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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Was it Barney Fife or Barney the purple dino.....I don't remember.......LMAO
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Groucho is my favorite.
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I think you guys would be wise to take the political talk somewhere else. People get banned for getting off topic like that, especially politics.
Member Since: November 24, 2005 Posts: 635 Comments: 26647
This basic premise becomes invisible in times like this. The government is not a revenue generating entity. They use money we give them. The more they spend the more we owe. It doesn't come from anyone else but you. You are and will always be part of the equation. We must spend wisely.
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LMFAO @ 337! hahahah!
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331. GWB, regardless of his socialism, won Florida by 25 votes or so. it WAS that close and it WAS legitimate. get over it!...he's not in office anymore--your favorite Marxist is.
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mmmmmm ... more interesting than this political whipping
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And every other year when someone said that fanny and freddy's policies were a serious threat to the health of the economy, a bunch of bleeding democrats came to the aid of all of the waitresses wanting a $500 K house with no money down.
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Quoting hurricane2009:


LMAO the GOP is so pathetic right now they will have no one even close to being in the white house by the next election


Why i wasn't talking politics.....Hurricane2009 you could get banned for such a remark!
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Wait a second, is that a blob????
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How about this, CO2, yep, is it really the problem we think it is? I really don't know after actually reviewing more Data than I cared to. There are more questions than answers. The root problem is we don't know how to accurately interpret what we see. But we will.

How accurate are the UN models we use to predict climate change. How good is the data we use in them? All have been questioned and all still remain questions.

We need to work together to find the truth. We are not there yet. I sit on a fence and don't know which way to jump and there is nobody that really does know yet. If they do, they are jumping to conclusions prematurely.

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321. the point in all of this is to highlight the fact that political positions (regardless of contrary data) and elections have consequences...consequences that will be heading the way of each and every American very shortly. this is the price we pay for ignorance and lack of personal research....
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4 and gone......is what its called......LOL
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Didn't Dr. Masters open the conversation when part of the Bill was for building a new NHC Center.....i could be wrong....i think that was one blog back......
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321. oh, I am, trust me. you just don't see the effort, yet :)
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320. Dr. M. provides and INVALUABLE service when it comes to tropical weather prediction and warning. I just think that his incessant need to affirm the AGW hypothesis is B.S. thanks for being honest on this point.

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Putting thousand of folks into mortgages they could never affor though the same junk math was an entirely democrat move. Caused an artifical housing market bubble that has since done what bubbles do best.
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316. WTF??? close your eyes and wait for the carbon tax to steamroll your ability to provide for you and your family. just don't come crying when it does......
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314. fair enough...however, the postings on this blog are responsible for the misleading and disinformation disseminated to hundreds, if not thousands, of blog readers. the blog owner, while not entirely responsible I must admit, has performed a disservice in not looking at all data sources and only presenting one side of the issue. that failure to look at all data has led to the Congress passing one of the most reprehensible and unconstitutional acts in the history of this Republic.
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Hey plandag.

We still talk AGW junk here, but not usually in da season.

You all know where I stand on the sham(ful) and fear mongering.
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309. so one's positions, regardless of political consequences, are above reproach on THEIR OWN website? wow.....that's a new one on me...
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Quoting pearlandaggie:
well, then, how about that *wonderful* cap-n-tax bill so many of you, including Dr. M., are in favor of? only one more house to pass and then we will ALL reap the benefits of doubled prices for energy, goods, food, and materials. you should be proud of yourselves on such an historic event coinciding with the founding of this wonderful country.....congrats on your destruction of it!!


First of all, I hope your day gets better. 2ndly, I don't think this blog is responsible for the bill that was submitted. Albiet, I don't like the fact that 300 pages were injected at 3am for a morning vote that passed. That is simply politics. This blog is not. DO I like it, no. Will it inspire me to vote, yes. I certainly would not want a multi-thousand dollar increase in my taxes and I hope level heads prevail in the end. I expect they will. Just my Pics on Weather Politics.

EDIT -- I would tell you also that the slanted science on both sides is about to be righted.
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Quoting pearlandaggie:
well, then, how about that *wonderful* cap-n-tax bill so many of you, including Dr. M., are in favor of? only one more house to pass and then we will ALL reap the benefits of doubled prices for energy, goods, food, and materials. you should be proud of yourselves on such an historic event coinciding with the founding of this wonderful country.....congrats on your destruction of it!!


Pearl i agree.....thats the worst bill ever passed in Congressional history......
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311. we need some MORE rain here in Pearland. we got an inch or so a couple of days ago but that didn't go very far. we need some more!
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Texasgulf -- 259

That makes at least League City and Humble with water rationing in effect. Not something you see around Houston very often.
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give me a damn break...the extent to which Dr. M. will present only one side of the AGW debate necessitates the inclusion of an opposing opinion. sorry to burst your bubble, but the wonderful Doc's predisposition TOWARDS AGW only levels responsibility for such heinous Congressional acts on those that would stifle debate for political reasons.

that is EXACTLY the tactic that has been used to stifle debate on this once-great website.
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Quoting hurricane2009:
Not to be rude, but last I checked this was a weather site, politics do not belong here
Not to say come in and bash Doc on his own blog site.
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Different view of , not much.
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well, then, how about that *wonderful* cap-n-tax bill so many of you, including Dr. M., are in favor of? only one more house to pass and then we will ALL reap the benefits of doubled prices for energy, goods, food, and materials. you should be proud of yourselves on such an historic event coinciding with the founding of this wonderful country.....congrats on your destruction of it!!
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Sorry, that's boring hurricane 09.
Time for me to go read a book.
Member Since: July 11, 2006 Posts: 14 Comments: 11328
Quoting AllStar17:


Nothing much. The NHC has issued a low probability alert for a non-tropical low in the north central atlantic. Possible slow development over the next few days. It has 3-4 days to develop before it is absorbed by a front. So, we may be watching for Ana. Stay tuned.

And you can see more convection firing over the center, so maybe we really do have something here.

but it looks like it will be absorbed by the front within the next 2-3 days I think there not enough convection over the center and wind shear in that area 20-30kts



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I like this one:
Link
From the 8 PM NHC Discussion:
A LARGE ATLANTIC OCEAN TROPICAL WAVE IS ALONG 31W TO THE SOUTH OF 18N MOVING WESTWARD 20 KT. THIS WAVE IS BROAD WITH THE LAST VISIBLE SATELLITE IMAGES OF THE DAY TODAY INDICATING AN AREA OF CYCLONIC TURNING COVERING THE AREA FROM 10N TO 20N BETWEEN 28W AND 40W. THE WAVE POSITION IS ROUGHLY IN THE CENTER OF THE CYCLONIC ENVELOPE WHERE CLOUD DRIFT WINDS SUGGEST A VORTICITY MAXIMUM NEAR 10N31W. SYNOPTIC PRESSURE OBSERVATIONS FROM THE CAPE VERDE ISLANDS SHOW A 3 MB PRESSURE INCREASE DURING AT LEAST THE LAST 24 HOURS. QUIKSCAT DATA REVEAL NORTHEASTERLY 20 KT TO 25 KT WIND SPEEDS TO THE WEST OF THE WAVE TO THE NORTH OF 14N DUE TO THE TIGHTENED PRESSURE GRADIENT BETWEEN THE WAVE AND THE SUBTROPICAL RIDGE. DEEP CONVECTIVE PRECIPITATION REALLY DOES NOT ACCOMPANY THIS WAVE. ITCZ PRECIPITATION IS BETWEEN 30W AND 40W TO THE SOUTH OF THE WAVE.
Member Since: July 11, 2006 Posts: 14 Comments: 11328

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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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