Remainder of July hurricane outlook

By: Dr. Jeff Masters , 2:31 PM GMT on July 15, 2009

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Not much has changed in the Atlantic since my early July Atlantic hurricane outlook posted two weeks ago. Tropical cyclone activity typically picks up a bit during the last half of July, but we are still a month away from when hurricane season really gets going. Since the current active hurricane period began in 1995, nine of 14 years (63%) have had a named storm form during the last half of July. We had two last-half-of-July named storms last year--Christobal and Dolly. As seen in Figure 1, most of the late 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.


Figure 1. Tracks of all tropical storms and hurricanes 1851 - 2006 that formed July 16 - 31.The Gulf of Mexico coast is the preferred strike location. There are still very few major Cape Verdes-type hurricanes forming in the last half of July.

Sea Surface Temperatures
Sea Surface Temperature (SST) anomalies have warmed slightly over the past two weeks, and are about 0.3°C (0.5°F) above average over the tropical Atlantic between Africa and Central America (Figure 2). These are some of the coolest SST anomalies for this time of year that we've seen since 1994. The strength of the Azores-Bermuda high has been near or slightly below average over the past two weeks, driving slightly below average trade winds. Weaker trade winds don't mix up as much cold water from the depths, and cause less evaporative cooling. The latest 2-week run of the GFS model predicts continued near-average or slightly below average-strength trade winds through the end of July, so SSTs should remain slightly above average during this period.


Figure 2. Sea Surface Temperature (SST) departure from average for July 13, 2009. SSTs were about 0.3°C (0.5°F) 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 in the area 5°N - 5°S, 120°W - 170°W, also called the "Niña 3.4 region", are now 0.4°C above the threshold for a weak El Niño, according to the Australian Bureau of Meteorology (Figure 3). An increase of another 0.1°C will push the current El Niño into the "moderate" category. NOAA's Climate Prediction Center issued an El Niño Advisory earlier this month. The 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 July 8, 2009, SSTs in the Niño 3.4 region had risen to 0.9°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 three 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.

The jet stream is forecast to maintain this two-branch pattern for the next week. However, during the final week of July, the subtropical jet is forecast to weaken. This will leave regions of low wind shear over the Caribbean and Gulf of Mexico for the final week of July (Figure 4), increasing the chances of hurricane development.


Figure 4. Wind shear in m/s between 200 mb and 850 mb on July 31, 2009, as forecast by the 00Z July 15, 2009 run of the GFS model. The subtropical jet is forecast to weaken by this time, leaving regions of low wind shear over the Caribbean and Gulf of Mexico for the final week of July. 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. Several well-developed African waves have been done in by dry air from Africa over the past few weeks.

Steering currents
The steering current pattern over the past few weeks has not changed much. A persistent trough of low pressure has remained entrenched over the Eastern U.S. all summer, bringing cool and relatively moist weather to the eastern half of the country. This trough is 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 strong trough over the Eastern U.S., which decreases the hurricane risk to the U.S. Gulf Coast. There is no telling what might happen to the steering current pattern during the peak months of August, September, and October, but it is often difficult to break a months-long steering current pattern like the current one.

Summary
Recent history suggests a 63% chance of a named storm occurring in the last 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 30% chance of a named storm forming this month. Such a storm would most likely form near the end of the month, when wind shear is expected to decline due to a weakening of the subtropical jet stream. The last time we went this long in the season without a named storm forming was in 2004, when the first storm (Alex) formed on August 1.

I'll have a new post on Friday.

Jeff Masters

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Quoting Tazmanian:
there is a 70 too 90% ch that this wont be 95L from this wave


based on what? lol
there is a 70 too 90% ch that this wont be 95L from this wave
Member Since: May 21, 2006 Posts: 5091 Comments: 115454
Quoting Stormchaser2007:


Lol I know how to read them...Just the fact the whole disturbance is engulfed in dry air is hampering its appearance a bit. Ill wait until tomorrow morning to see how convection builds back.


actually it is not engulfed in dry air by any means, it has a very large moisture field with it. Dry air has not hinder it very much at all and convection is building right now
Quoting Acemmett90:

it will be a year of invests jk
how would the blog react to this?
my guess it would send half the people on here to the nut house


I thought we were all in the "Nut House" already....
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Quoting hunkerdown:
You have to understand the image you are looking at. The funktop does not give the dramatic image that the rainbow does. You just have to know how to read them.


Lol I know how to read them...Just the fact the whole disturbance is engulfed in dry air is hampering its appearance a bit. Ill wait until tomorrow morning to see how convection builds back.
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Quoting TampaSpin:
Evening all......small chance it might make it to TD status just before the Shear hits it hard....In 5-7 days if this was in that location we could be starring down a hurricane in just a few days.......The shear conditions are just not favorable now.......but, next week is a different story.


Do you realy think this might have a chance mid to late next week??????

just wondering
Taco :-)
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Quoting KoritheMan:


That's the exact opposite of what the models are forecasting in the central and western Caribbean in 5-7 days from now.


yup exactly
Quoting weatherwatcher12:

He was on earlier

ok i havent seen him in a while. and levi is gone somewhere. hope all is alright with him as well.
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Quoting Stormchaser2007:
Pre 95L not looking so good. Ill wait till the 2am to really judge it.

You have to understand the image you are looking at. The funktop does not give the dramatic image that the rainbow does. You just have to know how to read them.
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Quoting TampaSpin:
Evening all......small chance it might make it to TD status just before the Shear hits it hard....In 5-7 days if this was in that location we could be starring down a hurricane in just a few days.......The shear conditions are just not favorable now.......but, next week is a different story.


That's the exact opposite of what the models are forecasting in the central and western Caribbean in 5-7 days from now.
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Quoting TampaSpin:
Evening all......small chance it might make it to TD status just before the Shear hits it hard....In 5-7 days if this was in that location we could be starring down a hurricane in just a few days.......The shear conditions are just not favorable now.......but, next week is a different story.


The wave will not be in that area for 4-5 days, I really think some are overplaying the shear that is in the Caribbean. All major models forecast that shear to lessen drastically over the next few days. The conditions around the wave now will allow for slow development.
Evening all......small chance it might make it to TD status just before the Shear hits it hard....In 5-7 days if this was in that location we could be starring down a hurricane in just a few days.......The shear conditions are just not favorable now.......but, next week is a different story.
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Quoting Tazmanian:
night all off to bed


Have a good sleep, TAZ! ;)
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Quoting Stormchaser2007:
Pre 95L not looking so good. Ill wait till the 2am to really judge it.



actually looks pretty good to me, a still picture many times doesnt show you the entire picture
Quoting VAbeachhurricanes:
where has drak been... did he leave?

He was on earlier
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night all off to bed
Member Since: May 21, 2006 Posts: 5091 Comments: 115454
Quoting StormJunkie:
Evening WS

My guess is the NHC is just trying to figure out what happens in the next two days. I don't think the yellow circle was based on any long term forecast...They are just to unreliable with undeveloped waves like this one.

Convection continues to expand...

What are you referring to as unreliable, the NHC or longer term forcasting of a wave of this character ?
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where has drak been... did he leave?
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Pre 95L not looking so good. Ill wait till the 2am to really judge it.

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Looks to me like it won't make it into the Caribbean. And appears to be taking a WNW track.
Link
Goodnight and dreams of happy places.
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Quoting StormJunkie:
Evening WS

My guess is the NHC is just trying to figure out what happens in the next two days. I don't think the yellow circle was based on any long term forecast...They are just to unreliable with undeveloped waves like this one.

Convection continues to expand...



You could be right in the money, 00z does'nt do anything with this wave but seem that GFS has been struggle this year.
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Quoting Acemmett90:

can't you take a joke taz you are to defencive please just lighten up and look at the future not just the present conditions and how the wave looks on sat



then why did t you this say joke at the end then so that way i would have new that you where olny jokeing
Member Since: May 21, 2006 Posts: 5091 Comments: 115454
gune= new blogging vocabulary. means the mighty cane! just like the two tone talk means the mighty biscuit wheels!!
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Quoting StormJunkie:
Evening WS

My guess is the NHC is just trying to figure out what happens in the next two days. I don't think the yellow circle was based on any long term forecast...They are just to unreliable with undeveloped waves like this one.

Convection continues to expand...


Must be reaching D-max over there
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I am confused.


What is a "gune" ?
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Quoting StSimonsIslandGAGuy:
The formula for finding the distance between longitude lines on the earth is you take the cosine of the latitude where the disturbance is and multiply it by 69 miles which is the length of a degree of longitude at the equator. At 11 north, that comes to 68 miles
.
So...
11 north 68
21 north 67
31 north 66 miles to a meter latitude?
(Yes, that is in the form of a question.)
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Evening WS

My guess is the NHC is just trying to figure out what happens in the next two days. I don't think the yellow circle was based on any long term forecast...They are just to unreliable with undeveloped waves like this one.

Convection continues to expand...

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The biscuit tone talk!!!!
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Quoting Acemmett90:

taz posting while intoxicated is illegal they can take away your blog licence and require you to goto blogging school lol jk




what the heck are you talking about
Member Since: May 21, 2006 Posts: 5091 Comments: 115454
The wave is not going to go poof. It has very good rotation to it and convection is flaring.
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For any Louisianans here (Patrap and atomaggie immediately come to mind), Jay Grimes is supposedly going to make an appearance at the Walgreens in Gonzales from 9-11 AM CDT Saturday morning. I'm going to be there. I thought you guys might like to know.
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Quoting RufusBaker:
Just what I thought. steering not looking good for west coast of FL. I got a bad feeling about this one.
You can't rely on the CMC. Also, keep in mind, at the moment it is just an area of interest currently with a less than 30% chance of development. Its not even an invest (well, at least not yet). People are only getting a little "hyper" active since a) this is the first area to track in a while; and b) its the first ATL area of 2009 to track. Due to these reasons, a "yellow circle" is being given a lot more attention than it would have been given in the past.

Now also keep in mind, things can change, for the good or bad, at any time and for any reason, so stay tuned...
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Quoting RufusBaker:
Just what I thought. steering not looking good for west coast of FL. I got a bad feeling about this one.




he is
Member Since: May 21, 2006 Posts: 5091 Comments: 115454
Who is jumping the gun?

I dont see anyone doing that
LOL whats not jump the gune here we have not has 95L here and you all are jumping the gune



guys cool it what watch it and see what it dos it may this go poof



what see what it dos 1st be for jumping the gune
Member Since: May 21, 2006 Posts: 5091 Comments: 115454
Just what I thought. steering not looking good for west coast of FL. I got a bad feeling about this one.
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Quoting RufusBaker:
provide link zone??


http://moe.met.fsu.edu/cgi-bin/cmctc2.cgi?time=2009071612&field=Sea+Level+Pressure&hour=Animation
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lol WS

that might be the smartest thing you have ever said on here lol
provide link zone??
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The 12Z CMC develops it after it crosses into the GOM, hits Florida, go figure.
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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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