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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Hurricane David's landfall in Southeast Florida on September 3-4, 1979. The loop is from the Miami, Florida WSR-57 radar and shows the approach of David from the Western Bahamas to landfall near Palm Beach, Florida. David made landfall as a Category Two with sustained winds of 100mph and a minimum central pressure of 970mb(28.64in). During the previous week, David had made disasterous landfalls at both Dominica and in the Dominican Republic, where the storm was near Category Five intensity.

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Here are some really cool radar loops of Hurricane Frederic's landfall at the Alabama/Mississippi border on September 12, 1979. The loops are from the Mobile, Alabama WSR-57 radar. The first is a long-range loop, the second a short-range close up. Frederic made landfall as a strong Category Three with sustained winds of 130mph and a minimum central pressure of 943mb(27.85in). At the time, Frederic was the costliest hurricane in U.S. history.

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Quoting StSimonsIslandGAGuy:


Well 1992 was an El Nino year and we got Andrew...


and he was a beast!
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Quoting jeffs713:
I have to ask a dumb question, at the risk of being flamed...

Why do some bloggers here *want* a storm to form? I just don't understand why someone wants destruction on that scale.


I dont think anyone wants destruction... at least i don't... I think it is more of the fascination of watching something spin up from a few clouds... I have a love for how mother nature does things.. Its a good question man... u probably wouldn't be here though if you didn't have the same fascination.. jmo
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Quoting jeffs713:
I have to ask a dumb question, at the risk of being flamed...

Why do some bloggers here *want* a storm to form? I just don't understand why someone wants destruction on that scale.


I can't speak for everyone here but I think quite a few of us, including myself, want a storm to form that just stays out to sea and doesn't affect anyone for something to watch.
LOL! at Teddy!

the tropical wave in SeCarrib is doing well... still getting sheared but keeps the convection coming.. if it can keep holding together we could see something there.
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I have to ask a dumb question, at the risk of being flamed...

Why do some bloggers here *want* a storm to form? I just don't understand why someone wants destruction on that scale.
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Quoting KoritheMan:


I am your father!


You don't know the power of the GFS!
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Here's a cool map to play with.

Link
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Quoting CybrTeddy:
Watch the ole star wars movies.
Dang, do they ever get old? Empire Strikes back is amazing!


I am your father!
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Quoting btwntx08:

finally they shaded aleast purple where are aoi in the eastern carribean

I like these people
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more likely for development for our AOI in SE carib
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927. 11117
Hopefully July remains inactive.
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Dr.Masters Sept 2008 entries.
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From Dr. Jeff Masters October 27th 2008 Blog Entry


Heavy Internet weather

A record six consecutive tropical storms and hurricanes pounded the U.S. this hurricane season, creating some serious "Internet weather"--a flood of high Internet traffic. On September 12, as Hurricane Ike bore down on the Texas coast, our popular weather web site wunderground.com recorded its busiest day ever--28 million page views, triple its normal traffic. We vaulted from a ranking of 107th to 75th on the Quantcast, Inc. list of most-trafficked web sites in September, thanks to the huge amount of web traffic created by Tropical Storm Fay, Hurricane Gustav, Hurricane Hanna, and Hurricane Ike. As hurricane season winds down, so has our ranking--we're down to 138th on the list of most-trafficked web sites. The ranking will rise again as we enter winter and winter storms begin pounding our population centers.
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Watch the ole star wars movies.
Dang, do they ever get old? Empire Strikes back is amazing!
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SomeRandomTexan

If El nino continues to build then it usually is more difficult to get Texas hurricanes from what I understand.. There are gurus like Weather456, Levi and Scottsvb and others who could really give you more info. The longer this high pressure stays over us here in SeTx the longer it will be before any chance of a storm.

Any storm in the Gulf under favorable atmospheric conditions SHOULD bomb out.. the water temps are insanely hot and running about 2 degrees above normal

Yeah, but I can't think that for as long as we have had the high,that it go away eventually and then there you go - open opportunity.
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You never know what can happen with the tropics though. Lower chance isn't no chance, so I have to agree with most people here and we need to watch.

As for the Caribbean AOI... Even so, there's a ton of shear despite the fact that it's lowering. It's worth watching somewhat but it's doubtful that anything will come out of it.

Of course, since I said it it'll probably form, lol
Quoting homelesswanderer:


Your welcome. Yeah I've heard a lot of people say that the risk to the gulf coast is lower. And that may be so. But since the NWS says ENSO makes no difference in our number of hits I guess we need to be vigilant every year. I think it basically comes down to the position of the Bermuda high. And from what I understand its supposed to be weaker and bigger similar to the 2008 set up. But we can't tell how big or what position it will be in too far in advanced. So I'd say everyone needs to keep an eye on things.


right on! I'm hating this pesky high that's over us now... we could use it later on in the season.. not so early
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Quoting SomeRandomTexan:
interesting Homeless!!

I wonder why everyone on here thinks otherwise? like Levi said though if a Storm comes from the carrib it can escape the east coast troughs and head west into the GOM...

Wow! Thanks for digging that up


Your welcome. Yeah I've heard a lot of people say that the risk to the gulf coast is lower. And that may be so. But since the NWS says ENSO makes no difference in our number of hits I guess we need to be vigilant every year. I think it basically comes down to the position of the Bermuda high. And from what I understand its supposed to be weaker and bigger similar to the 2008 set up. But we can't tell how big or what position it will be in too far in advanced. So I'd say everyone needs to keep an eye on things.
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Quoting Makoto1:


Oh, I know. It was bad enough being a 2 since it was so large... I know people in Houston (and my boyfriend was visiting family in Houston around that time too, which scared me), so I was watching closely. And hearing that Branson got damage doesn't shock me, it was a Tropical Storm all the way into Missouri, then became a strong extratropical low for Kentucky, Indiana, and Ohio to deal with.

I actually almost came on here then while the winds were going strong but I was afraid I'd blow out the circuit, lol


haha! its amazing how some of these storms just don't die.. they have a mind of their own...lol!
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Quoting SomeRandomTexan:


we evacuated to branson, missouri and there was quite a bit of damage there as well... over turned trailers and downed trees... I can only imagine if that storm came in as a 3 or 4


Oh, I know. It was bad enough being a 2 since it was so large... I know people in Houston (and my boyfriend was visiting family in Houston around that time too, which scared me), so I was watching closely. And hearing that Branson got damage doesn't shock me, it was a Tropical Storm all the way into Missouri, then became a strong extratropical low for Kentucky, Indiana, and Ohio to deal with.

I actually almost came on here then while the winds were going strong but I was afraid I'd blow out the circuit, lol
Quoting futuremet:
For those of you who want more access to the ECMWF--click here


Nice find!
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Quoting Makoto1:


Yeah, we sent most of our people down. They weren't even forecasting tropical storm-force winds here until 8AM that morning, 3 hours before it all hit. We ended up with sustained winds of around 65 mph, gusts to 75-80 mph. Now I was lucky because my little section of town is located on a separate power grid, so the worst effects at my house were power flickering and tons of small branches in the yard. It was quite a sight though...


we evacuated to branson, missouri and there was quite a bit of damage there as well... over turned trailers and downed trees... I can only imagine if that storm came in as a 3 or 4
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interesting Homeless!!

I wonder why everyone on here thinks otherwise? like Levi said though if a Storm comes from the carrib it can escape the east coast troughs and head west into the GOM...

Wow! Thanks for digging that up
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Quoting SomeRandomTexan:


A friend of mine got dispatched by the energy company from ohio down to texas... as soon as he got here they received another dispatch telling them they had to go back to ohio to repair lines there. poor guy was quite frustrated since he has family here and was excited to see them


Yeah, we sent most of our people down. They weren't even forecasting tropical storm-force winds here until 8AM that morning, 3 hours before it all hit. We ended up with sustained winds of around 65 mph, gusts to 75-80 mph. Now I was lucky because my little section of town is located on a separate power grid, so the worst effects at my house were power flickering and tons of small branches in the yard. It was quite a sight though...
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


From our NWS in Lake Charles

Possible Effects of ENSO (El Niño/Southern Oscillation)

Years of moderate to strong warm ENSO events were checked for any possible relationship with tropical cyclones affecting Louisiana and southeast Texas. These warm events seemed to have no significant correlation to an increase or decrease in tropical storms and hurricanes entering the area; it has been recently discovered though that it does make a difference further down the Texas coast.

Unexpectedly, ENSO events seemed to have a strong correlation to major hurricanes in this area. Five of the eight major hurricanes struck the region during the middle of moderate to strong El Niño events. If one expands the criteria to within one year of a moderate ENSO seven of eight become included. Further study is needed to totally resolve this issue.


Link
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Quoting Makoto1:


lol That reminds me... My mom actually forgot that Ike hit Texas. She remembered the damage it caused in Ohio but forgot about the coming from Texas part...


A friend of mine got dispatched by the energy company from ohio down to texas... as soon as he got here they received another dispatch telling them they had to go back to ohio to repair lines there. poor guy was quite frustrated since he has family here and was excited to see them
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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
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Quoting homelesswanderer:


Yes. I've noticed that. I think after Ike everybody is pretty on edge this time of year. Cuz they just won't stop coming. Lol. Geesh.


lol That reminds me... My mom actually forgot that Ike hit Texas. She remembered the damage it caused in Ohio but forgot about the coming from Texas part...
Quoting TexasHurricane:
SomeRandomTexan

I wonder if that means we will have a hurricane....LOL


If El nino continues to build then it usually is more difficult to get Texas hurricanes from what I understand.. There are gurus like Weather456, Levi and Scottsvb and others who could really give you more info. The longer this high pressure stays over us here in SeTx the longer it will be before any chance of a storm.

Any storm in the Gulf under favorable atmospheric conditions SHOULD bomb out.. the water temps are insanely hot and running about 2 degrees above normal
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Quoting SomeRandomTexan:
Hey homeless--

seems like there are more and more Texans getting on the blog here of late...


Yes. I've noticed that. I think after Ike everybody is pretty on edge this time of year. Cuz they just won't stop coming. Lol. Geesh.
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Okay so I've been looking at the temperatures in the Gulf and wow. There are two large warm eddy's that are expanding everyday. Anything that comes into the gulf with a llc and little shear will absolutely explode into a category 3. I'm talking Humberto-style. I hope I made some people happy.
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SomeRandomTexan

I wonder if that means we will have a hurricane....LOL
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Quoting SomeRandomTexan:


"High Pressure"


See? Lol
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Hey homeless--

seems like there are more and more Texans getting on the blog here of late...
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Quoting charlottefl:
Wow, can you say High pressure:




"High Pressure"
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Quoting charlottefl:
Wow, can you say High pressure:




Lol. We been singing that same tune for months in Texas now.
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Wow, can you say High pressure:


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AOI in the carrib will have a better shot I think... I'm not sure why the NHC isn't recognizing it.. the further it gets into the Western Carrib the better chances it will have... shear is decreasing but is still blowing off the convection right now
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well shear is decreasing
Link
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cycloone

yeah, I can't but think though, we will wake up one morning and be like wow - where did all theses stomes come from..... They will just forming out of the blue.
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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.