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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2061. beell
12Z GFS 500mb Vort at 192 hrs...

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Two people killed in Houston today by lightning

Link
Member Since: August 18, 2011 Posts: 0 Comments: 633
...FABIO WEAKENS A LITTLE...
------------------------------------------------- -------------------------------

2:00 PM PDT Sun Jul 15
Location: 17.4°N 118.2°W
Moving: WNW at 10 mph
Min pressure: 974 mb
Max sustained: 100 mph

Member Since: March 16, 2012 Posts: 127 Comments: 7948
Quoting washingtonian115:
Is that a tropical storm that is already out in the atlantic on on tropical?.


That particular system is extra-tropical.
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Hurricane Fabio:

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BULLETIN
HURRICANE FABIO ADVISORY NUMBER 16
NWS NATIONAL HURRICANE CENTER MIAMI FL EP062012
200 PM PDT SUN JUL 15 2012

...FABIO WEAKENS A LITTLE...


SUMMARY OF 200 PM PDT...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...17.4N 118.2W
ABOUT 660 MI...1060 KM SW OF THE SOUTHERN TIP OF BAJA CALIFORNIA
MAXIMUM SUSTAINED WINDS...100 MPH...160 KM/H
PRESENT MOVEMENT...WNW OR 300 DEGREES AT 10 MPH...17 KM/H
MINIMUM CENTRAL PRESSURE...974 MB...28.76 INCHES
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HURRICANE FABIO DISCUSSION NUMBER 16
NWS NATIONAL HURRICANE CENTER MIAMI FL EP062012
200 PM PDT SUN JUL 15 2012

FABIO HAS WEAKENED SLIGHTLY SINCE THE LAST ADVISORY. SATELLITE
IMAGES INDICATE THAT THE CONVECTIVE PATTERN HAS BECOME A LITTLE
LESS ORGANIZED DURING THE PAST FEW HOURS...WITH A FEW BREAKS OR DRY
SLOTS EVIDENT OVER THE WESTERN SEMICIRCLE. AN AVERAGE OF THE LATEST
DVORAK CI-NUMBERS FROM TAFB AND SAB YIELDS AN INITIAL WIND SPEED
ESTIMATE OF 85 KT. THE WEAKENING TREND IS FORECAST TO ACCELERATE
OVER THE NEXT COUPLE OF DAYS AS FABIO MOVES OVER MUCH COLDER WATER
AND INTO A PROGRESSIVELY DRIER ATMOSPHERIC ENVIRONMENT. THE
OFFICIAL FORECAST CLOSELY FOLLOWS THE SHIPS AND LGEM GUIDANCE...AND
BRINGS FABIO BELOW HURRICANE STRENGTH IN ABOUT 24 HOURS. THE
CYCLONE IS EXPECTED TO DEGENERATE TO A REMNANT LOW BY DAY 3 WHEN IT
WILL BE OVER SEA SURFACE TEMPERATURES BELOW 20C. DISSIPATION IS NOW
SHOWN AT THE END OF THE FORECAST PERIOD IN AGREEMENT WITH THE
GLOBAL MODELS.

THE HURRICANE IS GRADUALLY TURNING TO THE RIGHT...AND THE LATEST
INITIAL MOTION ESTIMATE IS 300/9. A MID- TO UPPER-LEVEL LOW
CURRENTLY OVER THE PACIFIC NORTHWEST IS EXPECTED TO DIVE SOUTHWARD
CAUSING THE SUBTROPICAL RIDGE TO BREAK DOWN. THIS STEERING PATTERN
SHOULD ALLOW FABIO TO TURN NORTHWESTWARD...AND THEN NORTHWARD OVER
THE NEXT 3 TO 4 DAYS. THE OFFICIAL FORECAST IS NUDGED A BIT TO THE
RIGHT...AND LIES CLOSE TO THE LATEST ECMWF RUN AND THE MULTI-MODEL
CONSENSUS.

FORECAST POSITIONS AND MAX WINDS

INIT 15/2100Z 17.4N 118.2W 85 KT 100 MPH
12H 16/0600Z 18.0N 119.4W 75 KT 85 MPH
24H 16/1800Z 19.0N 120.7W 60 KT 70 MPH
36H 17/0600Z 20.2N 121.3W 45 KT 50 MPH
48H 17/1800Z 21.5N 121.5W 35 KT 40 MPH
72H 18/1800Z 24.4N 121.5W 25 KT 30 MPH...POST-TROP/REMNT LOW
96H 19/1800Z 26.0N 121.0W 25 KT 30 MPH...POST-TROP/REMNT LOW
120H 20/1800Z...DISSIPATED

$$
FORECASTER CANGIALOSI
Member Since: February 11, 2012 Posts: 83 Comments: 7833
Quoting CybrTeddy:
ECMWF hinting at trough split mischief off the US East Coast at 192 hours, same as the GFS.


This morning's GGEM also showed trough split development by 192 hours.
Is that a tropical storm that is already out in the atlantic on on tropical?.
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ECMWF hinting at trough split mischief off the US East Coast at 192 hours, same as the GFS.


This morning's GGEM also showed trough split development by 192 hours.
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Closeup view of West African waves.

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The eye has become cloud-filled.

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.
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Quoting wxchaser97:
Fabio has peaked, should begin to weaken

I agree.
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Northern Lights in Duluth, Minnesota this morning taken by Chief Meteorologist Mark Tarello at KEYC News 12.

Member Since: August 31, 2009 Posts: 0 Comments: 5628
The west coast seabreeze pushed a little inland today and is now colliding with the stronger east coast seabreeze. Looks like more rain along the way for the coastline in a few hours.

Member Since: August 31, 2009 Posts: 0 Comments: 5628
Quoting Patrap:


You know, I used to stare at Goats too.
I suppose there are some around trained in paranormal warfare. Never read the non-fiction book it was based on but the film version of The Men Who Stare at Goats is great. Funny, yet not so funny.
Member Since: April 29, 2006 Posts: 154 Comments: 18710
Fabio has peaked, should begin to weaken
Member Since: March 16, 2012 Posts: 127 Comments: 7948
Member Since: March 16, 2012 Posts: 127 Comments: 7948
2041. beell
Quoting 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.


What I'd really like to see is the dropsondes from the high-altitude flights plotted for all the standard levels.

Similar to this:



Can you get right on that?
(j/k)
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Quoting WxGeekVA:
Well what do we have here...?

Yeah I was looking at that two.Convection has been consistent.
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Quoting washingtonian115:
I see something in the BOC.
A weak tropical wave
Member Since: March 16, 2012 Posts: 127 Comments: 7948
Quoting wxchaser97:
I see something in the BOC.
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Quoting MAweatherboy1:
Big time rain on the way for Alaska... Dry pretty much everywhere else though...


Above normal temops for everyone but the opacific coast and Alaska.
Member Since: March 16, 2012 Posts: 127 Comments: 7948
Member Since: March 16, 2012 Posts: 127 Comments: 7948
Big time rain on the way for Alaska... Dry pretty much everywhere else though...

Member Since: February 11, 2012 Posts: 83 Comments: 7833
7-DAY FORECAST
This Afternoon A chance of showers and thunderstorms. Partly sunny, with a high near 92. Calm wind. Chance of precipitation is 50%. Tonight A chance of showers and thunderstorms before 8pm. Partly cloudy, with a low around 69. East southeast wind 5 to 7 mph becoming calm in the evening. Chance of precipitation is 30%. Monday Sunny and hot, with a high near 94. Light and variable wind. Monday Night Partly cloudy, with a low around 75. South wind 5 to 9 mph becoming light southwest. Tuesday Mostly sunny and hot, with a high near 98. West wind 11 to 16 mph. Tuesday Night A chance of showers and thunderstorms. Mostly cloudy, with a low around 74. Chance of precipitation is 40%. Wednesday A chance of showers and thunderstorms. Partly sunny, with a high near 82. Chance of precipitation is 40%. Wednesday Night Partly cloudy, with a low around 64. Thursday Sunny, with a high near 82. Thursday Night Mostly clear, with a low around 62. Friday Sunny, with a high near 83. Friday Night Partly cloudy, with a low around 67. Saturday Mostly sunny, with a high near 87.
Member Since: March 16, 2012 Posts: 127 Comments: 7948
Quoting TomTaylor:
Just woke up here on the west coast at 11:23

"Summertime and the living's easy"


lol...........bankers hours tom?
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Member Since: March 16, 2012 Posts: 127 Comments: 7948
Member Since: March 16, 2012 Posts: 127 Comments: 7948
Quoting lottotexas:
and you live where ?


gotta be Louisiana
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Quoting yoboi:
this rain made me cook a shrimp, crawfish, oyster,tasso and okra stew for this eve...fresh tomato and cucumbers on the side with potato salad...the smell is killing me..


i got steak salad pasta salad and shrimps on the barbie! :)
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Quoting fmhurricane2009:

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


Come on, that pics really in Italy... Isn't that leaning tower on the right? LOl.
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Member Since: March 16, 2012 Posts: 127 Comments: 7948
It has weak 850 vort and low shear..



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Quoting WxGeekVA:
Well what do we have here...?


I was noticing that also.
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Member Since: March 16, 2012 Posts: 127 Comments: 7948
Quoting Civicane49:


That area east of Bermuda looks interesting.
Member Since: April 29, 2009 Posts: 75 Comments: 14308
Well what do we have here...?

Member Since: September 3, 2011 Posts: 13 Comments: 3474
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Quoting yoboi:
this rain made me cook a shrimp, crawfish, oyster,tasso and okra stew for this eve...fresh tomato and cucumbers on the side with potato salad...the smell is killing me..
and you live where ?
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The Slender game scared the crap out of me. I'm going to have nightmares from here on out lol.

Waves in the east Atlantic are emerging progressively stronger. It won't be long until we get our first Cape Verde storm of the season.

Member Since: July 6, 2010 Posts: 113 Comments: 32254
Quoting GeorgiaStormz:
BLOG = DEAD

the end

I don't like it when the blopg is dead, I can't think of anything to talk about. Maybe we will get a storm from the trough split later in the week.
Member Since: March 16, 2012 Posts: 127 Comments: 7948
Quoting fmhurricane2009:

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


Yeah it looks like we are probably going to get slammed by strong to severe thunderstorms here in the Tampa Bay area later today. Atmospheric moisture is very high once again as usual and much more instability is moving into place. I got 7 inches of rain during this last week, I wouldn't be surprised to see that total go up a lot more today.
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Member Since: March 16, 2012 Posts: 127 Comments: 7948
BLOG = DEAD

the end
Member Since: February 11, 2012 Posts: 0 Comments: 9731

I don't know if this is tropoical or not
Member Since: March 16, 2012 Posts: 127 Comments: 7948
Quoting fmhurricane2009:


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

(Credit: StormchaserWV
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2012. ncstorm
12z CMC





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Fabio is beginning to weaken.

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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.