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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2111. LargoFl
FLOOD ADVISORY
NATIONAL WEATHER SERVICE TAMPA BAY AREA - RUSKIN FL
513 PM EDT SUN JUL 15 2012

FLC017-053-152215-
/O.NEW.KTBW.FA.Y.0047.120715T2113Z-120715T2215Z/
/00000.N.ER.000000T0000Z.000000T0000Z.000000T0000 Z.OO/
HERNANDO FL-CITRUS FL-
513 PM EDT SUN JUL 15 2012

THE NATIONAL WEATHER SERVICE IN RUSKIN HAS ISSUED AN

* URBAN AND SMALL STREAM FLOOD ADVISORY FOR...
SOUTHERN CITRUS COUNTY IN FLORIDA.
NORTHERN HERNANDO COUNTY IN FLORIDA.

* UNTIL 615 PM EDT

* AT 513 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED
RAINFALL RATES OF TWO INCHES PER HOUR ASSOCIATED WITH THUNDERSTORMS
OVER THE ADVISED AREA...LOCALIZED FLOODING IS IMMINENT OR OCCURRING.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

KEEP CHILDREN FROM BEING SWEPT AWAY IN FLOODED DITCHES AND DRAINS.
FLOOD WATERS ARE USUALLY DEEPER THAN THEY APPEAR AND MAY STALL YOUR
VEHICLE. JUST ONE FOOT OF FLOWING WATER IS POWERFUL ENOUGH TO SWEEP
VEHICLES OFF THE ROAD. TURN AROUND...DONT DROWN.

&&

LAT...LON 2876 8251 2876 8230 2858 8230 2858 8251

$$
Member Since: August 6, 2011 Posts: 4 Comments: 40845
Quoting stormchaser19:
will be interesting the predictions of NOAA and CSU in August about the numbers of storms and hurricanes.

In june NOAA 9-15 storms , 4-8 hurricanes and 1-3 majors
CSU 13 storms , 5 hurricanes and 2 majors


4 storms- 1 huricane-0 majors, activity until now


Things should get active again with either a trough split storm or a cv storm in a few weeks.
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2109. LargoFl
......................................oh boy, we are going to get whacked big time along the gulf here
Member Since: August 6, 2011 Posts: 4 Comments: 40845
Quoting wxchaser97:

Did someone say SAL:
It should weaken some since the high won't be as strong.
Member Since: August 14, 2010 Posts: 10 Comments: 17477
will be interesting the predictions of NOAA and CSU in August about the numbers of storms and hurricanes.

In june NOAA 9-15 storms , 4-8 hurricanes and 1-3 majors
CSU 13 storms , 5 hurricanes and 2 majors


4 storms- 1 huricane-0 majors, activity until now

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Quoting HurricaneHunterJoe:
Interesting track.
N. and S. Korea NEED need the rain. But not potential flooding.
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Quoting Jedkins01:
How the heck is it possible for nearly this entire county to be avoided by thunderstorms on such an active day? And hear I thought we going to slammed in Pinellas like we did earlier this week. I guess the only thing predictable about weather is it's unpredictability.


I live in Palm Harbor and getting a really nice storm.
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2104. yoboi
Quoting lottotexas:
and you live where ?



louisiana
Member Since: August 25, 2010 Posts: 7 Comments: 2386
How the heck is it possible for nearly this entire county to be avoided by thunderstorms on such an active day? And hear I thought we going to slammed in Pinellas like we did earlier this week. I guess the only thing predictable about weather is it's unpredictability.
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TD 08W

Max forecasted winds are 45mph gusting to 60mph.
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Quoting washingtonian115:
Expect less SAL to come off the coast.Thus watch for development in the next week or two.

Did someone say SAL:
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Quoting stormchaser19:
NAO(NEGATIVE)



The forecast says will stay negative
Expect less SAL to come off the coast.Thus watch for development in the next week or two.
Member Since: August 14, 2010 Posts: 10 Comments: 17477
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Quoting Pirate999:


Good... And you guys need it bad. How is the aquifer?

We need 20" of rain - at once, with no evap - to reload our Edwards Aquifer and Highland Lakes. We've been getting an inch here, three there, over the last week so cumulatively, which nixed the fire danger. We need a good solid TS --OR-- a thick, sustained plume of moisture from EPAC and some fronts who know what to do with it.
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NAO(NEGATIVE)



The forecast says will stay negative
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Member Since: July 6, 2010 Posts: 113 Comments: 32508
Quoting redwagon:

Huge rains just starting now/incoming over Lake Travis. So Thankful.


Hopefully that Lake gets filled back up
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Quoting washingtonian115:
Area where Bermuda is is impressive looking.

Welcome back hurricaneDean07.


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Yeah it's impressive but it'll likely die off.
Member Since: August 14, 2010 Posts: 10 Comments: 17477
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MESOSCALE DISCUSSION 1471
NWS STORM PREDICTION CENTER NORMAN OK
0400 PM CDT SUN JUL 15 2012

AREAS AFFECTED...PARTS OF NWRN THROUGH N CNTRL NORTH DAKOTA

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 152100Z - 152230Z

PROBABILITY OF WATCH ISSUANCE...40 PERCENT

SUMMARY...ISOLATED SEVERE STORM DEVELOPMENT APPEARS POSSIBLE WITHIN
THE NEXT COUPLE OF HOURS...AND TRENDS ARE BEING MONITORED FOR AN
INCREASING SEVERE THREAT THAT COULD REQUIRE A WW LATER THIS
AFTERNOON.

DISCUSSION...ALTHOUGH AN 18Z SOUNDING FROM BISMARCK IS SUGGESTIVE OF
SUPPRESSED CONVECTIVE POTENTIAL DUE TO CAPPING ISSUES...RELATIVELY
LOW MOISTURE VALUES AND MODEST MIXED LAYER CAPE...OBSERVATIONAL AND
MODEL DATA INDICATE POTENTIALLY GREATER INSTABILITY ASSOCIATED WITH
HIGHER MOISTURE CONTENT AIR ALONG THE WARM FRONT IN CLOSER PROXIMITY
TO THE SURFACE LOW OVER NORTHWESTERN NORTH DAKOTA. AND IT APPEARS
THAT A ZONE OF ENHANCED LOW-LEVEL CONVERGENCE COUPLED WITH STRONG
LOW-LEVEL WARM ADVECTION COULD BECOME SUPPORTIVE OF AT LEAST
ISOLATED STORM DEVELOPMENT BY 22-23Z...WITH HIGHEST PROBABILITIES
NEAR/NORTH THROUGH EAST OF MINOT. IF THIS OCCURS... VERTICAL SHEAR
BENEATH 30-40 KT SOUTHWESTERLY 500 MB FLOW WILL BE SUPPORTIVE OF
ORGANIZED CONVECTIVE DEVELOPMENT...INCLUDING SUPERCELLS. CLOCKWISE
CURVED LOW-LEVEL HODOGRAPHS ARE SIZABLE... AND SUPPORTIVE OF SOME
TORNADIC POTENTIAL...BUT THIS THREAT MAY BE LIMITED BY SIZABLE
SUB-CLOUD TEMPERATURE/DEW POINT SPREADS. LOCALLY STRONG DAMAGING
WIND GUSTS MAY BECOME THE MORE PROMINENT SEVERE THREAT...WITH LARGE
HAIL ALSO POSSIBLE.

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8W
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Quoting Civicane49:
Area where Bermuda is is impressive looking.

Welcome back hurricaneDean07.
Member Since: August 14, 2010 Posts: 10 Comments: 17477
Quoting redwagon:

Huge rains just starting now/incoming over Lake Travis. So Thankful.


Good... And you guys need it bad. How is the aquifer?
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Link
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Quoting Civicane49:
Eastern Atlantic:


Impressive
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Quoting Pirate999:


Come on, that pics really in Italy... Isn't that leaning tower on the right? LOl.

Huge rains just starting now/incoming over Lake Travis. So Thankful.
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Eastern Atlantic:

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You know what the GFS is showing next week isn't to hard to accomplish..all depends on the shear.I remember how Bret and Cindy formed from the same frontal system.
Quoting TropicalAnalystwx13:
2012:



2011:

Not liking that TCHP in the N.W caribbean at all.Tropical system gets in there with favorable conditions and it's game over for somebody.
Member Since: August 14, 2010 Posts: 10 Comments: 17477


Storms Inbound
Member Since: September 3, 2011 Posts: 13 Comments: 3476
I'm Back!
I just returned from a stay in Crystal Beach - A small coastal town Parallel to Galveston.
The beach was a complete bummer though... 16 inches of rain kinda ruined the week of beach time that was planned... Out of the 7 days being there, we only got one partial sunny day... Houston got 30 inches total in some areas over the past 5 days...
High Island was flooding as we left this morning due to more continuous rain that came, and we ran into a large thunderstorm on I-10 that was cuasing flooding in low-laying areas of the Highway...
I'll post pictures of my stay in one comment here, and on my blog as well.
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TD 8W

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2072. KEEPEROFTHEGATE (Mod)
Quoting DavidHOUTX:
Two people killed in Houston today by lightning

Link
17 people got hit today in my region at a rib fest everyone safe

heavy storms this afternoon
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8W:



I'm not entirely sure that's a TD.
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Quoting TropicalAnalystwx13:
2012:



2011:



http://www.youtube.com/watch?v=nrhf_zgtmAg
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1924 2 SW BRETON BAY ST. MARYS MD 3822 7675 WATERSPOUT REPORTED TO HAVE MOVED ONSHORE ALONG WINDY LN NEAR COLTONS POINT. FALLEN TREES DAMAGED HOMES AND CARS. WATERSPOUT WAS NOTED BY SEVERAL OBSERVERS.
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Quoting Tazmanian:
WU seem a little bugey today
I have been having issues getting to the blog, I get an error message and have to refresh t get it to work.
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2012:



2011:

Member Since: July 6, 2010 Posts: 113 Comments: 32508
Quoting Tropicsweatherpr:
Closeup view of West African waves.


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

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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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