July Atlantic hurricane outlook
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
Reader Comments
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Fun fact: Fabio was one of my aunt's celebrity crushes.
well i do it for free
and in no way take any monies for my views on the subject of global killing
give up on the TWC stuff already
cause what ever is to be we face it together
and there is nothing no one can do to stop it
faster faster we go
3 ghosts...
Remnants of Hurricane Daniel south of Hawaii.
front edge is actually rollin' along like a cylinder:
You can WU me the other one. I would like to see it.
EPAC teleconnection?
ya don't pay my bills like they do....
I have been watching that complex for the past 3 days and it may have to be watched after it splashes to see how the conditions are and if it has the signature that our friend Levi is looking for.
I just did, "alter Schwede" ...
Agreed.
I have but one thing to say: zzzzzz
Did she or did she not believe it was butter? :-)
Funny, the exact opposite of the 2011 and 2012 Atlantic Hurricane season (so far)
There are no denialist who have a message other than "Here, stick your head in this dung pile so you don't hafta deal with reality."
Totally lacking in facts that back their argumentation, all denialist must depend on abrasiveness to drown out opposition...
...such as accusing people who like to bring facts into an argument of being abrasive.
Saying there is no permafrost in southern Alaska is as willfully (and possibly maliciously) wrong as saying there is no severe glacial reduction in southern Alaska.
Where there are glaciers, there is permafrost beneath.
Where glaciers are melting or have melted, the permafrost beneath is melting. Or has melted.
Yeesh, the Matterhorn and the Eiger in Europe are falling apart due to permafrost melting, causing major rockfalls and landslides in the process.
Why would southern Alaska be immune?
I didnt even realize that..you learn something new everyday..
Yep.
luck?
i dont really know, just the eye was off center so it dissipated faster and now its gone.
wasnt studying the demise too closely
Perhaps Emilia is passing over Daniel's cold wake?
for a while
What party? I mist it completely!!
Man Permafrost is going to be a lab anomaly.You are going to have to conserve it in bottles and jar's as it is not going to be a natural occurring event in the near future.
I mean where is everybody hiding here today? Tonight on this one?
Once you got rid of the permafrost, there is nothing left to melt, as ice is just a transient medium that stops ships passing in the night, there is no night in the Arctic summer!
the pay is not that great, the grand prize is a weekend with Al....
Solche Worte!! LOL I haven't heard that dialect in a long time. (Ich bin Norweger)
From KJAS: There were some isolated reports of flooding such as several streets here in Jasper and also a section of Farm to Market Road 1007 near Lake Sam Rayburn, where it is reported that anywhere from four to six inches fell in a short time.
Are you Norwegian?
Sure about that?
NATIONAL WEATHER SERVICE PHOENIX AZ
305 PM MST FRI JUL 13 2012
AZC013-140000-
/O.NEW.KPSR.FA.Y.0017.120713T2205Z-120714T0000Z/
/00000.N.ER.000000T0000Z.000000T0000Z.000000T0000 Z.OO/
MARICOPA AZ-
305 PM MST FRI JUL 13 2012
THE NATIONAL WEATHER SERVICE IN PHOENIX HAS ISSUED AN
* URBAN AND SMALL STREAM FLOOD ADVISORY FOR...
NORTHWESTERN MARICOPA COUNTY IN SOUTH CENTRAL ARIZONA...
* UNTIL 500 PM MST
* AT 302 PM MST NATIONAL WEATHER SERVICE RADAR CONTINUES TO SHOW A
STRONG THUNDERSTORM 4 MILES SOUTH OF AGUILA PRODUCING VERY HEAVY
RAINFALL. THIS THUNDERSTORM IS MOVING TO THE NORTH AT AROUND 15
MPH. RAINFALL ESTIMATES OF 1 TO 2 INCHES CAN BE EXPECTED.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
A FLOOD ADVISORY MEANS THAT NORMALLY DRY WASHES AND STREAMS WILL
SUDDENLY HAVE RUNNING WATER. UNBRIDGED CROSSINGS MAY BECOME
HAZARDOUS. THERE WILL BE PONDING OF WATER ON STREETS AND LOW SPOTS
CAUSING TRAFFIC TO BE IMPEDED. IF YOU ENCOUNTER PONDING OR FLOWING
WATERS...DO NOT ATTEMPT TO CROSS BY FOOT OR AUTOMOBILE. TURN
AROUND...DONT DROWN.
RUNOFF FROM HEAVY RAINFALL WILL CAUSE NORMALLY DRY WASHES TO RUN AND
CAUSE CONSIDERABLE PONDING OF WATER ON ROADS AND LOW LYING SPOTS.
UNBRIDGED CROSSINGS MAY BECOME TOO DANGEROUS FOR DRIVING.
&&
LAT...LON 3400 11329 3400 11302 3373 11303 3374 11330
$$
KUHLMAN
shear a little differ this time around...
LOL!
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