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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Quoting Acemmett90:

winds and presure is falling even with the shear at a bouy aleast 200 miles away
Station 42060
NDBC
Location: 16.500N 63.5W
Conditions as of:
Fri, 3 Jul 2009 17:50:00 UTC
Winds: ENE (60) at 17.5 kt gusting to 21.4 kt
Significant Wave Height: 5.9 ft
Dominant Wave Period: 5 sec
Atmospheric Pressure: 30.02 in and falling
Air Temperature: 83.5 F
Dew Point: 75.7 F
Water Temperature: 83.7 F


Pressures fall diurnally in the tropics at this time of day. That pressure reading is very high.
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Quoting wunderkidcayman:
Link
has the chance to develop

winds and presure is falling even with the shear at a bouy aleast 200 miles away
Station 42060
NDBC
Location: 16.500N 63.5W
Conditions as of:
Fri, 3 Jul 2009 17:50:00 UTC
Winds: ENE (60°) at 17.5 kt gusting to 21.4 kt
Significant Wave Height: 5.9 ft
Dominant Wave Period: 5 sec
Atmospheric Pressure: 30.02 in and falling
Air Temperature: 83.5 F
Dew Point: 75.7 F
Water Temperature: 83.7 F
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The sub-tropical jet screaming through the Caribbean won't let this wave develop. Just because a tropical wave has thunderstorms with it doesn't necessarily mean it has a chance. In occasions such as this, the thunderstorms are only a result of upper-level divergence, not of any particular effort by the tropical wave or favorable conditions. Once this gets west of the islands you'll see convection diminish considerably.
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My blog update.
Member Since: December 21, 2007 Posts: 13 Comments: 3046
Quoting wunderkidcayman:
Link
has the chance to develop

has upper level devergance

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Link
has the chance to develop
Member Since: June 13, 2009 Posts: 2 Comments: 12316
nice view of both waves
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Quoting KEEPEROFTHEGATE:
a watched pot never boils

lol

that is not true ive tried it
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Just stay calm folks, yall will get your Ana. And most likely this month too.
Member Since: July 8, 2005 Posts: 259 Comments: 24455
FOR THE EASTERN NORTH PACIFIC...EAST OF 140 DEGREES WEST LONGITUDE..

1. CLOUDINESS AND THUNDERSTORMS ARE ASSOCIATED WITH AN AREA OF
DISTURBED WEATHER LOCATED SEVERAL HUNDRED MILES SOUTH-SOUTHWEST OF
ACAPULCO MEXICO. SOME SLOW DEVELOPMENT OF THIS SYSTEM IS POSSIBLE
OVER THE NEXT FEW DAYS AS IT MOVES WEST-NORTHWESTWARD.

Okay here's something in the tropics to look at too.
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Quoting wunderkidcayman:




It doesn't matter how much convection gets fired up cause that strong shear is going to blow it away all day long.
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Interesting about TD 1, when I opened the link I expected it to be about the Florida low which got organized as it moved ashore in Al. and Ms. Any plans on declaring this one?
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Looks like the NOGAPS thakes that Subtropical Low to development.
Member Since: December 21, 2007 Posts: 13 Comments: 3046
Quoting AllStar17:
If the NHC is bored now......what do they do in the offseason?


Normally do research on past seasons...get ready for the Hurricane Conference is spring...and do speeches here and there.

They already did their report for TD 1.
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Wave is still holding together and firing convection despite strong shear.

Member Since: June 29, 2009 Posts: 13 Comments: 5315


Member Since: June 13, 2009 Posts: 2 Comments: 12316
a watched pot never boils

lol
Member Since: July 15, 2006 Posts: 175 Comments: 54781
If the NHC is bored now......what do they do in the offseason?
Member Since: June 29, 2009 Posts: 13 Comments: 5315
Quoting WPBHurricane05:
Why the heck do the keep talking about a Nontropical low in the North Atlantic...those form all the time. They must be really bored.

August 15th will soon be here. If we don't have a Named storm/hurricane by than, this blog will likely self destruct.


Only as bored as we are, lol

And I know... It's only early July, we've been spoiled lately, but I still want to track something, not even the WPAC has come through.
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Quoting WPBHurricane05:
Why the heck do the keep talking about a Nontropical low in the North Atlantic...those form all the time. They must be really bored.

August 15th will soon be here. If we don't have a Named storm/hurricane by than, this blog will likely self destruct.


I find it very frustrating that they'll name or notice these things way out in the middle of nowhere but then it's nearly impossible to get them to name systems like Alex and Gaston in 2004 that were very close to the coast. Obviously those 2 got named but there have been many systems including 90L this year that the NHC wouldn't even come close to naming, and they affected people. The Azores Low affects pretty much nobody. Apparently they don't realize that rogue storms such as the ones that can form off the Carolinas can capsize ships, and the ships aren't ready for it because the forecast says SW winds 15 knots with light showers...then they run into howling gales from the NE with thunderstorms and 15-foot waves and they're thinking where did this come from? The NHC more often than not doesn't even pay attention to such things, or name them if they meet criteria. The inconsistency is astounding.
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827. 7544
stop looking and something might form lol
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Why the heck do the keep talking about a Nontropical low in the North Atlantic...those form all the time. They must be really bored.

August 15th will soon be here. If we don't have a Named storm/hurricane by than, this blog will likely self destruct.
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My gosh, that wind shear just won't give in. And I badly want that thing to become a subtropical storm too in the central Atlantic and be a fish storm... Because people I know have started calling it "Diana's swirly thing." lol

But in all seriousness, it doesn't seem like it'll develop with the wind shear not looking to be letting up any before the cold front reaches it.
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Not much change.

000
ABNT20 KNHC 031747
TWOAT
TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
200 PM EDT FRI JUL 3 2009

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

A NON-TROPICAL AREA OF LOW PRESSURE LOCATED ABOUT 1000 MILES
WEST-SOUTHWEST OF THE AZORES CONTINUES TO PRODUCE AN AREA OF
SHOWERS AND THUNDERSTORMS DISPLACED TO THE EAST OF ITS CENTER.
UPPER-LEVEL WINDS REMAIN UNFAVORABLE FOR DEVELOPMENT OF THIS SYSTEM
INTO A TROPICAL OR SUBTROPICAL CYCLONE. THERE IS A LOW CHANCE...
LESS THAN 30 PERCENT...OF THIS SYSTEM BECOMING A TROPICAL OR
SUBTROPICAL CYCLONE DURING THE NEXT 48 HOURS.

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

$$
FORECASTER BEVEN

Member Since: June 29, 2009 Posts: 13 Comments: 5315
000
ABNT20 KNHC 031747
TWOAT
TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
200 PM EDT FRI JUL 3 2009

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

A NON-TROPICAL AREA OF LOW PRESSURE LOCATED ABOUT 1000 MILES
WEST-SOUTHWEST OF THE AZORES CONTINUES TO PRODUCE AN AREA OF
SHOWERS AND THUNDERSTORMS DISPLACED TO THE EAST OF ITS CENTER.
UPPER-LEVEL WINDS REMAIN UNFAVORABLE FOR DEVELOPMENT OF THIS SYSTEM
INTO A TROPICAL OR SUBTROPICAL CYCLONE. THERE IS A LOW CHANCE...
LESS THAN 30 PERCENT...OF THIS SYSTEM BECOMING A TROPICAL OR
SUBTROPICAL CYCLONE DURING THE NEXT 48 HOURS.

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

$$
FORECASTER BEVEN


Nothing much has changed.
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Quoting IKE:
1977...



They had a Category 5 that year too.
Only takes one.
Member Since: July 8, 2005 Posts: 259 Comments: 24455
Quoting Levi32:


It's taking it to sub-tropical. This is the kind of thing that can happen in this pattern.



Thank you. Looks like the CMC makes the 1st storm in the EPAC a hurricane.
Member Since: June 29, 2009 Posts: 13 Comments: 5315
well one model is bring 2 epac storms and a possible one off the carolinas
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Let's make sure we have this right for the 4th.

Eye protection --- √
Water (ice is water, right) --- √
Adult Supervision --- √
Water Mellon ( does that count as water too ) --- √

That covers it. Have a Happy all !

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Quoting IKE:
12Z CMC action off of the Carolina's

***inserts foot in mouth***

lmao
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Quoting AllStar17:
12Z CMC spins up 2 storms in the EPAC during that time period. And, we will have to watch the area off the Carolinas over the next week. Is the CMC making it a Tropical Storm (if not....how strong is it making it?)


It's taking it to sub-tropical. This is the kind of thing that can happen in this pattern. What it shows is a tropical storm but the CMC is the worst model for projecting intensity. It likes to bomb everything out no matter what....which makes it basically the model that shows the worst-case scenario every time.

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12Z CMC spins up 2 storms in the EPAC during that time period. And, we will have to watch the area off the Carolinas over the next week. Is the CMC making it a Tropical Storm (if not....how strong is it making it?)
Member Since: June 29, 2009 Posts: 13 Comments: 5315
..Lite fuse..!

....get away
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814. IKE
12Z CMC action off of the Carolina's

***inserts foot in mouth***
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting Patrap:
Google Images,


...."Animated fireworks"


thanks!
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Google Images,


...."Animated fireworks"
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811. IKE
And I was involved in one in the 70's...

Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting IKE:
1977...



LOL Hurricane Babe.
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Quoting Patrap:
Happy 4th of July Weekend..



Where did you get these animated fireworks. Oh and by the way have a safe 4th of july too.
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808. IKE
Quoting btwntx08:

u meant 1977 lol


Thank God for the edit feature.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Anta took a pretty interesting track. SW in the GOM into Old Mexico as a Cat. 5, interesting.
Member Since: June 29, 2009 Posts: 13 Comments: 5315
Quoting IKE:


I put up the wrong year. I edited to 1997.

u meant 1977 lol
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Quoting AllStar17:
Just a question--

When the jet stream moves north in a few days, will that create more favorable conditions in the GOM and Caribbean?


Maybe in the GOM, but the Caribbean is going to be plagued by upper lows and TUTTs for at least another week.
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804. IKE
1977...

Member Since: June 9, 2005 Posts: 23 Comments: 37858
803. IKE
Quoting AllStar17:


Looks like Alma made landfall in South America that year!


I put up the wrong year. I edited to 1977.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
802. IKE
I accidentally put up 1974. I edited to 1977.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting IKE:
I'm basing my thought on an increasing El Nino...I think shear is going to be a problem this year with Atlantic systems.

Here's the year 1977. I worked at a travel park on the Florida panhandle beaches that summer and don't remember any system affecting us. Sure enough there was nothing. Six systems the whole year! I don't remember anything affecting this area that entire decade....



Looks like Alma made landfall in South America that year!
Member Since: June 29, 2009 Posts: 13 Comments: 5315
800. IKE
I'm basing my thought on an increasing El Nino...I think shear is going to be a problem this year with Atlantic systems.

Here's the year 1977. I worked at a travel park on the Florida panhandle beaches that summer and don't remember any system affecting us. Sure enough there was nothing. Six systems the whole year! I don't remember anything affecting this area that entire decade....

Member Since: June 9, 2005 Posts: 23 Comments: 37858
Just a question--

When the jet stream moves north in a few days, will that create more favorable conditions in the GOM and Caribbean?
Member Since: June 29, 2009 Posts: 13 Comments: 5315
Levi, and causes more problems in here
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Quoting Levi32:


That's exactly why inactive Cape Verde seasons don't mean inactive or uncostly seasons. It causes more storms to form closer to home.


Yeah, and they could become just as dangerous as a large Cape Verde hurricane (i.e. Katrina - was not a CV storm)
Member Since: June 29, 2009 Posts: 13 Comments: 5315

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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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