Hurricane season 2005--why so active?

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

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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1392. Alec
9:01 PM EDT on June 22, 2006
what do you guys think Wilma will do???LOL
1391. Alec
8:58 PM EDT on June 22, 2006
Going back in time.....looks like im beeing watched!!!LOL
1390. Alec
4:35 AM GMT on October 14, 2005
hi i went back in time.......its friday oct14 have things changed...
1389. cajunkid
2:51 AM CDT on August 27, 2005
stormtop, You called it early wednesday, I just had a good time with my friends here at LSU and most of my friends from the NO now think this is the one, can't say I told them so , but I think its about to become too real for alot folks down here
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1388. 147257
11:32 AM GMT op 19 Augustus, 2005
yeah i see that one too pretty big :)
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9:01 PM GMT on August 05, 2005
Posted By: Alec at 9:44 PM GMT on August 04, 2005.
i can see that another wave is getting ready to come off Africa. Conditions are more condusive over there since the african dust plume has let up.

wrong again alec i gave you the article and i cant believe you said the dust is letting up ....the dust will be there another 2 weeks alec and anything that comes off the coast will have a very hard time developing.
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1386. Toyotaman
9:17 PM GMT on August 05, 2005
I'm not the best forecaster in the world.....but I don't post irresponsible statements because it's what I think

LOL, have we forgotten about emily, gert, the depression that never formed over puerto rice and the explosive growth of nothing over the bay of campeche!!!!!!!

Stormtop, you really need to quit blasting people on the blog who do not agree with you. GROW UP.
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1385. MDweather
4:33 PM EDT on August 05, 2005
nicolai I am 14 close to your age!
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1384. Raysfan70
8:34 PM GMT on August 05, 2005
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1383. punkasshans
3:32 PM EST on August 05, 2005
You have to click on Dr. Masters' main blog and you will find the new comments section.
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1382. Raysfan70
8:25 PM GMT on August 05, 2005
punk where is the new blog
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1381. Raysfan70
8:11 PM GMT on August 05, 2005
I understand that people have the OPINIONS but why must everybody always have to fight. Like people say this is a place for people talk and try and learn off people not to argue no one has true facts about anything unless they are From NOAA, I just want to learn like others. Please stop bickering
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1380. punkasshans
3:03 PM EST on August 05, 2005
New section created
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1379. pirateotobx
7:54 PM GMT on August 05, 2005
I'm going on vacation...ya'll have a good one!
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1378. Denials
2:48 PM CDT on August 05, 2005
Yes, definitely zoo-grade salt lick, not your regular table salt.
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1377. MrXpress
7:44 PM GMT on August 05, 2005
No one uses this blog as a 'public advisory', so no one is doing any harm by predicting future scenarios. This is just an informal discussion by people who aren't exactly the cream of the crop of meteorology (despite what some of you think). People might (and should) take what Steve Gregory and Jeff Masters have to say seriously, but it's pretty much assumed that every comment posted in response to the main blog post should be taken with the biggest grain of salt in the world.
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1376. 147257
07:44 PM GMT op 05 Augustus, 2005
i'm going again i see you guys on 5 pm and 11 pm and for the ones in Florida prolly a big thunderstorm again have fun and stay save
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1375. 147257
07:42 PM GMT op 05 Augustus, 2005
i agree with that
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1374. hazmat
7:34 PM GMT on August 05, 2005
yes...looks like we could have some homebrew stirring in the interesting to watch if anything develops.

still too soon to write td9 off yet...climatology speaking this season hasn't followed the rules.
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1373. 147257
07:35 PM GMT op 05 Augustus, 2005
ok i will try to say less but i will still say my opinion and why i think it :)
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6:24 PM GMT on August 05, 2005
147257, good predictions or's just plain irresponsible to tell the public not to worry or even watch a storm this far out. especially when the NHC is disagreeing.

I'm not the best forecaster in the world.....but I don't post irresponsible statements because it's what I think.

Anyway, I'm done discussing STORMTOP.....I'm sticking to my new 'skip-over' rule.

evolution dont you feel like a dam fool posting are a real should look at yourself in the know absolutely nada about forecasting hurricanes..stick to
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1371. 147257
07:25 PM GMT op 05 Augustus, 2005
so take youre cameras and film something beautifull for me :D

Alec is it still raining by you?
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1370. 147257
07:24 PM GMT op 05 Augustus, 2005
l0l i dont know the FSU site sorry :( but all i can tell you now is that i see a big storm forming above Florida is start like the same as yesterday®ion=CAR
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1369. Raysfan70
7:20 PM GMT on August 05, 2005
you all seem to know alot about your Hurricanes I see that everyone talks about the FSU model can you give the web site I have been intrested in this, and they said that it did a good job last year.
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1368. 147257
07:18 PM GMT op 05 Augustus, 2005
guys could someone take a look at 29 N 70 W there is a big clouds still growing
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1367. 147257
07:16 PM GMT op 05 Augustus, 2005
l0l are theyre more people of my age around 16
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1366. 147257
07:15 PM GMT op 05 Augustus, 2005
look here en click Trop FCst on and watch it now it still taking the path they predicted
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1365. Raysfan70
7:15 PM GMT on August 05, 2005
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1364. 147257
07:14 PM GMT op 05 Augustus, 2005
i'm a amateure too so dont cry :P how old are ya ?
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1363. Raysfan70
7:14 PM GMT on August 05, 2005
what is that
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1362. 147257
07:12 PM GMT op 05 Augustus, 2005
damn that noaa makes a good prediction path for TD 9
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1361. Raysfan70
7:09 PM GMT on August 05, 2005
I just want to try and learn more about the storms and what makes them do and go where they go? so i guess that I am an amature. Like it though when there is nobody arguing with anybody seems a waste of time to me.
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1360. 147257
07:11 PM GMT op 05 Augustus, 2005
btw call me nicolai :)
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1359. 147257
07:10 PM GMT op 05 Augustus, 2005
its not i want the glory :P i even didnt know where it was only recalling something ;)
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1358. 53rdWeatherRECON
3:02 PM EDT on August 05, 2005
147 didn't see that that post. I am not claiming to have discovered it but just that I noticed it with the mm5FSU computer model late yesterday and this morning. It's all amature hour all the time over here.
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1357. Raysfan70
6:58 PM GMT on August 05, 2005
yes that is Tampa Bay always go for the underdog. the system seems to be strong right now. Does it say anything abot movement?
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1356. 147257
06:58 PM GMT op 05 Augustus, 2005
news is 6 hours old :)
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1355. 147257
06:54 PM GMT op 05 Augustus, 2005
hmmz i didnt know where it was but i posted something like that today

Posted By: 147257 at 12:44 PM GMT op 05 Augustus, 2005.
site gives this warning

Currently, a weak upper-level low is situated over southern Mississippi-southern Alabama. Every once in a while, underneath such systems, a low-level circulation can form. It is an area to watch over the next few days.
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1354. 53rdWeatherRECON
2:51 PM EDT on August 05, 2005
:) :) Wow my first posts and I found something. Thanks MrXpress and Raysfan70.

By the way Raysfan is that - TB Devil Rays fan. I'm a bostonian displaced in Orlando. I go to every Sox vs. Rays games in tampa. I have become a huge fan of TB.
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1353. punkasshans
1:53 PM EST on August 05, 2005
Mid to upper level development means no tropical development. . just a nice low pressure system.
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1352. Raysfan70
6:51 PM GMT on August 05, 2005
I just wondering with the trough comeing down what they are going to bring for development in the Gulf now. Could make the whole season wild.
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1351. MrXpress
6:49 PM GMT on August 05, 2005
From the 2:05p NHC discussion

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1350. Raysfan70
6:47 PM GMT on August 05, 2005
i checked out your link earlier that is why I asked the question I thought but figurung it is so close to land nothing may come of it.
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1349. 147257
06:47 PM GMT op 05 Augustus, 2005
i dont see anything
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1348. 53rdWeatherRECON
6:45 PM GMT on August 05, 2005
I posted this 1 hour ago.

"Long time Lurker making first post ever.

While looking at the models for TD9 I was noticing a disturbance alot father to the east.(W coast of FL.)
I was wondering about the mm5FSU model from between 24h to 120h There appears to be something develop off the coast of the Florida Panhandle.Link
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1347. 147257
06:45 PM GMT op 05 Augustus, 2005
Raysfan70 i think there is something possible there but not for the next 3 days
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1346. Raysfan70
6:46 PM GMT on August 05, 2005
which way do you see it moving?
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1345. 53rdWeatherRECON
6:44 PM GMT on August 05, 2005

This image actually shows some rotation of the clouds and maybe convection???????
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1344. Raysfan70
6:43 PM GMT on August 05, 2005
Gulf Of Mexico
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1343. 147257
06:42 PM GMT op 05 Augustus, 2005
sorry my english is not that good whats GOM
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1342. Raysfan70
6:40 PM GMT on August 05, 2005
does anyone think something will form out there in the GOM?
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Dr. Masters co-founded wunderground in 1995. He flew with the NOAA Hurricane Hunters 1986-1990. Co-blogging with him: Bob Henson, @bhensonweather

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