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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A pretty big blowup of convecton on the coast of Nicaragua. I would also keep an eye on this.
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I would also keep an eye on this disturbance east of S america and see if this develops.
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Quoting Orcasystems:



Oh god...
That will get some of the people hopping :(
Who will be the first to ask if its going to hit Florida :(


lol lol lol
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lol lol lol lol lol
Member Since: July 15, 2006 Posts: 178 Comments: 56039
The last set of visible images did revealed a tight circulation but with convection sheared from it. If it is able to get convection building near the COC, it stands a chance, otherwise, little expected.



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Quoting Tazmanian:
NOTE: Where, oh where, might the next Invest begin?


maybe with our AOI in the North Atlantic?!

Member Since: June 29, 2009 Posts: 13 Comments: 5315
Quoting hurricane2009:


maybe the NHC will name it cuz they missed 92L lol


Well then....give it to names :) they missed 90 and 92L.

SubTropical Storm Anbilla
Member Since: June 29, 2009 Posts: 13 Comments: 5315
NOTE: Where, oh where, might the next Invest begin?
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Like we don't know where to get a TWO. Some sentence of interest, or two, would suffice nicely.
Member Since: August 16, 2007 Posts: 6 Comments: 12463
Quoting StormW:


Just went there...gotta subscribe.

What's your take on what I posted?


I am whit you and nrt's graphic. I don't think our current set qualifies for a non-classic, though moderate so far, El Nino.

I would like to read the full article before I go much further, though.

Good find, nrt.
Member Since: August 16, 2007 Posts: 6 Comments: 12463
This disturbance may have a chance if it can fire convection over the COC.....you can even see the COC on the infrared if you look closely

Member Since: June 29, 2009 Posts: 13 Comments: 5315
Quoting Weather456:


shock



Oh god...
That will get some of the people hopping :(
Who will be the first to ask if its going to hit Florida :(
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The forecast maps at the OPC show the system becoming associated within a frontal zone in 3-4 days so it could stand some chance until then.
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.
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Weather456,TWO for the Non-Tropical Low.Good catch.

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Some rotation Noted in the Main cell..

TVS in and out

Member Since: July 3, 2005 Posts: 428 Comments: 129841
Is there such a thing as La Nina Modoki?
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Quoting TexasHurricane:
so is this new El Nino Modoki, suppose to have effect on this season??


Not from what I can tell. Seems El Nino Modoki is characterized by warm SSTA in the Central Pacific and cool SSTA on both sides.


Click on image to view original size in a new window






From this powerpoint presentation: Seasonal Prediction Research and Development at the Australian Bureau of Meteorology
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526
WUUS54 KLIX 022345
SVRLIX
LAC103-030030-
/O.NEW.KLIX.SV.W.0136.090702T2345Z-090703T0030Z/

BULLETIN - EAS ACTIVATION REQUESTED
SEVERE THUNDERSTORM WARNING
NATIONAL WEATHER SERVICE NEW ORLEANS LA
645 PM CDT THU JUL 2 2009

THE NATIONAL WEATHER SERVICE IN NEW ORLEANS HAS ISSUED A

* SEVERE THUNDERSTORM WARNING FOR...
WEST CENTRAL ST. TAMMANY PARISH IN SOUTHEAST LOUISIANA...
THIS INCLUDES THE CITIES OF...MANDEVILLE...COVINGTON...

* UNTIL 730 PM CDT

* AT 643 PM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
SEVERE THUNDERSTORM CAPABLE OF PRODUCING DAMAGING WINDS IN EXCESS
OF 60 MPH. THIS STORM WAS LOCATED NEAR COVINGTON...AND MOVING
SOUTH AT 15 MPH.

* THE SEVERE THUNDERSTORM WILL BE NEAR...
MADISONVILLE BY 705 PM CDT...
MANDEVILLE BY 710 PM CDT...

PRECAUTIONARY/PREPAREDNESS ACTIONS...

THIS IS A DANGEROUS STORM. IF YOU ARE IN ITS PATH...PREPARE
IMMEDIATELY FOR DAMAGING WINDS...DESTRUCTIVE HAIL...AND DEADLY CLOUD
TO GROUND LIGHTNING. PEOPLE OUTSIDE SHOULD MOVE TO A SHELTER...
PREFERABLY INSIDE A STRONG BUILDING BUT AWAY FROM WINDOWS.
Member Since: July 3, 2005 Posts: 428 Comments: 129841
If we have a 0 year. we'll look back at 90L and 92L with more detail. lol
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Quoting hurricane2009:


oh great here come the downcasters lol

0 storms aint happenin


Downcaster? thats a first for me :)
Much nicer then some of the names I have been called :)
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NEXRAD Radar
New Orleans, Base Reflectivity 0.50 Degree Elevation Range 124 NMI


Hail to Inch and One Quarter in the Largo Cell.



Member Since: July 3, 2005 Posts: 428 Comments: 129841
Quoting hurricane2009:


I would think there is a 100% chance that Ana is our first named storm lol

Im just kidding 456, couldnt resist lol


lol. I caught that, too, but decided it was a good time to practice on my restraint for later in the season. (Not needling you about responding, though. Please to not think that.
Member Since: August 16, 2007 Posts: 6 Comments: 12463
Quoting hurricane2009:


I would think there is a 100% chance that Ana is our first named storm lol

Im just kidding 456, couldnt resist lol


Ah but is there?
If we have a zero year... the names would change :)
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Quoting hurricane2009:


I would think there is a 100% chance that Ana is our first named storm lol

Im just kidding 456, couldnt resist lol


lol, you got me there.
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Quoting Orcasystems:


Unlikely, but it would be a pleasant change.... mind you, a few bloggers on here would be almost suicidal.



That is correct
Member Since: June 29, 2009 Posts: 13 Comments: 5315
Storm, here is the source behind those El Nino, Webster study press releases: http://www.sciencemag.org/cgi/content/summary/sci;325/5936/47?maxtoshow=&HITS=10&hits=10&RESULTFORM AT=&fulltext=nino webster&searchid=1&FIRSTINDEX=0&resourcetype=HWCIT
Member Since: August 16, 2007 Posts: 6 Comments: 12463
160. mobal
Just a fast comment on postig a vote for Mike.

Last year I was taking a vacation in the keys and emailed Mike for suggestions on things to do and such. He was very helpful and BTW much liked there.

His photos I have seen are awesome and his blogs were good.

Take the time to vote for, IMO it is all good!

He has 211 votes now.......
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Quoting CybrTeddy:
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.


Late years

Hurricane Alicia 1983 - July 29
Hurricane Andrew 1992 - August 16
Hurricane Alex 2004 - July 31

Again, the longer Ana stays to form, the more likely she will be our first named storm and hurricane.
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Quoting StormW:
Weather456 7:27 PM EDT on July 02, 2009
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?

As in, to my understanding from reading on El Nino, that's where the warm tongue of water starts anyway. It comes in under the subsurface in the form of a Kelvin Wave, hits the S.A. coast, and sloshes upward and back toward the west. This is notable in El Nino animations, especially the 1997. So, I don't understand what he means by it may be a hybrid.


Oh ok, I see your point.
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Heads up on the south shore. This puppy has an amazing flash rate, I can tell ya...might not survive the trek across the lake, though.



I see the lightning is rather thick over to the east, too.

Member Since: August 16, 2007 Posts: 6 Comments: 12463
Quoting AllStar17:


I certainly would not have a problem with that :), but what are the chances of that?!


Unlikely, but it would be a pleasant change.... mind you, a few bloggers on here would be almost suicidal.

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Quoting Orcasystems:
Its not as if Florida appears to need any more moisture. They appear to have gotten a seasons worth in the last few weeks.



Broke most of us out of our drought.
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Its not as if Florida appears to need any more moisture. They appear to have gotten a seasons worth in the last few weeks.

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Quoting Orcasystems:


I don't have a problem with a zero year.


I certainly would not have a problem with that :), but what are the chances of that?!
Member Since: June 29, 2009 Posts: 13 Comments: 5315

AOI

AOI

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Quoting AllStar17:


That is an excellent point, and it is why everyone should remain prepared, no matter how quiet it is.


I don't have a problem with a zero year.
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Quoting CybrTeddy:
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.


That is an excellent point, and it is why everyone should remain prepared, no matter how quiet it is.
Member Since: June 29, 2009 Posts: 13 Comments: 5315
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: Posts: Comments:

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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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