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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LMAO!

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444. beell
Quoting vortfix:




Not a chance in Hades Pal!



Texas, vort. Not Hades. Try to keep up!
Member Since: September 11, 2007 Posts: 141 Comments: 16213
440. i haven't heard from my buddy in a LONG time. in fact, it would be difficult for me to remember his last name. the funny thing is, he graduated from the College of Less Conservative Arts (as he called it) with a degree in Journalism, I believe, before they eliminated that college, I believe.
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what i would do for a 2 day soaker... the only thing is we cry about it raining all the time so we get drought. Now we cry cuz everything is drying up so I am afraid we will get a flood..lol! seems to be the way things happen here.. always extremes.. just look at me..haha!
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Quoting Levi32:


Ya whatever.....

Look at the 700mb moisture field at 144hours:



There is a chance.




Not a chance in Hades Pal!

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WO-S always puts together some of the best football teams.. a lot of talent there..

besides getting in random debates on politics fishing is what I do to manage the stress levels..lol!
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439. beell
Quoting vortfix:
Here's the 5 Day QPF Beell.

I'm not as smart as you but it does not look that optimistic to me!


Photobucket


It is far from a sure thing, and it is a week away so nothing is certain, but a little hope and slide to the west could make all the difference-and certainly not a drought buster.
Member Since: September 11, 2007 Posts: 141 Comments: 16213
Quoting singlehander:
So nice map of everything in the Atlantic, can we assume there there was nothing happening in the Pacific? Or did the weather not reach the west coast of Mexico?


There is enough of a ridge building west of the Baja Peninsula that storms will be directed NW, but if they form close enough to the coast like Andres they can still cause problems. It will all depend on the location of the storm when it develops.
Member Since: November 24, 2005 Posts: 635 Comments: 26547
435. unfortunately, the GoM looks like Hurricane fuel as of late!
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431. i had a buddy that played DT for West Orange Stark, i believe. come on down to H-Town and we'll go fishin'...assuming you like fishing :)

432. kudos, my friend :) LOL
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So nice map of everything in the Atlantic, can we assume there there was nothing happening in the Pacific? Or did the weather not reach the west coast of Mexico?
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Quoting vortfix:
Here's the 5 Day QPF Beell.

I'm not as smart as you but it does not look that optimistic to me!


Photobucket


Ya whatever.....

Look at the 700mb moisture field at 144hours:



There is a chance.
Member Since: November 24, 2005 Posts: 635 Comments: 26547
433. beell
Quoting Levi32:


Yeah the last few runs of the GFS have been seeing some sort of trough-split but in the form of a whole trough breaking off from a trough lol. It's that kind of a tail hanging back too that can cause tropical trouble near the SE US coast, but hopefully it provides rain for Texas.


How did I know you were going to say "trough split"?
(j/k)

Looks fairly mild for now-but could see some severe out of this over MS and LA.
Member Since: September 11, 2007 Posts: 141 Comments: 16213
I wasn't going to gloat, you guys, but I gotta tell ya, it feels good to get called a complete asset by some anonymous commenter every once in a while.

Thanks!
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Quoting pearlandaggie:
424. where ya located? i'm one of those terroristic extremists defined in that recent DHS report! LOL

ya im one of those right-winged extremist... I'm in Orange... over to your East...
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It's all about the ridge man!

It's building in very strong.

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OSSGSS-- i think i just LMBO!!
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Here's the 5 Day QPF Beell.

I'm not as smart as you but it does not look that optimistic to me!


Photobucket
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424. where ya located? i'm one of those terroristic extremists defined in that recent DHS report! LOL
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Quoting Levi32:


The east Pacific will likely have attention by next week with a possible storm forming there from all that building heat.

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LOL @ 422! it takes PROFANITY to get you banned at work?!?!?!? LOL...it's just mere site categorization at the workplace for me!
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Quoting TampaSpin:


Those that attached another will get banned...if you didn't attack anyone there should be no reason......Dr. Masters talked about the bill on his last blog.


ok cool... i dont think i attacked anyone.. lol! never been banned and dont wanna start now..

pearlandaggie-- i like ur viewpoints... you sound like me :)
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LOL @ 418! brilliant!
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please guys enough with the language... we want to keep this blog open for people at work... at least i want to access it from work... and that kind of stuff does get picked up... please respect others before using profanity in any form

thanks :)
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Quoting beell:
Maybe some hope for rain here. A shear axis or a trough (not sure how it will play out- stretching from S TX up through LA and MS.

Both valid Thursday, July 9th
18Z GFS 500mb


18Z 850mb


Yeah the last few runs of the GFS have been seeing some sort of trough-split but in the form of a whole trough breaking off from a trough lol. It's that kind of a tail hanging back too that can cause tropical trouble near the SE US coast, but hopefully it provides rain for Texas.
Member Since: November 24, 2005 Posts: 635 Comments: 26547
Quoting SomeRandomTexan:
I got a feeling we all gonna get banned tonight... and just over a healthy debate...


Those that attached another will get banned...if you didn't attack anyone there should be no reason......Dr. Masters talked about the bill on his last blog.
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415. wouldn't be the FIRST TIME! LOL
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Humm, there may be something to Lurking.



And now for something completely different but related
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Quoting thunderblogger:
I'm out of here, people like hunkerdown and atomicaggie are why I'd rather lurk than take part, complete asses.
Its actually the complete asses who use this blog as official weather info (when there is far better out there) instead of what this is, a BLOG.
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Quoting hunkerdown:
Oh, and considering us South Floridians were in extreme drought conditions till recently, I can tell you that with our climate not being that far off from SE Texas, it is not a given that an ULL will bring any rain, significant or not.


Well it's never a given, and if it's just a 200mb low like this one is, it may not generate showers, but ULLs that extend down to 500mb will almost always cause thunderstorms in Texas in the summertime.
Member Since: November 24, 2005 Posts: 635 Comments: 26547
I got a feeling we all gonna get banned tonight... and just over a healthy debate...
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414. beell
Maybe some hope for rain here. A shear axis or a trough (not sure how it will play out)- stretching from S TX up through LA and MS. Along with another stalled frontal boundary along the northern gulf coast. The gulf is open over TX. It has been a while.

Both valid Thursday, July 9th
18Z GFS 500mb


18Z 850mb
Member Since: September 11, 2007 Posts: 141 Comments: 16213
406. just don't send any of that VORTICITY OUR WAY this season...i think i've paid my vorticity fees for at least the next 5 years! LOL
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Quoting hunkerdown:
Oh, and considering us South Floridians were in extreme drought conditions till recently, I can tell you that with our climate not being that far off from SE Texas, it is not a given that an ULL will bring any rain, significant or not.
please chill man... Levi knows his stuff and is GOOD! and the climates here in Texas is substantially different
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408: Nevermind, not worth the keystrokes. I don't have to respond. This crosses that line in the sand, though. See ya in 24 hours.
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Oh, and considering us South Floridians were in extreme drought conditions till recently, I can tell you that with our climate not being that far off from SE Texas, it is not a given that an ULL will bring any rain, significant or not.
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398. well, considering neither you or me have a working relationship, i will take that to mean someone else! if i'm banned and you never remember anything i've said...remember this--never stop asking questions regardless or HOW RIDICULOUS they may seem!

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I just checked and there is an area of elevated 850mb vorticity in the area I mentioned in the east Pacific that is most likely to develop.

Member Since: November 24, 2005 Posts: 635 Comments: 26547
Unfortunately the strong ridge will cut-off the moisture to Central/SE Texas.

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This is all friendly debate.. nobody get mad at anybody... It's just to foster thought... I don't think any of this is aimed at anyone... :)
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Quoting hurricane2009:


Dish it out? I never talk about politics on this site, EVER, but sometimes you just have to respond.

I would like to move on to talk about something weather-related, but that aint going to happen I guess.


I was talking about smart-a$$ comments with that. Not politics.

And I was teasing you!
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Quoting bappit:
maybe when that wave gets to the east Pac


All these waves crossing over are adding to the heat pool. The area of low to mid-level turning near 10N between 85W and 90W is what is most likely to develop.

Satellite Loop
Member Since: November 24, 2005 Posts: 635 Comments: 26547
The ridge is building in so strong...it will effectively cut-off the CONUS from any possible development.
At the same time the pressure gradient that will amp up through the Caribbean will shear anything to death!

Nowhere to go but the EPAC!

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TampaSpin--

hopefully that wave will fire back up tonight like it did last night.. could get interesting in a couple of days
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Quoting hunkerdown:
ULLs are not drought busters. ULLs are not a given to produce any rainfall.

If people want to know specific questions, and I am not sure that thunder did, maybe it should have been asked if the ULL will bring any needed relief to the drought stricken areas of Texas. Or maybe even check in with the local NWS.


An upper low in Texas would almost certainly result in afternoon showers given their climate, and I knew why he asked his question without him even mentioning the drought.
Member Since: November 24, 2005 Posts: 635 Comments: 26547

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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.