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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Quoting atmoaggie:


Watch it yes, but say it is a TD or TS and NHC is asleep at the wheel? If they were to call every wave that develops any convection a TS, the term TS loses meaning and the general populace grows complacent.

Not unlike a 70% false alarm rate for nadoes. I can tell ya, the city of Tulsa doesn't scurry in basements at the first alert of a nado warning...and ultimately will wish they had one day.

Why have any serious public announcements (i.e. forecast advisories, etc.) thus alerting the general public over a wave with no future? No good reason I can come up with. Until the threat is there for a system to have the potential to actually cause any damage, simply labeling it an invest and watching it further is plenty of action on it.


Well said
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Do not worry, everybody,
I am SURE storms will come....and the more you hope and hope the longer it will take for one to form. We will probably see Ana and maybe even Bill by the end of July. Conditions are forecast by shear models to become increasingly favorable across the basin over the next few weeks, so I am sure storms will come.
Member Since: June 29, 2009 Posts: 13 Comments: 5313
I see both Levi and FSUmet's points about the Caribbean wave. However, I do think this wave will be something to watch over the next few days. Tropical waves are not really affected by shear. So, moving through 30-40kts shouldn't kill it. Afterwards, it will be moving into a more favorable environment in the western caribbean, at which time, it will become an invest.

Hopefully it will keep moving west and make its way into the EPAC and form. And not drift NW into the GOMEX.
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Quoting Acemmett90:

you have point we have had two storms like 93L i belive that we need to watch this because when we turn our backs on the season we will gets slamed and people are gonna blame it on the nhc even though it was their falt for not paying attention people please have a safe season
ace


Watch it yes, but say it is a TD or TS and NHC is asleep at the wheel? If they were to call every wave that develops any convection a TS, the term TS loses meaning and the general populace grows complacent.

Not unlike a 70% false alarm rate for nadoes. I can tell ya, the city of Tulsa doesn't scurry in basements at the first alert of a nado warning...and ultimately will wish they had one day.

Why have any serious public announcements (i.e. forecast advisories, etc.) thus alerting the general public over a wave with no future? No good reason I can come up with. Until the threat is there for a system to have the potential to actually cause any damage, simply labeling it an invest and watching it further is plenty of action on it.
Member Since: August 16, 2007 Posts: 6 Comments: 12463
Quoting Acemmett90:

Not abviosly its obviosly lol just messing with you

Haha you spelled it wrong too with trying to correct me.Not obviosly its obviously.
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Quoting StormFreakyisher:

That's impossible.This has to be associated with the wave or it has sustainability to hold it self with this 30-40knt shear if it was convection to start all by itself.The wave is abviously producing this.


Read post 2116
Member Since: June 29, 2009 Posts: 13 Comments: 5313
Quoting fsumet:
To look at what Levi is talking about go here:
Atlantic CIMSS

You can see the upper level divergence from the TUTT helping vent the wave. You can also see the shear it is heading into as well. It also doesn't have much in the way of concentrated low level vorticity (so no spin). The wave isn't moving north, it is getting sheared off to the north. It will move with the lower level trade winds which are moving west. It is all in that link


Thanks FSU met! I think Levi was getting very frustrated trying to explain it to us! LOL!!
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Quoting tennisgirl08:


LOL! That is the point I was trying to make earlier about 93L. This particular wave looks like 93L and 93L didn't develop. So, I am wondering if the NHC is holding back b/c of what happened to 93L.


No, this is not at all related to 93L.
Member Since: June 29, 2009 Posts: 13 Comments: 5313
Quoting AllStar17:


Yeah, the convection is really not associated w/ the wave.

That's impossible.This has to be associated with the wave or it won't have the sustainability to hold it self with this 30-40knt shear if it was convection to start all by itself.The wave is obviously producing this.
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Quoting Acemmett90:

whats up stompetrol


Nothing much, how about you, just watching the weather as usual, so hot here, praying for rain , but don't want any storms, anyways I'm checking in for the night, G'Nite all.
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2131. fsumet
To look at what Levi is talking about go here:
Atlantic CIMSS

You can see the upper level divergence from the TUTT helping vent the wave. You can also see the shear it is heading into as well. It also doesn't have much in the way of concentrated low level vorticity (so no spin). The wave isn't moving north, it is getting sheared off to the north. It will move with the lower level trade winds which are moving west. It is all in that link
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Quoting atmoaggie:
Geeez, you guys ever heard about this story?
Link


LOL! That is the point I was trying to make earlier about 93L. This particular wave looks like 93L and 93L didn't develop. So, I am wondering if the NHC is holding back b/c of what happened to 93L.
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2129. JRRP
Quoting btwntx08:

read 2093 he agrees as well

2116...
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Quoting Levi32:


They generally label a tropical disturbance an invest if they decide it's an area of interest. The official definition doesn't even say that they label them based on any particular potential for development. A normal tropical wave in the Caribbean doesn't really qualify as an "area of interest" in terms of a tropical disturbance. And no it's not organized primarily due to the shear.

Back later.

But isnt that how we start tracking storms in the first place when they develop.So your saying it is not an area of interest like every other tropical wave that passes and sometimes develop BUT it is not an area of interest?Not to watch?
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Quoting Acemmett90:
allstar those people are fallowing the covection thats why


Yeah, the convection is really not associated w/ the wave.
Member Since: June 29, 2009 Posts: 13 Comments: 5313
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.


That is well stated. So, you think development may be possible beyond 72 hrs? You agree that the strong convection is moving north, but the wave itself is moving west. Some of these people persist that the wave is moving north.
Member Since: June 29, 2009 Posts: 13 Comments: 5313
2124. 7544
Quoting btwntx08:

read 2093 he agrees as well


wave looks good enough to keep our eyes on it imo might blow up alittle in dmax tonight tooo
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2123. Levi32
Quoting tennisgirl08:


Levi, I'm curious of your thoughts - is it not being labeled an invest b/c of shear ahead of it, or b/c of lack of organization with the wave? From the latest NHC discussion, they stated it was a well-defined wave. It seems reminiscent of 93L - one day looks organized, and then maybe the next day it could dissipate! Maybe that is why they are holding back. Just my thoughts!!


They generally label a tropical disturbance an invest if they decide it's an area of interest. The official definition doesn't even say that they label them based on any particular potential for development. A normal tropical wave in the Caribbean doesn't really qualify as an "area of interest" in terms of a tropical disturbance. And no it's not organized primarily due to the shear.

Back later.
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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.


Nice explanation, Levi! I am trying to learn.
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The forward speed of the Caribbean wave has slowed considerably IMO.
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How can you guys say that Hispanola is not going to get rain.Look at it, it is clearly getting closer to shore with convection exploding.
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2116. 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.
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Geeez, you guys ever heard about this story?
Link
Member Since: August 16, 2007 Posts: 6 Comments: 12463
2114. JRRP
Quoting Levi32:


The NHC is doing perfectly with the Atlantic systems. Ex-94L is not sub-tropical yet, and the wave in the Caribbean is not near as impressive as it appears to be to everyone. It's not a threat to develop.

i agree
the wave is seen well enough but far from seeing some development(primera traduccion)
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Quoting Levi32:


It's an illusion caused by that burst of convection expanding towards the south. This wave isn't organized enough to be labeled an invest.


Levi, I'm curious of your thoughts - is it not being labeled an invest b/c of shear ahead of it, or b/c of lack of organization with the wave? From the latest NHC discussion, they stated it was a well-defined wave. It seems reminiscent of 93L - one day looks organized, and then maybe the next day it could dissipate! Maybe that is why they are holding back. Just my thoughts!!
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2111. Levi32
Quoting tennisgirl08:
I know the NHC are the experts, but we have a clear TD or STD in the Atlantic - not labeled. And a very well-defined wave in the caribbean, that IMO, should be coded yellow. I am confused! They are sure being conservative. I know they must have their reasons, though.


The NHC is doing perfectly with the Atlantic systems. Ex-94L is not sub-tropical yet, and the wave in the Caribbean is not near as impressive as it appears to be to everyone. It's not a threat to develop.
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2110. JRRP
Quoting btwntx08:
the wave heading west its not gonna hit dr

the axis is moving west but the strong convecction is moving north
Link
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2109. Ossqss
Quoting CybrTeddy:


Translated (using FreeTranslation.com lol)
since my house the moon is seen outside. ... with some distant and high clouds to the southeastern south the relampagos are seen


Awesome, can you cut and past it and try it the other way to see if comes out the same in Spanish from English? Just curious and you have a head start :-)
Member Since: June 12, 2005 Posts: 6 Comments: 8186
I know the NHC are the experts, but we have a clear TD or STD in the Atlantic - not labeled. And a very well-defined wave in the caribbean, that IMO, should be coded yellow. I am confused! They are sure being conservative. I know they must have their reasons, though.
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2107. JRRP
Quoting CybrTeddy:


Translated (using FreeTranslation.com lol)
since my house the moon is seen outside. ... with some distant and high clouds to the southeastern south the relampagos are seen

thanks.... :P
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Quoting Acemmett90:
however unless the carib wave gains more vorctiy i will only watch it with the corner of my eye


It does have a bit of vorticity, but unfavorable shear should limit any development
Member Since: June 29, 2009 Posts: 13 Comments: 5313
2105. Levi32
Quoting fsumet:
I thought more about your correlation Levi that you can see in the western Atlantic in the Fall. This may be due to strong cold fronts moving further south and east than normal. This also basically ends the hurricane season for the Gulf early as well. So it's not so much a direct correlation with SST, it's more of a function of how El Nino affects the overall climate and the SST in the western Atlantic is a feedback from that effect.


I know, I didn't say it was direct. The water temperature in one ocean can't directly change the temperature of another. Most if not all effects of El Nino are felt strongest in the fall and winter, so that's not a surprise that it shows up more in the late hurricane season.
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2104. Dar9895
Quoting AllStar17:


You live in Santo Domingo?

Some interesting model tracks for 94E:

No matter this invest 94, it move away from Mexico and cooler water.
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I'm curious FSU met, what are your thoughts on this wave in the caribbean?
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Quoting stormpetrol:
From my house we can see the moon outside with some clouds high in the distance, at the southeast you can see the lightning.desde mi casa se ve la luna afuera.... con algunas nubes altas y distante al sur sureste se ven los relampago


To be honest my wife translated this for me, she is from Belize.
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Quoting AllStar17:
2091. Acemmett90

The wave itself is moving west, however

Looks like we will get some rain here
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2099. Dar9895
Quoting fsumet:
How each El Nino Progressed from last post (Just doing the last 4 El Ninos):

Peak Hurricane Season (Mid September) 2006


Peak Hurricane Season (Mid September) 2004


Peak Hurricane Season (Mid September) 2002


Peak Hurricane Season (Mid September) 1997



Mid November 2006


Mid November 2004


Mid November 2002


Mid November 1997

Very interesting that thing so if the 1997 el nino was the strongest that mean 2009 will be similar to 2002 or perhaps 2006, isn't it.
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Quoting Acemmett90:
wait ive been working hard the last few days how the heck did we end up at 94L


It was a non-tropical area of low pressure in the North Central Atlantic SW of the Azores. NHC still has a floater up on it, if you wanted to check. Could of become Sub-tropical, but was heavily sheared throughout it's life as an invest, thus no development.
Member Since: June 29, 2009 Posts: 13 Comments: 5313

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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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