July hurricane outlook

By: Dr. Jeff Masters , 7:26 PM GMT on July 02, 2009

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Atlantic tropical cyclone activity typically picks up a bit during the first half of July. Since the current active hurricane period began in 1995, seven of 14 years (50%) have had a named storm form during the first half of July. The busiest first half of July occurred in 2005, when three hurricanes formed. These included Hurricane Dennis and Hurricane Emily--the strongest hurricanes ever observed so early in the season. As seen in Figure 1, most of the early July activity occurs in the Gulf of Mexico, Western Caribbean, and Carolina waters. However, a few long-track "Cape Verdes" hurricanes begin to occur. These are spawned by tropical waves that come off the coast of Africa. Tropical waves serve as the instigators of about 85% of all major hurricanes. Last year's Hurricane Bertha was one such rare early July Cape Verdes hurricane. Bertha's 120 mph winds made it the sixth strongest early-season Atlantic hurricane on record. Bertha also set the record for farthest east formation as a tropical storm, hurricane, and major hurricane, so early in the season.


Figure 1. Tracks of all tropical storms and hurricanes 1851 - 2006 that formed July 1-15. North Carolina and the Gulf of Mexico coast from the Florida Panhandle to Texas are the preferred strike locations. Oddly, the Florida Peninsula has been struck by only two storms that formed in the first half of July.

Sea Surface Temperatures
Sea Surface Temperatures (SST) anomalies have warmed slightly over the past two weeks, but are close to average over the tropical Atlantic between Africa and Central America (Figure 2). These are the are the coolest SST anomalies we've seen since 1994. The strength of the Azores-Bermuda high has been near average over the past two weeks, driving near-average trade winds. Stronger-than-average trade winds were observed through most of the period November 2008 - May 2009, which helped cool the tropical Atlantic substantially. Strong winds mix up colder water from the depths and cause greater evaporative cooling. The latest 2-week run of the GFS model predicts continued average-strength trade winds through mid-July, so SSTs should remain near average during this period.

Typically, July tropical storms form over the Gulf of Mexico, Western Caribbean, and Gulf Stream waters just offshore Florida. SSTs are about 1.0°C above average for this time of year in the Gulf of Mexico, but near average elsewhere. July storms typically 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. There will be one or two fronts moving off the U.S. coast over the next two weeks, and we will need to watch these for development. Wind shear is too high and SSTs are usually too cold in July to allow African tropical waves to develop into tropical storms. African tropical waves serve as the instigators of about 85% of all major hurricanes,

Figure 2. Sea Surface Temperature (SST) departure from average for July 2, 2009. SSTs were near 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
El Niño conditions continue to amplify over the tropical Eastern Pacific. Ocean temperatures there rose 0.5°C over the past two weeks, and are now 0.45°C above the threshold for El Niño, according to the Australian Bureau of Meteorology (Figure 3). NOAA's Climate Prediction Center issued an El Niño Watch in early June, saying "that conditions are favorable for a transition from neutral to El Niño conditions during June - August 2009". The pattern of changes in surface winds, upper-level winds, sea surface temperatures, and deeper water heat content are all consistent with what has been observed during previous developing El Niños, and latest set of mid-June runs of the El Niño computer models are almost universally calling for El Niño conditions to become well-established for the peak months of hurricane season, August - October. It is likely that Atlantic hurricane activity will be suppressed in 2009 due to the strong upper-level winds and resulting wind shear an El Niño event usually brings to the tropical Atlantic.


Figure 3. 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 June 28, 2009, SSTs in the Niño 3.4 region had risen to 0.95°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: Australian Bureau of Meteorology.

Wind shear
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's band of strong high-altitude winds is the main source of wind shear in July over the Atlantic hurricane breeding grounds, since the jet is very active and located quite far south this time of year.

The jet stream over the past two months has been locked into a pattern where a southern branch (the subtropical jet stream) brings high wind shear over the Caribbean, and a northern branch (the polar jet stream) brings high wind shear offshore of New England. This often leaves a "hole" of low shear between the two branches off the coast of North Carolina, which is where Tropical Depression One formed at the end of May.

The jet stream is forecast (Figure 4) to maintain this two-branch pattern over the coming two weeks. This means that the waters offshore of the Carolinas are the most likely place for a tropical storm to form during this period.


Figure 4. Wind shear in m/s between 200 mb and 850 mb, as forecast by the 06Z July 02, 2009 run of the GFS model. The position and strength of the subtropical jet stream is forecast to change little over the next two weeks, and this jet will bring high wind shear to the Caribbean and Gulf of Mexico into mid-July. There will at times be a region of low shear between the polar jet (northern set of arrows on the plots) and the subtropical jet, allowing for possible tropical development off the coast of North Carolina. Wind speeds are given in m/s; multiply by two to get a rough conversion to knots. Thus, the red regions of low shear range from 0 - 16 knots.

Dry air and African dust
June and July are the peak months for dust coming off the coast of Africa, and the Saharan dust storms have been quite active over the past month. Expect dust from Africa to be a major deterrent to any storms that try to form between Africa and the Lesser Antilles Islands in July.

Steering currents
The steering current pattern over the past few weeks has not changed much, and is typical for June and 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. At present, it appears that the coming two weeks will maintain the typical July pattern, bringing many troughs of low pressure off the East Coast capable of recurving any July storms that might form. 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 2006 steering current pattern that recurved every storm out to sea--or the unfavorable 2008 pattern, that steered Ike and Gustav into the Gulf of Mexico.

Summary
Recent history suggests a 50% chance of a named storm occurring in the first half of July. Given that none of the computer models are forecasting tropical storm formation in the coming seven days, and SST and wind shear patterns look pretty average, I'll go with a 20% chance of a named storm forming during the first half of July.

Vote for Mike Theiss as an Antarctica blogger
Extreme weather photographer Mike Theiss, who wrote our Ultimate Chase photography blog for two years until a new job took him to South America, wants your help. He's entering a Quark Expeditions competition to receive an expense-paid 2-week trip to Antarctica, where he will do some intensive photography and blogging. In order to go, he needs the votes to show that he's a popular blogger. So, if you liked his posts while he was blogging for wunderground, and want to see him blog for wunderground during this potential Antarctica voyage, go to http://www.blogyourwaytoantarctica.com/blogs/view /220 and cast a vote. It takes about 3 minutes navigate through the registration and voting process. Mike will be back chasing hurricanes this August, and has promised to post his excellent storm photos on wunderground should we help him secure the Antarctica gig.

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

Jeff Masters

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EVERYONE HAVE A GREAT WEEKEND! Have a safe & Happy 4th!!
Member Since: Posts: Comments:
Quoting plywoodstatenative:
Tampa, that mess by the islands, what are the sst's in the area and shear values?


31deg Cel.....shear about 30-40kts..
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Quoting BenBIogger:


Please stop comparing this season to 2004


Its reasonable...cause its a fact that 2004 had a late starting season and was a weak el nino. No one here is saying it will be 2004.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
Quoting TampaSpin:


I don't know...We will see


Don't quote Ben, I think he is a troll
Member Since: June 29, 2009 Posts: 13 Comments: 5313
Quoting Weather456:
Late starters are not good:

1977 - Anita (cat 5 impacted Mexico) August 29
1983 - Alicia (cat 3 Texas) July 29
1992 - Andrew (cat 5 impacted South Florida) August 16
1998 - Alex - July 27 (Georges and Mitch, notable storms)
2002 - Arthur - July 14 (Isidore and Lili notable storms)
2004 - Alex - July 29 (Charley, Frances, Ivan and Jeanne notable storms)

All these names were retired the following year.


Please stop comparing this season to 2004
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Tampa, that mess by the islands, what are the sst's in the area and shear values?
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Quoting BenBIogger:


I agree we will see more fish storms this season

My Prediction

4 Named storms
1 hurricane
0 major hurricane

People need to stop comparing this season to 2004.


lol nice bait post
Member Since: August 2, 2007 Posts: 19 Comments: 19234
That swirl that we are seeing, is that MLC or Low level?
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Tropical Update
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Late starters are not good:

1977 - Anita (cat 5 impacted Mexico) August 29
1983 - Alicia (cat 3 Texas) July 29
1992 - Andrew (cat 5 impacted South Florida) August 16
1998 - Alex - July 27 (Georges and Mitch, notable storms)
2002 - Arthur - July 14 (Isidore and Lili notable storms)
2004 - Alex - July 29 (Charley, Frances, Ivan and Jeanne notable storms)

All these names were retired the following year.
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Quoting BenBIogger:


It will go poof later today


I don't know...We will see! Your more than likely correct tho!
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atmo, you haven't seen the nuttiest people trust me.
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Quoting AllStar17:
T-wave holding together in Caribbeani n the face of strong shear



It will go poof later today
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Quoting Skyepony:
Since ya'll are into July 4th safety~ Bottle rockets, bonfires, gasoline & lawn mowers aren't a good combination.. I don't care if you have on gloves & are holding a hose...

cg~ this is the easiest way to compare ENSO to other years..notice '04 is not even in the top six. 2006 is.. a trend for that year I see as a real possibility for some of this season's tracks is Carolina bred storms harassing the Azores & possibly Europe.


(you can almost always click on things I hang to see source & bigger)


I agree we will see more fish storms this season

My Prediction

4 Named storms
1 hurricane
0 major hurricane

People need to stop comparing this season to 2004.
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T-wave holding together in Caribbeani n the face of strong shear

Member Since: June 29, 2009 Posts: 13 Comments: 5313
New convection firing very near the center with the non-tropical low in the north central Atlantic

Member Since: June 29, 2009 Posts: 13 Comments: 5313
Bottle rockets, bonfires, gasoline & lawn mowers aren't a good combination.

Being an LSU fan, I must say, that sounds like a Bama-fan invention.
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730. Skyepony (Mod)
Since ya'll are into July 4th safety~ Bottle rockets, bonfires, gasoline & lawn mowers aren't a good combination.. I don't care if you have on gloves & are holding a hose...

cg~ this is the easiest way to compare ENSO to other years..notice '04 is not even in the top six. 2006 is.. a trend for that year I see as a real possibility for some of this season's tracks is Carolina bred storms harassing the Azores & possibly Europe.


(you can almost always click on things I hang to see source & bigger)
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Quoting TampaSpin:


People of all ages get hurt badly every year nearly in every community. Please protect the young especially so!


And I have a 2-yr-old and 4-yr-old. We'll let the 4-yr-old do a couple of sparklers if he listens as well as he did at new-years. Yes, I know they are hot...and so does he. We showed him how a sparkler can melt through an aluminum can.

Other than that, why spend $70 on the cheap stuff if you can spend nothing at all on watching some professionals put up some good stuff.

Patrap, you going to see the dueling barges on the MS river?
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728. DDR
Quoting potteryX:
DDR, heavy rain in Tobago here now. since 5:00 am, intermittent.
Strong gusts, squally conditions.
Word from central Trinidad, heavy rain.
About time too.......

I waited so long for some decent rain,now it seems were getting all at once,flash floods in the north of the isalnd.stay safe,btw alot of lightening.
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727. Skyepony (Mod)
cg~ Your seeing some blue on the temp map but those keys change so watch that in comparing maps. It's really the anomilies you should watch since the tresholds for ENSO are based on that. He's a look from top to bottom (surface to deep in the depths. Warmer than normal pretty much through out.

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Quoting Patrap:


Remember to be careful if using Class C or other Home Fireworks this weekend,use Eye Protection and have plenty of water on hand also.

Always have Adults suprevising as well.
Sober Adults.



People of all ages get hurt badly every year nearly in every community. Please protect the young especially so!
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My Tropical Update on my blog.
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Quoting atmoaggie:
Same to you, Patrap! Shouldn't be much of a fire threat around here for fireworks. This rain we have had in the last few days is surely going to save the fireworks stand owners' businesses.

The trick is going to be getting dry fireworks, though.


Remember to be careful if using Class C or other Home Fireworks this weekend,use Eye Protection and have plenty of water on hand also.

Always have Adults suprevising as well.
Sober Adults.

Member Since: July 3, 2005 Posts: 426 Comments: 128668
Quoting cg2916:
Does anyone have a link for archived El Nino maps? I need to compare our current El Nino, with the 2004, 2006, and more El Nino years?


Link
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Good morning all.

Tropical Tidbit for July 3rd, and 2009 hurricane analog years
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Same to you, Patrap! Shouldn't be much of a fire threat around here for fireworks. This rain we have had in the last few days is surely going to save the fireworks stand owners' businesses.

The trick is going to be getting dry fireworks, though.
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720. Skyepony (Mod)
mid atlantic swirl
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I just completed a Tropical Update if anyone would like to view! Have an great 4th of July Weekend and remember what the 4th is all about!

TampaSpins Tropical Update
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Quoting Patrap:
Happy 4th of July Weekend..



Thank you, you too!
Member Since: June 29, 2009 Posts: 13 Comments: 5313
Quoting cg2916:

I don't think it will develop.


If it did it would be slow to occur. I think you do have to watch the Caribbean and GOM as shear will be lessening over the next few days and we have a tropical wave that is in the eastern Caribbean, if it holds together, will be in a favorable environment and will bear watching.
Member Since: June 29, 2009 Posts: 13 Comments: 5313
Happy 4th of July Weekend..

Member Since: July 3, 2005 Posts: 426 Comments: 128668
Quoting 2010hurricane:




The Non-Tropical Low

I don't think it will develop.
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Quoting cg2916:

Where in the Atlantic is the third one?




The Non-Tropical Low
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Quoting hurricaneman123:
3 areas i would pay attention to



1 by the lesser Antilles is under high wind shear 2nd one in the Caribbean might develop and the one in the Atlantic has the highest chance of development out of the 3

Where in the Atlantic is the third one?
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1st of all thats old it dates back to june 24th and 2nd of all No we have EL Nino forming

Quoting cg2916:
Wait a minute... do we have a forming La Nina?
Member Since: May 21, 2006 Posts: 5091 Comments: 115243
Quoting cg2916:
Wait a minute... do we have a forming La Nina?

I hope so and it look like it is
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Quoting cg2916:
Wait a minute... do we have a forming La Nina?


Not Really. The first chart is just SST. The second chart is the El Nino/La Nina chart.
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3 areas i would pay attention to



1 by the lesser Antilles is under high wind shear 2nd one in the Caribbean might develop and the one in the Atlantic has the highest chance of development out of the 3
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Wait a minute... do we have a forming La Nina?
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development is always possible when you have fronts off the east coast and in the GOM. Thats hurricane season for you.
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development possible in the next 72 hours
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Blog Update
Reflector site for those at work, which now also includes Weather456, daily updates


AOI

AOI
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Does anyone have a link for archived El Nino maps? I need to compare our current El Nino, with the 2004, 2006, and more El Nino years?
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Quoting atmoaggie:


Yep, was little intense here, yesterday. And there was a Covington blogger on here that had a tree on their house, power was down in a lot of places, etc.

I cannot imagine enjoying clinging to the underside of a tent (to keep it from flying or collapsing) at a festival during that.

Man that sucks. Got to feel bad for all of them just looking forward to a good weekend and trying to make a few dollars. Look slike we could have another day like that again this afternoon.
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Quoting potteryX:
DDR, heavy rain in Tobago here now. since 5:00 am, intermittent.
Strong gusts, squally conditions.
Word from central Trinidad, heavy rain.
About time too.......


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Quoting Patrap:
This occurred on the N. Shore of Lake Pontchartrain yesterday.30 Mile N of New Orleans.

Big Thunderstorm,

VIDEO: High winds from a thunderstorm mar opening of Mandeville Seafood Festival.

Hurricane force Winds.




Yep, was little intense here, yesterday. And there was a Covington blogger on here that had a tree on their house, power was down in a lot of places, etc.

I cannot imagine enjoying clinging to the underside of a tent (to keep it from flying or collapsing) at a festival during that.
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Quoting TampaSpin:
Things in the Tropics are starting to get interesting in about 4 days in the Caribbean and just East of the Caribbean.

The Caribbean has 2 items of interest. First a strong wave is located at 12N 62W ! It is currently under some strong 30-40kt shear but, forecast to move into better condition with about 15-20kts of shear. So this needs to be monitored. The Shear forecast shows the Caribbean to be better in some parts and worse in others for Tropical Development. The extreme NW Caribbean has low Shear, the Central will have 20-30kt, while the Eastern Caribbean is forecast for lower Shear also. The 2nd item in the Caribbean is an ULL to MidLevel Low in the NW Caribbean located at 18N 85W. This showing some signs of trying to possibly make it to the surface as it moves into the GOM. This needs to be watched very closely.

MY FAVORITE LOOP TO SEE EVERYTHING!

Click to loop..


Current Shear


Shear Forecast 3 days out click to loop....



That wave looks like a swooping bird or a jet
Member Since: September 30, 2007 Posts: 9 Comments: 15940

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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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