July Atlantic hurricane outlook

By: Dr. Jeff Masters , 12:55 PM GMT on July 13, 2012

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It's mid-July, and we have yet to see a named storm form in the Atlantic this month. The computer models are not predicting any development through at least July 20, and if we make it all the way to the end of the month without a named storm forming, it will be the first July since 2009 without a named storm. Since the current active hurricane period began in 1995, 13 of 17 years (76%) have had a named storm form during July. The busiest July occurred in 2005, when five named storms and two major hurricanes formed. These included Hurricane Dennis and Hurricane Emily--the strongest hurricanes ever observed so early in the season. Only eight major hurricanes have formed in July since record keeping began in 1851. As seen in Figure 1, most of the last half of July activity occurs in the Gulf of Mexico and waters off the Southeast U.S. coast. These type of storms form when a cold front moves off the U.S. coast and stalls out, with the old frontal boundary serving as a focal point for development of a tropical disturbance (as happened for Alberto, Beryl, Chris, and Debby in 2012.) There will be at least two cold fronts moving off the U.S. Mid-Atlantic coast over the next two weeks. The first of these fronts will push offshore around July 20, and we will need to watch the waters offshore of North Carolina for development then. Formation potential will be aided by ocean temperatures that are about 0.7°C (1°F) above average along the U.S. East Coast.


Figure 1. Tracks of all tropical storms and hurricanes 1851 - 2006 that formed July 16-31. The U.S. coast from North to Texas are the preferred strike locations. Only a few storms have formed in the tropical Atlantic and Caribbean in July. Wind shear is typically too high and SSTs too cool in July to allow African waves in the Caribbean and tropical Atlantic to develop into tropical storms. However, a few long-track "Cape Verdes" hurricanes have occurred in July, spawned by tropical waves that came off the coast of Africa. African tropical waves serve as the instigators of about 85% of all major hurricanes.


Figure 2. The seasonal distribution of Atlantic hurricane activity shows that July typically has low activity. Image credit: NHC.

Sea Surface Temperatures: slightly above average
The departure of Sea Surface Temperatures (SST) from average over the tropical Atlantic between Africa and Central America was about 0.3°C above average during June (Figure 3.) This figure has not changed much over the first two weeks of July. These temperatures are not warm enough to appreciably affect the odds of a July named storm or hurricane. The strength of the Azores-Bermuda high has been near average over the past two weeks, driving near-average trade winds. The latest 2-week run of the GFS model predicts continued average-strength trade winds through late-July, so SSTs should remain about 0.3°C above average during this period, due to average amounts of cold water mixing up from below due to the wind action on the water.


Figure 3. Sea Surface Temperature (SST) departure from average for July 12, 2012. SSTs were 0.3°C above average over the tropical Atlantic's Main Development region for hurricanes, from Africa to Central America between 10° and 20° North Latitude. Note the large region of above average SSTs along the Equatorial Pacific off the coast of South America, the hallmark of a developing El Niño episode. Image credit: NOAA/NESDIS

El Niño on the way?
For two consecutive weeks, ocean temperatures 0.5 - 0.6°C above average have been present in the tropical Eastern Pacific, which is right at the threshold for a weak El Niño episode. NOAA's Climate Prediction Center has issued an El Niño Watch, and gives a 61% chance that El Niño conditions will be present during the August - September - October peak of the Atlantic hurricane season. The likely development of a full-fledged El Niño episode means that Atlantic hurricane activity will probably be suppressed in 2012, due to the strong upper-level winds and high wind shear these events typically bring to the tropical Atlantic.


Figure 4. Sea Surface Temperature (SST) departure from average for the the equatorial Eastern Pacific (the area 5°N - 5°S, 120°W - 170°W, also called the "Niña 3.4 region"). El Niño conditions exist when the SST in this region rises 0.5°C above average. As of July 9, 2012, SSTs in the Niño 3.4 region had risen to 0.5°C above average. To be considered an "El Niño episode", El Niño conditions must occur for five consecutive months, using 3-month averages. Image credit: NOAA Climate Prediction Center.

Wind shear: above average
Wind shear is usually defined as the difference in wind between 200 mb (roughly 40,000 foot altitude) and 850 mb (roughly 5,000 foot altitude). In most circumstances, wind shear above 20 knots will act to inhibit tropical storm formation. Wind shear below 12 knots is very conducive for tropical storm formation. High wind shear acts to tear a storm apart. The jet stream has two bands of strong high-altitude winds that are currently bringing high wind shear to the Atlantic. The southern branch (subtropical jet stream) is bringing high wind shear to the Caribbean, and the northern branch (polar jet stream) is bringing high wind shear to the waters offshore of New England. This configuration often leaves a "hole" of low shear between the two branches, off the Southeast U.S. coast and over the Gulf of Mexico. The jet stream is forecast to maintain this two-branch pattern over the coming two weeks. Wind shear has been about 10 - 20% higher than average over the first two weeks of July, and is predicted to be mostly above average for the coming two weeks. This will cut down on the odds of a July storm.


Figure 5. Vertical instability over the Caribbean Sea in 2012 (blue line) compared to average (black line.) The instability is plotted in °C, as a difference in temperature from near the surface to the upper atmosphere. Thunderstorms grow much more readily when vertical instability is high. Instability has been lower than average, due to an unusual amount of dry air in the atmosphere, reducing the potential for tropical storm formation. Image credit: NOAA/NESDIS/CIRA.

Dry air: above average
As seen in Figure 5, there has been an unusual amount of dry, stable air in the Caribbean this year creating low levels of vertical instability. This has occurred due to a combination of dry air from Africa, and upper-atmosphere dynamics creating large areas of sinking air that dry as they warm and approach the surface. The Gulf of Mexico and tropical Atlantic between the coast of Africa and the Lesser Antilles have also seen low vertical instability this summer. June and July are the peak months for dry air and dust coming off the coast of Africa, and the Saharan dust storms have been quite active over the past two weeks. Expect dry air to be a major deterrent to any storms that try to form in the tropical Atlantic during July.

Steering currents: average
The predicted steering current pattern for the next two weeks is a typical one for July. We have an active jet stream bringing many troughs of low pressure off the East Coast of the U.S. These troughs are frequent enough and strong enough to recurve any tropical storms or hurricanes that might penetrate north of the Caribbean Sea. Steering current patterns are predictable only about 3 - 5 days in the future, although we can make very general forecasts about the pattern as much as two weeks in advance. There is no telling what might happen during the peak months of August, September, and October--we might be in for a repeat of the favorable 2010 and 2011 steering current pattern, which recurved most storms out to sea--or the unfavorable 2008 pattern, which steered Ike and Gustav into the Gulf of Mexico.

Summary: a below average chance of a July tropical storm
Given that none of the computer models are forecasting tropical storm formation in the coming seven days, SSTs are only slightly above average, and wind shear and vertical stability are above average, I'll go with a 30% chance of a named storm forming in the Atlantic during the remainder of July.


Figure 6. Hurricane Emilia over the Eastern Pacific at 20:35 UTC July 10, 2012. At the time, Emilia was a Category 3 hurricane with 125 mph winds. Emilia peaked earlier in the day as a Category 4 storm with 140 mph winds--the strongest hurricane in the East Pacific so far in 2012. Image credit: NASA.

An active Eastern Pacific hurricane season
It's been a very active start to the Eastern Pacific hurricane season, where we've already had six named storms, four hurricanes, and three intense hurricanes. A typical season has 4 named storms, 2 hurricanes, and 0 intense hurricanes by July 14. The formation of Tropical Storm Fabio on July 12 marks the 4th earliest formation of the Eastern Pacific's season's sixth storm. The record is held by the year 1985, when the season's sixth storm formed on July 2. Record keeping began in 1949.

Have a great weekend, everyone, and I'll be back Monday with a new post.

Jeff Masters

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1511. JLPR2
Quoting Ameister12:

This too.


Hmm... A cat 4 in my area...

Cat 4 winds + a somewhat decaying and fragile power gird = no blog for me and for awhile. XD
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Quoting floridaboy14:
one of the hardest storm tracks to get. all the models were disagreeing. all the models show nothing developing in july. what analouge year does 2012 remind you of so far involving the enso and how the azores bermuda high is postioned?
2004 and 2002
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Blog update.
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Quoting Levi32:


I think it was because the ridge was too meridionally-aligned (too north-south), which allowed height rises over Texas that blocked westward movement. It's a classic steering lesson that we should all remember.
one of the hardest storm tracks to get. all the models were disagreeing. all the models show nothing developing in july. what analouge year does 2012 remind you of so far involving the enso and how the azores bermuda high is postioned?
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it looks like the cape verde season is trying to take shape those waves coming off africa look a little ominous
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Quoting WxGeekVA:


That Central African disturbance has a good spin to it.
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1505. hydrus
Quoting EricSFL:

With all the crap that you people post, you consider that trolling?
Who is "you People"? Are you insinuating that everyone here posts crap?..Do you believe all people that were born, lived and died before Jesus taught, and the Old Testament was written went to hell? A few people talk about one of the many calenders that have been in existence for millenniums and then you cast your judgement on what an entire nation has become.?..
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Member Since: September 3, 2011 Posts: 13 Comments: 3474
Quoting Levi32:


I think it was because the ridge was too meridionally-aligned (too north-south), which allowed height rises over Texas that blocked westward movement. It's a classic steering lesson that we should all remember.


what caused that NE jog before the stall that helped to tip the balance?
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Member Since: September 3, 2011 Posts: 13 Comments: 3474
Member Since: September 3, 2011 Posts: 13 Comments: 3474
Quoting Levi32:


I think it was because the ridge was too meridionally-aligned (too north-south), which allowed height rises over Texas that blocked westward movement. It's a classic steering lesson that we should all remember.


So she didn't hump the ridge enough?
Member Since: September 3, 2011 Posts: 13 Comments: 3474
And this ?

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Quoting yoboi:



who ya talkin about


forget it.
it was sarcasm
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1496. Levi32
Quoting floridaboy14:
why didnt debby move into texas like many thought?


I think it was because the ridge was too meridionally-aligned (too north-south), which allowed height rises over Texas that blocked westward movement. It's a classic steering lesson that we should all remember.
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Quoting TropicalAnalystwx13:

1% chance.


nice avatar.
keep it
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1494. Patrap
Betsy was my first dance with a Eyewall to be retired. I was 5.7 years old at the time.

The next would be Elena in 85, then K in 2005.

Betsy was also the first US Hurricane to result in a Billion Dollars damage.

Thus the nickname then of "Billion Dollar Betsy".

Member Since: July 3, 2005 Posts: 426 Comments: 128639
Category 2 Hurricane Fabio:

Member Since: July 21, 2011 Posts: 83 Comments: 7167
Quoting windshear1993:
you thnk debby will be retired

1% chance.
Member Since: July 6, 2010 Posts: 113 Comments: 32262
1489. Grothar
This one caught a lot of people off guard. Hurricane Betsy. All the experts said it was going North and we let down our guard. It had a very large eye and the hurricane winds in Miami lasted well over 10 hours. Even though it was in South Dade, there was damage well into Broward County well to its North.

Member Since: July 17, 2009 Posts: 71 Comments: 26472
Quoting KoritheMan:


At first glance I thought that was Fabio. I was all like "OMG"
lmaoooo i thought it was too
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Member Since: July 21, 2011 Posts: 83 Comments: 7167
Quoting TropicalAnalystwx13:

Debby just annoyed me. I guess it could be considered interesting.
you thnk debby will be retired
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Quoting Levi32:


Debby was the toughest track forecast we have seen in decades.
why didnt debby move into texas like many thought?
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1482. Grothar
Quoting Ameister12:

This too.


Oh, I remember that one. 1899 was a bad year.
Member Since: July 17, 2009 Posts: 71 Comments: 26472
Member Since: July 21, 2011 Posts: 83 Comments: 7167
Semi-weather related..

Just heard about the sink hole out in Colorado.
Apparently, the heat caused the still-frozen underground beams of an abandoned underground train line to thaw, and the result is now a 100 foot sink hole... pretty unique situation.



"The depth of the hole is estimated to be about 100 feet, and since the depths reach so far into the earth, much of the soil was still frozen until very recently -- when the soil thawed, the hole was exposed."

Link

Edit: Abandoned underground train line revealed by 100 foot sink hole... Sounds like something that could be made into a cool mystery novel too.
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Quoting Grothar:
This one would have driven the blog crazy.


This too.
Member Since: August 9, 2009 Posts: 10 Comments: 5026
Quoting GeorgiaStormz:
I see nothing happened on this blog since i left.
No intelligent discussions.
Just some mayan nonsense and some toddlers squabbling.
hmmmm.
we need a storm

I had a go at the Mayan crap at 1419, I see you have it nailed at, 1463, a few others have had a go.
Best thing with all this probabilty/possibility theory stuff is wait and see!
You never know something might just coincidentally go wrong on the big day all all the screamers will say the Mayans told us so!
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Member Since: July 6, 2010 Posts: 113 Comments: 32262
Fabio has strengthened into a Cat. 2 Hurricane:

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1474. Grothar
This one would have driven the blog crazy.

Member Since: July 17, 2009 Posts: 71 Comments: 26472
Quoting BarometerGirl:
Fabio was going W this morning and now going WNW, so looks like he beginning to take that northern turn. I feel his eye on San Diego.

OK experts out there, Fabio will completely peter out by then, right? San Diego will not even be prepared for the 2+ inches of rain a tropical depression could bring --completely unprepared for even a tropical storm-much less a hurricane. Rain welcome and needed here, but many areas of SD floods when it rains hard for more than 15 minutes.

The surfers will love it.

I'm no expert, but yes, Hurricane Fabio will dissipate before reaching California. Sea Surface Temperatures between its current position and California are entirely too cool to sustain a tropical cyclone. Not to mention the system will enter higher wind shear and a much more stable environment by 72 hours out.



Member Since: July 6, 2010 Posts: 113 Comments: 32262
.
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Quoting KoritheMan:


Take that back! Debby was at one point forecast to be in my backyard.

Debby came THROUGH my backyard.
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Fabio was going W this morning and now going WNW, so looks like he beginning to take that northern turn. I feel his eye on San Diego.

OK experts out there, Fabio will completely peter out by then, right? San Diego will not even be prepared for the 2+ inches of rain a tropical depression could bring --completely unprepared for even a tropical storm-much less a hurricane. Rain welcome and needed here, but many areas of SD floods when it rains hard for more than 15 minutes.

The surfers will love it.
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Quoting Ameister12:
I agree with all4hurricanes, although I did love seeing Chris become a hurricane, Beryl was my favorite Atlantic tropical cyclone this season.



nothing else has compared
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Quoting Ameister12:
I agree with all4hurricanes, although I did love seeing Chris become a hurricane, Beryl was my favorite Atlantic tropical cyclone this season.


Too bad it didn't have another few hours over the Gulf Stream...could have become the season's first hurricane. In May.
Member Since: July 6, 2010 Posts: 113 Comments: 32262
Quoting Grothar:


Very big



On first glance it looks like two on one entity,but is really one and it has an evident circulation.
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Quoting Grothar:
Good evening boys and girls.

What's up Grothar?
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Link


Dewpoints still up there on central gulf coast....

nice little all purpose display using left drop

down menu
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I agree with all4hurricanes, although I did love seeing Chris become a hurricane, Beryl was my favorite Atlantic tropical cyclone this season.

Member Since: August 9, 2009 Posts: 10 Comments: 5026
I see nothing happened on this blog since i left.
No intelligent discussions.
Just some mayan nonsense and some toddlers squabbling.
hmmmm.
we need a storm
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Quoting Grothar:


Very big


Those 3 disturbances you have posted in the picture there would be going on the size of the GOM if they were relocated!
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Since there is a little interest in doomsday today has anyone done any calculations on what the CME of 150 yrs. ago would do, taking into consideration that he magnetic field is 10 to 15% weaker.That maybe the 2012 shakeup with the most probability. And there was some discussion about the earth/sun alignment thru the center of the universe. That being as the sun travels around the galaxy every 26 thousand yrs. it pass thru the mid point directly opposite the galactic center, like a pony on a merry go round.I don't think it has anything to do with an annual event. I think some people believe we will pass thru more cosmic crap along the accretion disk. Just asking because it maybe the wrong time, but if someone knows the answer it's probably on this blog.
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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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