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 AllStar17:


And unfortunately we know about 04 and 05, and for that matter last year
Yep. The last few years have had some powerful and devastating hurricanes.
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1696. IKE
12Z ECMWF develops that eastern Caribbean wave into a hurricane....in the east Pac...
Member Since: June 9, 2005 Posts: 23 Comments: 37858
1695. KEEPEROFTHEGATE (Mod)
latest info on east pacific invest 94E

ATTENTION...NATIONAL HURRICANE CENTER



NCEP COUPLED GFDL HURRICANE MODEL FORECAST MADE FOR



TROPICAL DEPRESSION INVEST 94E



INITIAL TIME 12Z JUL 5



DISCLAIMER ... THIS INFORMATION IS PROVIDED AS GUIDANCE. IT

REQUIRES INTERPRETATION BY HURRICANE SPECIALISTS AND SHOULD

NOT BE CONSIDERED AS A FINAL PRODUCT. PLEASE SEE THE TPC/NHC

OFFICIAL FORECAST.





FORECAST STORM POSITION



HOUR LATITUDE LONGITUDE HEADING/SPEED(KT)



0 16.3 108.9 290./14.0

6 16.8 109.9 296./10.7

12 17.0 111.1 281./11.8

18 17.4 112.0 297./ 9.1

24 17.7 112.9 288./ 9.1

30 17.9 113.9 277./10.3

36 17.9 115.2 270./11.7

42 17.7 115.9 260./ 7.4

48 17.7 116.8 268./ 7.7

54 17.6 117.5 263./ 7.2

60 17.6 117.9 265./ 4.1

66 17.5 118.3 261./ 3.7

72 17.5 118.6 272./ 2.7

78 17.6 119.0 284./ 3.8

84 17.7 119.2 284./ 2.4

90 17.7 119.7 269./ 4.6

96 17.5 120.0 247./ 2.9

102 17.5 120.1 249./ 1.3

108 17.4 120.2 216./ 1.3

114 17.4 120.4 265./ 2.2

120 17.2 120.7 243./ 3.0

126 17.1 121.1 257./ 4.2



490

WHXX01 KMIA 051839

CHGE77

TROPICAL CYCLONE GUIDANCE MESSAGE
1839 UTC SUN JUL 5 2009



DISCLAIMER...NUMERICAL MODELS ARE SUBJECT TO LARGE ERRORS.

PLEASE REFER TO NHC OFFICIAL FORECASTS FOR TROPICAL CYCLONE

AND SUBTROPICAL CYCLONE INFORMATION.



EAST PACIFIC OBJECTIVE AIDS FOR



DISTURBANCE INVEST (EP942009) 20090705 1800 UTC



...00 HRS... ...12 HRS... ...24 HRS. .. ...36 HRS...

090705 1800 090706 0600 090706 1800 090707 0600



LAT LON LAT LON LAT LON LAT LON

BAMS 16.4N 109.9W 17.4N 112.2W 18.0N 114.3W 18.5N 116.4W

BAMD 16.4N 109.9W 17.1N 112.0W 17.6N 114.0W 18.1N 116.0W

BAMM 16.4N 109.9W 17.2N 112.0W 17.7N 114.1W 18.2N 116.0W

LBAR 16.4N 109.9W 17.1N 112.4W 17.9N 115.3W 18.6N 118.2W

SHIP 25KTS 27KTS 31KTS 34KTS

DSHP 25KTS 27KTS 31KTS 34KTS



...48 HRS... ...72 HRS... ...96 HRS. .. ..120 HRS...

090707 1800 090708 1800 090709 1800 090710 1800



LAT LON LAT LON LAT LON LAT LON

BAMS 18.9N 118.3W 19.5N 121.7W 19.8N 125.0W 19.7N 128.2W

BAMD 18.5N 118.1W 19.3N 121.9W 20.5N 125.2W 21.7N 128.0W

BAMM 18.6N 118.1W 19.5N 121.9W 20.4N 125.2W 21.2N 128.2W

LBAR 19.5N 121.3W 22.3N 126.0W 27.0N 127.7W 33.9N 124.9W

SHIP 36KTS 35KTS 30KTS 24KTS

DSHP 36KTS 35KTS 30KTS 24KTS



...INITIAL CONDITIONS...

LATCUR = 16.4N LONCUR = 109.9W DIRCUR = 280DEG SPDCUR = 13KT

LATM12 = 16.0N LONM12 = 107.3W DIRM12 = 282DEG SPDM12 = 13KT

LATM24 = 15.2N LONM24 = 104.7W

WNDCUR = 25KT RMAXWD = 90NM WNDM12 = 25KT

CENPRS = 1008MB OUTPRS = 1011MB OUTRAD = 150NM SDEPTH = M

RD34NE = 0NM RD34SE = 0NM RD34SW = 0NM RD34NW = 0NM



$$

NNNN


Member Since: Posts: Comments:
Wave in the Caribbean has a 1% chance. Its already under some southerly shear. But, look at the high clouds in the W. carib moving due east. Not a good pattern for tropical cyclone formation in July. Like Masters said, we will prob have to wait until late July for Ana, unless one of those random subtropical storms forms in the Central Atlantic.
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Quoting stormwatcherCI:
Unfortunately.


And unfortunately we know about 04 and 05, and for that matter last year
Member Since: June 29, 2009 Posts: 13 Comments: 5313
Quoting AllStar17:


That is correct. 2004 had an El Nino similar to this one (weak) and we all know about that year.
Unfortunately.
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Quoting howarjo1943:
I am fairly certain that El Nino will not have a big impact on this hurricane season. Looking back, the Atlantic season has only been really affected when El Nino has been moderate to strong 1982-1983(strong), 1990-1994(moderate), and 1997(strong) come to mind. I am pretty certain that El Nino won't reach those levels this season.


That is correct. 2004 had an El Nino similar to this one (weak) and we all know about that year.
Member Since: June 29, 2009 Posts: 13 Comments: 5313
1689. KEEPEROFTHEGATE (Mod)
drama time
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I am fairly certain that El Nino will not have a big impact on this hurricane season. Looking back, the Atlantic season has only been really affected when El Nino has been moderate to strong 1982-1983(strong), 1990-1994(moderate), and 1997(strong) come to mind. I am pretty certain that El Nino won't reach those levels this season.
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Quoting AllStar17:
Let's not argue. Of course, we do not want lives taken but we do like to track tropical cyclones (ones that are not destructive and dangerous and do not affect land).
Not arguing but look at what you said and how it sounds before you post it.
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Let's not argue. Of course, we do not want lives taken but we do like to track tropical cyclones (ones that are not destructive and dangerous and do not affect land).
Member Since: June 29, 2009 Posts: 13 Comments: 5313
Quoting WeatherStudent:


DO NOT bend my words unecessarily out of context please, thanks.
You were the one who said it was a shame. IMO it is a blessing.
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Quoting WeatherStudent:


It really ain't; however, it's a real shame that the current wind shear values surrounding it aren't being to nice to it prsently, wouldn't you think so?


That isn't a shame, that's a good thing, unless you are interested in seeing lives potentially ruined.
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Quoting WeatherStudent:


It really ain't; however, it's a real shame that the current wind shear values surrounding it aren't being to nice to it prsently, wouldn't you think so?


Well, it says wind shear is high on the maps, but if you look at the satellite it does not look like it is being sheared that badly. Also, shear could become more favorable over the next few days.
Member Since: June 29, 2009 Posts: 13 Comments: 5313
Skyepony---

What are your thoughts on the wave in the C Caribbean?
Member Since: June 29, 2009 Posts: 13 Comments: 5313
1677. Skyepony (Mod)
press~ Not liking how the doldrums are sitting on the areas we last saw the TCHP getting warm..

Cosmic~ Awesome train wreck
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Even some rotation if you look closely around 15 N 67 W. Any thoughts? Getting more circular, too. This definitely should be watched.

Caribbean Visible Loop
Member Since: June 29, 2009 Posts: 13 Comments: 5313
Wave in Central Caribbean not looking too bad.

Member Since: June 29, 2009 Posts: 13 Comments: 5313
A little off topic here, but I found a great video of a tornado derailing a train. What a train wreck! It reminds me of the current state of the GOP.Link
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Quoting vortfix:
Decisions, decisions...Link

LOL, but really only one prerequisite - just COLD! ;)
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1672. msphar
Where is Dorado ? Which part of the island ?
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Just saw on MSN weather that Montego Bay, Jamaica had 2.76 in. rain in the last 24 hrs
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I am at 18N 66W Dorado PR and just had a nice tropical wave come over that flooded the streets other than that it was a non event. NOAA made it sound like there was going to be extreme cloud to ground Lightning and winds up to 35mph I saw neither. I cannot speak for Ponce that was hit by harder cells than me but it was interesting.

I must update my information. I no longer live in New Mexico I live in Dorado Puerto Rico now :)
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1667...Sky...that's an interesting product...
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1. SHOWERS AND THUNDERSTORMS ASSOCIATED WITH AN AREA OF LOW PRESSURE
LOCATED ABOUT 375 MILES SOUTHWEST OF MANZANILLO MEXICO HAVE
DECREASED DURING THE LAST FEW HOURS.
HOWEVER...CONDITIONS STILL
APPEAR FAVORABLE FOR DEVELOPMENT OF THIS SYSTEM
...AND THERE IS
POTENTIAL FOR THE LOW TO BECOME A TROPICAL DEPRESSION DURING THE
NEXT COUPLE OF DAYS AS IT MOVES WEST-NORTHWESTWARD AT 10 TO 15 MPH.
THERE IS A MEDIUM CHANCE...30 TO 50 PERCENT...OF THIS SYSTEM
BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS.
Member Since: July 8, 2005 Posts: 259 Comments: 24186
1667. Skyepony (Mod)
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Quoting vortfix:
Decisions, decisions...Link


LOL!!! Too cute!!!!
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Hello Everyone...

Am I missing anything???...heheheh...
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Quoting beell:
LOL-he said "bear watching"



...with the tropics quiet, "beer watching" sounds just fine passin' the time to me too. ;)
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Quoting Stormchaser2007:
Mostly 30C:


Member Since: September 30, 2007 Posts: 9 Comments: 15940
Quoting AussieStorm:
I'm off to bed... night all.
P.S Federer won Wimbledon
5-7 7-6 7-6 3-6 16-14
Cheers AussieStorm


I saw some of that...very intense game.
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Clear skies mean high TCHP later on.

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Quoting CybrTeddy:
Here's something that bugs me, both the WPAC and EPAC are below average and its an El Nino year.


EPAC should be on fire
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I'm off to bed... night all.
P.S Federer won Wimbledon
5-7 7-6 7-6 3-6 16-14
Cheers AussieStorm
Member Since: September 30, 2007 Posts: 9 Comments: 15940
Mostly 30C:

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Here's something that bugs me, both the WPAC and EPAC are below average and its an El Nino year.
Member Since: July 8, 2005 Posts: 259 Comments: 24186
Quoting SomeRandomTexan:


current ssts

try this.. looks like most of the gulf is running 30 degrees celcius

and FLA. coast


and hotter further up
Member Since: September 30, 2007 Posts: 9 Comments: 15940
thats a strong negative pulse around july 20th over africa
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Quoting AussieStorm:

May 19 was the last update


No they stopped updating around June 23 then the images reset to May 19 for some reason. They better fix it soon.
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Quoting Stormchaser2007:


Its fine...I dont know of any other TCHP sites though.

May 19 was the last update
Member Since: September 30, 2007 Posts: 9 Comments: 15940
Quoting extreme236:


Looks pretty good at the moment. I say it develops later tonight or early tomorrow.


Yes it does. The broad circulation it had yesterday has consolidated and convection is on the increase. I think it should become a TD either later today or Monday.
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Interesting.

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current ssts

try this.. looks like most of the gulf is running 30 degrees celcius
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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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