July Atlantic hurricane outlook

By: Dr. Jeff Masters , 12:55 PM GMT on July 13, 2012

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It's mid-July, and we have yet to see a named storm form in the Atlantic this month. The computer models are not predicting any development through at least July 20, and if we make it all the way to the end of the month without a named storm forming, it will be the first July since 2009 without a named storm. Since the current active hurricane period began in 1995, 13 of 17 years (76%) have had a named storm form during July. The busiest July occurred in 2005, when five named storms and two major hurricanes formed. These included Hurricane Dennis and Hurricane Emily--the strongest hurricanes ever observed so early in the season. Only eight major hurricanes have formed in July since record keeping began in 1851. As seen in Figure 1, most of the last half of July activity occurs in the Gulf of Mexico and waters off the Southeast U.S. coast. These type of storms 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 (as happened for Alberto, Beryl, Chris, and Debby in 2012.) There will be at least two cold fronts moving off the U.S. Mid-Atlantic coast over the next two weeks. The first of these fronts will push offshore around July 20, and we will need to watch the waters offshore of North Carolina for development then. Formation potential will be aided by ocean temperatures that are about 0.7°C (1°F) above average along the U.S. East Coast.


Figure 1. Tracks of all tropical storms and hurricanes 1851 - 2006 that formed July 16-31. The U.S. coast from North to Texas are the preferred strike locations. Only a few storms have formed in the tropical Atlantic and Caribbean in July. Wind shear is typically too high and SSTs too cool in July to allow African waves in the Caribbean and tropical Atlantic to develop into tropical storms. However, a few long-track "Cape Verdes" hurricanes have occurred in July, spawned by tropical waves that came off the coast of Africa. African tropical waves serve as the instigators of about 85% of all major hurricanes.


Figure 2. The seasonal distribution of Atlantic hurricane activity shows that July typically has low activity. Image credit: NHC.

Sea Surface Temperatures: slightly above average
The departure of Sea Surface Temperatures (SST) from average over the tropical Atlantic between Africa and Central America was about 0.3°C above average during June (Figure 3.) This figure has not changed much over the first two weeks of July. These temperatures are not warm enough to appreciably affect the odds of a July named storm or hurricane. The strength of the Azores-Bermuda high has been near average over the past two weeks, driving near-average trade winds. The latest 2-week run of the GFS model predicts continued average-strength trade winds through late-July, so SSTs should remain about 0.3°C above average during this period, due to average amounts of cold water mixing up from below due to the wind action on the water.


Figure 3. Sea Surface Temperature (SST) departure from average for July 12, 2012. SSTs were 0.3°C above 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 on the way?
For two consecutive weeks, ocean temperatures 0.5 - 0.6°C above average have been present in the tropical Eastern Pacific, which is right at the threshold for a weak El Niño episode. NOAA's Climate Prediction Center has issued an El Niño Watch, and gives a 61% chance that El Niño conditions will be present during the August - September - October peak of the Atlantic hurricane season. The likely development of a full-fledged El Niño episode means that Atlantic hurricane activity will probably be suppressed in 2012, due to the strong upper-level winds and high wind shear these events typically bring to the tropical Atlantic.


Figure 4. 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 July 9, 2012, SSTs in the Niño 3.4 region had risen to 0.5°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: NOAA Climate Prediction Center.

Wind shear: above average
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 has two bands of strong high-altitude winds that are currently bringing high wind shear to the Atlantic. The southern branch (subtropical jet stream) is bringing high wind shear to the Caribbean, and the northern branch (polar jet stream) is bringing high wind shear to the waters offshore of New England. This configuration often leaves a "hole" of low shear between the two branches, off the Southeast U.S. coast and over the Gulf of Mexico. The jet stream is forecast to maintain this two-branch pattern over the coming two weeks. Wind shear has been about 10 - 20% higher than average over the first two weeks of July, and is predicted to be mostly above average for the coming two weeks. This will cut down on the odds of a July storm.


Figure 5. Vertical instability over the Caribbean Sea in 2012 (blue line) compared to average (black line.) The instability is plotted in °C, as a difference in temperature from near the surface to the upper atmosphere. Thunderstorms grow much more readily when vertical instability is high. Instability has been lower than average, due to an unusual amount of dry air in the atmosphere, reducing the potential for tropical storm formation. Image credit: NOAA/NESDIS/CIRA.

Dry air: above average
As seen in Figure 5, there has been an unusual amount of dry, stable air in the Caribbean this year creating low levels of vertical instability. This has occurred due to a combination of dry air from Africa, and upper-atmosphere dynamics creating large areas of sinking air that dry as they warm and approach the surface. The Gulf of Mexico and tropical Atlantic between the coast of Africa and the Lesser Antilles have also seen low vertical instability this summer. June and July are the peak months for dry air and dust coming off the coast of Africa, and the Saharan dust storms have been quite active over the past two weeks. Expect dry air to be a major deterrent to any storms that try to form in the tropical Atlantic during July.

Steering currents: average
The predicted steering current pattern for the next two weeks is a typical one for 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. 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 2010 and 2011 steering current pattern, which recurved most storms out to sea--or the unfavorable 2008 pattern, which steered Ike and Gustav into the Gulf of Mexico.

Summary: a below average chance of a July tropical storm
Given that none of the computer models are forecasting tropical storm formation in the coming seven days, SSTs are only slightly above average, and wind shear and vertical stability are above average, I'll go with a 30% chance of a named storm forming in the Atlantic during the remainder of July.


Figure 6. Hurricane Emilia over the Eastern Pacific at 20:35 UTC July 10, 2012. At the time, Emilia was a Category 3 hurricane with 125 mph winds. Emilia peaked earlier in the day as a Category 4 storm with 140 mph winds--the strongest hurricane in the East Pacific so far in 2012. Image credit: NASA.

An active Eastern Pacific hurricane season
It's been a very active start to the Eastern Pacific hurricane season, where we've already had six named storms, four hurricanes, and three intense hurricanes. A typical season has 4 named storms, 2 hurricanes, and 0 intense hurricanes by July 14. The formation of Tropical Storm Fabio on July 12 marks the 4th earliest formation of the Eastern Pacific's season's sixth storm. The record is held by the year 1985, when the season's sixth storm formed on July 2. Record keeping began in 1949.

Have a great weekend, everyone, and I'll be back Monday with a new post.

Jeff Masters

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Fabio is beginning to weaken.

Member Since: July 21, 2011 Posts: 83 Comments: 7167

Image shows a nice shelf cloud during the late morning hours in Downtown Tallahassee, FL. This was forming as a result of a quickly moving yet feeble seabreeze outflow boundary. Pop up- Svevere storm threat (T ) increase over all of florida as a cold core of air aloft provides more energy, (-10 to -13 degrees C) or (5 degrees F). This simulates the Cold/Warm Clash in the midwest (although on a smaller scale.)

The worst storms during the next few days should shift to interior then drift towards W Coast of FL as seabreeze front collaspes w/o dinurnal support.

Storms moving in to Central Lee County in SWFL so I need to start monitoring for wind gusts/downbursts so I can report them to NWS Ruskin, FL

GTG
FM
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15/1800 UTC 17.2N 117.8W T4.5/5.0 FABIO -- East Pacific
15/1800 UTC 15.8N 138.7W TOO WEAK EMILIA -- East Pacific
CI# /Pressure/ Vmax
5.7 / 956.3mb/107.2kt


Final T# Adj T# Raw T#
5.6 5.5 5.5

Member Since: March 16, 2012 Posts: 127 Comments: 7948
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Up-close view of the Poland tornado.
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Fabio down to 100 mph.

EP, 06, 2012071518, , BEST, 0, 172N, 1178W, 85, 974, HU,
Member Since: July 6, 2010 Posts: 113 Comments: 32256
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In response to Levi's Poll: I like the plane. It is more clear for someone like me that is a novice. Plus...I just like the way it looks....
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Quoting GeorgiaStormz:


dis aint the epac.

thats 2-4 TCs?
no way
The GFS has been showing this similar scenario for a few runs now. I think we could see atleast one storm come from the trough sopilt.
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2002. hydrus
Quoting Grothar:
Exactly as I predicted in my blog 5 days ago. How do I know these things??

Experience probably.
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2001. Patrap
Member Since: July 3, 2005 Posts: 426 Comments: 128636
2000. ncstorm
I see the models are still calling for development off the NC/SC coast

12z Euro running now
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Quoting TomTaylor:
Yes.

If SST anomalies were going straight up we'd get a full blown El Nino much faster. Of course, it is only normal to see periods of slight cooling, referred to as noise or stair-stepping.
thanks
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Quoting wxchaser97:


dis aint the epac.

thats 2-4 TCs?
no way
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1996. barbamz
Quoting GeorgiaStormz:


did the guy inthe 2nd video say cool, tornado?


Ehhm, no. As much as I could get from google translator (I don't speak polish) it seems to be a curse ;-)

There are more videos available but don't be afraid I won't send them all. If you are bored just admire the beautiful landscape of Poland.



Others:

youtube link

youtube link
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Quoting TomTaylor:
There's potential for a little trough split action off the east coast around next weekend or maybe slightly thereafter as ridging builds eastward. At least that's what models were showing yesterday, haven't checked them yet this morning. I'm not looking forward to tracking a little TS outside of the tropics but it will be something to watch for if the models continue to show this solution.

The GFS continues to show the development of two named storms from a trough split by the middle to late portion of next week.
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Quoting Levi32:


This is not cooling. This is noise.

Well technically it is cooling lol
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Quoting floridaboy14:
thank you for the explanation. will this affect how fast the el nino develops ?
Yes.

If SST anomalies were going straight up we'd get a full blown El Nino much faster. Of course, it is only normal to see periods of slight cooling, referred to as noise or stair-stepping.
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Quoting Levi32:


Probably not this month. The only sparkle of potential action is the CFSv2 and JMA ensembles showing a burst of southeasterly winds moving into the southeast Caribbean during Weeks 3 and 4, something that could generate some activity if it comes to fruition, but the month-long forecasts often change a lot.

There's potential for a little trough split action off the east coast around next weekend or maybe slightly thereafter as ridging builds eastward. At least that's what models were showing yesterday, haven't checked them yet this morning. I'm not looking forward to tracking a little TS outside of the tropics but it will be something to watch for if the models continue to show this solution.
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Light rain showers headed for NHMS.
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Quoting Levi32:


Small fluctuations that, compared with the average variation of the data set, are insignificant, and do not represent a trend of any kind.
thank you for the explanation. will this affect how fast the el nino develops ?
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Quoting barbamz:
Impressive video of one of the three tornados yesterday in northeast Poland. Some injuries, lots of damage.



Edit: Another one



did the guy inthe 2nd video say cool, tornado?
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Two areas I'm watching:



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Quoting stormchaser19:
I repeat I think el Nino is taking his time.........Todays prelimar values for SOI continue to be positive for eight days consecutive

july 8 6.52
july9 5.05
july 10 6.46
july 11 12.25
july 12 18.22
july 13 15.82
july 14 8.92

And Today preliminar values July 15 20.50

Clearly El nino is delayed for now.

Link
If we use the closest analog years for what we've seen so far this summer, that being the record breaking heat in July for the Midwest, we have to go back to 1934.

If we want to compare the eastern Pacific, in terms of the number of early storms, then we must use 1985. I'm just using Dr. Masters recent comments here.

In both of these years, what appeared to be a developing El Nino, began to swing to neutral, and continued roughly until the hurricane season ended.

Also during these years, there was a fairly pronounced shift west in the hurricane tracks for the Atlantic Basin. You don't see a lot of recurvature during these two analog years.

I think we may be in for a rough ride, but of course a glorious one for those who enjoy that sort of thing.







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1984. LargoFl
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Quoting TropicalAnalystwx13:
Just waiting for the blog to wake back up..
Just woke up here on the west coast at 11:23

"Summertime and the living's easy"
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1982. LargoFl
Member Since: August 6, 2011 Posts: 4 Comments: 39116
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1980. LargoFl
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Quoting Levi32:
So how about if I use the current motion of the plane to extrapolate its position forward from the latest data point such that it is out of the way of the data. The actual position of the plane 30 seconds later usually doesn't deviate much from the previous flight path anyway, so it would be reasonably accurate. Like this:

I like this

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1978. Levi32
Quoting floridaboy14:
levi what do you mean by this is noise?


Small fluctuations that, compared with the average variation of the data set, are insignificant, and do not represent a trend of any kind.
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1977. LargoFl
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Hey folks,look at this circulation at 10N-30W.



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1974. barbamz
Impressive video of one of the three tornados yesterday in northeast Poland. Some injuries, lots of damage.



Edit: Another one

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Quoting Levi32:
Good afternoon all. If I could get a quick opinion poll from you guys:

For live plotted recon data, would you rather that the latest observation in the set be highlighted and "bolded" (top image), or would you rather have an image of an airplane located at the latest data point and rotated in the aircraft's direction of travel (bottom image). I need to decide which to use. Personally I like the plane, but I'm curious which you guys prefer. Sometimes the plane can get in the way of the data.

Highlighted:



Aircraft Icon:



I've been gone for awhile so I just saw this, plane.
Member Since: March 16, 2012 Posts: 127 Comments: 7948
Quoting TropicalAnalystwx13:
Sigh...

"DVORAK T-NUMBERS WERE UP
TO T7.0 FROM TAFB AND SAB AT 0000 UTC...AND T6.5 AND T7.0 FROM TWO
FORMS OF THE UW-CIMSS ADT. SINCE THE WHITE RING DOES NOT ENTIRELY
WRAP AROUND THE EYE AT THIS TIME...THE INITIAL INTENSITY IS BEING
RAISED TO 135 KT."

Igor should have been upgraded to a Category 5.


not that it really matters, didnt hit anywhere till it was weaker
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Quoting Levi32:


This is not cooling. This is noise.

levi what do you mean by this is noise?
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1970. Levi32
Thanks for the input on the graphic everyone. Sorry to invade the blog with that lol. I just needed some new pairs of eyes: been staring at the code for this for days now. It's a work in progress, but will be going live pretty soon.
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CI# /Pressure/ Vmax
5.7 / 956.4mb/107.2kt


Final T# Adj T# Raw T#
5.6 5.7 5.7

Estimated radius of max. wind based on IR : 27 km

Center Temp : +5.4C Cloud Region Temp : -60.0C

Scene Type : EYE

Positioning Method : RING/SPIRAL COMBINATION

Ocean Basin : EAST PACIFIC
Dvorak CI > MSLP Conversion Used : PACIFIC

Tno/CI Rules : Constraint Limits : NO LIMIT
Weakening Flag : ON
Rapid Dissipation Flag : OFF

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Quoting TropicalAnalystwx13:
Just waiting for the blog to wake back up..


im up.
but there is nothing to talk about.

so im watching tom and jerry
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Quoting Levi32:
Good afternoon all. If I could get a quick opinion poll from you guys:

For live plotted recon data, would you rather that the latest observation in the set be highlighted and "bolded" (top image), or would you rather have an image of an airplane located at the latest data point and rotated in the aircraft's direction of travel (bottom image). I need to decide which to use. Personally I like the plane, but I'm curious which you guys prefer. Sometimes the plane can get in the way of the data.

Highlighted:



Aircraft Icon:




If you're interested in a compromise, you could place a less obtrusive symbol/shape at the location of the plane, and then have a small Legend with the place icon relating to the symbol at the bottom-left of the image.
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Just waiting for the blog to wake back up..
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1963. Patrap
Quoting Grothar:


She's in Miami, and who told???


You know, I used to stare at Goats too.
Member Since: July 3, 2005 Posts: 426 Comments: 128636
Sigh...

"DVORAK T-NUMBERS WERE UP
TO T7.0 FROM TAFB AND SAB AT 0000 UTC...AND T6.5 AND T7.0 FROM TWO
FORMS OF THE UW-CIMSS ADT. SINCE THE WHITE RING DOES NOT ENTIRELY
WRAP AROUND THE EYE AT THIS TIME...THE INITIAL INTENSITY IS BEING
RAISED TO 135 KT."

Igor should have been upgraded to a Category 5.
Member Since: July 6, 2010 Posts: 113 Comments: 32256
Quoting Levi32:


This is not cooling. This is noise.



was wondering about that.
but with all the articles abounding and blog despair i thought maybe it wasnt noise after all.
It still might not be, never know if its noise or a setback.
He's coming anyway, no way to stop El Nino now
Member Since: February 11, 2012 Posts: 0 Comments: 9731

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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.