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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1755. hurricanejunky
2:59 PM GMT on July 17, 2009
1668. Great post. I'm sure all the rational people on here will agree.
Member Since: August 28, 2006 Posts: 6 Comments: 2895
1754. jurakantaino
2:21 PM GMT on July 17, 2009
1668- MR,FISHINFOOL 33825

Finally someone that makes sense here,thank Mr.Fishinfool,agree,100%. The name calling here is outrageous and disrespectful. This is a weather blog to exchange ideas and inform the public including those that doesn't have the knowledge but that are interested in the subject.
Member Since: July 31, 2008 Posts: 0 Comments: 730
1753. nrtiwlnvragn
2:19 PM GMT on July 17, 2009
New Blog
Member Since: September 23, 2005 Posts: 13 Comments: 10458
1752. RitaEvac
2:11 PM GMT on July 17, 2009
Quoting StormSurgeon:


Oh no! Guess I better board up!


lol
Member Since: July 14, 2008 Posts: 1 Comments: 9625
1751. StormSurgeon
2:08 PM GMT on July 17, 2009
Quoting RitaEvac:
Looks like a NOLA/Mobile strike from the system at 35W lol


Oh no! Guess I better board up!
Member Since: September 1, 2007 Posts: 0 Comments: 1793
1750. nrtiwlnvragn
2:01 PM GMT on July 17, 2009
Recent ASCAT pass

Member Since: September 23, 2005 Posts: 13 Comments: 10458
1749. Cotillion
1:57 PM GMT on July 17, 2009
Quoting SpicyAngel1072:
1719. Cotillon

Can you please explain the map to me...I understand the green in the El Nino..correct? But what is the orange and does it disappear beacause of the El Nino?

Why because of the map can August get hairy?

Sorry so many questions...just trying to learn.


It's a MJO map. Basically, the green is conducive to cyclogenesis, and the orange is the opposite.

It's just another cycle which factors into whether it's favourable for a storm to grow. Last year it appeared to be very important, this year hard to say.
Member Since: August 23, 2008 Posts: 7 Comments: 5300
1748. SpicyAngel1072
1:53 PM GMT on July 17, 2009
1719. Cotillon

Can you please explain the map to me...I understand the green in the El Nino..correct? But what is the orange and does it disappear beacause of the El Nino?

Why because of the map can August get hairy?

Sorry so many questions...just trying to learn.
Member Since: September 1, 2008 Posts: 0 Comments: 315
1747. AllStar17
1:53 PM GMT on July 17, 2009
Not to bring up Abrams, but she basically just wrote off the African wave in the first sentence she said in the tropical update.

"Doesn't really look like this thing is going to turn into much, and really affect us."

Member Since: June 29, 2009 Posts: 13 Comments: 5238
1746. RitaEvac
1:52 PM GMT on July 17, 2009
Looks like a NOLA/Mobile strike from the system at 35W lol
Member Since: July 14, 2008 Posts: 1 Comments: 9625
1745. BenBIogger
1:52 PM GMT on July 17, 2009
Quoting StormSurgeon:


If you make it to Mobile, hit Wintzells and order the oyster sampler......pure heaven.


I don't live in Louisiana anymore. I currently live in Miami.

But, I still have relatives near mobile and most likely return for just a week during winter.
Member Since: March 19, 2009 Posts: 0 Comments: 1419
1744. RitaEvac
1:51 PM GMT on July 17, 2009
Its so dry, that a farmer threw his cigarrete of his tractor and the whole farm blew up like gasoline was sprayed on the field....lol
Member Since: July 14, 2008 Posts: 1 Comments: 9625
1743. BurnedAfterPosting
1:51 PM GMT on July 17, 2009
Quoting NoNamePub:
K-S-U WILDCATS!!!!
Made it to our 1st Post Season!

Tampa - That low is well south of were your sheer map was showing creased sheer.


dont even bother trying to convince him, its a waste of time
1742. philliesrock
1:50 PM GMT on July 17, 2009
Talk about a huge ridge...Euro gets it to 600 dm out in the Atlantic! It's 240 hours out, but still very impressive.

Member Since: June 29, 2006 Posts: 65 Comments: 3197
1741. NoNamePub
1:50 PM GMT on July 17, 2009
K-S-U WILDCATS!!!!
Made it to our 1st Post Season!

Tampa - That low is well south of were your sheer map was showing creased sheer.
Member Since: July 13, 2007 Posts: 0 Comments: 518
1740. StormSurgeon
1:46 PM GMT on July 17, 2009
Quoting BenBIogger:


I once lived near sorrento. I used to travel to a restaurant in gonzalez called Sno's


If you make it to Mobile, hit Wintzells and order the oyster sampler......pure heaven.
Member Since: September 1, 2007 Posts: 0 Comments: 1793
1739. RitaEvac
1:46 PM GMT on July 17, 2009
Member Since: July 14, 2008 Posts: 1 Comments: 9625
1737. BenBIogger
1:38 PM GMT on July 17, 2009
Quoting alaina1085:
Im in Gonzales, LA... ABout 15 minutes away from Baton Rouge.


I once lived near sorrento. I used to travel to a restaurant in gonzalez called Sno's
Member Since: March 19, 2009 Posts: 0 Comments: 1419
1736. BurnedAfterPosting
1:36 PM GMT on July 17, 2009
new shear map out, 60 knots of shear NE of the Islands is gone and the rest of the shear has started to retreat slightly
1735. AllStar17
1:36 PM GMT on July 17, 2009
Quoting IKE:
According to the 6Z GFS...shear to the yellow-circled blob's west, should left out over time...


That is what has been predicted for a few days now. Which, that is not good. A favorable environment, and this thing will strengthen.
Member Since: June 29, 2009 Posts: 13 Comments: 5238
1734. Orcasystems
1:34 PM GMT on July 17, 2009
Blog Update
Reflector site for those at work, which includes Weather456, daily updates


AOI

AOI
Member Since: October 1, 2007 Posts: 81 Comments: 26493
1733. StormSurgeon
1:27 PM GMT on July 17, 2009
Quoting Funkadelic:


Univ. Miami all the way! More of a baseball guy though


The Canes are cool. LSU fans are loving baseball about now. Oops, I forgot, this is a weather blog.....LOL
Member Since: September 1, 2007 Posts: 0 Comments: 1793
1732. StormSurgeon
1:25 PM GMT on July 17, 2009
Quoting alaina1085:
Im in Gonzales, LA... ABout 15 minutes away from Baton Rouge.


I have a lot of family in Tiger Town (BR). Hope to get that way soon.
Member Since: September 1, 2007 Posts: 0 Comments: 1793
1730. alaina1085
1:20 PM GMT on July 17, 2009
Im in Gonzales, LA... ABout 15 minutes away from Baton Rouge.
Member Since: August 2, 2006 Posts: 0 Comments: 1240
1729. IKE
1:20 PM GMT on July 17, 2009
I agree that it needs to go west, for now....
Member Since: June 9, 2005 Posts: 23 Comments: 37858
1728. NEwxguy
1:19 PM GMT on July 17, 2009
GM,all,I see we are arguing about shear again,the usual debate in here.
Member Since: September 6, 2007 Posts: 862 Comments: 15053
1727. IKE
1:19 PM GMT on July 17, 2009
1726. BurnedAfterPosting
1:14 PM GMT on July 17, 2009
Quoting TampaSpin:


It will start at 50W IMO....but, 55W for sure....the Shear is not going to relax like many are thinking...It actually will increase some before it decreases......Here is the 24hr shear tendency map.....LOOK!



Um the shear tendency maps show what shear has done in the PAST 24 hours, not what it will do in the next 24 hours
1725. TampaSpin
1:11 PM GMT on July 17, 2009
Quoting BenBIogger:
Imo shear will rip it apart once it reaches 55w.




It will start at 50W IMO....but, 55W for sure....the Shear is not going to relax like many are thinking...It actually will increase some before it decreases......Here is the 24hr shear tendency map.....LOOK!

Member Since: September 2, 2007 Posts: 177 Comments: 20430
1724. StormSurgeon
1:09 PM GMT on July 17, 2009
Quoting alaina1085:
WOOT StormSurgeon!! Tiger fan here as well.


Isn't everybody? Where are you? Mobile here.
Member Since: September 1, 2007 Posts: 0 Comments: 1793
1722. BenBIogger
1:05 PM GMT on July 17, 2009
Imo shear will rip it apart once it reaches 55w.


Member Since: March 19, 2009 Posts: 0 Comments: 1419
1721. alaina1085
1:05 PM GMT on July 17, 2009
WOOT StormSurgeon!! Tiger fan here as well.
Member Since: August 2, 2006 Posts: 0 Comments: 1240
1720. StormSurgeon
1:04 PM GMT on July 17, 2009
Pat, I think it's time for Yukon.
Member Since: September 1, 2007 Posts: 0 Comments: 1793
1719. Cotillion
1:02 PM GMT on July 17, 2009


Not too promising... August could get hairy.

Member Since: August 23, 2008 Posts: 7 Comments: 5300
1717. RitaEvac
12:58 PM GMT on July 17, 2009
Member Since: July 14, 2008 Posts: 1 Comments: 9625
1716. StormSurgeon
12:56 PM GMT on July 17, 2009
GEAUX Tigers!

Member Since: September 1, 2007 Posts: 0 Comments: 1793
1715. TampaSpin
12:52 PM GMT on July 17, 2009
Oh well......the models all agree with you all trying to wish Ana........good luck.
Member Since: September 2, 2007 Posts: 177 Comments: 20430
1714. IKE
12:44 PM GMT on July 17, 2009
Quoting TampaSpin:


I didn't say Storm said it would get ripped apart i said that....


...here's what you said....

"""Thanks StormW you just emphasized what i said last nite......I was telling everyone that it had a 2 day window ton increase then shear would rip it apart starting Sunday...""".....

That reads like you think he agrees with what you said....
Member Since: June 9, 2005 Posts: 23 Comments: 37858
1713. TampaSpin
12:41 PM GMT on July 17, 2009
Quoting IKE:


He didn't say it would get ripped apart.

Here's what StormW said....

"""None of the computer models shows this wave developing, however, current real time wind shear from CIMSS, and the current run of the forecast wind shear maps from FSU indicate this wave to be located in a conducive environment, albeit the northern portion of this wave is sitting in a small trof axis. The wave will need to clear this axis before any possible further development can take place. Also, based on the wind shear forecast (06Z), this wave may encounter some increasing wind shear in about 42-48 hours...just enough to slow development. For this wave to survive, it needs to move due west, and remain at 15N or below. Should this wave get caught in the NW steering flow in a few days...it will encounter increasing wind shear from the NW. So, time will tell. Of course, these parameters can always change.""".......


He's saying it's future may depend on it's movement...either W or NW.

Gotta get ready for work....


I didn't say Storm said it would get ripped apart i said that....
Member Since: September 2, 2007 Posts: 177 Comments: 20430
1711. antonio28
12:40 PM GMT on July 17, 2009
I see a new Blog coming! LOL
Member Since: July 15, 2008 Posts: 0 Comments: 799
1710. IKE
12:39 PM GMT on July 17, 2009
Quoting TampaSpin:
Thanks StormW you just emphasized what i said last nite......I was telling everyone that it had a 2 day window ton increase then shear would rip it apart starting Sunday...


He didn't say it would get ripped apart.

Here's what StormW said....

"""None of the computer models shows this wave developing, however, current real time wind shear from CIMSS, and the current run of the forecast wind shear maps from FSU indicate this wave to be located in a conducive environment, albeit the northern portion of this wave is sitting in a small trof axis. The wave will need to clear this axis before any possible further development can take place. Also, based on the wind shear forecast (06Z), this wave may encounter some increasing wind shear in about 42-48 hours...just enough to slow development. For this wave to survive, it needs to move due west, and remain at 15N or below. Should this wave get caught in the NW steering flow in a few days...it will encounter increasing wind shear from the NW. So, time will tell. Of course, these parameters can always change.""".......


He's saying it's future may depend on it's movement...either W or NW.

Gotta get ready for work....
Member Since: June 9, 2005 Posts: 23 Comments: 37858
1709. wunderkidcayman
12:39 PM GMT on July 17, 2009

well well look at this
Member Since: June 13, 2009 Posts: 2 Comments: 9547
1708. K8eCane
12:38 PM GMT on July 17, 2009
SURFACE WAVE/LOW EMERGING FROM THE NORTHEAST GULF OF MEXICO SUN
AFTERNOON WILL MOVE NORTHEAST ALONG THE COAST. AS THIS SYSTEM MOVES
NORTHEAST BROAD 5H TROF WILL BECOME BETTER DEFINED...PULLING THE
WAVE A LITTLE FARTHER INLAND. HAVE HIGHEST POPS IN THE PERIOD SUN
NIGHT...THOUGH STILL PLENTY OF UNCERTAINTY REGARDING THE SYNOPTIC
FEATURES SO KEEPING POPS IN THE CHANCE RANGE SUN NIGHT.

from wilmington nc discussion
Member Since: April 26, 2006 Posts: 5 Comments: 3040
1707. TampaSpin
12:35 PM GMT on July 17, 2009
Thanks StormW you just emphasized what i said last nite......I was telling everyone that it had a 2 day window ton increase then shear would rip it apart starting Sunday...
Member Since: September 2, 2007 Posts: 177 Comments: 20430
1706. K8eCane
12:34 PM GMT on July 17, 2009
Quoting IKE:


True...

It probably won't amount to anything tropically...


supposed to bring us more rain on the east coast
Member Since: April 26, 2006 Posts: 5 Comments: 3040
1705. IKE
12:33 PM GMT on July 17, 2009
Extended discussion from Mobile,AL. talks about another trough the end of next week...

"[SATURDAY THROUGH SUNDAY NIGHT]...BY SATURDAY MORNING THE BASE OF
LARGE LONGWAVE UPPER TROUGH WILL HAVE SETTLED OVER THE NORTHERN GULF
OF MEXICO...WITH THE SURFACE COLD FRONT REACHING THE I-10 CORRIDOR.
WHILE THE NORTHERN HALF OF THE FORECAST AREA DRIES OUT UNDER MID
LAYER SUBSIDENCE REGION...THE SOUTHERN HALF (INCLUDING MARINE AREAS)
WILL STILL SEE ISOLATED/SCATTERED SHOWERS/THUNDERSTORMS NEAR THE
FRONTAL ZONE ON SATURDAY. THE UPPER TROUGH WILL CONTINUE TO DIG
DEEPER INTO THE NORTHERN GULF OVER THE WEEKEND AND BECOME RATHER
HIGHLY AMPLIFIED BY SUNDAY NIGHT...AS COLD FRONT MOVES SOUTH OF THE
COAST. MOST OF THE FORECAST AREA SATURDAY NIGHT THROUGH SUNDAY NIGHT
WILL REMAIN RAIN-FREE...EXCEPT FOR ISOLATED SHOWERS/THUNDERSTORM
COVERAGE ACROSS THE IMMEDIATE COASTAL ZONES. DAYTIME HIGH
TEMPERATURES BOTH DAYS WILL BE ABOUT 3 DEGREES BELOW NORMAL...WITH
HIGHS IN THE UPPER 80S. THE DRIER AIR IN THE WAKE OF THE FRONT WILL
BRING OVERNIGHT LOWS ABOUT 6 TO 10 DEGREES BELOW NORMAL...WITH LOWS
RANGING FROM AROUND 60 DEGREES FAR INLAND ZONES TO AROUND 70 DEGREES
ALONG THE BEACHES. /22

.LONG TERM [MONDAY THROUGH FRIDAY]...MID/UPPER LEVEL SUBSIDENCE IN
THE WAKE OF ONE UPPER TROUGH AND THE APPROACH OF ANOTHER TROUGH WILL
KEEP MOST OF THE AREA WITHOUT RAIN THROUGH WEDNESDAY. HOWEVER ENOUGH
LOW LEVEL MOISTURE WILL REMAIN FOR ISOLATED SHOWERS OR THUNDERSTORMS
TO DEVELOP...MAINLY DURING THE AFTERNOON HOURS. DEEPER MOISTURE WILL
WORK ITS WAY BACK INTO THE REGION BY THURSDAY (AHEAD OF THE OTHER
TROUGH)
ALLOWING A WETTER PATTERN (SCATTERED SHOWERS AND
THUNDERSTORMS) TO DEVELOP THURSDAY AND FRIDAY. HIGH TEMPERATURES
WILL BE AROUND 90 DEGREES EACH AFTERNOON...WITH LOWS MODERATING FROM
THE 60S AREA WIDE BACK TO NEAR NORMAL AFTER MID WEEK."
Member Since: June 9, 2005 Posts: 23 Comments: 37858

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About JeffMasters

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.