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 Weather456:
Does look like a sheared subtropical system



Well, looks can certainly be decieving, as was the case with 90L, as everyone thought it was TS Ana...I certainly did
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This would mean that at least one more landfalling hurricanes should be expected by around 2004.

Not bad. He nailed that too. We had 2 hurricanes in that period. Bret 99 and Claudette 2003. Thats just spooky. Lol.
Member Since: August 15, 2008 Posts: 10 Comments: 3665
Quoting Weather456:
It is interesting for now but expected to become associated with a frontal zone over the next 3-5 days and not an ideal situation when looking for subtropical development. But until then, it can still be monitored just incase.


Thank you. So, it still should be monitored
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Does look like a sheared subtropical system

Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting TampaSpin:
Big time thunderstorms building off shore of TAmpa.....we are really going to get the rain.......wow!


Hey Tim what would you estimate the timeframe for that reaching us? I'd like to get home before that arrives. TIA
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Quoting Weather456:


I'll get to that in a sec.


OK, I will be interested to see what your thinking is.
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It is interesting for now but expected to become associated with a frontal zone over the next 3-5 days and not an ideal situation when looking for subtropical development. But until then, it can still be monitored just incase.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Ooops. Sorry. Forgot to say it was written in 1999. And here's the link to the whole article if anyone is interested. :)

Link
Member Since: August 15, 2008 Posts: 10 Comments: 3665
Quoting AllStar17:
Weather456- What do you think of the non-tropical low in the North Atlantic at about 35 N 45 W?


I'll get to that in a sec.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Thought this was interesting. Found it in a report on Texas Tropical History. New to me anyway. :)



Long term trends/hurricane cycles. Studies were made back in the 1950's by Dr. W. Armstrong Price on hurricane incidence along the Texas coast and the sunspot cycle. Regardless of whether or not it is due to sunspots or some other interannual climate cycle, using data back to 1829 that are periods in the climatological record of "hurricane-rich" and "hurricane poor" sets of years. A hurricane-rich set of year is represented by an average of 8 storms making landfall over an average of 10 years, plus or minus a couple of either. A hurricane-poor set of years is represented by an average of 2 storms making landfall over an average of 14 years, plus or minus a couple of either.

Using this pattern, he correctly predicted the hurricane-rich period he was entering in 1956 (it lasted from 1954-1971). Using this pattern, it is noted that the Texas coast has been in a hurricane-poor period since 1990. This would mean that at least one more landfalling hurricanes should be expected by around 2004. Thereafter, a hurricane-rich period would begin, lasting until approximately 2015, in which nearly eight hurricanes would make landfall. Remember, it only takes one hurricane making landfall in your location to create grief for you and your loved ones.

Link
Member Since: August 15, 2008 Posts: 10 Comments: 3665
We've actually got a few days of Partly Cloudy forecasts now in the Northeast, good for a change. For the past week and a half there has been a chance of scattered thunderstorms
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Mike Theiss now has 168 votes.
Member Since: July 11, 2006 Posts: 14 Comments: 11424
RitaEvac--6

Thanks for the info. 100 or more again today. This is a brutal summer for Houston. We got our first showers for the month of June near the end and they broke the string of record highs seven days in a row. The rain amounts were modest at best, though, and the heat is settling back in now. Looks grim.
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Quoting Weather456:
I do not think at the rate of warming, the El Nino will be at levels of 1997. If this El Nino isn't even warming as fast as 2006, how can it be at levels of 2002 or 1997 (which both had an episode figure of 0.4 by June). Eventually we might get to those levels but for September? An El Nino similar 2004 and 2006 seems favorable. Whether or not it follows either year is to be seen. It should also be noted that shear was very prevalent early in 2004 and even experts thought the El Nino of that year was affecting the season causing a downward revision of numbers by August 1 2004.


Oh yeah definitely not even close to 1997. This is going to be a weak possibly low-end moderate event that won't even last that long. It can't be that strong when it's just a reaction to the cold PDO.
Member Since: November 24, 2005 Posts: 635 Comments: 26701
Quoting Weather456:
I do not think at the rate of warming, the El Nino will be at levels of 1997. If this El Nino isn't even warming as fast as 2006, how can it be at levels of 2002 or 1997 (which both had an episode figure of 0.4 by June). Eventually we might get to those levels but for September? An El Nino similar 2004 and 2006 seems favorable. Whether or not it follows either year is to be seen. It should also be noted that shear was very prevalent early in 2004 and even experts thought the El Nino of that year was affecting the season causing a downward revision of numbers by August 1 2004.


Good because I want a nice little Tropical Storm to track
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The sky here is yellow and brown. Storms in area.
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Quoting CaneWarning:


Where did you see that? I must've missed it.

Hey CaneW! You can scroll through all the various entries and it lists how many votes each currently has. When I voted Mike was at 151. Some guy, I think from South America, had over 650.
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Weather456- What do you think of the non-tropical low in the North Atlantic at about 35 N 45 W?
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Gbguy I pointed that out yesterday. caused a major awe.
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Big time thunderstorms building off shore of TAmpa.....we are really going to get the rain.......wow!
Member Since: September 2, 2007 Posts: 179 Comments: 20448
I do not think at the rate of warming, the El Nino will be at levels of 1997. If this El Nino isn't even warming as fast as 2006, how can it be at levels of 2002 or 1997 (which both had an episode figure of 0.4 by June). Eventually we might get to those levels but for September? An El Nino similar 2004 and 2006 seems favorable. Whether or not it follows either year is to be seen. It should also be noted that shear was very prevalent early in 2004 and even experts thought the El Nino of that year was affecting the season causing a downward revision of numbers by August 1 2004.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting Gumbogator:
10 N and 29 W (wave) covers 1000 NM. Holy***!!


If it could consolidate some of its energy and gather some convection around a tighter structure, it may be something to watch, but for now it is just a large gyre of cyclonic turning with a tropical wave.
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Quoting tropicfreak:


Well more than that. I wouldn't be surprised to see a major hurricane or 2 out there. Definetly will see at least 10 named storms. 4 of whichwill be hurricanes ( not including major


Possibly
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10 N and 29 W (wave) covers 1000 NM. Holy***!!
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I bought a waterproof video camera and all-out storm gear for this season...I plan on intercepting any hurricanes that come within a few hundred miles. Hopefully I get some decent footage and good stories to tell. Not that I particularly want any storms to strike, but in the event they do, I wouldn't mind capturing some of it. Safely, of course.
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Quoting BenBIogger:
My predictions

4 named storms
1 hurricanes
0 major hurricanes






Well more than that. I wouldn't be surprised to see a major hurricane or 2 out there. Definetly will see at least 10 named storms. 4 of whichwill be hurricanes ( not including major
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I can see that even a malicious keystroke logger code designer would replace a certain someone with empty space. Painful to read.
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CybrTeddy - OK
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Quoting CybrTeddy:
Either a non-Tropical Low or a Sub-Tropical system. Sheared in nature.


A lot of convection on the east side of the disturbance too and little( if any) to no convection on the west side. The center of the storm ( where all the spinning is coming from) is on the west side where there is no activity
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I can't help but noticing a lot of people trying to call the season early, saying how "slow" it will likely be. I seem to remember a certain A storm that didn't form until August. What would it matter if there were only 10 storms, or 7, or however few, if there's still that one that hits home?
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Quoting AllStar17:


Not necessarily, many bloggers on here have said to look close to home for some homegrown cyclones due to the more unfavorable environment in the MDR.......but anyways all one can do is be prepared, watch, and wait.


Don't quote Ben he's a troll. Just trying to get an reaction.
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Quoting BenBIogger:
IMO looks like every tropical system this year will be a fish storm


Not necessarily, many bloggers on here have said to look close to home for some homegrown cyclones (and those would not be fishies) due to the more unfavorable environment in the MDR.......but anyways all one can do is be prepared, watch, and wait.
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Quoting AllStar17:


SavannahStorm-
What is that QuikScat of?


Our area of sheared swirly-ness.
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Ben--

there will be at least 1 Carrib or GOM storm.. those cant be fish... not possible
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and I just voted for Mike.. good luck to him.

that brought him to 160 (I think)
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Quoting SavannahStorm:


SavannahStorm-
What is that QuikScat of?
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IMO looks like every tropical system this year will be a fish storm
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Quoting Weather456:
Interesting little feature



That looks like a sheared Sub-Tropical Storm, doesn't it?
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Quoting hurricane2009:
Also I would watch that area at 32.5N 47W

It is an area from the old frontal boundry, surface low looks to be with it. These kinds of systems can sneak up on us in terms of developing


I know. This system could be reminiscent of Tropical Storm Jerry I believe it was in 2007. I am surprised the NHC has not mentioned it yet. Maybe they will at 8. I clearly has a LLC, and convection (even though it is sheared to the east)
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Either a non-Tropical Low or a Sub-Tropical system. Sheared in nature.
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Quoting CatastrophicDL:
I voted for Mike, but we need to step it up. It looks like there are 7 bloggers that are Mike's main competition and while six are all pretty close in votes, one has over 4 times the votes Mike's got. So tell everyone to vote for Mike. Antarctica is one of my dream vacations - I bet it will be AWESOME! Go Mike!


Where did you see that? I must've missed it.
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My predictions

4 named storms
1 hurricanes
0 major hurricanes




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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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