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 was reading too about the showdown....WOW...that was something....
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Do we have an AOI in the Atlantic, I see? 456, that QUIKSCAT image shows a pretty well defined circulation. The problem is, all the clouds are getting sheared to the east, and there is no deep convection with it. So for me, development, no.
Member Since: December 21, 2007 Posts: 13 Comments: 3046
Quoting IKE:


No...I was reading back to the showdown on here earlier this morning between 2009 and vort and a couple of others.

While I'm laying in bed sawing logs:)
Ike it started last night about 10:30-1100pm. And was all started by pearlandaggie putting political crap on a weather blog. And let me tell ya, it went haywire after that.
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Good morning IKE...:)
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593. IKE
Here's some good news. I finally got an afternoon thunderstorm at my house yesterday. My first real rain in 3-4 weeks. Had about an inch yesterday.

On the Navy site for invests..."NOTE: Where, oh where, might the next Invest begin?".........

Is there no invest on the planet? Great news....
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Quoting scottiesaunt:
Mike Theiss currently in 4th place. Come on folks, lets vote.


I voted..:)
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Mike Theiss currently in 4th place. Come on folks, lets vote.
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Good Morning everyone...WOW!! Whatta morning on the blog eh? LOL!!!
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588. IKE
Quoting CybrTeddy:


7 AM Here.


No...I was reading back to the showdown on here earlier this morning between 2009 and vort and a couple of others.

While I'm laying in bed sawing logs:)
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Quoting IKE:
Folks arguing on a tropical weather blog at 3 in the morning...



7 AM Here.
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585. IKE
Folks arguing on a tropical weather blog at 3 in the morning...

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Late starters are not good:

1977 - Anita (cat 5 impacted Mexico) August 29
1983 - Alicia (cat 3 Texas) July 29
1992 - Andrew (cat 5 impacted South Florida) August 16
1998 - Alex - July 27 (Georges and Mitch, notable storms)
2002 - Arthur - July 14 (Isidore and Lili notable storms)
2004 - Alex - July 29 (Charley, Frances, Ivan and Jeanne notable storms)

All these names were retired the following year.
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583. IKE
I'll go with nothing the first half of July. Is it possible to have nothing for June and the entire month of July?

According to the ECMWF, it shows nothing in the Atlantic through the 13th....Link
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Good Morning;

Tropical Update


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post 580--the wind woke me here in Tobago.
First real squall of the season. Coming in sideways, it nice, man.
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Tropical wave passing through Trinidad this morning....very heavy rainfall right now.
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Quoting robbieNDBC:
Oh yeah as soon as I saw it today I was thinking "sub-tropical" to myself. I'm not at work so I don't have all my links to the shear maps!


It looks to be under about 30 knots of shear... And it doesn't look like it drops to less than about 20 or 25 along its path. It'll have to fight to pull together, that's for sure.
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Oh yeah as soon as I saw it today I was thinking "sub-tropical" to myself. I'm not at work so I don't have all my links to the shear maps!
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Quoting robbieNDBC:
Wow if ever there was a "need" for a tropical system, this would be the time. Yall don't need to argue on the internet. I didn't even look at the previous pages because it's almost 3 in the morning and I think I got the gyst of it.

But yall come on! Let's talk weather! That's something we all are here to discuss and learn about! I'm not sure what is the issue with the guy who supposedly can't speak as proficiently as the rest of us, but I bet there are people here who start reading all these acronyms (MJO, SAL, AEJ, TUTT) and they get just as lost! So if you don't understand someone, just do the ignore user or politely skim over their stuff and let's get back to the fun/interesting stuff!

Now about that yellow circle in the central Atlantic...



Probably the best post here.

Anyway, the shear still seems to be stopping it from really getting together. It has a chance if the shear can get down just a little, probably to become subtropical, but it doesn't have too much time, maybe 3 days until that front catches up with it.

I do find it interesting that we've been looking that far up in the Atlantic so early for subtropical systems though, I don't remember doing this before (though I'm sure I'm missing something)
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Wow if ever there was a "need" for a tropical system, this would be the time. Yall don't need to argue on the internet. I didn't even look at the previous pages because it's almost 3 in the morning and I think I got the gyst of it.

But yall come on! Let's talk weather! That's something we all are here to discuss and learn about! I'm not sure what is the issue with the guy who supposedly can't speak as proficiently as the rest of us, but I bet there are people here who start reading all these acronyms (MJO, SAL, AEJ, TUTT) and they get just as lost! So if you don't understand someone, just do the ignore user or politely skim over their stuff and let's get back to the fun/interesting stuff!

Now about that yellow circle in the central Atlantic...
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guys the dust over east and central atlantic is becoming weaker

look at the last few frames as well
Link
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571. Skyepony (Mod)
Had the same Yukatan seabreezes drift off into the BOC lastnight only to collapse from shear in the morning. These look pretty good for 20-30kts they are under currently, if it hasn't fallen a little. Maybe interesting tomarrow if the seabreeze developes & gets sucked in by the ULL.
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560. that's your opinion and that's wonderful--i have no problems with it. i'm sure you will never see this reply due to your rush to judgment. however, i'm only asking that the same proficiency of the English language is used on an ENGLISH blog as the converse requirement would be for a foreign language blog. that's all. i'll be honest....I've been reading Taz's entries for a LONG TIME and there are times when I have NO CLUE WHAT HE IS SAYING. maybe your interpretations skills are better than mine, but this is STILL AN ENGLISH BLOG and INTERPRETATION SKILLS SHOULD NOT BE A PART OF THAT.
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Sometimes ignore is just not enough. Sigh. :( Taz, if you're out there, I enjoy your posts. You've never been anything but polite. And if English is not your first language let me say your English is a lot better than my any other language. I think you're doing fine. And to anyone who might think so, nobody speaks for me. If you're speaking for yourself knock yourself out. But you don't know what I think so don't assume to speak for me. Attacking people is not cool. And I DO care about the weather in other parts of the world. And see absolutely nothing wrong with discussing it on a weather blog. Theres my opnion. POOF if you must. :)
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LOL @ 558!
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Same here, night all.
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549. if that post made any sense, i guess i could have taken it to heart! LOL
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Quoting Levi32:


LOL good one!

Nothing in the tropics. We may have to keep an eye on the Carolina coasts next week, and might also get an east Pacific storm, but for now it's all quiet. I hope it stays that way tomorrow so I can post a blog I've prepared for something else, and I can only post such things during quiet periods lol.


all's quiet for now. good to know.
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Quoting pearlandaggie:
i know this is in direct conflict with some of you liberal do-gooders. just send me a PM if you want to continue the discussion. otherwise, support me in the fact that Taz needs to speak better English before posting on this board.


and how would you describe yourself? as a conservative a** who is an intellectual know-it-all. likes to hear himself talk and speaks excellent English. At least Taz talks about the weather on a "weather" blog. I have been lurking and all you have done is berade others and talk politics. Go carry on your intellectual nonsense in some other blog!

POOF!!!
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Quoting pearlandaggie:
543. actually, i'm a very NICE person so long as the discussion adheres to a simple baseline...that being the TRUTH. i get a bit cranky when the discussion strays from the truth OR THE ENGLISH LANGUAGE.......
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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.