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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Go North Blob babby, go North. Be a fish!
Member Since: Posts: Comments:
Quoting atmoaggie:


You know, the Met.

The Metropolitan Opera.

Excuse me sir, but we all know he was referring to the Metropolitan Museum of Art, whose record at predicting tropical cyclone development is second only to The MoMa!
Member Since: Posts: Comments:
RE 884. Ossqss

Oh sorry, misunderstanding, I didn't imply that you made the vid.
I sort of guessed that you posted it for general blog entertainment and I found it quite funny albeit somewhat obscure. And it had me looking for evidence against the theory voiced in the vid so I had some entertainment tonight.

Keep on posting funny tropical weather related vids as long as we don't have anything else to watch but some tropical waves. You never know what you might learn even from fun stuff. *thumbs up*

-------------------------------------------
And 872. atmoaggie

brilliant stuff. The laugh of the day for me, you made my day.
Member Since: August 20, 2007 Posts: 12 Comments: 639
901. Drakoen
10:02 PM GMT on July 16, 2009
Quoting WeatherStudent:
Quickly, someone find and give Bill Gates something to do ASAP. Foolish redundant idiot, he'll never EVER be able to tane hurricanes. Man will never supercede Mother Nature in no shape, way, or form, EVER. That'll be the day, right guys?



drama drama drama
Member Since: October 28, 2006 Posts: 57 Comments: 30565
899. LPStormspotter
9:53 PM GMT on July 16, 2009
Quoting atmoaggie:


If you do the same in the "modify profile" section, rather than at the top o' the blog, it will work and stick. Might get there by clicking the "Settings" at the top by your handle...I think.


Thank you
Member Since: July 17, 2008 Posts: 0 Comments: 385
898. wunderkidcayman
9:50 PM GMT on July 16, 2009
Who is he? A met? What are his thoughts on the system, my friend?
short version of Meteorological office and he is a friend name alan might be a invest and possible td2 or a very weak ts but the ts is a very big maybe
Member Since: June 13, 2009 Posts: 2 Comments: 12168
897. WxLogic
9:47 PM GMT on July 16, 2009
Quoting atmoaggie:


Our own scripts in a combination of bash, csh and perl on open source Linux. We have been using Slackware for the OS. (We like the install procedure; it lets us not install a lot of fluff. Very customizable.)


Sweet... gotta love open source... ok back to business... hehe.
Member Since: August 14, 2008 Posts: 4 Comments: 4977
896. atmoaggie
9:46 PM GMT on July 16, 2009
Quoting BurnedAfterPosting:


What Met?


You know, the Met.

The Metropolitan Opera.
Member Since: August 16, 2007 Posts: 6 Comments: 12463
894. atmoaggie
9:45 PM GMT on July 16, 2009
Quoting LPStormspotter:
Question???
I clicked on show all and some on here are still not showing. I have to click on message.
Why is that?


If you do the same in the "modify profile" section, rather than at the top o' the blog, it will work and stick. Might get there by clicking the "Settings" at the top by your handle...I think.
Member Since: August 16, 2007 Posts: 6 Comments: 12463
893. BurnedAfterPosting
9:43 PM GMT on July 16, 2009
Quoting wunderkidcayman:
Whose they, however
the guy I spoke to at the met


What Met?
892. atmoaggie
9:42 PM GMT on July 16, 2009
Quoting WxLogic:


You guys using Open source LINUX, or proprietary platforms (e.g. SUN, HP-UX, etc...)?


Our own scripts in a combination of bash, csh and perl on open source Linux. We have been using Slackware for the OS. (We like the install procedure; it lets us not install a lot of fluff. Very customizable.)
Member Since: August 16, 2007 Posts: 6 Comments: 12463
890. wunderkidcayman
9:40 PM GMT on July 16, 2009
Whose they, however
the guy I spoke to at the met
Member Since: June 13, 2009 Posts: 2 Comments: 12168
888. LPStormspotter
9:37 PM GMT on July 16, 2009
Question???
I clicked on show all and some on here are still not showing. I have to click on message.
Why is that?
Member Since: July 17, 2008 Posts: 0 Comments: 385
887. wunderkidcayman
9:36 PM GMT on July 16, 2009
Quoting BurnedAfterPosting:
you said we WILL see a yellow circle at 8pm and that you talked to someone in the weather office to confirm that

I am saying, those are pretty steep comments to make

Also comparing an undeveloped tropical wave to any past storm isnt very insightful.

sorry I mean to say we might it and they said it is possible
Member Since: June 13, 2009 Posts: 2 Comments: 12168
885. BurnedAfterPosting
9:32 PM GMT on July 16, 2009
you said we WILL see a yellow circle at 8pm and that you talked to someone in the weather office to confirm that

I am saying, those are pretty steep comments to make

Also comparing an undeveloped tropical wave to any past storm isnt very insightful.
884. Ossqss
9:31 PM GMT on July 16, 2009
864, I don't make them, I just post some that may be interestingly entertaining and have some value. Ya just never know what you can find sometimes :)

BTW, many high value ships, and some vehicles, have MRAD or LRAD on them already for protection.
Member Since: June 12, 2005 Posts: 6 Comments: 8186
883. wunderkidcayman
9:30 PM GMT on July 16, 2009
Quoting BurnedAfterPosting:


That is some pretty steep allegations, I would say you are wrong, but we will see.

just saying maybe it will maybe it won't time, dust and wind shear will tell
Member Since: June 13, 2009 Posts: 2 Comments: 12168
882. OhioCanes1667
9:29 PM GMT on July 16, 2009
Quoting wunderkidcayman:
good afternoon everyone you will see a yellow circle at the 8:00 two I have been watching it all day and I was at the met office today working and we talked about it and it is possible we will see a ts fay event but maybe weaker


Ummm the atlantic is about as clear this late into the season as I ever remember it being (having lurked here for a couple of years)....
881. BurnedAfterPosting
9:27 PM GMT on July 16, 2009
Quoting wunderkidcayman:
good afternoon everyone you will see a yellow circle at the 8:00 two I have been watching it all day and I was at the met office today working and we talked about it and it is possible we will see a ts fay event but maybe weaker


That is some pretty steep allegations, I would say you are wrong, but we will see.
880. LPStormspotter
9:26 PM GMT on July 16, 2009
Quoting wunderkidcayman:
good afternoon everyone you will see a yellow circle at the 8:00 two I have been watching it all day and I was at the met office today working and we talked about it and it is possible wee will see a ts fay event but maybe weaker


Thanks for your insight
Member Since: July 17, 2008 Posts: 0 Comments: 385
879. WxLogic
9:26 PM GMT on July 16, 2009
Quoting atmoaggie:
Such a thing would be somewhat funny, but is awful close to reality for me.

Real life scripting: If NDBC has a data outage, or a lot of their data becomes stale by more than 2 hours, my phone actually does go off every 20 minutes.

Same with GFS.
Same with WaveWatch.
Same with NASA GSFC SST.
Same with Navy SST analysis.
Same with Ocean Forecast Salinity.
And others.


You guys using Open source LINUX, or proprietary platforms (e.g. SUN, HP-UX, etc...)?
Member Since: August 14, 2008 Posts: 4 Comments: 4977
877. atmoaggie
9:21 PM GMT on July 16, 2009
Such a thing would be somewhat funny, but is awful close to reality for me.

Real life scripting: If NDBC has a data outage, or a lot of their data becomes stale by more than 2 hours, my phone actually does go off every 20 minutes.

Same with GFS.
Same with WaveWatch.
Same with NASA GSFC SST.
Same with Navy SST analysis.
Same with Ocean Forecast Salinity.
And others.
Member Since: August 16, 2007 Posts: 6 Comments: 12463
876. wunderkidcayman
9:18 PM GMT on July 16, 2009
good afternoon everyone you will see a yellow circle at the 8:00 two I have been watching it all day and I was at the met office today working and we talked about it and it is possible we will see a ts fay event but maybe weaker
Member Since: June 13, 2009 Posts: 2 Comments: 12168
875. WxLogic
9:16 PM GMT on July 16, 2009
Quoting atmoaggie:


I've already got dibs to write a script that scans this, and all other blogs every 20 seconds, searches for use of the word "Carolinas" (grep -i to find all upper and lower case combinations), compares the offense against a database of previous offenses, and sends Presslord a text message, email, IM, sets off his house alarm, and car alarm if it is indeed a new offense. (just kidding about the car alarm)

Almost done with it. In testing now. Hey Press, was it loud at your house a couple of minutes ago?


LMAO!!!
Member Since: August 14, 2008 Posts: 4 Comments: 4977
874. WxLogic
9:14 PM GMT on July 16, 2009
Quoting weatherblog:
NAM shouldn't be used for anything invloving tropical cyclones. The best tool for that is the GFS, GFDL, EMCWF, HWRF, UKMET, and NOGAPS


Indeed... is good for anyone that is not aware of this to know. I use NAM for other purposes, but don't belittle NAM as it has proven itself a couple times in this and past seasons.
Member Since: August 14, 2008 Posts: 4 Comments: 4977
873. SavannahStorm
9:13 PM GMT on July 16, 2009
Quoting atmoaggie:


I've already got dibs to write a script that scans this, and all other blogs every 20 seconds, searches for use the word "Carolinas" (grep -i to find all upper and lower case combinations), compares the offense against a database of previous offenses, and sends Presslord a text message, email, IM, sets off his house alarm, and car alarm if it is indeed a new offense. (just kidding about the car alarm)

Almost done with it. In testing now. Hey Press, was it loud at your house a couple of minutes ago?


LOL!
Member Since: September 22, 2005 Posts: 18 Comments: 2343
872. atmoaggie
9:11 PM GMT on July 16, 2009
Quoting Myakka:
Me giving back: If anyone can think of a helpful software utility (IM alert, analysis, whatever) I could write to help out the community please private message me. I have over 11 years of software development experience and want to give back when possible.


I've already got dibs to write a script that scans this, and all other blogs every 20 seconds, searches for use of the word "Carolinas" (grep -i to find all upper and lower case combinations), compares the offense against a database of previous offenses, and sends Presslord a text message, email, IM, sets off his house alarm, and car alarm if it is indeed a new offense. (just kidding about the car alarm)

Almost done with it. In testing now. Hey Press, was it loud at your house a couple of minutes ago?
Member Since: August 16, 2007 Posts: 6 Comments: 12463
871. LPStormspotter
9:10 PM GMT on July 16, 2009
Quoting cchsweatherman:
Just been lurking mainly periodically throughout the afternoon, but have now decided to join in on the discussion.

Seems like the main conversation has focussed on the strong tropical wave crossing 30W this afternoon. It does look rather impressive since it does have a well-defined, albeit broad low-level circulation. But, I don't believe the convection that has been seen developing has been from the tropical wave, but rather the usual mass low-level convergence associated with the ITCZ. Before we can really get a good judgment on this disturbance, we need this to leave the ITCZ and become a solitary feature.

For right now, with little computer model support and considering the distance away from any land, there's nothing to become excited or concerned about. We still have plenty of time to watch this feature before it could even potentially become a concern.


Like always such knowledge
Member Since: July 17, 2008 Posts: 0 Comments: 385
870. cchsweatherman
9:08 PM GMT on July 16, 2009
Just been lurking mainly periodically throughout the afternoon, but have now decided to join in on the discussion.

Seems like the main conversation has focussed on the strong tropical wave crossing 30W this afternoon. It does look rather impressive since it does have a well-defined, albeit broad low-level circulation. But, I don't believe the convection that has been seen developing has been from the tropical wave, but rather the usual mass low-level convergence associated with the ITCZ. Before we can really get a good judgment on this disturbance, we need this to leave the ITCZ and become a solitary feature.

For right now, with little computer model support and considering the distance away from any land, there's nothing to become excited or concerned about. We still have plenty of time to watch this feature before it could even potentially become a concern.
Member Since: April 14, 2007 Posts: 8 Comments: 5169
869. LPStormspotter
9:08 PM GMT on July 16, 2009
Gezzz.. Where did everyone go?
Member Since: July 17, 2008 Posts: 0 Comments: 385
868. Cavin Rawlins
9:00 PM GMT on July 16, 2009
Quoting weatherblog:
NAM shouldn't be used for anything invloving tropical cyclones. The best tool for that is the GFS, GFDL, EMCWF, HWRF, UKMET, and NOGAPS


Correct.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
867. weatherblog
8:57 PM GMT on July 16, 2009
NAM shouldn't be used for anything invloving tropical cyclones. The best tool for that is the GFS, GFDL, EMCWF, HWRF, UKMET, and NOGAPS
Member Since: July 10, 2006 Posts: 27 Comments: 1623
866. LPStormspotter
8:56 PM GMT on July 16, 2009
Quoting RitaEvac:
But it could of been messed up and meant August and September,


Nawww.. Lets stick with the 1st one. besides for those of us that moved back home in Feb. are not ready to leave again..lol
Member Since: July 17, 2008 Posts: 0 Comments: 385
865. WxLogic
8:53 PM GMT on July 16, 2009
18Z NAM... is now becoming more in line with the CMC southern track. As expected (at least from me) the strong open wave should be traversing the Carib. Island chains in 84 to 96 hours and emerging south of Cuba... will be interesting to see how the trough split is going to play out as well as shear later in the period.
Member Since: August 14, 2008 Posts: 4 Comments: 4977
864. taistelutipu
8:52 PM GMT on July 16, 2009
RE: 777.
quite odd theory in this video. I don't think it can be taken seriously (it was a joke, wasn't it?) because I doubt that there is any scientific evidence that counter-clockwise spinning storms are stronger than the clockwise counterparts in the Southern hemisphere.

I would say no, because the lists of the most intense cyclones for each basin contain category 5 storms. Most of these storms occur in the West Pacific but since this basin has most storms anyways it is expected to have the biggest number of cat. 5 storms, too.

So I don't think that the spinning direction has any influence on the intensity since the coriolis force is the reason why it is different in each hemisphere.

Finally I don't want to imagine what amplitude for these 'counterwaves' would be needed to have any influence on a hurricane. Even if they are beyond our range of hearing you never know whether whales, birds or insects go nuts or die after being exposed to them.

Ok, I admit it. I'm bored. Otherwise it would have never got that much pondering. But now I know what I suspected, there can be cat. 5 cyclones anywhere in the tropical basins and I found a handy list of notable cyclones. Boredom sorted. :-)
Member Since: August 20, 2007 Posts: 12 Comments: 639
863. RitaEvac
8:52 PM GMT on July 16, 2009
But it could of been messed up and meant August and September,
Member Since: July 14, 2008 Posts: 1 Comments: 9630
862. RitaEvac
8:50 PM GMT on July 16, 2009
One good thing going for us is the Almanac was wrong about a storm hitting TX in June, so everything is looking good down the road
Member Since: July 14, 2008 Posts: 1 Comments: 9630
861. smmcdavid
8:50 PM GMT on July 16, 2009
press... are you in here causing trouble again? What have I told you?
Member Since: September 20, 2005 Posts: 31 Comments: 2309
860. jeffs713
8:48 PM GMT on July 16, 2009
Quoting caneluver:
no development expected in the near term...........


Looks to be developing to me, convectioin with some spin going on

Its still fresh off the coast, needs to persist some more. Keep in mind the spin doesn't look to be pronounced at the low level per quikscat.
Member Since: August 3, 2008 Posts: 16 Comments: 5886
859. RitaEvac
8:47 PM GMT on July 16, 2009
Gulf and Carribbean are cooking, breeding ground later this season
Member Since: July 14, 2008 Posts: 1 Comments: 9630
858. presslord
8:46 PM GMT on July 16, 2009
...which, by the way, is in South Carolina...
Member Since: August 13, 2007 Posts: 0 Comments: 10492
857. HadesGodWyvern (Mod)
8:46 PM GMT on July 16, 2009
National Hurricane Center
Tropical Cyclone Advisory #28
TROPICAL DEPRESSION, FORMER CARLOS (EP042009)
21:00 PM UTC July 15 2009
====================================

At 18:00 PM UTC, Tropical Depression, Former Carlos (1007 hPa) located at 9.4N 136.4W or 1724 NM west-southwest of the southern tip of Baja California Peninsula has sustained winds of 25 knots with gusts of 35 knots. The cyclone is reported as moving west at 14 knots.

THIS IS THE FINAL ADVISORY ON THIS SYSTEM FROM THE NATIONAL HURRICANE CENTER
Member Since: May 24, 2006 Posts: 51 Comments: 45651
856. Cavin Rawlins
8:45 PM GMT on July 16, 2009
I did saw the the visible images but I would look for persistence, becuz we all know how the wave had looked just 2 days ago. Also, waves don't go poof, convection do. Wave axis always remains regardless of the enviroment. Also a vigorous tropical wave as those currently in the Atlantic are troublesome when they reach the Western Caribbean, not just in tropical development but heavy rains. Most of the major flooding events in the islands are caused by tropical waves. Most recent, the wave that spawned Jeanne in 2004.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
855. RitaEvac
8:45 PM GMT on July 16, 2009
Member Since: July 14, 2008 Posts: 1 Comments: 9630

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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.