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 Chicklit:
Sorry guys.
Carry on about the Azores.
Don't mind me.


Is there something you would like to talk about instead?
Member Since: June 29, 2009 Posts: 13 Comments: 5315
Quoting hurricane2009:


Its still being sheared, it has to be able to maintain convection over its center, hasnt done that yet.


Yeah...but the key is to continue to fire convection as well as maintain it
Member Since: June 29, 2009 Posts: 13 Comments: 5315
north central atlantic? ho hum.
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Quoting wunderkidcayman:
hi guys what did I miss today


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.
Member Since: June 29, 2009 Posts: 13 Comments: 5315
Quoting wunderkidcayman:
hi guys what did I miss today

Current discussion is tropical storm warnings about the Azores (island off Portugal) in 2006.
So obviously, not much. There's a mid-level disturbance in the Caribbean. There's a system undergoing shear east of the Antilles, and there's a pretty good wave further out in the Atlantic, maybe around 35, dunno, haven't checked lately. At least that's what comes to mind. And there's something headed to the Azores that could become a storm within 48 hours...that's generally it, I think.
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Sorry guys.
Carry on about the Azores.
Don't mind me.
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hi guys what did I miss today
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Quoting hurricane2009:


Um did you read how this came about? NHC mentioned an area in the 8pm TWO that is headed towards the Azores. That is how we got on that topic.


Exactly
Member Since: June 29, 2009 Posts: 13 Comments: 5315
Quoting Chicklit:
This is sad...you are posting tropical storm warnings for the Azores from 2006.
Read a book! Something will happen.
Just not right now.


Well, our AOI is closest to the Azores, so it got me thinking about tropical cyclones and the Azores
Member Since: June 29, 2009 Posts: 13 Comments: 5315
This is sad...you are posting tropical storm warnings for the Azores from 2006.
Read a book!
Something will happen. Just not right now.
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Quoting hurricane2009:


The NHC didnt only posted the watch they didnt issue it


So I was right to begin with.....they post it but the Weather Service in the Azores issues it and the NHC does not
Member Since: June 29, 2009 Posts: 13 Comments: 5315
Actually NHC does issue warnings for the Azores (this was the first adv. in which advisories were issued for the Azores during Gordon):

ZCZC MIATCPAT2 ALL
TTAA00 KNHC DDHHMM
BULLETIN
HURRICANE GORDON ADVISORY NUMBER 32
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL072006
500 PM AST MON SEP 18 2006

...GORDON THREATENS THE AZORES...

AT 500 PM AST...2100 UTC...THE WEATHER SERVICE OF THE AZORES HAS
ISSUED A TROPICAL STORM WATCH FOR THE AZORES ISLANDS. A TROPICAL
STORM WATCH MEANS THAT TROPICAL STORM CONDITIONS ARE
POSSIBLE WITHIN THE WATCH AREA...GENERALLY WITHIN 36 HOURS.
Member Since: June 29, 2009 Posts: 13 Comments: 5315
You were right, Gordon of '06 did pass through the Azores, I forgot about that
Member Since: June 29, 2009 Posts: 13 Comments: 5315
Quoting StSimonsIslandGAGuy:
Well I would think that the government of Portugal would issue hurricane warnings for the Azores, not the NHC.

I pulled up an image of all hurricanes to move through the Azores:



That would make sense, thank you.
Member Since: June 29, 2009 Posts: 13 Comments: 5315
Quoting jrweatherman:
260. hurricane2009 9:54 PM EDT on July 02, 2009
Quoting jrweatherman:
Why are so many people comparing this year to 2004?


Weak El Nino which has developed very similarly to 2004, also of course we have had no storms yet either

So far very similar to 2004


But weren't their other years over the record books in which there was a weak El Nino and that year was much quieter? 2004 was devistating to Florida.


Probably, but there have been other years similar to 04, not necessarily affecting Florida, though
Member Since: June 29, 2009 Posts: 13 Comments: 5315
Quoting jrweatherman:
260. hurricane2009 9:54 PM EDT on July 02, 2009
Quoting jrweatherman:
Why are so many people comparing this year to 2004?


Weak El Nino which has developed very similarly to 2004, also of course we have had no storms yet either

So far very similar to 2004


But weren't their other years over the record books in which there was a weak El Nino and that year was much quieter? 2004 was devistating to Florida.



2004 also didn't stat till July.
Member Since: July 8, 2005 Posts: 259 Comments: 24574
260. hurricane2009 9:54 PM EDT on July 02, 2009
Quoting jrweatherman:
Why are so many people comparing this year to 2004?


Weak El Nino which has developed very similarly to 2004, also of course we have had no storms yet either

So far very similar to 2004


But weren't their other years over the record books in which there was a weak El Nino and that year was much quieter? 2004 was devistating to Florida.
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Quoting CybrTeddy:
We could see a Sub-Tropical system out of the Atlantic Low. Its well organized, the shear though is high.


Yeah.....but it was mentioned just a few posts ago on the blog that it's pressure is 1016 mb. Does that matter? If it is a storm it's a storm.
Member Since: June 29, 2009 Posts: 13 Comments: 5315
We could see a Sub-Tropical system out of the Atlantic Low. Its well organized, the shear though is high.
Member Since: July 8, 2005 Posts: 259 Comments: 24574
bring on EL Nino



EL Nino EL Pass O
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Quoting AllStar17:


I know that, but it still does bear watching, and I knew that the Azores do have hurricanes and TS's, but are they ever under a TS/Hurr. advisory? I have never seen it.


I think 2006 Gordon had hurricane warnings for the Azores.

And yes, the pressure is pretty high, but considering how high the pressures are around it the low may not have to deepen as much as something in the deep tropics.
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Evening all

I need a hand testing the shiny new Portlight Chat. Think a few of you could come over and join us for the testing?
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they found the Qeen bess in a jacket at a bassball game
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Quoting StSimonsIslandGAGuy:
Tropical cyclones visit the Azores with some frequency. A few have even been hurricanes.

The low is currently analyzed as being 1016 mb, forecast to deepen to 1014 mb. It has a long long way to go before being a tropical storm


I know that, but it still does bear watching, and I knew that the Azores do have hurricanes and TS's, but are they ever under a TS/Hurr. advisory? I have never seen it.
Member Since: June 29, 2009 Posts: 13 Comments: 5315
Quoting StSimonsIslandGAGuy:
Tropical cyclones visit the Azores with some frequency. A few have even been hurricanes.

The low is currently analyzed as being 1016 mb, forecast to deepen to 1014 mb. It has a long long way to go before being a tropical storm



You had 1003 last week if I recall correctly, at you home.
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Quoting jrweatherman:
Why are so many people comparing this year to 2004?


Because of the lack of activity so far in the season.

2004 did not have a named storm until July 31st, so comparisons can be made to the inactivity.

Also, 2004 had a weak El Nino....and so does this year.

That is why many bloggers are saying this....and they are saying it because there are some downcasters saying this season will be a bust, but in reality it is just normal for this time of a hurricane season.
Member Since: June 29, 2009 Posts: 13 Comments: 5315
I live in Humble, Tx just North of Houston. We got a notice on the door today about water rationing.

Due to extreme drought, over 5-weeks without any substantial rain, the following is in effect:

1) No water for non-critical uses. No washing the car, no spraying off driveway or sidewalk, no pressure washing the house or hosing out gutters. If your house is on fire, it's ok (according to notice) to use water as this is considered an extenuating circumstance.

2) Even/Odd house #'s: Watering lawn, filling swimming pool, watering garden only allowed on even/odd days depending on your house #, and then only between the hours of 5:00pm-10:00am.

This may not seem like a big deal... but this is SouthEast Texas! Normally we have more than enough rainfall. This is not hot, dry Texas... but rather swampy, rainy, almost-Louisiana Texas.

The last year we had a drought like this (I think) was back in 1999.

It's not forecast to rain until Friday, July 10th. Still 8 more days without rain. DRY and HOT! Feels like Arizona.
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oh is looking forword too window 7
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Quoting jrweatherman:
Why are so many people comparing this year to 2004?


I don't know
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Why are so many people comparing this year to 2004?
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Quoting StSimonsIslandGAGuy:
There is a yellow area on the NHC page designating a low in the central Atlantic which could be of interest.


That is the one on my above comment (east of 50 W)
Member Since: June 29, 2009 Posts: 13 Comments: 5315
When is the last time advisories were issued to warn the Azores of a tropical cyclone?? Does anyone know?
Member Since: June 29, 2009 Posts: 13 Comments: 5315
Quoting AllStar17:
Convection firing very close to COC of our AOI(albeit not extremely intense)

IMO, I think if convection continues to fire near the center, we may have ourselves 94L to track tomorrow.




Loop
Link


I agree!!!
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Convection firing very close to COC of our AOI(albeit not extremely intense)

IMO, I think if convection continues to fire near the center, we may have ourselves 94L to track tomorrow.




Loop
Link
Member Since: June 29, 2009 Posts: 13 Comments: 5315
Oss: cyberstudder, like it.

Happened and unfixible due to my posting by boysenberry, I mean, blackberry.
Member Since: August 16, 2007 Posts: 6 Comments: 12463
atmo

mail
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Dang, errantlty. Where you at, Lacombe?
Member Since: August 16, 2007 Posts: 6 Comments: 12463
Link

support barometer bob show log in now live show
Member Since: July 15, 2006 Posts: 178 Comments: 55995

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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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