June hurricane season outlook; Bahamas disturbance fizzles

By: Dr. Jeff Masters , 3:12 PM GMT on June 16, 2007

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An area of disturbed weather with heavy thunderstorm activity is over the Bahama Islands, and shows no signs of organization. The system crossed Cuba last night, brushed South Florida, and brought heavy rains of 2-4" inches over these areas. The system will bring another 1-2" to the Bahamas before heading northeast out to sea. The disturbance is now entering an area with very high wind shear of 30 knots, and is no longer a threat to develop into a tropical depression. The system could develop into an extratropical storm. No Hurricane Hunter missions are planned into the system, and NHC no longer thinks highly enough of it to offer their suite of early model tracks. There are no other threat areas to discuss, and none of the models are showing any new developments over the coming week. I'll repost my June hurricane season outlook below, and have a new blog on Monday!

Jeff Masters

Last half of June climatology
The last half of June is usually one of the quietest portions of hurricane season. In the 12 years since the current active hurricane period began in 1995, only four tropical storms formed in the last half of June. Thus, recent history gives us a 33% chance of a last-half-of-June named storm. None of those four storms since 1995 became a hurricane, and hurricanes are quite rare in June. Only one major hurricane has 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 primary breeding grounds for last half of June tropical storms is the western Gulf of Mexico (Figure 1).


Figure 1. Tracks of all tropical storms and hurricanes since 1851 that formed June 16-30. The western Gulf of Mexico is the preferred location for storm formation in late June. Interestingly, the eastern Gulf of Mexico sees the most early June storms.

Sea Surface Temperatures
Sea Surface Temperatures (SSTs) have remained about 0.5-1.0 C above average over the tropical Atlantic over the past two weeks. An area of cooler than average SSTs that surrounded Florida in early June has shrunk, and the entire Gulf of Mexico is now warmer than average. However, while SSTs are above normal, they are still far cooler than the peak temperatures that occur in August-October. This will limit the regions where tropical storm formation can occur this month to the Gulf of Mexico, Western Caribbean, and Gulf Stream waters just offshore Florida, where water temperatures are warmest (Figure 2). 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.


Figure 2. Sea Surface Temperature (SST) departure from average for June 14, 2007. Image credit: NOAA.

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, there is less heat energy available this year than in 2005, which recorded the highest SSTs and TCHP ever measured in the tropical Atlantic. I expect that the TCHP will continue to remain below 2005 levels this year, so we should not see as many intense hurricane as we saw in 2005.


Figure 3. Tropical Cyclone Heat Potential (TCHP) for June 14 2005 (top) and June 14 2007 (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 still quite high, but lower than in 2005. 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.

Wind shear over the past 11 days (Figure 4, top image) has been above 20 knots over most of the breeding grounds for June tropical storms--the Gulf of Mexico, Western Caribbean, and Bahama waters. While the shear has been below average (Figure 4, bottom image), any wind shear above 20 knots is high enough to discourage tropical storm formation. This is very typical for June, when the jet stream is still very active and quite far south. The jet stream will gradually weaken as summer progresses, bringing lower wind shear and greater chances for tropical storm formation. The extreme southwestern Caribbean has seen shear below 10 knots, but no tropical waves or remains of old cold fronts have moved into this region to trigger tropical storm formation. The latest two-week forecast from the GFS model predicts that wind shear will be near normal levels across the Caribbean, Gulf of Mexico, and tropical Atlantic for the remainder of June.


Figure 4. Top: Average wind shear over the past 11 days. Wind shear is the difference in wind between 200 mb (roughly 40,000 foot altitude) and 850 mb (roughly 5,000 foot altitude) in meters per second (multiply by two to get the approximate wind shear in knots). In most circumstances, wind shear above 20 knots (10 m/s, the blue colors in the top image) will act to inhibit tropical storm formation. Wind shear below 12 knots (6 m/s, the orange colors) is very conducive for tropical storm formation.
Bottom: Departure of wind shear from average for the past 11 days in meters per second. Note that wind shear has been below average over most of the tropical Atlantic and Gulf of Mexico over the past 11 days.

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, though.

Steering currents
The steering current pattern for the first half of June featured a pattern much like we saw in 2006, with an active jet stream bringing many troughs of low pressure off the East Coast of the U.S. I expect this pattern to continue for the remainder of June, and the troughs should be frequent enough and strong enough to recurve any tropical storms of hurricanes that penetrate north of the Caribbean Sea. Steering current patterns are not predictable more than about two weeks in advance, and there is no telling if we are in for a repeat of the favorable 2006 steering current pattern that recurved every storm out to sea. It is encouraging to note that in 2006 the steering current pattern locked into place in late May and stayed that way for almost the entirety of the hurricane season. The atmosphere often stays locked in to a particular steering pattern for an entire summer.

Summary
Recent history suggests a 33% chance of a named storm occurring in the second half of June. Given that the current SST pattern and two-week wind shear forecast look fairly typical for June, I'll go with a 30% chance of a named storm forming during the last half of June.

Jeff Masters

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622. WPBHurricane05
2:08 PM GMT on June 18, 2007
NEW BLOG
Member Since: July 31, 2006 Posts: 56 Comments: 8112
621. WPBHurricane05
2:04 PM GMT on June 18, 2007
I never knew that. I wonder which season the birds migrate.
Member Since: July 31, 2006 Posts: 56 Comments: 8112
620. Chicklit
2:01 PM GMT on June 18, 2007
During the months of June and July, the Bay of Campeche is considered one of the "hot" breeding spots for Atlantic hurricanes.[1] The bay is also considered the eastern border on the main migration routes for birds in the Americas.[2] Wikipedia
Member Since: July 11, 2006 Posts: 14 Comments: 11173
619. WPBHurricane05
1:58 PM GMT on June 18, 2007
Theres nothing of real interest in the tropics currently. It has been brought up before that June isn't suppose to be active. A disturbance has to have a LLC to be looked at with great interest. The GFS doesn't show anything forming and there isn't anything out there that could form. Wind shear is around 20-30 knots which wouldn't allow for tropical storm formation.
Member Since: July 31, 2006 Posts: 56 Comments: 8112
618. Chicklit
1:54 PM GMT on June 18, 2007
Anybody know what they are saying about the blob in the Bay of Campeche?
Member Since: July 11, 2006 Posts: 14 Comments: 11173
617. catastropheadjuster
1:53 PM GMT on June 18, 2007
Good Morning all. Hope everyone had a nice Father's Day. Nothing brewing in the tropics when does it really start up?
Member Since: August 24, 2006 Posts: 21 Comments: 3652
616. fldoughboy
1:52 PM GMT on June 18, 2007
The Tropics are the clearest I EVER seen it...Well, going to work...bye
612. stoormfury
1:25 PM GMT on June 18, 2007
miamihurricane12

this area is the monsoon trough. sometimes there are perturbations from this trough which goes on to develop into something. this one would expect during the july -sept period.
Member Since: August 22, 2006 Posts: 0 Comments: 2600
611. WPBHurricane05
1:21 PM GMT on June 18, 2007
TORNADO WARNING
NATIONAL WEATHER SERVICE MIAMI FL
911 AM EDT MON JUN 18 2007

THE NATIONAL WEATHER SERVICE IN MIAMI HAS ISSUED A

* TORNADO WARNING FOR...
EXTREME EAST CENTRAL MIAMI-DADE COUNTY IN SOUTH FLORIDA.

* UNTIL 930 AM EDT

* AT 906 AM EDT...THE PUBLIC REPORTED A WATERSPOUT OVER BISCAYNE
BAY WHICH MAY AFFECT MIAMI BEACH TO VIRGINIA KEY AREAS. THIS
TORNADO WILL MOVE EAST AT 5 MPH.
Member Since: July 31, 2006 Posts: 56 Comments: 8112
610. stormhank
1:14 PM GMT on June 18, 2007
Hey guys,,, i got a ?? last couple weeks i cant get the TSR forecast to come up for me.. It says do I want to save or find a site to open it. it takes me to adobe which I already have installed? any ideas?? I cant even open up PDF files from hurricane center archives either?
Member Since: September 8, 2005 Posts: 0 Comments: 1385
606. SCwxwatch
12:43 PM GMT on June 18, 2007
Its Working Now SJ.

They Must have been updating
605. miamihurricane12
12:42 PM GMT on June 18, 2007


this area of disturbed weather has persisted for a day and a half now, it has held its own unlike the other african waves so far...what do you guys think?
603. StormJunkie
12:13 PM GMT on June 18, 2007
Thanks SC. If anyone finds out anymore info on it please WUmail me. Hopefully it will be back up and running soon. Not sure what I would do with out the GHCC.
Member Since: August 17, 2005 Posts: 26 Comments: 15644
601. SCwxwatch
12:08 PM GMT on June 18, 2007
not loading for me either SJ
600. StormJunkie
12:06 PM GMT on June 18, 2007
Anyone else having trouble with the GHCC site? Can not seem to get it to load.
Member Since: August 17, 2005 Posts: 26 Comments: 15644
599. franck
11:51 AM GMT on June 18, 2007
practically zero...low or depression could form in the environment, but not a storm.
Member Since: August 30, 2005 Posts: 0 Comments: 1150
598. underthunder
11:35 AM GMT on June 18, 2007
morning..anyone notice the blob just below the mex. tex. border..it seems to be heading east..just wondering with the temps. of the water in that area..what would be the chances of development?
Member Since: August 9, 2006 Posts: 0 Comments: 96
597. Chicklit
11:11 AM GMT on June 18, 2007
Hey good morning! The blob I was so concerned about yesterday has been ripped to shreds. (There's a lesson in there...) JFl...relax. Stand on your head, maybe; that always gets blood flowing away from the emotions and back to the brain. We're exchanging opinions; don't take it personally.
JP06 is a most trusted and conscientious participant of this blog who has made a lot of friends here, but it's not a clique...Everyone is always willing to talk to anyone! There's a lot of info, exchange of ideas, varying levels of knowledge and no requirement that everyone agree.
Member Since: July 11, 2006 Posts: 14 Comments: 11173
596. SCwxwatch
10:53 AM GMT on June 18, 2007
Clicks?
Ego's?

I bring nothing to the table when it comes to this blog , but I sure learn alot. And pick up a bunch of awesome links along the way.

Sometimes Ill get replies, Sometimes I get ignored. That doesnt dicourage me though. I try to get in where I fit in but the chances of me fitting in are less than 10% (Due to the lack of weather forcasting skills)
But I still get in anyway. :P

It's a big ole interweb and getting worked up over someone elses opinion is certainly a waste of energy. Just do as some do to me, Act like you dont see the post.

Ya can't set the hook on a fish that don't bite ;)

Good Morning Everyone!!
595. stoormfury
10:36 AM GMT on June 18, 2007
tropical wave heading for southern windwards.looks like a rainy day come wed.
Member Since: August 22, 2006 Posts: 0 Comments: 2600
592. StormJunkie
9:38 AM GMT on June 18, 2007
Morning all ☺
Anyone else having trouble with the GHCC site? Can not seem to get it to load.
Member Since: August 17, 2005 Posts: 26 Comments: 15644
590. KoritheMan
7:51 AM GMT on June 18, 2007
I haven't ganged up on you. I try and treat everyone equally. I love to make peace with people on here.
Member Since: March 7, 2007 Posts: 553 Comments: 19911
586. KoritheMan
6:48 AM GMT on June 18, 2007
Yeah, I won't be concerned. Unless it keeps its identity this time tommorow. Then maybe.
Member Since: March 7, 2007 Posts: 553 Comments: 19911
585. KoritheMan
6:47 AM GMT on June 18, 2007
jp, thanks. Good night.
Member Since: March 7, 2007 Posts: 553 Comments: 19911
582. KoritheMan
6:45 AM GMT on June 18, 2007
WAIT JP! DON'T GO YET! I WANNA ASK YA SOMETHING!

What if the upper-level circulation works its way to the surface? Then what? Or at least the mid-levels by earlier today?

JFLORIDA, seriously calm DOWN. jp is RIGHT when he says not everyone will agree with you. That is what makes us different. We are PEOPLE, each with our own likes/dislikes/agreements/disagreements. GET USED TO IT...
Member Since: March 7, 2007 Posts: 553 Comments: 19911
581. KoritheMan
6:44 AM GMT on June 18, 2007
stormybil, SSTs are marginal, but not exactly precise for tropical cyclogenesis. The wave is a bit far south for me to think much of it, but rest assured, I WILL WATCH IT FOR YOU! Also, I think the recent cooling of the GoM is attributed to a kelvin wave, perhaps? I don't know ALL the mechanics of a kelvin wave, but I do know some. Is it possible equatorial East Pacific SSTs could warm, while the GoM cools cause of kelvin wave activity?
Member Since: March 7, 2007 Posts: 553 Comments: 19911
577. stormybil
6:36 AM GMT on June 18, 2007
and no strom is the same we learn here from every new one that pops up . and these days that can happen at any hour , stay tuned
573. stormybil
6:32 AM GMT on June 18, 2007
here you go Link

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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.