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 TexasHurricane:
For those in SE Texas..

I was with my family today and we were talking about this hurricane season. My dad told me that someone (can't remember who) who has predicted some storms (here the past couple years - may be longer but first we have heard) has predicted a bad storm for our area this year....saying that Port Arthur (which is not far from us) is suppose to get messed up pretty bad. Supposedly he has been right about these past storms. What is funny (not funny haha),is that this about the 3rd time I have heard something like this.....

Not saying this is going to happen,i mean who knows...but, I thought i'd just let you know what I heard.... Season is slow right now, but we still have a few months to go.


Ugh! Port Arthur is just a couple miles south of me... I reside in Orangefield.. that would not be good... that would bring huge devastation to the oil industry as well.

There's always a bright side to everything... that would give me a reason to go see a good friend of mine a couple states north
Member Since: August 30, 2007 Posts: 0 Comments: 1857
For those in SE Texas..

I was with my family today and we were talking about this hurricane season. My dad told me that someone (can't remember who) who has predicted some storms (here the past couple years - may be longer but first we have heard) has predicted a bad storm for our area this year....saying that Port Arthur (which is not far from us) is suppose to get messed up pretty bad. Supposedly he has been right about these past storms. What is funny (not funny haha),is that this about the 3rd time I have heard something like this.....

Not saying this is going to happen,i mean who knows...but, I thought i'd just let you know what I heard.... Season is slow right now, but we still have a few months to go.
Member Since: July 2, 2009 Posts: 0 Comments: 2811
1495. JRRP
long range....ufff how many time i do not see this from gfs????

Member Since: August 16, 2007 Posts: 0 Comments: 5961
was hurricane2009 under a different alias last year?
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Quoting StormW:


Voted for ya Mike!

Wish you the best.

same here
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1492. scott39
do any future models show developement in the carrb when the wind shear goes down?
Member Since: June 13, 2009 Posts: 0 Comments: 6857
Quoting MikeTheiss:
Thanks Dr. Masters for such a great blog about the July Hurricane Outlook and Thanks for mentioning to your views about the contest I entered to go to Antarctica...

Please everyone help me live my dream and go to Antarctica ! I am doing all i can to campaign this out and make it happen. PLEASE VOTE for me (Mike Theiss). You can see all the info and see the voting instructions at the following link: www.HelpMikeWin.com



hope you win. voted 4 ya.
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Thanks Dr. Masters for such a great blog about the July Hurricane Outlook and Thanks for mentioning to your views about the contest I entered to go to Antarctica...

Please everyone help me live my dream and go to Antarctica ! I am doing all i can to campaign this out and make it happen. PLEASE VOTE for me (Mike Theiss). You can see all the info and see the voting instructions at the following link: www.HelpMikeWin.com

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Quoting Orcasystems:


Nope.. not banned


If the person did not create a blog, then the blog would appear to be active. JFV's first account will not say "this is user has been banned".
Member Since: July 19, 2008 Posts: 43 Comments: 4051
Lol SRT. So THATS what that sound is! :)
Member Since: August 15, 2008 Posts: 10 Comments: 3665
1485. JRRP
Member Since: August 16, 2007 Posts: 0 Comments: 5961
Quoting homelesswanderer:
Hot Fourth of July will turn into wet week ahead

A little break from the heat is in store this upcoming week. Monday through Friday calls for scattered showers and thunderstorms. Remember the safety rule of thunderstorms and lightning, when thunder roars, go indoors.

SRT there's our relief. Finally! Lol. Good evening all.


I believe I can hear my grass bursting out into the Hallelujah chorus!
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Quoting SomeRandomTexan:

I havent seen him nor pearlandAggie on


Nope.. not banned
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Quoting Chicklit:
Hurricane2009 didn't get banned, did he?

I havent seen him nor pearlandAggie on
Member Since: August 30, 2007 Posts: 0 Comments: 1857
Hot Fourth of July will turn into wet week ahead

A little break from the heat is in store this upcoming week. Monday through Friday calls for scattered showers and thunderstorms. Remember the safety rule of thunderstorms and lightning, when thunder roars, go indoors.

SRT there's our relief. Finally! Lol. Good evening all.
Member Since: August 15, 2008 Posts: 10 Comments: 3665
fireworks! a symbol of Americas greatness.. a reminiscent of the rockets red glare
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Hurricane2009 didn't get banned, did he?
Watched some really nice fireworks on the beach tonight.
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talking about AUSTRALIA looks like we have El Nino with severe drought

Link
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1477. hahaguy
Just got back form watching fireworks , I see the blog is having a slow night.
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wave at 74 west still persistant
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Im pretty sure sometime in the next 4 weeks we will see Ana and possibily Bill. Lets have some patience.
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Quoting StormW:


Pretty much Taz...The atmospheric signals have been going on for about a month now...just waiting for the ocean to respond fully.



cool
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Blog Update
Reflector site for those at work, which now also includes Weather456, daily updates


INVEST 94L

AOI
Member Since: October 1, 2007 Posts: 81 Comments: 26511
Quoting StormW:


Pretty much Taz...The atmospheric signals have been going on for about a month now...just waiting for the ocean to respond fully.

How will the ocean respond to the effects of El Nino. Lower temps?
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hi guys when will I see development and when will we get some heavy rain here
Member Since: June 13, 2009 Posts: 2 Comments: 12139
Quoting futuremet:


This might all eventually lead to a greater chance of tropical cyclone development near the latter part of this month...


That is when I expecting increase chances of TC genesis - July 16 - 31. MJO also returns during that period.
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Evening Storm and Happy 4th to you and yours.
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Quoting WeatherStudent:


What might all of this eventually lead to, FM? Good evening Mr. W!


This might all eventually lead to a greater chance of tropical cyclone development near the latter part of this month...
Member Since: July 19, 2008 Posts: 43 Comments: 4051
Quoting StormW:


Ya can pick out a wave south of Puerto Rico.


Yes, these waves will have to be watched closely as they near the Caribbean.
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1462. bappit
Hope y'all caught some fireworks.

1456
Ooooooooo, all I see is 40 knots of shear across most of the Carribean. Go north young blob.
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Quoting StormW:


A little late ay Daniel?...ya think.



do you think El Nino is here now???
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The NAM continues to show increasing moisture in the west Caribbean over the next couple of days. It also seem to be forecasting the subequatorial ridge to establish over the area, providing semi-favorable conditions for tropical cyclogenesis. Nevertheless, conditions will not be marginally favorable until Wednesday. The GFS and other global models are expecting shear to drop to favorable levels in the Caribbean late next week. Thus, any moisture advection or fluctuations in the area should be closely monitored.

Increasing moisture



Decreasing shear....GFS is forecasting even lower shear values beyond that



Establishing STR (NAM)

Member Since: July 19, 2008 Posts: 43 Comments: 4051
From 8 p.m. NHC Discussion:
A TROPICAL WAVE EXTENDS FROM 20N54W TO 6N56W MOVING W 20-25 KT.
THIS LARGE AND HIGH AMPLITUDE WAVE COINCIDES WITH A MAXIMUM IN DEEP LAYER MOISTURE AS OBSERVED ON THE TPW PRODUCT FROM CIMSS. A VORTICITY/MOISTURE MAXIMUM IS ALSO EVIDENT W OF THE ANALYZED AXIS NEAR 14N59W APPROACHING THE LESSER ANTILLES. SCATTERED MODERATE CONVECTION IS FROM 7N-13N BETWEEN 52W-57W AND FROM 13N-17N BETWEEN 58W-63W...LIKELY SUPPRESSED BY SAHARAN DUST.
Link
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Happy Fourth of July.
Shear is low in the northern Caribbean and Antilles.

Link
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blog is moving slow... we need some weather! another day of 100 degree temps here in SeTx.. we are supposed to get some relief this week... we need it!
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1454. Ossqss
Humm, time for a re-run. Boom :) Slow night eh?
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Conditions at 42001 as of
(7:50 pm CDT on 07/04/2009)

Wind Direction (WDIR): SW ( 220 deg true )
Wind Speed (WSPD): 7.8 kts
Wind Gust (GST): 9.7 kts
Wave Height (WVHT): 1.3 ft
Dominant Wave Period (DPD): 4 sec
Average Period (APD): 4.3 sec
Atmospheric Pressure (PRES): 30.01 in
Pressure Tendency (PTDY): 0.00 in ( Steady )
Air Temperature (ATMP): 84.6 F
Water Temperature (WTMP): 88.3 F
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Great site for forecasting severe weather. It has extensive model data on some of the fundamental factors of tornadogenesis. Click here
Member Since: July 19, 2008 Posts: 43 Comments: 4051
wind shear is runing 5 to 10kt this about evere where

Link
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1449. Skyepony (Mod)
One Person Killed At Fourth Of July Gathering

Posted: 6:52 pm EDT July 4, 2009Updated: 7:28 pm EDT July 4, 2009
LAKELAND, Fla. -- Officials say one person was killed in a lightning strike at a Fourth of July gathering in Central Florida and 18 others have been taken to local hospitals.

According to Polk County spokeswoman Cindy Rodriguez, 80 or more people were gathered outside a Lakeland home when lightning hit a wooden pole barn Saturday. The event was apparently part of a church function.

Crews transported 12 patients to Lakeland Regional Medical Center, four to a Plant City hospital and three more patients to a medical center in Bartow. Their conditions, ages, and genders weren't immediately released.

The name of the person killed in the lightning strike was also not released.
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1448. beell
Safe travels, Mel-you may have to cross a stalled frontal boundary if you are on MOD-I20. Nothing too bad, I don't think. Just Hot!!!



DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1220 PM CDT SAT JUL 04 2009

...CNTRL HIGH PLAINS/SRN PLAINS...

A FEW MARGINALLY SEVERE STORMS MAY OCCUR SUNDAY AFTERNOON
MAINLY NEAR A FRONTAL BOUNDARY WHERE MODEL FORECASTS SHOW
SUBSTANTIAL DIRECTIONAL SHEAR AND POCKETS OF MODERATE INSTABILITY.
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1447. KEEPEROFTHEGATE (Mod)
heres a movie to watch

Link
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About

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