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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I like what 456 said
'The longer we wait for Ana the stronger it will be'

Look at Andrew, Alex, late formers and bang, Major Canes.
Member Since: July 8, 2005 Posts: 259 Comments: 24167
Quoting StormW:
Weather456 7:00 PM EDT on July 02, 2009
Quoting PensacolaBuoy:
Associated Press Article 7/2/2009:

El Nino may have a split personality

The warming of the tropical Pacific Ocean has long been known to affect weather around the world, but researchers now say it may come in two forms with different impacts.

The traditional El Nino tends to reduce the number of Atlantic hurricanes. But a form Georgia Tech scientists call El Nino Modoki can lead to more hurricanes than usual in the Atlantic Ocean. Modoki, from Japanese, refers to something that is "similar but different."

Rest of article: Link


Very interesting indeed


In this statement from the article, if they mean starting in the EPAC, anybody find this "hybrid" a little peculiar?

"We spent all last week trying to figure that out," Webster said. 'It looks like it might be a hybrid," with warming starting in the east and them moving west, possibly meaning more hurricanes late in the season.



In terms of?
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Quoting stormwatcherCI:
I just voted too. He's at 201 now.

cool, thanks.
SOME other person from USA had like 500 or more votes! i wonder what blog is supporting him, cmon guys, vote for MIKE!!!
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Quoting Stormchaser2007:
Mikes in 6th place.
By my count he is 4th place. He has 206 and the other 3 have 560,248 and 233 respectively.
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so is this new El Nino Modoki, suppose to have effect on this season??
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Mikes in 6th place.
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2004 and 1969, very interesting years.
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Quoting PensacolaBuoy:
Associated Press Article 7/2/2009:

El Nino may have a split personality

The warming of the tropical Pacific Ocean has long been known to affect weather around the world, but researchers now say it may come in two forms with different impacts.

The traditional El Nino tends to reduce the number of Atlantic hurricanes. But a form Georgia Tech scientists call El Nino Modoki can lead to more hurricanes than usual in the Atlantic Ocean. Modoki, from Japanese, refers to something that is "similar but different."

Rest of article: Link


Very interesting indeed
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Just voted for Mike. 203 now.
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Quoting messageinabottle:
I just voted for Mike, hes at 195 votes now!!!
I just voted too. He's at 201 now.
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Quoting hurricane2009:


I feel both 90L and 92L should have been named and yes I think the NHC has been conservative this season

That being said they know what they are doing and they handled 93L perfectly.


I do believe that 90 and 92L were both storms, and yes, they handled 93L perfectly.
I know this blog was filled with some downcasters, and some wishcasters who thought it was going to hit Tampa as a major
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Quoting CybrTeddy:


90L was very likely Ana, so was 92L.
We should have been looking at Claudette if they weren't so conservitive this year.


Right on.
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Quoting StSimonsIslandGAGuy:
And on another note, Mike Theiss is behind by 75 votes people! C'mon y'all vote for him!


Can we vote more than once?
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He is up to 199 now.
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Associated Press Article 7/2/2009:

El Nino may have a split personality

The warming of the tropical Pacific Ocean has long been known to affect weather around the world, but researchers now say it may come in two forms with different impacts.

The traditional El Nino tends to reduce the number of Atlantic hurricanes. But a form Georgia Tech scientists call El Nino Modoki can lead to more hurricanes than usual in the Atlantic Ocean. Modoki, from Japanese, refers to something that is "similar but different."

Rest of article: Link
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does anybody think that monster wave at 35w and moving fast, will be anything in a couple of days?
Member Since: June 13, 2009 Posts: 0 Comments: 6858
No tropical storms or hurricanes developed in June 2004. This is not unusual, with 50% of all Junes in the long-term record registering no tropical activity. Sea surface temperatures (SSTs) were near average across the tropical Atlantic, though above average in a broad band across the North Atlantic from Spain to Florida. Climatologically, if tropical activity occurs in June, it is most likely in the western Caribbean, Gulf of Mexico or far western Atlantic along the U.S. east coast.

Source: NCDC
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I just voted for Mike, hes at 195 votes now!!!
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Quoting StSimonsIslandGAGuy:
Our 20% chance of rain came in today :)



and your gettin' more.. Lucky.
We vacationed to jekyll island (which i think is right below st simons) a week and a half ago.. It was awesome except for the heat
index every day being at least 115. And the beach water was like bath water. HOT!
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I see alot of A, B, & C names in all that spaghetti!

And boy, that's alot of spaghetti!

Good chance (more than 50%, IMO) that we see our first Cat 1 or stronger this month.
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Both 90L and 92L really had non tropical origins, so did TD 1, so in terms of deep tropical activity, 2009 has had none so far.
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121. Donna
I just went and voted for Mike, it would be really cool if he got it. And, i would love learning more about Antarctica through his eyes.

there are two people ahead of him - the first one is a youngish woman that doesn't speak of any experience blogging, the second sounds like he would be good and has done a lot of nature blogging.

so .... if you want Mike to win, vote! :)

best
Donna
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Quoting AllStar17:


Was that Laura from last year??? It does seem like the NHC has been conservative this year. If it is a storm and meets all the criteria, name it! Did you think 90L was TS Ana (in May), and what did you think of 92L (in the NA which may have been Subtropical)


90L was very likely Ana, so was 92L.
We should have been looking at Claudette if they weren't so conservitive this year.
Member Since: July 8, 2005 Posts: 259 Comments: 24167
Quoting CybrTeddy:


Well it looks to me it likely is. Its to far north though and away from land for the NHC to consider naming it. But if they named Lauren this certainly meets the critera.


Was that Laura from last year??? It does seem like the NHC has been conservative this year. If it is a storm and meets all the criteria, name it! Did you think 90L was TS Ana (in May), and what did you think of 92L (in the NA which may have been Subtropical and could have been named Bill.....and all the talk of a quiet season would be non-existent)
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Where is that so-called sheared subtropical system?
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92L report should be ready by Monday. Then TD 1 later.

90L Reviewed
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Quoting Weather456:
Does look like a sheared subtropical system



Well it looks to me it likely is. Its to far north though and away from land for the NHC to consider naming it. But if they named Lauren this certainly meets the critera.
Member Since: July 8, 2005 Posts: 259 Comments: 24167
Anyone have any thoughts on Texas for this hurricane season? Most memorable for us was Rita and Ike
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Quoting RMM34667:


Hey Tim what would you estimate the timeframe for that reaching us? I'd like to get home before that arrives. TIA
all that rain will dasapate before reaching the coast it happens every time
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Quoting TexasHurricane:
Are upper level lows something to be watched or not?

It takes a surface low to make a tropical system, so generally, no.
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Quoting TexasHurricane:
Are upper level lows something to be watched or not?


Sometimes they should be watched, but it takes several days for them to develop because they have to work down to the surface, and in this instance it should not be watched, it will run into land soon....and often they do not develop
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The ULL continues to enhance convection near Central America (i.e. Nicaragua and Honduras)

What will the environment be like in the Caribbean after the ULL clears out?? Just curious.


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Are upper level lows something to be watched or not?
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Quoting messageinabottle:


This is very interesting HW, thank you.
ANd by the way, HELLO ALL.


You're welcome. :)
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Should of clarified - upper features.
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Quoting hurricane2009:


There is a surface low in the NW Caribbean?


Upper low.
Member Since: November 24, 2005 Posts: 635 Comments: 26654
Quoting hurricane2009:


There is a surface low in the NW Caribbean?


I believe it is an upper-level low...but I am not positive
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Quoting homelesswanderer:
Ooops. Sorry. Forgot to say it was written in 1999. And here's the link to the whole article if anyone is interested. :)

Link


This is very interesting HW, thank you.
ANd by the way, HELLO ALL.
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Click for loop

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The 1977 season was very inactive, with only 6 named storms. The Atlantic basin was not alone in this inactivity, though; the 1977 Pacific hurricane season was also inactive as was the 1977 Pacific typhoon season. The cause is unknown.

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Quoting Weather456:
Does look like a sheared subtropical system



Well, looks can certainly be decieving, as was the case with 90L, as everyone thought it was TS Ana...I certainly did
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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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