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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2297. IKE
Quoting Acemmett90:

i cant belive im saying this buti agree with weather student the the carib storm is the gfs storm
by the way it has some good out flow



?
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Finally, some decent rain moving into the Florida panhandle!
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GFS developing the next strong TW and taking it towards the Bahamas by 22 July

Member Since: July 24, 2005 Posts: 407 Comments: 19076
Good Morning;

No new blog today but:

Tropical Update

This is the only area models really agree on this week: Near Bermuda



Member Since: July 24, 2005 Posts: 407 Comments: 19076
Texas will be hit twice.
One little hurricane and one major.
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...IT
APPEARS THAT FRONT IS STALLED OVER NE TEXAS AND CENTRAL LOUISIANA.....

NOOOOOOOOOOOOOO!!! Lol

Oh phew. It says we're still sposed to get rain. We saw a lot of lightning tonight er last night. Hubby said was heat lightning. Guess he was right. Anyway hang in there SE TX looks like the rains coming. :)
Member Since: August 15, 2008 Posts: 10 Comments: 3665
Quoting btwntx08:
wow the nhc is taking to long to name this td 3e.....it is definity already and way it looks they may skip td status to go to ts


In their defense, convection waned significantly prior to this recent burst. They want to see persistence and expansion of the convection before they classify it, and I'm sure that with this recent burst (which looks to be expanding and taking on some slight banding features), they will classify it.
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2285. Levi32
Well I'm out now. Goodnight all.
Member Since: November 24, 2005 Posts: 635 Comments: 26661
2284. Levi32
Quoting TexasHurricane:
Levi32

actually humberto was pretty cool to watch and all. I just don't want no cat 3 (or 2 like Ike)or higher sneaking up on me without us having time to leave....


Well yeah that's exactly the fear right there. Humberto was no biggy but 24 more hours over water and you would have had a big problem.
Member Since: November 24, 2005 Posts: 635 Comments: 26661
Here is an Interesting Statistic...

We are even with 2008 as far as Invests go...
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Levi32

actually humberto was pretty cool to watch and all. I just don't want no cat 3 (or 2 like Ike)or higher sneaking up on me without us having time to leave....
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2281. Levi32
Quoting TexasHurricane:
Levi32

I guess we can all try to predict the season but considering all the parts that have to come into play, who in the heck knows.....

Thinking of the close to home developements makes me think of Hurricane Humberto. We were under a tropical storm warning and woke up in the middle of the night to a cat 1.....



Yeah, seasonal forecasts are still long-shots at best, but we can get a general idea of what things "should" be like. Predicting landfalls though is pretty much flipping a coin still. I have the areas that I think are at higher risk this year but like I said everyone should be ready. Anybody can get hit in any pattern, any year.

Hopefully no Humbertos...

Quoting TheWeatherMan504:
Levi,
I'm thinking this year will be rather similar to 2006. That's just my hunch...


I would agree with that in terms of the bulk of tracks focused more north and east. It is one of the analog years I talked about in my blog on Friday.
Member Since: November 24, 2005 Posts: 635 Comments: 26661
tennisgirl08

hmmmmm, we live on the northern texas coast. Close to LA border....
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Levi,
I'm thinking this year will be rather similar to 2006. That's just my hunch...
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Levi32

I guess we can all try to predict the season but considering all the parts that have to come into play, who in the heck knows.....

Thinking of the close to home developements makes me think of Hurricane Humberto. We were under a tropical storm warning and woke up in the middle of the night to a cat 1.....

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Thought this was an interesting website. Not sure who this Jim guy is, but found it interesting that he pinpoints certain cities. Looks like he believes the Caribbean, South Florida, and Northern Gulf Coast will be the hotspots this year. Doesn't mention much of texas!!

http://www.hurricanecity.com/predictions.htm
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2275. Levi32
Quoting TexasHurricane:
Levi32

yeah, I can't help but think that for as long as we have had it, that we are having it to early in the season and when the peak of hurricane seaon comes it will be tired of our area and move. I mean I can't see a high just sitting on us for months on end...


Yeah....it has been going through oscillations to the west and east, but generally centered over your area. The CFS keeps it in the same place all summer, but we all know models can be flawed. Also home-brew developments close to the coast wouldn't necessarily be blocked by the ridge, and the chances for those kind of things spinning up within the gulf this year are higher than long-track storms entering the gulf from somewhere else.
Member Since: November 24, 2005 Posts: 635 Comments: 26661
Levi32

yeah, I can't help but think that for as long as we have had it, that we are having it to early in the season and when the peak of hurricane seaon comes it will be tired of our area and move. I mean I can't see a high just sitting on us for months on end...
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2272. Levi32
Quoting TexasHurricane:
Levi32

What are your thoughts for Texas this year?
Just curious....


Well.....Texas is a big question mark lol. I know that's not fun to hear. I'm not expecting a bulk of gulf tracks this year, but the slogan around here is "it only takes one". The big ridge that has been over you guys will block any storms coming if it stays in its current position for the rest of the summer. However, all it takes is a little shift of the high to the north or to the east for a storm to be able to make a run at your coast. If that happens, it could be a problem due to the big high heating up the waters in the western Gulf of Mexico.

In my opinion (again just my opinion) the SE United States coastline is at the most risk this year, but the gulf coast is always at risk as well. We will likely get a few storms in there, just like most years. Hopefully your "high of doom" stands its ground and protects you this summer, but don't hang your hopes on it. Again everyone should be ready every year, no matter what.
Member Since: November 24, 2005 Posts: 635 Comments: 26661
2270. Levi32
Quoting WeatherStudent:
But in all seriousness Levi, please do not deny me teh fact that you certainly aren't very smart when it comes to this field of study? :) You're up there with the elite bloggers of this site.


"aren't".........LOL :)

Well I thank you for the compliment =) I am here to learn and hopefully help others to understand some of the things I learn.
Member Since: November 24, 2005 Posts: 635 Comments: 26661
Levi32

What are your thoughts for Texas this year?
Just curious....
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2267. Levi32
Quoting WeatherStudent:


Thanks for the wise unput, i'll take it into consideration asap. Lastly, what about Oct. storms for us?


Pretty much the same as the above. In October storms from the east are even more unlikely due to troughs starting to dig farther south as winter approaches. In October the biggest threat to south Florida is storms recurving out of the NW Caribbean.
Member Since: November 24, 2005 Posts: 635 Comments: 26661
2265. Levi32
Quoting WeatherStudent:



Fair enough, thanks a million for your torough explination my friend. Hey, now that I've got you to my self on here, I live in South Florida, what might I expect down here come August and September based on what your seeing for teh rest of teh season. I'd really apprecaite your feedback here, since you appear to be unbelivably intellegent when it comes to understabding how tropical meteorology functions, kid. :)


Lol....you flatter me but as I tell everyone I am not a Meteorologist so keep that in mind when digesting my opinions.

Florida is at high risk every single season, no matter how you slice it. It gets hit more than any other state. If we're talking about Andrew-type tracks (long-track storms from the east), I think they're more unlikely this year due to the east coast trough forecast to stay pretty much in the same spot all summer. which I discussed in my hurricane outlook. However that doesn't mean it can't happen if the ridge moves over the east coast for a week allowing a storm to go west. Also, storms forming close by (which is a concern this year for everybody) say near the Bahamas, could have more of a chance of hitting Florida without recurving. Of course storms threatening to hit Florida from the NW Caribbean are a concern as well.

Overall I think Florida is at normal risk this year, which is already pretty high to begin with. As always, be ready =)
Member Since: November 24, 2005 Posts: 635 Comments: 26661
2263. Levi32
Quoting WeatherStudent:


I know, but by then we'll be closer to the Cape Verde Season, so it wouldn't appear totally impossible, or would it, accoring to your expertise, Levi? In addition to that, by then shouldn't the basin be MUCH MORE favorable out there than it is tonight, my friend? :)


No it's not totally impossible. I'm always watching the African waves, but right now it is unlikely that one will develop. We'll see what the 2nd half of July has to bring, but right now I have little faith in the GFS ghost-storms. If it shows it consistently for several model runs and properly moves it down the time-increments, then I'll pay attention. Right now it's too far out.

As far as overall conditions in the basin....the GFS shows TUTTs and upper lows dancing around for most of the forecast period, making upper-level conditions hostile in most areas. The current run shows a worst-case scenario giving the ghost-storm unbelievable ventilation, but again this is just one freak run. It won't be the same on the 6z or 12z runs I guarantee it. Conditions aren't ripe for development for the first half of July. Development chances increase more towards the end of the month when we get the MJO upward-motion pulse back into the Atlantic. Right now all I'm really concerned about is the SE US coast this week.
Member Since: November 24, 2005 Posts: 635 Comments: 26661
2260. Levi32
Quoting Levi32:


I see nothing of significance. I still see the low it forms on the tail-end of that front off the Carolinas in a couple days. I've been watching that area for a week now. We'll see how that turns out. We may see something try to go warm-core in that area. Otherwise....the model is empty of trouble =)


Yeah WS before you say anything I see the ghost storm in the long-range hours. I'll believe it when I see it. Right now the east Atlantic is not open for business. The GFS has been trying to develop waves out there for weeks now. This is also the first run it shows it on.
Member Since: November 24, 2005 Posts: 635 Comments: 26661
Quoting RitaEvac:
Nothing is going to happen for another week. Now other story is this.... hot and extremely dry in TX, driest ever seen in most areas of the Gulf coast. Expect a storm to hit TX starting now and on into September. Expect torrential rains. It's a fact when the TX coast burns up a storm will arrive.....ladies and gentlemen sit back in awe and watch it evolve

where exactly in Texas are you expecting it to arrive? Any thoughts?
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2257. Levi32
Quoting WeatherStudent:
Good Monday morning, all! Hey guys, any one of y'all happen to check out the latest version of the GFS 00z model run this morning in full yet? If not, please check it out and give me your two-cents worth in regards to it, ASAP. Thank you very much, :)


I see nothing of significance. I still see the low it forms on the tail-end of that front off the Carolinas in a couple days. I've been watching that area for a week now. We'll see how that turns out. We may see something try to go warm-core in that area. Otherwise....the model is empty of trouble =)
Member Since: November 24, 2005 Posts: 635 Comments: 26661
2256. Levi32
Quoting TampaSpin:


You sure your looking in the CAribbean...

Link


Positive. The first spin was an illusion caused by a convective burst expanding towards the south. In the last couple frames it is possible the recent MCC is leaving behind a residual mid-level vortex, but that will fade very quickly if that is the case. There is no spin directly associated with the wave.
Member Since: November 24, 2005 Posts: 635 Comments: 26661
Quoting Levi32:
The only thing in the upper levels in the Caribbean is a TUTT that is currently shearing that tropical wave. There is no spin of any kind associated with the wave.


You sure your looking in the CAribbean...

Link
Member Since: September 2, 2007 Posts: 178 Comments: 20443
Looks like the wave in the eastpac has persistent convection and good shape to it. It looks very organized to me.
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2252. Levi32
Quoting scott39:
Levi,i reread your explanation on this wave in the carrib. you mentioned 2or3 days it could have a more favorable enviroment.Do you expect it to survive to get that chance?


Tropical waves don't get killed by shear. The convection associated with them does, but not the wave itself. Upper-level conditions will be slightly more favorable in 2-3 days over the western Caribbean but still less than ideal, and with the strong low-level easterlies I don't think it has much of a chance. After that it will be over central America for a few days before finally emerging in the east Pacific, which is where I think it will develop if it's destined to develop at all.
Member Since: November 24, 2005 Posts: 635 Comments: 26661
2250. scott39
Levi,i reread your explanation on this wave in the carrib. you mentioned 2or3 days it could have a more favorable enviroment.Do you expect it to survive to get that chance?
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Very well said. Thanks Levi
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Personally, living in SE TX, I would much rather have a few days of moderate rain (like 1.5 - 2 inches per day), rather than 2 days of torrential rain. Even with how parched the land is right now, if we just get dumped on, most of it will end up running off. If you get the same amount of rain spread out more or less evenly over a couple of days, it has a better chance to soak in and do some good.
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2247. Levi32
Quoting HurricaneJoe:


So this thing could develop? Please, enlighten me, I'm only 18. Don't know much about what they're going to do.


We youngins need to have faith in ourselves =D I'm 17 myself lol. Here this is my posts from earlier explaining what's going on:

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.


To add to that, even though the divergence aloft is enhancing thunderstorm activity, the shear that accompanies it is causing t-storms to collapse, come back in another area, collapse, pop up again, etc...the cycle never ends because the tops of the thunderstorms get blown apart by the shear. You need sustained convection that is allowed to grow, which requires light winds aloft (light wind shear). Once you get that, you can get a surface low and a more organized system. Right now this tropical wave is not organized. It is a well-defined wave but until it gets into a more favorable environment aloft that is all it will be, and a rainmaker for Caribbean countries.


Also, easterly trade winds in the Caribbean are very fast right now and that ruins surface convergence, which makes it very hard for tropical waves to amplify. That alone makes me think it won't develop, without even thinking about upper-level conditions. I don't think it's a threat until it gets into the eastern Pacific.

[edit] - here's the link to the upper-level winds I was refering to above.
Member Since: November 24, 2005 Posts: 635 Comments: 26661

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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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