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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2247. Levi32
Quoting HurricaneJoe:


So this thing could develop? Please, enlighten me, I'm only 18. Don't know much about what they're going to do.


We youngins need to have faith in ourselves =D I'm 17 myself lol. Here this is my posts from earlier explaining what's going on:

Quoting Levi32:
Let me try explaining this. Look at the upper winds. There is a TUTT (basically upper trough) positively tilted through the Central Caribbean and extending north of Hispaniola. Look on the east side of this trough near and north of Hispaniola and Puerto Rico. See the batch of strong wind barbs pointing NE? That is creating upper divergence over the tropical wave that is taking air out of the top of the system. Since air is being taken out of the top air has to rise from the bottom to replace it. The rising air condenses and forms all those thunderstorms that makes it look so menacing. At the same time there is 30-40 knots of shear over the entire central/eastern Caribbean due to the upper trough. Just because a tropical wave has thunderstorms doesn't always mean it is a threat to develop. In this case it is not, at least for the next 2-3 days.


To add to that, even though the divergence aloft is enhancing thunderstorm activity, the shear that accompanies it is causing t-storms to collapse, come back in another area, collapse, pop up again, etc...the cycle never ends because the tops of the thunderstorms get blown apart by the shear. You need sustained convection that is allowed to grow, which requires light winds aloft (light wind shear). Once you get that, you can get a surface low and a more organized system. Right now this tropical wave is not organized. It is a well-defined wave but until it gets into a more favorable environment aloft that is all it will be, and a rainmaker for Caribbean countries.


Also, easterly trade winds in the Caribbean are very fast right now and that ruins surface convergence, which makes it very hard for tropical waves to amplify. That alone makes me think it won't develop, without even thinking about upper-level conditions. I don't think it's a threat until it gets into the eastern Pacific.

[edit] - here's the link to the upper-level winds I was refering to above.
Member Since: November 24, 2005 Posts: 635 Comments: 26700
Quoting Levi32:
The only thing in the upper levels in the Caribbean is a TUTT that is currently shearing that tropical wave. There is no spin of any kind associated with the wave.


So this thing could develop? Please, enlighten me, I'm only 18. Don't know much about what they're going to do.
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2245. Levi32
The only thing in the upper levels in the Caribbean is a TUTT that is currently shearing that tropical wave. There is no spin of any kind associated with the wave.
Member Since: November 24, 2005 Posts: 635 Comments: 26700
2244. scott39
tampa spin what does way up in the upper levels mean?
Member Since: June 13, 2009 Posts: 0 Comments: 6912
The Spin in the Caribbean is way up in the Upper Levels....Good Morning everyone!
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2242. scott39
Quoting Levi32:
By definition that system already is TD 3-E. I have no idea why they're not classifying it yet. If they wait too long it will skip straight to TS. Maybe they won't even name it then...
Member Since: June 13, 2009 Posts: 0 Comments: 6912
2241. Levi32
By definition that system already is TD 3-E. I have no idea why they're not classifying it yet. If they wait too long it will skip straight to TS. Maybe they won't even name it then...
Member Since: November 24, 2005 Posts: 635 Comments: 26700
Quoting tennisgirl08:
Ha! Yes, today. Maybe he will post about possibilities for the latter part of July.


Or the possibility of this wave in the Caribbean developing?
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Ha! Yes, today. Maybe he will post about possibilities for the latter part of July.
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Quoting tennisgirl08:
I wonder what Dr. Master's post will be about tomorrow??

You mean today lol.
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94E is on its way to be TD 3E
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I wonder what Dr. Master's post will be about tomorrow??
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Quoting CybrTeddy:


Mornin here lol. Im about to hit the hay! Night all

Have fun sleeping with the bedbugs unless you really mean your sleeping in a haysack.
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Can we just hit the Atlantic pinata and see if a hurricane pops out.Heck no!
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Quoting CybrTeddy:


Mornin here lol. Im about to hit the hay! Night all


Good night.
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Quoting RitaEvac:
Nothing is going to happen for another week. Now other story is this.... hot and extremely dry in TX, driest ever seen in most areas of the Gulf coast. Expect a storm to hit TX starting now and on into September. Expect torrential rains. It's a fact when the TX coast burns up a storm will arrive.....ladies and gentlemen sit back in awe and watch it evolve


what is sad is your right...lol.. the year of Rita we saw a very similar situation here in SeTx.. Hot and dry.. looks like we are fixing to get a break in the weather though... rain possible this week!!!!!!!
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Quoting KoritheMan:


Good evening Cyber.


Mornin here lol. Im about to hit the hay! Night all
Member Since: July 8, 2005 Posts: 259 Comments: 24578
Never realized the La Nina of 1988 was so strong:



Never seen anything like that before.
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2227. Levi32
ECMWF/GFS 8-10 day 500mb comparison. East coast trough and negative NAO remain the central features of the Atlantic long-wave pattern.

Member Since: November 24, 2005 Posts: 635 Comments: 26700
Seems like the Carribean can't poop out a hurricane.IT'S CONSTIPATED!
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Quoting CybrTeddy:


Agreed, I doubt we'll see development, atleast in the next week, from this system. Or really, anything out there.


Good evening Cyber.
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Quoting KoritheMan:


While it is true that perhaps Drak should not have made such an assertion (given that our forecasts 10 days out are still iffy at best), I respectfully disagree that the Caribbean wave is going to develop, at least over the next few days. If it enters the Eastern Pacific, it may find a favorable upper wind environment to take advantage of then, at which point it would not be a surprise at all to see it become a tropical cyclone.

And even if this wave were to enter the Gulf of Mexico, shear only briefly becomes favorable.


Agreed, I doubt we'll see development, atleast in the next week, from this system. Or really, anything out there.
Member Since: July 8, 2005 Posts: 259 Comments: 24578
Quoting KoritheMan:


...The rain. >_>

I know it's a joke.I know how you feel like when I was begging for rain a month ago with the Florida drought.
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Quoting StormFreakyisher:

A man shouting for help?


...The rain. >_>
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Quoting KoritheMan:


Here's to hoping for it in southeastern Louisiana as well...

A man shouting for help?
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Quoting RitaEvac:
Here in TX this is what were all waiting for...



God?
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Quoting RitaEvac:
Here in TX this is what were all waiting for...




Here's to hoping for it in southeastern Louisiana as well...
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Here in TX this is what were all waiting for...


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2217. Levi32
Quoting StormFreakyisher:

If it is not a threat to land than might as well not watch it, at least for me.Unless it you want to track it and study it or whatever.I leave that up to NHC's job.My job is to TRACK ANYTHING a THREAT to land especially me lol.


That's understandable, but Meteorologists track everything. I enjoy trying to forecast a storm even if it's out in the middle of nowhere. The fascinating aspects of the weather are present everywhere, not just close to the coast.
Member Since: November 24, 2005 Posts: 635 Comments: 26700
Quoting Levi32:


Most of the time yes, but not all the time. And it doesn't have to be a threat to land for it to be worth watching.

If it is not a threat to land than might as well not watch it, at least for me.Unless it you want to track it and study it or whatever.I leave that up to NHC's job.My job is to TRACK ANYTHING a THREAT to land especially me lol.
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Quoting Levi32:


Most of the time yes, but not all the time. And it doesn't have to be a threat to land for it to be worth watching.


This. lol

Look at it this way SF: 94E in the Eastern Pacific is on the verge of becoming a tropical depression. It probably isn't going to be a threat to land, but does that mean that it isn't worth watching? Hardly.

I would like, SF, for you to give me one good reason as to why a fish storm doesn't bear watching.
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2213. Levi32
Quoting StormFreakyisher:

Yeah but the ones that form off the fonts this time of the month move off to the northeast if they develop and become fish storms right?


Most of the time yes, but not all the time. And it doesn't have to be a threat to land for it to be worth watching.
Member Since: November 24, 2005 Posts: 635 Comments: 26700
2212. Patrap
Well..when sumthing gets to 90 West and Moving North,..I'll panic then.

Im prepared as could be and have a Good plan always.



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Quoting StormFreakyisher:

Yeah but the ones that form off the fonts this time of the month move off to the northeast if they develop and become fish storms right?


Usually, but not always.

Why are you hoping for a landfall, anyway?
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2210. Levi32
Quoting StormW:


Just came back on.


Just playin.....good evening by the way lol.
Member Since: November 24, 2005 Posts: 635 Comments: 26700
Patrap let me borrow his Voodo stick and I'm telling you all its coming, the Saving Grace of torrential rains will come to us.
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2208. Patrap
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Quoting StormW:
Which wave is everyone bickering about?
this one Link
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Quoting StormW:
Which wave is everyone bickering about?


The one about to enter the central Caribbean.
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Quoting Levi32:


Not really. 93l formed from a mid-level low that moved north from the eastern pacific and interacted with a tropical wave that was much farther north than the current wave near the Nicaraguan coast. It will be in the eastern Pacific within 36 hours where it has better chances to develop.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The only area where I think we could see anything of remote interest over the next week will be off the SE US coast as old fronts get dragged through there. We could get cyclogenesis at the tail-end of those fronts and depending on how things evolve we might see something try to go warm-core.

Yeah but the ones that form off the fonts this time of the month move off to the northeast if they develop and become fish storms right?
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Nothing is going to happen for another week. Now other story is this.... hot and extremely dry in TX, driest ever seen in most areas of the Gulf coast. Expect a storm to hit TX starting now and on into September. Expect torrential rains. It's a fact when the TX coast burns up a storm will arrive.....ladies and gentlemen sit back in awe and watch it evolve
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2202. Levi32
Quoting StormW:
Which wave is everyone bickering about?


You mean you can't figure it out? lol....the one south of Hispaniola.
Member Since: November 24, 2005 Posts: 635 Comments: 26700
Quoting btwntx08:

thats not right to say that i say something will form and its in the carribean right now!


While it is true that perhaps Drak should not have made such an assertion (given that our forecasts 10 days out are still iffy at best), I respectfully disagree that the Caribbean wave is going to develop, at least over the next few days. If it enters the Eastern Pacific, it may find a favorable upper wind environment to take advantage of then, at which point it would not be a surprise at all to see it become a tropical cyclone.

And even if this wave were to enter the Gulf of Mexico, shear only briefly becomes favorable.
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2199. Levi32
Quoting scott39:
Thanks levi i learned something. would you say this wave is toast, or if not what would you give it % wise in next couple of days?


Member Since: November 24, 2005 Posts: 635 Comments: 26700
The Big storm is still yet to come.Don't know when but it's coming."The calm before the storm" applies to this,sorry.Do fireworks play a role in fireworks?No I don't mean does weather play a role in fireworks.I MEANT what I MEANT!LOL!Like so much smoke is emitted in our atmoshphere on 4th of July does it enhance cloud development,rain?Or does it make temperatures cooler with all the smoke or what?
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2197. Patrap
.."I gotta tell ya Folks,this Wave is Impressive for early July"..

..Back to you in the Studio.

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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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