Hurricane season begins today; normal June activity expected

By: Dr. Jeff Masters , 1:38 PM GMT on June 01, 2009

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Hurricane season is upon us, and it's time to take a look at the prevailing conditions and 2-week forecast for tropical cyclone activity in the Atlantic. June is typically the quietest month of the Atlantic hurricane season. On average, we see only one named storm every two years in June. Only one major hurricane has made landfall in June--Category 4 Hurricane Audrey of 1957, which struck the Texas/Louisiana border area on June 27 of that year, killing 550. The highest number of named storms for the month is three, which occurred in 1936 and 1968. In the fourteen years since the current active hurricane period began in 1995, there have been eleven June named storms (if we include last year's Tropical Storm Arthur, which really formed on May 31). Five tropical storms have formed in the first half of June in that 14-year period, giving a historical 36% chance of a first-half-of-June named storm.


Figure 1. Tracks of all June tropical storms and hurricanes, 1851 - 2007.

Sea Surface Temperatures
Sea Surface Temperatures (SSTs) are close to average over the tropical Atlantic between Africa and Central America this year (Figure 2). These temperatures are some of the coolest we've seen since 1995, when the current active hurricane period began. This year's cool SSTs should prevent a repeat of the unforgettable Hurricane Season of 2005, which had the highest SSTs on record in the tropical Atlantic. Note also that SSTs along the Equatorial Pacific off the coast of South America are quite a bit above average, signaling the possible start of an El Niño episode. As I discussed in Friday's post, odds are increasing for a weak El Niño to form in time for hurricane season, and this should cut down on the number and intensity of Atlantic tropical storms and hurricanes this year. However, if an El Niño is developing, it shouldn't start affecting Atlantic hurricane activity until August.

Typically, June storms only form over the Gulf of Mexico, Western Caribbean, and Gulf Stream waters just offshore Florida, where water temperatures are warmest. SSTs are 26 - 28°C in these regions, which is about 0.5°C above average for this time of year. June 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. African tropical waves, which serve as the instigators of about 85% of all major hurricanes, are usually too far south in June to trigger tropical storm formation. Every so often, a tropical wave coming off the coast of Africa moves far enough north to act as a seed for a June tropical storm. This was the case for Arthur of 2008 (which also had major help from the spinning remnants of the Eastern Pacific's Tropical Storm Alma). Another way to get Atlantic June storms is for a disturbed weather area in the Eastern Pacific Intertropical Convergence Zone (ITCZ) to push north into the Western Caribbean and spawn a storm there. This was the case for Tropical Storm Alberto of 2006 (which may have also had help from an African wave). SSTs are too cold in June to allow storms to develop between the coast of Africa and the Lesser Antilles Islands--there has only been once such development in the historical record--Ana of 1979, which coincidentally will be the name given to this year's first storm.


Figure 2. Sea Surface Temperature (SST) departure from average for June 1, 2009. SSTs were near average over the tropical Atlantic. Note the large region of above average SSTs along the Equatorial Pacific off the coast of South America, signaling the possible start of an El Niño episode. Image credit: NOAA/NESDIS.

Tropical Cyclone Heat Potential
It's not just the SSTs that are important for hurricanes, it's also the total amount of heat in the ocean to a depth of about 150 meters. Hurricanes stir up water from down deep due to their high winds, so a shallow layer of warm water isn't as beneficial to a hurricane as a deep one. The Tropical Cyclone Heat Potential (TCHP, Figure 3) is a measure of this total heat content. A high TCHP over 80 is very beneficial to rapid intensification. As we can see, the heat energy available in the tropical Atlantic has declined considerably since 2005, when the highest SSTs ever measured in the tropical Atlantic occurred. TCHP this year is similar to last year's levels, which were high enough to support five major hurricanes.


Figure 3. Tropical Cyclone Heat Potential (TCHP) for May 31 2005 (top), May 31 of last year (middle) and May 30 2009 (bottom). TCHP is a measure of the total heat energy available in the ocean. Record high values of TCHP were observed in 2005. TCHP this year is much lower, and similar to last year. Image credit: NOAA/AOML.

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 June 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 few weeks 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 leaves a "hole" of low shear between the two branches off the coast of North Carolina, which is where Tropical Depression One formed. The low shear "hole" has dipped down into the northern Gulf of Mexico a few times. Disturbance 90L, which almost developed into a tropical storm before it came ashore in Mississippi/Alabama on May 23, took advantage of one of these low-shear areas.

The jet stream is forecast to maintain this two-branch pattern over the coming ten days. This means that the waters offshore of the Carolinas are the most likely place for a tropical storm to form during this period, though the northern Gulf of Mexico will at times have shear low enough to allow tropical storm formation. The latest 16-day forecast by the GFS model (Figure 4) predicts that the subtropical jet will weaken and retreat northwards by the middle of June, creating low-shear conditions over the Caribbean. This is a typical occurrence for mid-June, and we need to start watching the Western Caribbean for tropical storm formation by the middle of the month.


Figure 4. Wind shear forecast from the 00Z GMT June 1, 2009 run of the GFS model for June 1 (left panel) and June 17 (right panel). Currently, the polar jet stream is bringing high wind shear to the waters offshore New England, and the subtropical jet is bringing high wind shear to the Caribbean. This leaves the waters off the coast of North Carolina under low shear, making this area the most favored region for tropical storm formation over the next 7 - 10 days. By June 17, the subtropical jet is expected to weaken and move northwards, leaving the Caribbean under low shear, and favoring that region for tropical storm formation. 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
It's too early to concern ourselves with dry air and dust coming off the coast of Africa, since these dust outbreaks don't make it all the way to the June tropical cyclone breeding grounds in the Western Caribbean and the Gulf of Mexico. Developing storms do have to contend with dry air from Canada moving off the U.S. coast; this was a key reason why 2007's Subtropical Storm Andrea never became a tropical storm. Dr. Amato Evan of the University of Wisconsin will issue his dust forecast for the coming hurricane season later this week, and I'll be discussing his forecast in an upcoming post.

Steering currents
The steering current pattern over the past few weeks has been typical for June, with 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 June pattern, bringing many troughs of low pressure off the East Coast capable of recurving any June 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 36% chance of a named storm occurring in the first half of June. The current conditions in the atmosphere and ocean are near average, so expect about a 1/3 chance of a named storm between now and June 15. The computer models are currently not forecasting development of any tropical storms over the next seven days.

I'll have an update Tuesday afternoon, when I'll discuss the Colorado State University June Atlantic Hurricane season forecast by Dr. Phil Klotzbach and Dr. Bill Gray, which will be issued Tuesday morning.

My next analysis and 2-week outlook for hurricane season is scheduled for June 13.

Jeff Masters

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Quoting Levi32:


1001mb pressure is squarely in the middle of the range of a typical minimal tropical storm, and the winds are right there near TS threshold. What we need is a new QuikSCAT pass, then we'll see what it looks like.


Hi Levi,
when will that new QuikSCAT pass be?
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In relation to the item in the Atlantic--- How many folks do you think are getting paychecks to make calls on those types of systems? I would bet hundreds upon hundreds. If it merited an invest label or name, they would have placed one on it. That is there actual job, right? Perhaps they may still do so. Just my unpaid opinion :)
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Quoting Ossqss:


Interesting seeing the tops blow off of those.

Yeah right now I have some pretty serious overcast from those tops.

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Quoting jeffs713:
I was waiting for someone to post the nor'easter with an eye pic.

Just because it looks like a STS or TS, doesn't mean it is one. Also, this system doesn't have the pressure or winds to support an upgrade.


1001mb pressure is squarely in the middle of the range of a typical minimal tropical storm, and the winds are right there near TS threshold. What we need is a new QuikSCAT pass, then we'll see what it looks like.
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I think this thing has missed its chance at getting upgraded; convection is on the decrease, and will only weaker further as it tracks to the north. Even if NHC did designate it as subtropical, it wouldn't be Ana, as neither the QUIKSCAT or the Dvorak estimates support TS winds. Still, I don't think 92L is out of the question.
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287,288 you are right first time lately I seen low level clouds moving west and upper moving north.
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Hiexpress:expecting a few showers and a isolated strong t-storm or 2,as the SE flow returns to the central fl peninsula,imo
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Quoting HIEXPRESS:
"Summer" creeping back north after a brief retreat
FL Radar


Interesting seeing the tops blow off of those.
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On Yahoo's main page they have a video on front page of a new danger that forecaster are concerned about pop up hurricanes.They say lately that storms are popping up very close to u.s. coast allowing little time for warning.
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Quoting jeffs713:
I was waiting for someone to post the nor'easter with an eye pic.

Just because it looks like a STS or TS, doesn't mean it is one. Also, this system doesn't have the pressure or winds to support an upgrade.


Again...Quikscat shows 30 to 35 mph winds with a closed low. I think that link/picture has only been posted a dozen times already.
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"Summer" creeping back north after a brief retreat
FL Radar
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000
ABPZ30 KNHC 011631
TWSEP
MONTHLY TROPICAL WEATHER SUMMARY
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
800 AM PDT MON JUN 01 2009

FOR THE EASTERN NORTH PACIFIC...EAST OF 140 DEGREES WEST LONGITUDE..

NO TROPICAL CYCLONES WERE OBSERVED DURING MAY IN THE EASTERN NORTH
PACIFIC. ON AVERAGE A TROPICAL STORM FORMS ONCE EVERY OTHER
MAY. HOWEVER...THIS IS THE FIRST TIME SINCE 1999 THAT NO TROPICAL
CYCLONES WERE OBSERVED DURING THE MONT
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Quoting TampaSpin:


StillWaiting if you are going to want an invest with everything with a blob of clouds this year...Its gonna be a long season of over Hype for ya...LOL...enjoy your day.


It's a great day to be a american,a president who actually is pro-active when it comes to TC season,lol....you still proud to be american TS???,or do you still feel like someone pi$$ed in your cornflakes????,lol....
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Quoting jeffs713:
I was waiting for someone to post the nor'easter with an eye pic.

Just because it looks like a STS or TS, doesn't mean it is one. Also, this system doesn't have the pressure or winds to support an upgrade.


40mph winds and 1001mb pressure doesnt warrant an upgrade?
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Models slowly moves it northward

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Quoting Weather456:
It seems they have begun to issue Dvorak numbers on it.


I'd say having a tropical reading could possible be a positive sign for it in the sense of being classified, just my opinion.
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It seems they have begun to issue Dvorak numbers on it.
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Quoting jeffs713:
I was waiting for someone to post the nor'easter with an eye pic.

Just because it looks like a STS or TS, doesn't mean it is one. Also, this system doesn't have the pressure or winds to support an upgrade.


Uh, I'd have to disagree with that. QS and other data clearly show pressure and winds high enough for an upgrade.
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Quoting weatherblog:
While this should be named, I doubt it will be. If I remember back from Vince (which formed in October '05), it took them awhile to name it. I remember by the time they gave him tropical storm status, he was already a hurricane.


They are pretty conservative with these types of systems.
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Different prespective if you will.

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I was waiting for someone to post the nor'easter with an eye pic.

Just because it looks like a STS or TS, doesn't mean it is one. Also, this system doesn't have the pressure or winds to support an upgrade.
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Quoting DDR:
Hi 456,Trinidad and the windwards got some rain today,the rains came right on time,as you know the weather has become unpredictable in recent years.


Glad to here. I didnt provide a detailed discussion today but you can thank the recent passage of a tropical wave.
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01/1745 UTC 39.9N 24.7W T1.5/1.5 INVEST -- Atlantic
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Quoting CycloneOz:
Here's another one...



On December 12, 2002, a strong low-pressure system could be seen whirling away just south of Kamchatka Peninsula and the Aleutian Islands in the northwestern Pacific. The above true-color image of the low-pressure system was acquired by the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument, flying aboard NASA?s Terra spacecraft. The tip of the peninsula can be seen in the upper left-hand corner of the image.


That's a very common presentation of deep-pressure systems here in Alaska out in the Aleutians. They get well-wrapped but that system wasn't even close to a polar low or a sub-tropical hybrid of any kind. It was starting to become warm-secluded but not very strongly.
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Heres the Blizzard of 2006 or as I like to call it,

Armageddon Blizzard of 06!

Beautiful eye.
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While this should be named, I doubt it will be. If I remember back from Vince (which formed in October '05), it took them awhile to name it. I remember by the time they gave him tropical storm status, he was already a hurricane.
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Here's a really cool one! You can see that the thing is truely low pressure...and it even has an eye dead smack in the middle. LOOK AT THAT CIRCULATION!!!!

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266. DDR
Hi 456,Trinidad and the windwards got some rain today,the rains came right on time,as you know the weather has become unpredictable in recent years.
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This thing is looking more tropical and less subtropical.
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Here's another one...



On December 12, 2002, a strong low-pressure system could be seen whirling away just south of Kamchatka Peninsula and the Aleutian Islands in the northwestern Pacific. The above true-color image of the low-pressure system was acquired by the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument, flying aboard NASA?s Terra spacecraft. The tip of the peninsula can be seen in the upper left-hand corner of the image.
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How will the dissipating low at 27W 47N, just north of this developing system affect it if at all?
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Quoting jeffs713:
Here's an idea...

Maybe they are labeling it an invest not for tropical purposes because of the very low SSTs, but so they can position a floater over it while its available (early in the season), and assist the Europeans in forecasting.


That would be true but the Invest consist of GOES-12 images and GOES-12 resolution decreases as one moves east from 60W where it is stationed. The Europeans would use MSTAT which is station at 0E for better resolution.
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All right, I'll play the liberal side. This will form... maybe.
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So whats going on in the tropics?
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Well-defined secondary wind field, but keep in mind this image is at least 13 hours old now.

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Quoting cg2916:

Andrea had an eye well before it formed. Most subtropicals have an "eye".


The eye has become much better defined thus supporting the theory of a strengthening LLC.
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Here's an idea...

Maybe they are labeling it an invest not for tropical purposes because of the very low SSTs, but so they can position a floater over it while its available (early in the season), and assist the Europeans in forecasting.
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Quoting CycloneOz:
This looks like a hurricane, too...but it was at Iceland.



Eh thats pretty obvious that its an extra tropical storm.
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Quoting Stormchaser2007:


QUICKSCAT clearly shows a LLC. The only reason the LLC doesnt look complete is because the Azores are in the way.


Wait till 8:00 PM or :50 past the hours.
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society better get back to basics, all this scientific/technically not a storm because of this criteria this that.... it's storm swirling over the ocean has wind, it's a storm.
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Scratch that last part about the low pressure center. 1001 is pretty low for hat sotrm.
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Quoting cg2916:

The QuikSCAT and 18Z surface analysis.


QUICKSCAT clearly shows a LLC. The only reason the LLC doesnt look complete is because the Azores are in the way.

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Quoting cg2916:
Guys, there's a reason the NHC hasn't named it Ana. It lacks a real low pressure center and low-level circulation.


It is analysed as a 1001 mb non tropical low and has had a circulation for days now, clearly evident on visible animations and quikscat.

And one of the reason they may have found interest in it is due to the change in structure:

Saturday

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This looks like a hurricane, too...but it was at Iceland.

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Quoting Stormchaser2007:


Exactly. It cant get more evident that theres a low level circulation.

Andrea had an eye well before it formed. Most subtropicals have an "eye".
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Quoting Weather456:


The closest station found so far



Thanks, that is interesting. I wonder if there are any ship reports on this item?
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Quoting Ossqss:
Is there any equipment on the islands in that area that could tell us what the pressure is?

Current surface features is showing 1001 mb Link
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Quoting Stormchaser2007:


Where are you getting this from?

The QuikSCAT and 18Z surface analysis.
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Quoting weatherblog:
It has an eye, is that not enough evidence of a circulation? lol


Exactly. It cant get more evident that theres a low level circulation.
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Quoting Cazatormentas:
Another case of an INVEST far away from NHC jurisdiction.........?


NHC declares all tropical and subtropical systems that form in the Atlantic Ocean north of the equator.
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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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