Hurricane season 2005--why so active?

By: Dr. Jeff Masters , 7:31 PM GMT on August 01, 2005

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This will be my last blog entry until August 12; I'm vacationing far from the tropics (Yellowstone!) to appreciate some mountain weather.

Today's monthly summary of hurricane activity for July issued by the National Hurricane Center (NHC) states:

"The month of July saw unprecedented tropical cyclone activity in the Atlantic Basin...with the development of five named storms...Tropical Storm Cindy...Hurricane Dennis...Hurricane Emily... Tropical Storm Franklin...and Tropical Storm Gert. The previous record for named storms that formed in July was four. The two major hurricanes that developed during the month tied a record set in 1916. The July activity follows an unusually active month of June ...And the seven named storms that have formed thus far in 2005 represent a record level of activity for the first two months of the season."

Why has this hurricane season been so active? Part of the reason lies in a decades-long natural cycle in hurricane activity that in 1995 switched to a high-hurricane activity mode. Hurricane activity has been above normal since 1995, and will likely continue to be for the rest of this decade and the next.

Additionally, there are six key ingredients are necessary for tropical cyclone formation (you can read about these in full detail in the Tropical Cyclone FAQ. We'll focus on three of them in particular that have been highly conducive to tropical cyclone formation during this remarkable hurricane season of 2005.


Vertical Wind Shear
Hurricanes need low values of vertical wind shear between the surface and the upper atmosphere (the jet stream level, typically 35,000 - 40,000 feet high in the tropics). Vertical wind shear is the magnitude of wind change with height. High vertical wind shear can disrupt a tropical cyclone trying to form by literally tearing it apart. High wind shear also can weaken or destroy a healthy tropical cyclone by interfering with the organization of deep convection around the cyclone center. Typically, 20 knots (23 mph or 10 m/s) or less difference in wind speed between the surface and upper atmosphere is considered favorable for hurricanes. In June and July of 2005, wind shear values were 20 - 40% below normal for the Gulf of Mexico and Caribbean Sea, the primary genesis locations for the seven tropical cyclones that formed. Wind shear values this low are highly favorable for tropical cyclone formation (see plots below).



Figure 1. Average amount of vertical wind shear (in black) and observed wind shear (in blue) for 2005 for the western Caribbean. Credit: Colorado State University (NOAA/CIRA)



Figure 2. Average amount of vertical wind shear (in black) and observed wind shear (in blue) for 2005 for the eastern Caribbean. Credit: Colorado State University (NOAA/CIRA)

Sea Surface Temperatures
Hurricanes need ocean waters of at least 26.5C (80 F) through a depth of about 50 meters to form or maintain their strength. The warmer the water, the better, since a hurricane is a huge heat engine. Sea surface temperatures (SSTs) are at the highest levels ever observed in the Atlantic, for the 50 years we have records. As of July 31, typical tropical Atlantic SSTs were about 2F (1.1C) above normal.



Figure 3. The Sea Surface Temperature departure from normal (in degrees C) for July 31, 2005. A large area of above normal SSTs (yellows and light greens) covers virtually the entire North Atlantic Ocean. The cold wake of Hurricane Emily is still apparent between the Yucatan Peninsula and southern Texas. Credit: U.S. Navy.

Moist Air
Hurricanes need moist air in the mid-troposphere (5 km or 3 mi altitude). Dry air interferes with the development of the large thunderstorm complexes needed to get a tropical storm going. Until the last week of July, the air over the tropical Atlantic and Caribbean Sea has been very moist. Since then, several large dust storms have moved off of the coast of Africa, accompanied by copious amounts of dry air that has interfered with tropical storm formation. TOMS aerosol data shows a large area of dust covering the entire tropical eastern Atlantic today.

Is Global Warming to Blame?
How much, if any, of this year's activity is due to global warming? That's a difficult question to answer. The research published so far shows that global warming cannot be linked to an increase in the number of hurricanes. So, this season's exceptional number of storms is probably unrelated to global warming. However, there is considerable debate whether or not sea surface temperatures and hurricane intensity have been affected by global warming. It is possible that the remarkable intensity of the hurricanes seen so far this season can be partially blamed on global warming. However, much more research needs to be done on this subject before we can link global warming with hurricane intensity. I plan to write a detailed article on the subject later this season, after I've had time to read the new research linking hurricane intensity to global warming, due to be published in Nature magazine on Sunday, August 7.

Dr. Jeff Masters

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692. 147257
03:50 PM GMT op 04 Augustus, 2005
alec the whole caribean sea and the gulf of mexico is warm
Member Since: August 2, 2005 Posts: 7 Comments: 68
691. weatherboyfsu
3:48 PM GMT on August 04, 2005
147257...arent you hurricaneking or no?
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690. punkasshans
10:47 AM EST on August 04, 2005
The caribbean does not have to worry too much about this storm. The storm will go north. Keep an eye on it, but I dont see it staying to the south. If you just look at where Harvey is, and how the wind patters in the upper atmosphere are at the current time, the storm will travel north. Harvey has pushed the high to the east.

I give the storm 2-3 days to quickly strengthen. Then watch for a stronger northward trend. The only threat this storm has to the islands is on the north side, should the storm direction "flatten" out and travel more to the west later in its lifetime. Even that I dont see happening.
689. Alec
11:45 AM EDT on August 04, 2005
hello. it's way too early to speculate where this soon to be TD#9 going to go in the long term. The models are trending this thing to go N of the windward islands and then take a slight turn to the west. I remember Floyd got into those waters just n of the islands and expanded in size. The strength of the high is critical in knowing where this thing will end up but remember if it gets near the bahamas those water temps are very warm.
688. 147257
03:46 PM GMT op 04 Augustus, 2005
weatherboy we dont know it it seems pretty organised to me so i expected it was a TD by 11 am but still isnt :S
Member Since: August 2, 2005 Posts: 7 Comments: 68
687. 147257
03:44 PM GMT op 04 Augustus, 2005
and undertaker one more thing for us is the storm more dangerous then for everyone else if it goes over a land it lose a lot of strenght fast but a island like us it laughing about it it weaks only a bit and the second over land its more easy to send hulp then to a island
Member Since: August 2, 2005 Posts: 7 Comments: 68
686. weatherboyfsu
3:41 PM GMT on August 04, 2005
Whats up guys.......whats wrong with the area(TD#9)???? Im working so I dont have the time to investigate the area....I come on here during the day to see the lastest scoop......whats the deal......Hawkeye!!!!!ALEC!!!!Turtle!!!!
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685. 147257
03:42 PM GMT op 04 Augustus, 2005
yes i'm from curacao you was lucky last year with Ivan just 50 miles south of youre island it had a westward track :) i think that still beter when ivan going over you as a cat 5
Member Since: August 2, 2005 Posts: 7 Comments: 68
684. Undertaker
10:39 AM EST on August 04, 2005
147257 well lets just pray it does not come here and from what it looks like it could take that west ward track for the next 2 days and then when its ready to turn north I fear Jamaica will be in its path. By the way you're from the caribbean right?
Member Since: August 4, 2005 Posts: 0 Comments: 50
683. 147257
03:39 PM GMT op 04 Augustus, 2005
pirateotobx do you have pictures of Isabel i saw wonderfull pictures of that storm but the storm is tracking wnw like you can see on this map http://vortex.accuweather.com/hurricane/regions.asp?anim=LOOP&type=wv&large=1&site=ATL®ion=HATL
Member Since: August 2, 2005 Posts: 7 Comments: 68
682. 147257
03:35 PM GMT op 04 Augustus, 2005
l00k i'm not skilled but i'm watching every hurricane for days with all the information what i can get but to my opinion could this one for the SSS islands and later a concern for Florida
Member Since: August 2, 2005 Posts: 7 Comments: 68
681. pirateotobx
3:30 PM GMT on August 04, 2005
I'm in North Carolina about an hour north of Wilmington on the coast and like Florida we have seen many storms since 96. Bertha(96), Fran(96), Bonnie(98), Dennis(twice with it's little loop-de-loop in (99), Floyd(99), Isabel(03) the leftovers of Charley(04)(which was a strong tropical storm when it came through... Yes this storm will form...just hope it curves out to sea.....( the price for living at the coast) ...I wouldn't live anywhere else though...
680. 147257
03:34 PM GMT op 04 Augustus, 2005
if it does it could be a major hurricane the lastest update is here

http://vortex.accuweather.com/hurricane/regions.asp?anim=LOOP&type=IR&large=1&site=ATL®ion=ATLE
Member Since: August 2, 2005 Posts: 7 Comments: 68
679. MDweather
3:32 PM GMT on August 04, 2005
147257 what do you think will happen with that possible TD9?
678. spagetio
3:32 PM GMT on August 04, 2005
Yikes! Looks like it's headed straight for Florida...
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677. 147257
03:31 PM GMT op 04 Augustus, 2005
following the last picture is maybe the comming TD 9 or Irene going to wnw
Member Since: August 2, 2005 Posts: 7 Comments: 68
676. 147257
03:28 PM GMT op 04 Augustus, 2005
undertaker i dont agree with you the atlantic ocean is warm enough but when it enters the caribean sea it could be a disaster for Curacao and Jamaica last time Emily strenght in less then 24 hours to a cat 4
Member Since: August 2, 2005 Posts: 7 Comments: 68
675. MDweather
3:24 PM GMT on August 04, 2005
Hello guys and girls. This is my first comment. I'm from Maryland and we were hit very hard by Isabel in 2003. Does anyone think that storm west-southwest of the cape vedre islands will form?
674. pirateotobx
3:26 PM GMT on August 04, 2005
latest track for "eventually" Irene.....
Link


I told you that name sounded like a good one to me. Then Katrina....
673. Undertaker
10:19 AM EST on August 04, 2005
If the wave continues on its west ward track, then I beleive it will become one of the biggest and strongest hurricanes we ahve ever seen and it will gain strenght if it makes it to the warm waters of the caribbean sea and that my friends is not good news for us in the caribbean. It does seem as if it will continue west and affect the lesser antilles by sunday or monday. What do you guys think.
Member Since: August 4, 2005 Posts: 0 Comments: 50
672. punkasshans
10:10 AM EST on August 04, 2005
"Apparently NHC was not convinced by the radar."

this was a satellite picture, not a radar
671. Undertaker
10:06 AM EST on August 04, 2005
Hey, I am new on this forum and I find all your opinions and comments very interesting. I am currently watching the wave near the Cape Verde Islands and wondering if it will make it's way into the carribean sea, because that would be real bad for us. I am from Jamaica and very concern. do you guys think it will make it's way here. We have experienced Dennis and Emily which devasted our north east coast and southwest cost respectively.
Member Since: August 4, 2005 Posts: 0 Comments: 50
670. spagetio
3:07 PM GMT on August 04, 2005
From the 11:30 a.m. update:

A broad low pressure area associated with a tropical wave is located
about 575 miles west-southwest of the Cape Verde Islands. Satellite
images and ship observations indicate a tropical depression may be
forming and if this trend continues...advisories will be initiated
later today or tonight. This system is expected to move toward the
west or west-northwest during the next few days.
Member Since: Posts: Comments:
669. DauphinIslandDunes
3:02 PM GMT on August 04, 2005
I am surprised that TD9/Tropical Storm Irene did not become official just now. Apparently NHC was not convinced by the radar. Link
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668. punkasshans
10:03 AM EST on August 04, 2005
To give everyone an idea of how much force that is, as compared to a 5 kg rock headed at you at 30 mph (13.41 m/s) (ie if someone threw it at you)
is only 5*13.4*13.4 = 9*10^2 Newtons

Basically, dont get hit by a tree flying 100 mph. . it might hurt a little!
667. punkasshans
10:01 AM EST on August 04, 2005
100 mph is 44.7 m/s

5 tons is obout 4500 kg

SO: F=mv^2 = 4500*44.7*44.7 = 9*10^6 Newtons (about)
666. Alec
11:03 AM EDT on August 04, 2005
im leaving......be back later........Alec....OUT!!!
665. pirateotobx
2:53 PM GMT on August 04, 2005
back in a bit....
664. Alec
10:54 AM EDT on August 04, 2005
fine...........ill stick with weather....sorry..
663. Denials
9:51 AM CDT on August 04, 2005
Alec...quit your spell checking, please.

1. Your last spelling correction was *wrong*. Not everyone uses American English. Organised is quite proper if you grew up learning British English.

2. It's annoying.

3. It takes up disk space and makes it harder to read this blog, and it doesn't provide any value to the discussion. It also makes the page take longer to load.
662. Alec
10:52 AM EDT on August 04, 2005
that was encouraging punk.
661. punkasshans
9:50 AM EST on August 04, 2005
Interesting that harvey is still stregthening. . and now they are saying it might become a hurricane (however, this doesnt mean much for anyone)
660. 147257
02:51 PM GMT op 04 Augustus, 2005
be back over 10 minuts
Member Since: August 2, 2005 Posts: 7 Comments: 68
659. 147257
02:50 PM GMT op 04 Augustus, 2005
http://vortex.accuweather.com/hurricane/regions.asp?anim=LOOP&type=IR&large=1&site=ATL®ion=CATL look to this picture :) TS HARVEY and coming TD 9
Member Since: August 2, 2005 Posts: 7 Comments: 68
658. Alec
10:49 AM EDT on August 04, 2005
organized* -----now im quiting on spell checking. too much to keep up with.
657. punkasshans
9:45 AM EST on August 04, 2005
Alec has an issue with spelling, for some reason he has to correct everyone.

Anyway, thanks for that one website, thats kinda cool how it can show all the low pressure systems (or cyclones)

11 am. . cant wait to see if they report anything new, or at least in the 11:30 am tropical formation report.

And alec, if you really want to find out how much 5 tons is in the metric system. . along with mph. . the internet is a great place to look it up. you are a student, you should know how to find these things rather than asking others to do it for you
656. 147257
02:47 PM GMT op 04 Augustus, 2005
like i seen it is it very organised
Member Since: August 2, 2005 Posts: 7 Comments: 68
655. Alec
10:44 AM EDT on August 04, 2005
yeah. go to our individual blogs ther're considered chatrooms by some.
654. Denials
9:45 AM CDT on August 04, 2005
The 10am update on Harvey is out and no TD9 as of yet.
653. 147257
02:42 PM GMT op 04 Augustus, 2005
are you updating every time here? looks irritating to me i still thinks its better that we have a chatroom somewhere
Member Since: August 2, 2005 Posts: 7 Comments: 68
652. Alec
10:41 AM EDT on August 04, 2005
Excist? kinda sounds like exorcist. you mean exist right?-just joking
651. 147257
02:38 PM GMT op 04 Augustus, 2005
i stay present until 11 AM then i go after the newest weather update and i think we hear then if TD 9 Excist
Member Since: August 2, 2005 Posts: 7 Comments: 68
650. 147257
02:34 PM GMT op 04 Augustus, 2005
present
Member Since: August 2, 2005 Posts: 7 Comments: 68
649. pirateotobx
2:31 PM GMT on August 04, 2005
present
648. Alec
10:30 AM EDT on August 04, 2005
hello? anyone here or did i just get left?
647. Alec
10:24 AM EDT on August 04, 2005
those*
646. Alec
10:22 AM EDT on August 04, 2005
one of these days thoses crazy reporters will find themselves floating in 10ft of water by the storm surge.
645. outrocket
9:15 AM CDT on August 04, 2005
very well could alec,sadly we may see this one day on TV.As reporters try to stand in face of these beast sooner or later 1lb.object at say 100mph with force of 5 tons will show all watching.Thats a high price to pay to sell an ad...
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644. 147257
02:19 PM GMT op 04 Augustus, 2005
working now stupid internet i have
Member Since: August 2, 2005 Posts: 7 Comments: 68
643. pirateotobx
2:18 PM GMT on August 04, 2005
site must be busy or updating...It's slow but it just re-loaded forme...
642. Alec
10:18 AM EDT on August 04, 2005
It was weird that about all the models had it coming to Tampa but one outlier model had it turning to the right earlier. That one outlier turned out to be the "truth"

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Dr. Masters co-founded wunderground in 1995. He flew with the NOAA Hurricane Hunters from 1986-1990. Co-blogging with him: Bob Henson, @bhensonweather

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