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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current ssts

try this.. looks like most of the gulf is running 30 degrees celcius
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Quoting Stormchaser2007:
94E will be entering a more stable environment soon.



Looks pretty good at the moment. I say it develops later tonight or early tomorrow.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
Quoting SomeRandomTexan:
my bad then... i will go get another


Its fine...I dont know of any other TCHP sites though.
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94E will be entering a more stable environment soon.

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my bad then... i will go get another
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Quoting CybrTeddy:


Arent they the same people who said there would only be like 10 storms in 2007? And 6 this year?


Nope.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
Quoting SomeRandomTexan:


thats not the current sst?


No it hasnt updated in a while.
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Quoting Stormchaser2007:


Its been that way since late june. Something is wrong with the site.


thats not the current sst?
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been out for a while what are we looking at in the tropics as far as the atlantic area? trying to get updated.
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Quoting Stormchaser2007:
Potentially dangerous times ahead? lol



Wow, that is the most favorable conditions across the Atlantic I have seen all season, assuming red is favorable shear.
Member Since: June 29, 2009 Posts: 13 Comments: 5315
Quoting vortfix:
Look at all the models you want.
The UK has it pegged for now:



MET OFFICE TROPICAL CYCLONE GUIDANCE FOR NORTH-EAST PACIFIC

AND ATLANTIC

GLOBAL MODEL DATA TIME 00UTC 05.07.2009

NO TROPICAL CYCLONES ANALYSED OR FORECAST TO DEVELOP
IN THIS AREA IN THE NEXT THREE DAYS

THIS INFORMATION IS PROVIDED AS GUIDANCE FOR TROPICAL CYCLONE
RSMCS. IT REQUIRES INTERPRETATION BY TROPICAL CYCLONE SPECIALISTS
AND SHOULD NOT BE CONSIDERED AS A FINAL PRODUCT

MET OFFICE, EXETER, UK

TOO 050502




Arent they the same people who said there would only be like 10 storms in 2007? And 6 this year?
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Potentially dangerous times ahead? lol

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Quoting SomeRandomTexan:


current TCHP


Its been that way since late june. Something is wrong with the site.
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current TCHP
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1630. IKE
What the models do show is plentiful rains over the eastern gulf-coast states.

ROTFL.
Member Since: June 9, 2005 Posts: 23 Comments: 37860
Wimbledon update

Federer leads 11-10 in the 5th set
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1628. beell
LOL-he said "bear watching"

Wonder if S TX will get a little rain?

think I'll go outside and wait-Good Afternoon, ya'll
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1627. Patrap
New Orleans Last evening 9pm CST,Dueling Fireworks Barges on the Mississippi River..



Member Since: July 3, 2005 Posts: 428 Comments: 129844
Quoting floridastorm:
the tropics are quiet


The EPAC has a possible storm brewing, and some models are predicting some development in the
Atlantic over the next 2 weeks. They may be quiet now, but this is typical and the tropics still bear watching.
Member Since: June 29, 2009 Posts: 13 Comments: 5315
the tropics are quiet
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1623. beell
See ya later Oss!
Grin and bear it!
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Quoting Ossqss:


Thanks, here is what I had for UK met. L8R

Link

Thanks
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1621. beell
Quoting KEHCharleston:
1603. beell
Still here - Thanks beell


Sure thing! I guess a shorter answer and one more towards your question-a tendency chart cannot easily tell you if the trend in one direction or the other will continue. A shear model would be better after 24 hours.
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1619. Dar9895
Quoting beell:
Morning, all,

GFS is finally starting to look normal for mid-July. Strong signals in the model for two or three strong tropical waves that make the traverse across the Atlantic. First one to enter the Carribean next Monday or Tuesday. A stronger modeled wave behind this one. Change is in the air?

Both charts @700mb
07/05 06Z GFS at 216 hrs
Tuesday, 07/14


From the 00Z at 228 hrs
Tuesday, 07/14

Yep this model seems very reasonable.
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1618. Ossqss
Quoting AussieStorm:

Ossqss, Found this Google Earth add-on for TCHP
Link


Thanks, here is what I had for UK met. L8R

Link
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1616. KEEPEROFTHEGATE (Mod)
foolcasting

rofl
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1614. KEEPEROFTHEGATE (Mod)
Quoting vortfix:
Models, models, models.


More models.




reaching reaching reaching
more reaching

lol
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Quoting IKE:


I'm fixing to get 2+ inches, maybe more, in the next few days.

12Z GFS aims the eastern Caribbean wave into the BOC.....


Does it show any development?
Member Since: June 29, 2009 Posts: 13 Comments: 5315
Quoting AussieStorm:

I have the same

Does anyone have a link to the UK met?

Ossqss, Found this Google Earth add-on for TCHP
Link
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Our wave in the Caribbean firing off convection west of the islands. Maybe this will end up having a chance after all. Does anyone see rotation on this visible imagery?

Caribbean Visible Loop
Member Since: June 29, 2009 Posts: 13 Comments: 5315
1609. KEEPEROFTHEGATE (Mod)
Quoting IKE:
Buoy 42001...180 NM south of SW Pass,LA., yesterday afternoon...

water temp...88.9 degrees.
once it gets to 92 then 885 300 3238 ft but i rather not
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Awesome site I found yesterday has the ECMWF model updating faster than any other site, with 6-hour QPF maps and surface temps to 240. Try it out for today's 12z run.

Problem is, I don't think it'll be free for long. Enjoy it while it lasts.

Link
Link
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here is more more mode runs mainey for CA but it dos show the oh USA the gulf the E PAC

here the link

Link
Member Since: May 21, 2006 Posts: 5091 Comments: 115454
Quoting Ossqss:


Neat stuff, I bearly passed :)


Can anyone obtain the latest TCHP depth? Each site I go to has it for May 19, unless it is just me and my PC.

I have the same

Does anyone have a link to the UK met?
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1605. Ossqss
Quoting beell:
Awareness Test


Neat stuff, I bearly passed :)


Can anyone obtain the latest TCHP depth? Each site I go to has it for May 19, unless it is just me and my PC.
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1603. beell
Still here - Thanks beell
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1603. beell
Quoting KEHCharleston:
STUPID QUESTION TIME

The usefulness of the Shear Tendency Chart for the last 24 hours, would depend on how fluid shear is - how quickly it changes? Does shear change over a matter of days or hours?

What would be a better predictor. Shear Tendency Charts or Shear Models?

I hope this makes sense.


Morning, KEH,
If you are still here.
Shear Tendency charts are fine. But if the shear over your AOI is 40 knots, a 10 knot trend downwards is not a great amount of help.

Shear models are a better tool, imo. Works even better with a quick look at the 200mb and 850 mb charts also.

Strong upper level winds (200mb) from the west and strong low level (850mb) winds from the east result in one of the most sheariest scenarios in the southern MDR. These winds would be added together. 30@200mb + 20@850mb = approx 50 knots of zonal (east/west) shear.

30 knots from the east at 200mb, 20 from the east at 850mb yields 10 knots of zonal shear.

Hope this helps some.
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1602. IKE
Quoting AussieStorm:
4Day Precipitation


I'm fixing to get 2+ inches, maybe more, in the next few days.

12Z GFS aims the eastern Caribbean wave into the BOC.....
Member Since: June 9, 2005 Posts: 23 Comments: 37860
1601. Patrap
GOM 60 Hour Water Surface Temperature Forecast Model
Member Since: July 3, 2005 Posts: 428 Comments: 129844
http://www.nrlmry.navy.mil/archdat/atlantic/winds/scatt/qscatt/20090705.1400.qscatt.scatt.wind.atl.x. png
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Couple of flare ups in the Caribbean
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4Day Precipitation
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1597. beell
1577.
WU got their alphabet confused again.
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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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