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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3133. Grothar
Quoting 3123. GeoffreyWPB:
Excerpt from Miami NWS Disco

* WATCHING TROPICAL STORM CHANTAL

WEATHER DURING THE LONG TERM FORECAST PERIOD WILL BE HIGHLY
DEPENDENT ON THE TRACK OF TROPICAL STORM CHANTAL. NHC IS FORECASTING
CHANTAL TO TURN NW-N AFTER CROSSING HISPANIOLA, AS A BREAK IN THE
SUBTROPICAL RIDGE OCCURS. THIS WOULD TAKE CHANTAL TO OUR EAST ACROSS
THE BAHAMAS FRIDAY-SATURDAY. GUIDANCE IS IN RATHER GOOD AGREEMENT ON
THIS GENERAL TRACK. HOWEVER, THINGS CAN CHANGE SO THIS WILL OF
COURSE CONTINUE TO BE WATCHED CLOSELY. WHAT IS INTERESTING IS WHAT
THE LATEST GFS 09.00Z RUN SHOWS EARLY NEXT WEEK. IT BUILDS A RIDGE
BACK IN NORTH OF CHANTAL SUN-TUE, FORCING THE CYCLONE ON A WESTWARD
COURSE WITH EVEN A SLIGHT BEND SW AND ACROSS CENTRAL FLORIDA.
NOW, THIS IS JUST ONE MODEL RUN, BUT THIS JUST SHOWS THAT EVERYONE
IN FLORIDA SHOULD CONTINUE TO MONITOR THE LATEST FORECASTS ON
CHANTAL OVER THE COMING DAYS. ANOTHER POSSIBILITY IS FOR CHANTAL
TO WEAKEN ALL TOGETHER WHILE CROSSING HISPANIOLA, THOUGH THIS IS
NOT CURRENTLY FORECAST. ECMWF CONTINUES TO SHOW CHANTAL AS AN OPEN
WAVE MOVING INTO THE BAHAMAS, BUT THIS MODEL DIDN`T INITIALIZE
CHANTAL WELL.

AND WHILE WE ARE CLOSELY MONITORING CHANTAL INTO THIS WEEKEND,
ANOTHER TROPICAL SYSTEM COULD BE DEVELOPING OVER THE TROPICAL
ATLANTIC AS PER THE GFS. ACTIVE TIMES AHEAD.



Many of the models have been shifting Chantal west much earlier than previous models. The GFS solution has been moving the turn further South on each run

Member Since: July 17, 2009 Posts: 63 Comments: 23676
3132. ncstorm
Good Morning All..

Member Since: August 19, 2006 Posts: 13 Comments: 13421
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Enter stage right:

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3128. Grothar
Member Since: July 17, 2009 Posts: 63 Comments: 23676
Quoting 3083. NasBahMan:
Morning Baha,

Light rain and thunder in Briland this morning...looks like it will be pouring soon...sky is very dark looking towards Lutra
Sure does look like it's going to be overcast for much of the day here.

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Quoting 3118. gator23:
I wonder how many WU members will stay say its going to Texas today?


There is a lot of complicated weather north and north east of this tiny system.

Personally, I think the NHC has this puppy dead to rights.

Texas casters will have to come out in force before Chantal gets north of Hispanola, because Chantal is likely to still be well within the projected cone at that point in its journey.
Member Since: August 26, 2006 Posts: 10 Comments: 3420
From TS to Hurricane what will it be
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3124. Grothar
Member Since: July 17, 2009 Posts: 63 Comments: 23676
Excerpt from Miami NWS Disco

* WATCHING TROPICAL STORM CHANTAL

WEATHER DURING THE LONG TERM FORECAST PERIOD WILL BE HIGHLY
DEPENDENT ON THE TRACK OF TROPICAL STORM CHANTAL. NHC IS FORECASTING
CHANTAL TO TURN NW-N AFTER CROSSING HISPANIOLA, AS A BREAK IN THE
SUBTROPICAL RIDGE OCCURS. THIS WOULD TAKE CHANTAL TO OUR EAST ACROSS
THE BAHAMAS FRIDAY-SATURDAY. GUIDANCE IS IN RATHER GOOD AGREEMENT ON
THIS GENERAL TRACK. HOWEVER, THINGS CAN CHANGE SO THIS WILL OF
COURSE CONTINUE TO BE WATCHED CLOSELY. WHAT IS INTERESTING IS WHAT
THE LATEST GFS 09.00Z RUN SHOWS EARLY NEXT WEEK. IT BUILDS A RIDGE
BACK IN NORTH OF CHANTAL SUN-TUE, FORCING THE CYCLONE ON A WESTWARD
COURSE WITH EVEN A SLIGHT BEND SW AND ACROSS CENTRAL FLORIDA.
NOW, THIS IS JUST ONE MODEL RUN, BUT THIS JUST SHOWS THAT EVERYONE
IN FLORIDA SHOULD CONTINUE TO MONITOR THE LATEST FORECASTS ON
CHANTAL OVER THE COMING DAYS. ANOTHER POSSIBILITY IS FOR CHANTAL
TO WEAKEN ALL TOGETHER WHILE CROSSING HISPANIOLA, THOUGH THIS IS
NOT CURRENTLY FORECAST. ECMWF CONTINUES TO SHOW CHANTAL AS AN OPEN
WAVE MOVING INTO THE BAHAMAS, BUT THIS MODEL DIDN`T INITIALIZE
CHANTAL WELL.

AND WHILE WE ARE CLOSELY MONITORING CHANTAL INTO THIS WEEKEND,
ANOTHER TROPICAL SYSTEM COULD BE DEVELOPING OVER THE TROPICAL
ATLANTIC AS PER THE GFS. ACTIVE TIMES AHEAD.
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last night my ruler said butterfly island its going to be close
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3121. gator23
Looks like she is firing convection and kicking out her dry air. Could she be getting stronger?
Quoting 3115. SFLWeatherman:
Convection firing.
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Quoting 3118. gator23:
I wonder how many WU members will still say its going to Texas today?


We don't know where it's going. How far west it goes depends entirely on how much westward-building ridging we get in the Bahamas.
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Will she or won't she survive Hispaniola? That is the big question for the USA.
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3118. gator23
I wonder how many WU members will still say its going to Texas today?
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Intensity update at 8 am EST?
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a new burst of convection near centre of Chantal it is about 160 mls east of st lucia and about 70 mls ne of barbados
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Convection firing.
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3114. gator23
Happens all the time.

See links for facts:
Link

Link


Quoting 3063. jeffreeysweetypie:
honestly i cant ever remember a storm comming up from puerto rico then suddenly take a quick turn into florida so with that chantal wont hit florida with thism drastic quick left turn as they say
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any wind shear for the tropical storm
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Quoting 3104. islander101010:
ecuador not enough storms no thanks


Yes...the most severe weather here is torrential rain that can flood the rivers and take out villages downstream.

The volcanoes are pretty cool.

But I had a personal choice to make. I had to choose between living in hurricane alley or in a place where I could ask for and be granted asylum.
Member Since: August 26, 2006 Posts: 10 Comments: 3420
Quoting CycloneOz:


OMG...Isaac and the St. Charles County Mounties. Remember me almost going to jail because I was live streaming the landfall in Boutee?

There are stories about cops out of control all over America.

As far as being "chased out," I do not say the following lightly, given my propensity for diving head-first into dangerous situations:

I evacuated the United States, mate.


Well, I'm glad your still around and oh yeah, i remember you almost getting put in the can. Good times mate. Stay safe down there.
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Quoting 3080. CycloneOz:


Yes, I should be taking more pictures. And I will over time.

Right now, I am busy learning Spanish. I am only at a 2nd grade level. It is surprisingly difficult to learn.

The seasons here are measured in less than 5 degrees difference. It is like always living in a Springtime environment. In the AM...it is around 50 degrees, warming to around 70 around noon.

I live at 8,600 feet (2,900 meters) in the Andes Mountains.


That sounds like the perfect weather. I may just have to retire there.

I wonder if the 54 mph gust in St. Lucia is from a stray rain band from Chantal as the storm is still a ways away from the island (and not too strong anyhow)?
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3105. msphar
Barbados looks to be getting wet
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ecuador not enough storms no thanks slu thats about right 11 28=40mph
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Quoting 3100. AtHomeInTX:
Sorry Allan. That was just to one run. Here's the main link to pick which model, run, etc Link
Haha don`t worry :)I just loop them all.
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3102. SLU
Winds in Barbados - WSW @ 10mph. Pressure dropped to 1011.

Closed low confirmed.
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Sorry Allan. That was just to one run. Here's the main link to pick which model, run, etc Link
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Quoting 3095. emguy:


Agree to disagree...Chantal had a thunderstorm die off earlier...likely due to dry air coupled with rapid forward speed. As far as shear goes, it may have appeared to be that way, but notice there is no blow off to the cloud tops of the current thunderstorms. It's not a shear issue with her, and she survived the bad stuff.
Agreed.
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Quoting 3092. AtHomeInTX:


sure Link
Thanks.
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Barbados Radar

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3095. emguy
Quoting 3081. Gearsts:
Shear


Agree to disagree...Chantal had a thunderstorm die off earlier...likely due to dry air coupled with rapid forward speed. As far as shear goes, it may have appeared to be that way, but notice there is no blow off to the cloud tops of the current thunderstorms. It's not a shear issue with her, and she survived the bad stuff.
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Quoting 3088. Grothar:


Spanish is really very easy. The trick in learning a language is not to translate from English, but think in the language you are learning. The first 4 or 5 languages are usually the hardest.


I am trying very hard to turn the English off in my head, but I have had and made straight "A's" in advanced English courses.

I am at a 2nd grade level in Spanish...and it is almost time for me to get to work learning more.
Member Since: August 26, 2006 Posts: 10 Comments: 3420
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Quoting 3090. allancalderini:
Yeah I see do you have the link Athom I would really appreciate it.


sure Link
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Quoting 3077. AussieStorm:


Did you get chased out of the States mate?
Ecuador, geez. Last year you were in NOLA for Isaac and this year your in Ecuador. Where to next year.


OMG...Isaac and the St. Charles County Mounties. Remember me almost going to jail because I was live streaming the landfall in Boutee?

There are stories about cops out of control all over America.

As far as being "chased out," I do not say the following lightly, given my propensity for diving head-first into dangerous situations:

I evacuated the United States, mate.
Member Since: August 26, 2006 Posts: 10 Comments: 3420
Quoting 3086. AtHomeInTX:


Morning Allan. Not sure where that storm came from but it looked like another wave moving NW through the Caribbean that didn't spin up until then. If the GFS is any indication it could get very busy.
Yeah I see do you have the link Athom I would really appreciate it.
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3088. Grothar
Quoting 3080. CycloneOz:


Yes, I should be taking more pictures. And I will over time.

Right now, I am busy learning Spanish. I am only at a 2nd grade level. It is surprisingly difficult to learn.

The seasons here are measured in less than 5 degrees difference. It is like always living in a Springtime environment. In the AM...it is around 50 degrees, warming to around 70 around noon.

I live at 8,600 feet (2,900 meters) in the Andes Mountains.


Spanish is really very easy. The trick in learning a language is not to translate from English, but think in the language you are learning. The first 4 or 5 languages are usually the hardest.
Member Since: July 17, 2009 Posts: 63 Comments: 23676
Recon left yet?
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Quoting 3078. allancalderini:
Hello At home and good morning everyone.Omg this run is exciting it has a tc north of Honduras.


Morning Allan. Not sure where that storm came from but it looked like another wave moving NW through the Caribbean that didn't spin up until then. If the GFS is any indication it could get very busy.
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Morning Baha,

Light rain and thunder in Briland this morning...looks like it will be pouring soon...sky is very dark looking towards Lutra
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About JeffMasters

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