.

1. A VIGOROUS UPPER-LEVEL LOW IS PRODUCING A LARGE AREA OF DISTURBED
WEATHER ACROSS THE CENTRAL AND SOUTHERN BAHAMAS AND ADJACENT
ATLANTIC WATERS. THERE ARE NO SIGNS OF A SURFACE CIRCULATION AND
PRESSURES ARE HIGH IN THE AREA. THIS SYSTEM HAS A LOW CHANCE...
NEAR 0 PERCENT...OF BECOMING A TROPICAL CYCLONE DURING THE NEXT
48 HOURS AS IT MOVES WESTWARD AT 10 TO 15 MPH. HOWEVER...THIS
DISTURBANCE WILL PRODUCE PERIODS OF LOCALLY HEAVY RAINFALL AND
GUSTY WINDS ACROSS THE BAHAMAS THROUGH TOMORROW MORNING...AND
ACROSS PORTIONS OF THE SOUTHERN FLORIDA PENINSULA ON TUESDAY AND
WEDNESDAY.

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

&&
PUBLIC ADVISORIES ON TROPICAL STORM CHANTAL ARE ISSUED UNDER WMO
HEADER WTNT33 KNHC AND UNDER AWIPS HEADER MIATCPAT3.
FORECAST/ADVISORIES ISSUED UNDER WMO HEADER WTNT23 KNHC AND UNDER
AWIPS HEADER MIATCMAT3.

$$
FORECASTER STEWART
NNNN
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Waters may be cooler over the Bahamas but if we look now it is supportive of all that convection. Chantal could do the same if it makes it there.
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Occasionally, this is a good chart to review. It shows the differences in the layers in millibars and feet. Notice that Chantal's vorticity (while still somewhat elongated, unsymmetrical) is greatest at the 850/700mb layers and considerably smaller at the 500mb layer and non-existent at the 200mb layer. Obviously, this helps denote that Chantal is still a small, shallow system that is trying to organize, but still quite an immature system.

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I suspect when the HH gets into Chantal they will find a stronger storm, as sat photos are showing more organisation
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Member Since: June 30, 2013 Posts: 12 Comments: 8087
Quoting 579. Camille33:

Ignored.


Don't care, bye
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12z Navgem takes whats left of Chantal up the west coast of Florida into the panhandle..
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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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