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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1047. Levi32
Quoting K8eCane:


ok thanks Levi
he just used to be here a lot
are you still thinking some sort of low off Carolinas next week?


I think we'll see a low try to develop on the tail of that front, but whether it becomes warm-core or not is something we won't know until it happens.
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we used to have a whole family of coons and foxes come up and feed on our back patio.. they are so funny to watch!

rabies eek!
Member Since: August 30, 2007 Posts: 0 Comments: 1857
Thanks KEH! I'll remember that on July 4th and will raise a toast to "our" lil' sister state (yeah I'm in NC).
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1044. Ossqss
I know we all joke about Cantori, but did you know this

And gone, after doing a Raccoon check outside since I had one that we caught with rabies this AM.

If you see them during the day, stay away.


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Quoting willdunc79:
KEHCharleston can you please please tell me why is that tree and crescent moon the SC state symbol? Nobody has been able to tell me why as of yet?

Yep
Great question for Independence Day.

On June 28, 1776 (Carolina Day), one of the most decisive Patriot victories was fought on Sullivan's Island which forms a part of our harbor. The fort was hastily constructed of palmetto logs and sand. Pretty spongy walls - which worked to absorb the impact of the cannon balls.

The Crescent Moon in British heraldry stands for a second son. It was a reminder to the British that they were firing on their own.
Also, many of the early planters (investors in the colony) were second sons of families of the nobility. First sons inherited the ancestral lands - so these second sons wanted to set up their own estates - and had the money to do so.

ADDED

The crescent moon was used with the word Liberty on the flag that flew during the battle. The Palmetto tree was added later. It is one of the most recognized state symbols I have been told.

After the victory, messengers were sent to Philly where the Continental Congress was convened - took about a week. The message was that the British could be defeated. The Continental Congress was working on a Declaration the would state our independence from England. The rest is history, so when you raise that toast on the 4th - do not forget to raise one for us here in the Palmetto State.

SC fought more battles (except for NY, I believe), lost more lives (per capita) and spent more money in the cause of Independence, than any other colony
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1042. BtnTx
Quoting Ossqss:


LOL, hummmm~ :P

Nightall --

Try this, Keh Urban dictionary

-Thanks Ossqss, I am old & still learning, night all..
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KEHCharleston can you please please tell me why is that tree and crescent moon the SC state symbol? Nobody has been able to tell me why as of yet?

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KEH you made my night! ROFL!!!
Member Since: August 30, 2007 Posts: 0 Comments: 1857
Ossqss - Was just kidding (or should I say j/k).
However, I often have to puzzle out the short hand. Thanks for the link - I just book marked it!

MODIFIED: I did not have a TV hooked up to cable - no weather channel. When I first started reading this blog, folks kept talking about a Cantori. It was a term with which I was NOT familiar, and I just could not figure out what a Cantori was. - true story
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1038. scott39
the wave in the carrb is moving fast 30mph.
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1037. Ossqss
Quoting KEHCharleston:
Laugh Out Loud!
Yikes, I thought it meant Lots Of Luck


LOL, hummmm~ :P

Nightall --

Try this, Keh Urban dictionary
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1036. GBguy88
What are the odds that blob over the Yucatan could drift into the Bay of Campeche and cause trouble?
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1035. scott39
is the wave at 60w starting to encounter that westerly shear?
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1034. BtnTx
My wife just told me that LOL also means Lots of Luck. Wishing Good Weather to all
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Laugh Out Loud!
Yikes, I thought it meant Lots Of Luck
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Quoting presslord:
K8....You didn't say "the Carolinas", did you?


Out to sea garbage...
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1031. Ossqss
Quoting BtnTx:


LOL Example: very funny ??? LOL



Hummm, I saw a commercial once that said, laughter adds 8 years to you life. I will take that risk :)


Give Your Body a Boost -- With Laughter
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1030. Patrap
Though well to the west of Federic,NOLA remembers the Storm well as it was a Narrow turn off the Mouth of the River as He Slid NNe to Mobile..that spared us.

Federic was also a Large Hurricane as well...with a Big Wind Field
Member Since: July 3, 2005 Posts: 426 Comments: 128645
1029. beell
YW Homeless!
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1028. beell
Quoting BtnTx:
LOL why do so many bloggers post stuff that has nothing to do with laughing and include LOL very often LOL ?? LOL


Probably at least three reasons.
1. LOL I think you're an idiot
2. LOL Anything I say is certainly up for discussion and is not posted as gospel.
3. LOL I think something is funny

LOL
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1027. scott39
patrap thanks for the radar loop on fredric. we had just moved to mobile sept 1st of 79. I was a 10 year old kid and didnt now what to expect. That night was the most terrifing night of my life.Outside our house sounded like trains going over us.I had heard years later that there were 220 tornadoes.Fredric ripped mobile and mobile county where we lived, like a buzz saw.Ive been hooked ever since.
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1026. BtnTx
Quoting ALCoastGambler:
LOL not that old. barely remember the hurricane....lol


LOL Example: very funny ??? LOL
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Thanks for that outlook Beell.
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1024. Ossqss
Sometimes you need to Laugh Out Loud .....


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TWC classic documentary

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1022. BtnTx
LOL why do so many bloggers post stuff that has nothing to do with laughing and include LOL very often LOL ?? LOL
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K8....You didn't say "the Carolinas", did you?
Member Since: August 13, 2007 Posts: 0 Comments: 10492
1020. K8eCane
Quoting Levi32:


He left WU a while back.


ok thanks Levi
he just used to be here a lot
are you still thinking some sort of low off Carolinas next week?
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1019. Levi32
Quoting K8eCane:
whatever happened to Weatherguy03?


He left WU a while back.
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hey haboobs... look at the shear tendency map.. shear will be decreasing in carrib.. the thing has been getting sheared the whole time and it still keeps ticking
Member Since: August 30, 2007 Posts: 0 Comments: 1857
1017. beell
Evening, bloggers-a few un-solicited opinions:
On the large scale, a few changes ahead towards the middle of next week. There has been a good model signal of a more zonal (west to east) flow at the mid and upper for quite a few runs. Always easy to get ripples in this zonal flow in the form of a short wave or vort max.
The first shortwave to give a slight chance of rain over TX and a better chance for points east early next week and beyond. The first of at least one of the potential areas of interest as it makes its way off the east coast.

The zonal pattern should end the constant E coast troughing and allow a strong appearance of the low level A/B high-or at least the Bermuda portion along and south of the southern edge of the upper flow. The ridge axis running somewhere along 30N from the western ATL to west TX. Ridge-building north towards the Great Lakes. For the first time in a while, strong return flow off the Gulf. An uptick in severe over the central plains might also accompany these changes.

The Sonoran ridge still in place advecting hot, dry air on a more SW to NE trajectory around the western periphery of the low level ridge. A short-term heat wave developing over the northern plains and the midwest towards the end of next week as this airmass slowly creeps up around the ridge. Hot Chicago?

If I had to guess how this would affect steering for any lower-latitude tropical distubance? Without the benefit of an east coast trough, it would go due west till it rounded the ridge.

Somebody else can suggest when we might see that (lol).
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It looks like Ull is going to run out of time when it hits that penninsula.
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1015. K8eCane
whatever happened to Weatherguy03?
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Quoting SomeRandomTexan:
impressive maps there homeless!!
you have been doing some digging today! good work! It would have been amazing to stay through Rita... just seeing how all the mighty pines were snapped like matchsticks was amazing... that storm had some furry...


Lol. Yeah I been digging. Don't think I'm brave enough to have gone through that one. But I did find somthing that explained a lot.

During the early morning hours, the eye of Rita passed east of Jefferson County as it moved over Orange County. Winds rapidly shifted from northwest to southwest and weakened. Water levels at Port Arthur were beginning to decrease. Water levels at inland river sites, on the other hand, continued to rise during the morning of the 24th, and crested during the afternoon.

By that time she'd already broke and pushed all the trees to the south. Yep she wasnt nuttin nice!

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it goes from nothing to a semi spiraled band... could be an interesting feature to watch over the next couple of days to see if it makes it to the surface.. looks to move Nw until bumps against the High then back to the SW..
Member Since: August 30, 2007 Posts: 0 Comments: 1857
The best shot for something is the wave just north of SA. Even that has basically no shot because it is about to get destroyed by shear.
Member Since: May 20, 2009 Posts: 0 Comments: 1640
Quoting TampaSpin:
Zoom in here too.....Keep in mind this is in the ULL....not saying it will develop but, the possiblity could happen if this keeps going...

Link

Dang you had me excited that something real might be out there. That ULL is weak and wont form anything. I wouldnt hold your breathe on it. It looks like nothing for the next week or so.
Member Since: May 20, 2009 Posts: 0 Comments: 1640
I see what your saying Tampa... and it is firing some t-storms... the area it is ripe for development...
Member Since: August 30, 2007 Posts: 0 Comments: 1857
Zoom in here too.....Keep in mind this is in the ULL....not saying it will develop but, the possiblity could happen if this keeps going...

Link
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Quoting SomeRandomTexan:
how so Tampa?


Its currently an Upper Level Low....i believe this might try to work its way down to a surface LOw in time.....It just appears to be the type that would do such a thing.....Look at this loop South of the Western Tip of Cuba......Link
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Quoting KEHCharleston:
954. KEEPEROFTHEGATE
Thanks. Hope Canada Day was super!

Has anyone seen Cotillion on the blogs lately?

havent seen him in a while
Member Since: August 30, 2007 Posts: 0 Comments: 1857
954. KEEPEROFTHEGATE
Thanks. Hope Canada Day was super!

Has anyone seen Cotillion on the blogs lately?
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I would love to see things get interesting in a couple of days. I am ready for something good to track and forecast out.
Member Since: May 20, 2009 Posts: 0 Comments: 1640
how so Tampa?
Member Since: August 30, 2007 Posts: 0 Comments: 1857
impressive maps there homeless!!
you have been doing some digging today! good work! It would have been amazing to stay through Rita... just seeing how all the mighty pines were snapped like matchsticks was amazing... that storm had some furry...
Member Since: August 30, 2007 Posts: 0 Comments: 1857
Evening everyone.....everything in the Caribbean is in the Mid and Upper level Lows. The ULL located at 18N 85W is starting fire up around the Low.....This could get very interesting in a few days!

Link
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1001. Ossqss
Just helpin to turn the page. L8R
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Quoting jeffs713:

Ike hit the Turks and Caicos Islands as a Cat 4, and also hit Cuba as a Cat 4.

Also... Ike put out a heck of a lot of damage for "just a cat 2". Check out my current blog for some examples.


Yes he did. That was one terrible Cat 2.
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Quoting StSimonsIslandGAGuy:
Ike wasn't a major hurricane. He was 'just' a two.

Ike hit the Turks and Caicos Islands as a Cat 4, and also hit Cuba as a Cat 4.

Also... Ike put out a heck of a lot of damage for "just a cat 2". Check out my current blog for some examples.
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Quoting SomeRandomTexan:
albeit that 1 of the strongest canes to hit the area was in an El Nino year and that was Hurricane Audrey i think it was 1957


If ever there was an argument of pressure vs category this might just be it. I was amazed at the comparisons. Almost mirror images.

audrey

audrey/rita
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A few hours old (the link ), but lots of busy and odd looking stuff going on up there Kman, for sure.

Link
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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.