August hurricane outlook

By: Dr. Jeff Masters , 3:02 PM GMT on July 31, 2009

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The Atlantic remains quiet today, with no threat areas to discuss and no models calling for tropical storm formation over the seven days. Not much has changed in the Atlantic since my mid-July Atlantic hurricane outlook posted two weeks ago. However, we are now at the cusp of when hurricane activity begins a steep rise (Figure 1). Early August is typically when wind shear begins a major decline, sea surface temperatures continue to rise, African dust and dry air outbreaks diminish, and the African Monsoon and Intertropical Convergence Zone (ITCZ) become quite active, spawning frequent and powerful tropical waves. These tropical waves serve as the instigators of about 85% of all major hurricanes.

Since the current active hurricane period began in 1995, ten out of fourteen years (71%) have had a named storm form during the first half of August, with an average of 1.4 named storms per year. The last nine years in a row have had a named storm form during the first half of August, but the previous four year stretch (1996 - 1999), did not have any storms form.


Figure 1. The seasonal distribution of Atlantic hurricane activity shows a steep rise at the beginning of August. Image credit: NHC.

Sea Surface Temperatures
Eighty-five percent of all major hurricanes form in the Main Development Region (MDR) of the Atlantic, from the coast of Africa to the coast of Central America, between 10° and 20° latitude. This region also spawns 60% of all weaker hurricanes and tropical storms. Sea Surface Temperature (SST) anomalies in the MDR have slowly but steadily risen during July, and now stand at a respectable 0.5°C (0.9°F) above average (Figure 2). SSTs are well below the record levels observed in 2005 and 2006, when they were up to 2°C above average over large portions of the Main Development Region. Still, there is plenty of heat energy available for strong hurricanes to form this year. The strength of the Azores-Bermuda high has been below average over the past month, driving 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 slightly below average-strength trade winds through mid-August, so SST anomalies should continue to warm during this period.


Figure 2. Sea Surface Temperature (SST) departure from average for July 30, 2009. SSTs were about 0.5°C (0.9°F) above 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 an El Niño episode. Image credit: NOAA/NESDIS

El Niño
El Niño conditions have remained steady over the tropical Eastern Pacific over the past month. Ocean temperatures in the area 5°N - 5°S, 120°W - 170°W, also called the "Niño 3.4 region", remain at 0.8°C above average, which is 0.3°C above the threshold for a weak El Niño, according to the Australian Bureau of Meteorology (Figure 3). An increase of another 0.2°C would push the current El Niño into the "moderate" category. NOAA's Climate Prediction Center issued an El Niño Advisory earlier this month, and predicts that El Niño conditions will intensify over the next few months, and last through the coming winter. The latest set of mid-July runs of the El Niño computer models are almost universally calling for El Niño conditions to remain 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. The NOAA CFS model is calling for continued above-average wind shear over most of the tropical Atlantic for the August-September-October peak part of hurricane season.


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 "Niño 3.4 region"). El Niño conditions exist when the SST in this region rises 0.5°C above average. As of July 31, 2009, SSTs in the Niño 3.4 region had risen to 0.83°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, but in August the jet stream retreats to the north, and wind shear typically falls.

Wind shear over the past month (Figure 4) has mostly been above average over the tropical Atlantic, particularly over the Caribbean. The presence of El Niño conditions over the tropical Eastern Pacific may be primarily responsible for this enhanced shear. However, wind shear has been slowly falling over the southern portion of the Caribbean and southern MDR over the past week, and is forecast by the GFS model to fall to near-average levels by mid-August. This should present a more favorable environment for hurricanes to form in by mid-month.


Figure 4. Departure of wind shear from average in m/s for the 1-month period ending July 27, 2009. Higher than average wind shear (blue colors) was observed over the Caribbean. The El Niño conditions over the tropical Eastern Pacific may be primarily responsible for this enhanced shear. Image credit: NOAA Climate Prediction Center.

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 diminish in the coming month, allowing a greater chance for African tropical waves to develop.

Steering currents
The steering current pattern has remained virtually the same all summer. A persistent trough of low pressure has remained entrenched over the Eastern U.S., bringing cool and relatively moist weather to the northeastern portion 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. It is often difficult to break a months-long steering current pattern like the current one, and it's reasonable to forecast that the current steering pattern will continue to dominate into September.

Summary
Recent history suggests a 71% chance of a named storm occurring in the first half of August. However, this is not a typical year. The ITCZ has been remarkably inactive, and there have been an unusually low number of tropical waves coming off the coast of Africa. Although SST anomalies should continue to rise and wind shear should slowly fall over the next few weeks, the computer models suggest no significant changes to the current inactive weather pattern. I'll go with a 30% chance of a named storm forming in the first half of August.

I'll have a new post on Monday.

Jeff Masters

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Quoting AussieStorm:

Just right click on the image and select copy image location.
Ok Thanks.
Member Since: July 14, 2009 Posts: 51 Comments: 1731
Quoting cyclonekid:

I'm talking about posting the pic... of the TWO. :D Sorry for any misunderstandings

Just right click on the image and select copy image location.
Member Since: September 30, 2007 Posts: 9 Comments: 15940
I was looking for a link like this and found this...much more widespread then the other...it even inculdes the Indian Ocean. :D

Link
Member Since: July 14, 2009 Posts: 51 Comments: 1731
The monsoon trough extends very far out from Africa, all the way to 45W. The monsoon trough and ITCZ are basically equatorial troughs but the ITCZ is convergence between SE and NE Trades (not very conducive for circulation) but the monsoon trough lies between SW and NE (very conducive for circulation. Out feature nearing 30W is embedded in the monsoon trough, so be careful when attributing the likelihood of development based on "its embedded in the ITCZ". The monsoon trough accounts for more than 80% of EPAC and WPAC cyclones.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting Weather456:


near 51W, I assume. QuikSCAT also captured half of turning at the surface. Don't see it tied to anything significant but been watching it.
Yep that's it
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Quoting cyclonekid:

I see some cyclonic turning....anyone else see it?


near 51W, I assume. QuikSCAT also captured half of turning at the surface. Don't see it tied to anything significant but been watching it.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting AussieStorm:

EPAC Tropical Weather Outlook
Link

I'm talking about posting the pic... of the TWO. :D Sorry for any misunderstandings
Member Since: July 14, 2009 Posts: 51 Comments: 1731

GOESEastIR
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Quoting cyclonekid:

How do you post that TWO...i've been trying ever since i joined WU.

EPAC Tropical Weather Outlook
Link
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Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting Weather456:
Rainbow imagery revealed the postion of the ITCZ near 11-12N. The feature nearing 30W and a little south of the ITCZ near 9-10N. The ITCZ is rather high and could only mean one thing - the CATL is not as stable as one may think. Also notice the convective burst associated with the feature approaching 30W.

I see some cyclonic turning....anyone else see it?
Member Since: July 14, 2009 Posts: 51 Comments: 1731
2149. IKE
Quoting sporteguy03:


looks like something is near 30W if not a wave just ITCZ??


That's what it is according to the NHC...ITCZ.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Rainbow imagery revealed the postion of the ITCZ near 11-12N. The feature nearing 30W and a little south of the ITCZ near 9-10N. The ITCZ is rather high and could only mean one thing - the CATL is not as stable as one may think. Also notice the convective burst associated with the feature approaching 30W.
Member Since: July 24, 2005 Posts: 407 Comments: 19076

AtlanticWideView
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Quoting AussieStorm:
Will we get 2 Canes or will they tear each other up or possible Fujiwara Effect.


FOR THE EASTERN NORTH PACIFIC...EAST OF 140 DEGREES WEST LONGITUDE..

1. AN AREA OF DISTURBED WEATHER LOCATED ABOUT 1100 MILES SOUTHWEST OF
THE SOUTHERN TIP OF BAJA CALIFORNIA HAS BECOME BETTER ORGANIZED
OVER THE PAST SEVERAL HOURS. CONDITIONS APPEAR FAVORABLE FOR
ADDITIONAL DEVELOPMENT...AND THIS SYSTEM COULD BECOME A TROPICAL
DEPRESSION OVER THE NEXT DAY OR SO AS IT MOVES WESTWARD OR
WEST-NORTHWESTWARD AT AROUND 15 MPH. THERE IS A MEDIUM CHANCE...30
TO 50 PERCENT...OF THIS SYSTEM BECOMING A TROPICAL CYCLONE DURING
THE NEXT 48 HOURS.

2. SHOWERS AND THUNDERSTORMS ASSOCIATED WITH A BROAD AREA OF LOW
PRESSURE LOCATED ABOUT 700 MILES SOUTH OF THE SOUTHERN TIP OF BAJA
CALIFORNIA HAVE INCREASED AND BECOME BETTER ORGANIZED OVER THE PAST
SEVERAL HOURS. THIS SYSTEM ALSO HAS THE POTENTIAL TO DEVELOP INTO
A TROPICAL DEPRESSION OVER THE NEXT DAY OR SO AS IT MOVES WESTWARD
TO WEST-NORTHWESTWARD AT AROUND 15 MPH. THERE IS A MEDIUM
CHANCE...30 TO 50 PERCENT...OF THIS SYSTEM BECOMING A TROPICAL
CYCLONE DURING THE NEXT 48 HOURS.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.

$$
FORECASTER PASCH/ROBERTS

How do you post that TWO...i've been trying ever since i joined WU.
Member Since: July 14, 2009 Posts: 51 Comments: 1731
Quoting IKE:
Last Update: 3-AUG-2009 09:00am EDT

Although it may seem like the Atlantic hurricane season is off to a slow start when compared to recent years, the average date of development for the season's first hurricane is Aug. 14. Though most of the Atlantic Basin is free of activity, there are a few tropical waves we are watching.

There are just two tropical waves are located near 38 west and 63 west. The tropical wave along 38 west has only a few showers and thunderstorms along its southern edge. The rest of the wave is embedded with a deep layer of Saharan dust that is preventing showers and thunderstorms from developing. This area of Saharan dust will travel westward toward the Caribbean, preventing development of any system in the tropical Atlantic for the next few days.

The tropical wave along 63 west is even less organized and only has a handful of showers associated with it. This wave is not expected to enhance shower and thunderstorm activity in the Caribbean as it passes through today and tomorrow.

By AccuWeather.com Meteorologist Mike Pigott..........


What happened to the "wave" accuweather had further east of 38W? The one everyone in here is following? I guess it wasn't a wave after all.....NHC never had it as a wave.


looks like something is near 30W if not a wave just ITCZ??
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Quoting mikatnight:
Monday, August 17th...hmmmmmm



Of course, it was a Sunday night - going on through Monday morning - on another August 17th, a long long time ago...Camille.
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Is there any chance what's off the coast of Georgia and South Carolina could develop?
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Wave nearing 30W continues to become better organize.



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2140. IKE
Last Update: 3-AUG-2009 09:00am EDT

Although it may seem like the Atlantic hurricane season is off to a slow start when compared to recent years, the average date of development for the season's first hurricane is Aug. 14. Though most of the Atlantic Basin is free of activity, there are a few tropical waves we are watching.

There are just two tropical waves are located near 38 west and 63 west. The tropical wave along 38 west has only a few showers and thunderstorms along its southern edge. The rest of the wave is embedded with a deep layer of Saharan dust that is preventing showers and thunderstorms from developing. This area of Saharan dust will travel westward toward the Caribbean, preventing development of any system in the tropical Atlantic for the next few days.

The tropical wave along 63 west is even less organized and only has a handful of showers associated with it. This wave is not expected to enhance shower and thunderstorm activity in the Caribbean as it passes through today and tomorrow.

By AccuWeather.com Meteorologist Mike Pigott..........


What happened to the "wave" accuweather had further east of 38W? The one everyone in here is following? I guess it wasn't a wave after all.....NHC never had it as a wave.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
2139. cg2916
Looks like the Pacific calls for more attention than the Atlantic. That wave looks like it won't make it, in my opinion. Now, if 9L is the one on the right, I think that it will develop before 99L, but who knows?

I'm surprised by how much the models pick up on activity due to the MJO. Although the MJO DOES help activity pick up. It looks like to me that the main reason it's been so quiet lately is because tropical waves die out before they get a chance due to the SAL, and maybe the MJO will change that.
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Quoting clwstmchasr:
We know too well what The Mighty Atlantic is capable of delivering!

Chicklit. Is it my imagination or am I seeing some mid-level cloud rotatation at 9N 52W? Look at the visible as well.

Great swing clw...yeah, there's some rotation there as well. But as Ike pointed out, Shear is set up as a nice 'roadblock' in the Caribbean. Of course, the problem is, after that there is wave after wave and another one is about to come off Cape Verde at maybe a higher latitude. As 456 said, they have to break out of the ITCZ and then there's the MJO pattern predicted to change. But also there's a new burst of SAL from CV, so that would inhibit a higher lat. wave. Hopefully, Dr. Masters will address all of this in his blog promised for today.
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look around 35-40West in a few days for possible development that is an area that CV systems tend to get going.
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Anyone care to outline the major factors preventing development and the forecast of them now and during the next 2 weeks? Thanks...
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Monday, August 17th...hmmmmmm

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moistureladenseas
We know too well what The Mighty Atlantic is capable of delivering!
And here come's another one... forpetesake
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seems developed, any sugest track?
Member Since: July 21, 2009 Posts: 0 Comments: 552
98E has a good CH of becomeing name 1st be for 99E i say 99E has too move a way a little more be for it can do some in
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oops nevere mine i this look what we had last


round 1


90E bust

91E bust

92E be comes TD 1E


93E be comes ANDRES

94E be comes BLANCA

95E be comes CARLOS

96E be comes DOLORES

97E be comes LANA


97E was LANA
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Morning looks pacific has some activity.
Member Since: July 21, 2009 Posts: 0 Comments: 552
the potential for hyper activity in the eastern atlantic is very evident as the waves line up over africa
Member Since: August 22, 2006 Posts: 0 Comments: 2715
Good Morning All.........Other than the wave now just past the CV islands (that while holding on to convection is still embedded in the ITCZ as noted by 456 and others), it's pretty much crystal clear out there (and very dry in the Central Atlantic). Hate late starting seasons because of the potential for a real big storm out of the blocks...Again, and in terms of historical/analog comparisons, the average start date of an August season is August 14th..........Let's see what will happen over the next two weeks.
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Quoting Tazmanian:



did they for get 97E???


invest_RENUMBER_ep972009_ep062009.ren


Lana
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Quoting nrtiwlnvragn:
EP 98 2009080312 BEST 0 129N 1115W 25 0 DB



did they for get 97E???
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EP 99 2009080312 BEST 0 100N 1208W 25 0 DB
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Quoting IKE:
Look at the continued shear(road blocks) in the Caribbean and north of 18 north, east of the islands. To me it's El Nino. Plus the east-PAC is soon to have more systems....



Ike this is a pretty typical sign of el nino with fast westerlies across most of the caribbean and gom no suprise there.
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Active wave across the atl last night looks less organized this morning likly due to sal in the vicinity.
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456. i am in total agreement with your analysis. i did indicate the same in my earlier comments. somehow i still believe that the system will be a TD/ WEAK TS by the time it reaches the islands on the weekend
Member Since: August 22, 2006 Posts: 0 Comments: 2715
EP 98 2009080312 BEST 0 129N 1115W 25 0 DB
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Jasonisuncoolman10

You better behave with your knew handle, or you'll be banned for good this time.
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Interesting lol



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Anyone notice the stationary convection at about 30N 80W?

Link

Just a stationary thunderstorm?
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Tropical Update
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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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