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 Acemmett90:
wait ive been working hard the last few days how the heck did we end up at 94L


It was a non-tropical area of low pressure in the North Central Atlantic SW of the Azores. NHC still has a floater up on it, if you wanted to check. Could of become Sub-tropical, but was heavily sheared throughout it's life as an invest, thus no development.
Member Since: June 29, 2009 Posts: 13 Comments: 5315
From my house we can see the moon outside with some clouds high in the distance, at the southeast you can see the lightning.desde mi casa se ve la luna afuera.... con algunas nubes altas y distante al sur sureste se ven los relampago
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2091. Acemmett90

The wave itself is moving west, however
Member Since: June 29, 2009 Posts: 13 Comments: 5315
Quoting JRRP:
desde mi casa se ve la luna afuera.... con algunas nubes altas y distante al sur sureste se ven los relampagos


Translated (using FreeTranslation.com lol)
since my house the moon is seen outside. ... with some distant and high clouds to the southeastern south the relampagos are seen
Member Since: July 8, 2005 Posts: 259 Comments: 24580
Anyone out there, like me, that has given MS the boot, is running Ubuntu and cannot wait for all of the checks to get firefox 3.5 look here: Link

Worked for me.
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Acemmett90 ---

Yes, it has been a hot topic on the blog tonight.
Member Since: June 29, 2009 Posts: 13 Comments: 5315
2088. JRRP
Quoting redwagon:
desde mi casa se ve la luna afuera.... con algunas nubes altas y distante al sur sureste se ven los relampagos
-------------
Over at my house we're drinking Fire Moon ale.. with queso at high noon, but my distant cousin's mom just threw a lamp at me.

wrong translation
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vivo en Santo Domingo
-----------
Livin' large this Sunday evening
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Africa Next Generation Satellite

Does anyone see rotation with the wave just off the coast? Just curious.
Member Since: June 29, 2009 Posts: 13 Comments: 5315
2084. fsumet
I thought more about your correlation Levi that you can see in the western Atlantic in the Fall. This may be due to strong cold fronts moving further south and east than normal. This also basically ends the hurricane season for the Gulf early as well. So it's not so much a direct correlation with SST, it's more of a function of how El Nino affects the overall climate and the SST in the western Atlantic is a feedback from that effect.
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desde mi casa se ve la luna afuera.... con algunas nubes altas y distante al sur sureste se ven los relampagos
-------------
Over at my house we're drinking Fire Moon ale.. with queso at high noon, but my distant cousin's mom just threw a lamp at me.
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Quoting JRRP:

vivo en Santo Domingo


You live in Santo Domingo?

Some interesting model tracks for 94E:
Member Since: June 29, 2009 Posts: 13 Comments: 5315
2078. tropicfreak 9:07 PM CDT on July 05, 2009

thanks
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2079. JRRP
Quoting tropicfreak:


????????????????????????????????

vivo en Santo Domingo
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Quoting ajcamsmom2:
2068. tropicfreak 8:59 PM CDT on July 05, 2009

Your post just shows up as a red x to me...can you post a link???


www.wunderground.com/tropical
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Quoting JRRP:
desde mi casa se ve la luna afuera.... con algunas nubes altas y distante al sur sureste se ven los relampagos


????????????????????????????????
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AOI

AOI
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2068. tropicfreak 8:59 PM CDT on July 05, 2009

Your post just shows up as a red x to me...can you post a link???
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2073. KEEPEROFTHEGATE (Mod)
image a of 956 pm edt
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2071. JRRP
desde mi casa se ve la luna afuera.... con algunas nubes altas y distante al sur sureste se ven los relampagos
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Better yet, a Tropical Depression in the EPAC is maybe being ignored.
Member Since: June 29, 2009 Posts: 13 Comments: 5315
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latest quikscat of former 94L
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2066. Levi32
Quoting tropicfreak:
How is shear looking ahead of this disturbance?


See for yourself:



The shear in a sense is the only reason this wave has a lot of convection. It's all due to upper divergence. This wave is far less than it appears to be.
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SST's look good ahead of this disturbance. Waters are just warm enough.
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1965. stormpetrol 11:57 PM GMT on July 05, 2009
Looks like former 94L at least to me could actually be STS right now IMO at least looking at the quikscat.
Quoting reedzone:
http://www.ssd.noaa.gov/goes/flt/t1/avn-l.jpg

Sub-Tropical Depression being ignored in the Atlantic folks?? Say it ain't so lol.

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How is shear looking ahead of this disturbance?
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2062. fsumet
How each El Nino Progressed from last post (Just doing the last 4 El Ninos):

Peak Hurricane Season (Mid September) 2006


Peak Hurricane Season (Mid September) 2004


Peak Hurricane Season (Mid September) 2002


Peak Hurricane Season (Mid September) 1997



Mid November 2006


Mid November 2004


Mid November 2002


Mid November 1997
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2061. Levi32
Quoting reedzone:
http://www.ssd.noaa.gov/goes/flt/t1/avn-l.jpg

Sub-Tropical Depression being ignored in the Atlantic folks?? Say it ain't so lol.



Not yet. It needs that convection to stick around for a while to warm its core. It's running out of time as it moves over colder and colder SSTs. We'll see. It still has frontal features attached to it too.
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I can foretell a few days down the road from now that this thing becomes an invest or possibly even a TD and this blog will be an anthill. I will have an overflow blog if needed. Which tells me I haven't updated in a while. Perhaps I should do it tomorrow.
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2059. Levi32
Quoting tennisgirl08:
Can someone please look at this link??

http://www.goes.noaa.gov/HURRLOOPS/huwvloop.html

Are my eyes playing tricks on me or is there some rotation? Maybe mid-level. This tropical wave looks really good to me right now. Shouldn't it at least be an invest? Just IMO.


It's an illusion caused by that burst of convection expanding towards the south. This wave isn't organized enough to be labeled an invest.
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http://www.ssd.noaa.gov/goes/flt/t1/avn-l.jpg

Sub-Tropical Depression being ignored in the Atlantic folks?? Say it ain't so lol.

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Quoting tennisgirl08:
Can someone please look at this link??

http://www.goes.noaa.gov/HURRLOOPS/huwvloop.html

Are my eyes playing tricks on me or is there some rotation? Maybe mid-level. This tropical wave looks really good to me right now. Shouldn't it at least be an invest? Just IMO.

I know right!It looks like that big blob of convection to the north of the wave is trying to wrap around.Circulation or LLC or what?Label as a low?
Link
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Caribbean wave appears to be slowing in forward speed possible MLC at 16N/70.5W
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Quoting tennisgirl08:
Can someone please look at this link??

http://www.goes.noaa.gov/HURRLOOPS/huwvloop.html

Are my eyes playing tricks on me or is there some rotation? Maybe mid-level. This tropical wave looks really good to me right now. Shouldn't it at least be an invest? Just IMO.


The one S of Puerto Rico? It looks good to me too. It looks like it just started spinning.
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2054. Levi32
Quoting fsumet:
Levi your 2 maps don't show the Atlantic much. Both are from the Pacific. I don't see any noticeable change in the Atlantic except in the Gulf from the image on the left.


Yeah but you can clearly see what the trend is. There is a correlation, you'll learn about it in any report on El Nino. It's not the strongest correlation the Atlantic has with El Nino, as things like the NAO can strongly influence SSTs in the tropical Atlantic, but El Nino does tend to bring down the SSTs. Again, we are in the warm phase of the AMO, which will tend to offset any cooling effect by an El Nino event. Also we haven't had a really strong El Nino since 1997, and weaker events don't always influence all the atmospheric parameters.
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Quoting VAbeachhurricanes:


i realize that an el nino and la nina occur in the pacific i just thought that SST'S around the world should react accordingly (energy can't be created nor destroyed) more or less energy in the pacific = more or less around the globe correct or no?


The earth's oceans aren't a closed system, though. Energy from the sun, geothermal sources, ice melt, amount of freshwater runoff, wind energy, and other factors all affect SSTs.
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Can someone please look at this link??

http://www.goes.noaa.gov/HURRLOOPS/huwvloop.html

Are my eyes playing tricks on me or is there some rotation? Maybe mid-level. This tropical wave looks really good to me right now. Shouldn't it at least be an invest? Just IMO.
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Quoting fsumet:
Levi your 2 maps don't show the Atlantic. Both are from the Pacific.


look at the gulf, hot during la nina, cold during el nino
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2050. beell
Quoting tennisgirl08:


I agree! So which year can we compare the most to this year? Based on those maps he showed.


I like 07/02/02-3rd one down from the top. But I am not fluent with el nino.
What say you?
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Quoting RainyEyes:


That has to be one of the saddest things I have ever read. Those that died, you can read and know that it was the entire family. And the 9 and 11 year old...how sad:-(

It was like a bomb was dropped...it was near US 192 near 5 miles or so from Disney..
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2047. fsumet
Levi your 2 maps don't show the Atlantic much. Both are from the Pacific. I don't see any noticeable change in the Atlantic except in the Gulf from the image on the left. The images don't say when in the year this occurs though either.
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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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