Outlook for the remainder of hurricane season

By: Dr. Jeff Masters , 8:15 PM GMT on September 15, 2006

Could Ernesto end up being the worst the hurricane season of 2006 has to dish out? With the season more than half over, and no landfalling storms in sight, this year in no way resembles the Hurricane Season of 2005, when we had 15 named storms, 8 hurricanes, and 4 major hurricanes by this date. Our tally so far this year is a relatively meager 8 named storms, 2 hurricanes, and 1 major hurricane, right near average. Looking at the plot of typical hurricane activity for the Atlantic (Figure 1), we see that we are almost a week past the peak of hurricane season, which was September 10. We still have a long road ahead--hurricane activity stays high for another four to five weeks, on average. Let's analyze analyze what the remainder of hurricane season may have in store for us.

Figure 1. Ernesto--the main event of the hurricane season of 2006? Image credit: NOAA Visualization Lab.

Figure 2. Climatological Atlantic hurricane and tropical storm activity.

Sea Surface Temperatures (SSTs)
It's mid-September, and SSTs have peaked in the Atlantic and are on a slow decline. Still, water temperatures will remain warm enough to support hurricanes throughout usual Atlantic development areas through the end of October. SSTs are 0.5-1.5°C warmer than normal right now (Figure 3), which is a huge amount of extra heat energy. The Bermuda High has stayed relatively weak all of August and September, leading to lighter trade winds that have kept the ocean warm due to reduced evaporative cooling.

Figure 3. Difference of SSTs from normal for Sep 11, 2006.

Wind shear and El Niño
An El Niño is on the way, according to the latest El Niño discussion posted September 7 by NOAA's Climate Prediction Center. A steady warming of the waters in the Equatorial Pacific near the coast of South America, combined with stronger than usual westerly winds over the Equatorial Pacific, point toward the emergence of a weak El Niño episode beginning in October or November. As most of you know, El Niño conditions put a major damper on both the number and intensity of Atlantic tropical cyclones. This is primarily due to increased wind shear. The upper air winds that develop when one heats the Equatorial Eastern Pacific waters tend to blow from west to east over the Atlantic at high speed. Since the tropical Atlantic trade winds near the surface typically blow the opposite direction, this creates a lot of shear that makes it difficult for a tropical cyclone to survive. Since the peak portion of hurricane season began in late August, wind shear over the tropical Atlantic, western Caribbean, eastern Caribbean, and Gulf of Mexico has been near or below normal, so there is no sign that a developing El Niño is suppressing hurricane activity yet. When I eyeball the shear forecast for the coming two weeks from the GFS model, I don't see any sign that an El Niño-induced increase in shear is in the offing this September.

While the lack of wind shear would seem to favor an active hurricane season, what wind shear we have had has been of exceptionally high quality. The jet stream has spun off a continual series of upper level "cold lows" over the Bahamas and central Caribbean that have brought hostile wind shear to any tropical waves or tropical storms that have tried to approach. This jet stream pattern has been in place since early June, and shows no signs of changing through the end of September.

Dry air and vertical instability
Hurricanes like plenty of moist, unstable air. This has been lacking this year, thanks to an above-average amount of dry Saharan air coming off the coast of Africa. For example, take a look at the instability plot for the eastern Caribbean, where many of last year's fiercest storms formed. Instability has been well below normal this year. Model projections through the rest of September show no change to the basic atmospheric pattern over the Atlantic, and I expect lack of instability will continue to inhibit hurricane development.

Steering pattern
The large scale jet stream pattern and associated positioning of the Bermuda High has remained unchanged since early June, and is forecast to remain the same through the end of September. This pattern puts a trough of low pressure over the U.S. East Coast, which will act to recurve storms approaching the U.S. or Caribbean. Now that we are entering late September, the troughs are getting stronger and extending farther south, making recurvature even more likely. The current pattern has been for tropical waves that form into tropical storms to emerge from Africa at about the latitude of the Cape Verde Islands (12-15 north latitude). This is far enough north to make recurvature very likely. This pattern is forecast to continue through the end of September, and I don't expect any of these African systems will be able to avoid recurvature. We will probably get two or three more of these recurving storms before the usual end to the African tropical storm season in early October.

Given that the current jet stream pattern that favors recurving storms and shear-producing upper level lows over the Bahamas and central Caribbean is forecast to continue until the end of September, plus Bill Gray's September 1 forecast of only two named storms and one non-major hurricane in October, I don't believe any major hurricanes will affect the U.S. or Caribbean the remainder of hurricane season. I expect one or two tropical storms or Category 1 hurricanes will form in October from the remains of old cold fronts that push off the coast of the U.S. A hurricane of this nature is most likely to affect the west coast of Florida or the Outer Banks of North Carolina, and rarely has enough time over water to make it to Category 3 status. In total, I expect 5 more named storms, 3 hurricanes, and 1 major hurricane this season.

Additional thoughts
I answered a series of questions on what the rest of this year's hurricane season might be like for Texas, the Katrina disaster, and the global warming/hurricane connection for houstonist.com that appeared in today's edition.

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1240. neutrino006
10:08 PM GMT on September 18, 2006
Hello everybody. I'm new here, so I'm gonna introduce myself somehow: I live in Romania, and my hobbyes are the meteorology and everything concernes about that. So, I observed that if a hurricane reaches or not the US coast, it affects dramaticaly our weather. If a hurricane makes a "landing", our clime is warm and most of all clear. But if not, we have a really ugly weather, and this year I counted in nearby 3 tornadoes, due to a massive condensations of oceanic water vapors that condences over mountains...
So, from here, I am monitoring the tropical activity and I see that Gordon is in route to Europe, and it is possible to track Hellen after him too. If that so, we're gonna have a bad winter, with a lot of snow, but not so cold like past years when it doesn't snow a bit. Am I right?
1239. stormtracker06
6:14 PM GMT on September 18, 2006
Why is it that people have such a hard time using blogs for the topics for which they are intended? What a waste of space...taken from people who are truly interested in having intelligent discussions on the topics presented.
Member Since: April 8, 2006 Posts: 0 Comments: 0
1236. StoryOfTheHurricane
4:10 PM GMT on September 16, 2006
who cares? this place is a zoo. im going to FLAHurricane where they know what they're talking about
1235. WPBHurricane05
4:08 PM GMT on September 16, 2006
if you all care there is a NEW BLOG
Member Since: July 31, 2006 Posts: 56 Comments: 8112
1232. StoryOfTheHurricane
4:02 PM GMT on September 16, 2006
its obvious magic is leaving to continue his work as a janitor.. lol
1231. StoryOfTheHurricane
4:00 PM GMT on September 16, 2006
now im getting told to drop it when ive been the one telling ST and SJ to drop it, its been dropped because i had to continue to clear up what i said because they obviously didnt understand what i meant, just let it go.
1230. StoryOfTheHurricane
3:58 PM GMT on September 16, 2006
look at Bob Dylan's picture? lol you are something else MagicFan...HAHAHAHAHHAHAHAHAHAHA
1229. HurricaneRoman
3:58 PM GMT on September 16, 2006
god magicsfan lol ur mean. . but i see ur point
Member Since: February 25, 2006 Posts: 2 Comments: 973
1226. CaneAddict17
3:56 PM GMT on September 16, 2006
Member Since: August 31, 2006 Posts: 5 Comments: 156
1224. Hellsniper223
3:55 PM GMT on September 16, 2006
Posted By: magicfan1423 at 10:53 AM EST on September 16, 2006.
disagree, arguing just makes you look like an A**.

I agree... maybe you should just drop it... Let people do as they please... Lmao.. You're just invigorating the situation.
Member Since: March 28, 2006 Posts: 0 Comments: 16
1222. HurricaneRoman
3:54 PM GMT on September 16, 2006
No need to tell taz...story u do keep bringing it up like on ur last 6 post..... umentioned something about the arguement and st and sj stopped it a while ago.....
Member Since: February 25, 2006 Posts: 2 Comments: 973
1221. sandcrab39565
3:54 PM GMT on September 16, 2006
Nash, I understand it has gone crazy. I shure wish Rand had not been banned. I have seen worse than that on here without any action taken. Whats your take in the new blob just off of the Cape?
Member Since: June 25, 2006 Posts: 36 Comments: 9972
1219. WPBHurricane05
3:54 PM GMT on September 16, 2006
new blog
Member Since: July 31, 2006 Posts: 56 Comments: 8112
1211. nash28
3:50 PM GMT on September 16, 2006
Hey sandcrab. Well, looks like some crazy stuff happened on here after I left last night.

I got my ass chomped off in the morning on here and then Rand gets banned.

If it weren't for the NHC, you'd never know we still had Helene to deal with...
Member Since: July 11, 2005 Posts: 190 Comments: 16972
1208. hazmat
3:45 PM GMT on September 16, 2006
On another note,,,how about you GUYS continue your fight off the board. It's been what an hr now? Just when I think there's hope this place goes to hell in a handbasket real quick...shame it has the potential to be right up there with some of the other, better, message boards but this "mine is bigger than yours" really brings the place down.

Flame away...doesn't matter at this point...you know there used to be a bunch of pros that would come here...they're gone now...imagine that.
1207. sandcrab39565
3:44 PM GMT on September 16, 2006
Good day to you Nash hows it going.
Member Since: June 25, 2006 Posts: 36 Comments: 9972
1205. nash28
3:42 PM GMT on September 16, 2006
Has the fighting continued from last night?
Member Since: July 11, 2005 Posts: 190 Comments: 16972
1203. Cavin Rawlins
3:41 PM GMT on September 16, 2006
TS Helene

Member Since: July 24, 2005 Posts: 407 Comments: 19076
1201. hazmat
3:40 PM GMT on September 16, 2006
Highlights from the 11 disco...moving NW near 14mph...max sustained winds @ 75mph w/higher gusts...platueau of intensity around 72hrs...slight weakening thereafter...on SW side of deep-layer ridge & headed towards break in ridge which is partially produced by Gordon...GIV research mission enroute as part of Salex Experiment.

Great to watch Helene form from afar.
1200. moonlightcowboy
3:39 PM GMT on September 16, 2006
uuuggh, arggh....trying to patiently wait for the good Dr., or someone's direction to Rand's blog, too(por favor).

Windows, I don't care how many windows you have. I think I have that many in my foyer. As far as attacks, sure you bet, when someone is unduly picking up and twisting what someone else said...and btw, didn't say with arrogance.

Uuuuummmm, take your "kumabaya" and well, you know what you can do with it.

Story, man, no use trying to reason with this s__t. Later man.
Member Since: July 9, 2006 Posts: 184 Comments: 29641
1199. Cavin Rawlins
3:39 PM GMT on September 16, 2006
Tazmanian, west into Panama/Costa Rico, and it has little chance due to its location (its near landmasses)
Member Since: July 24, 2005 Posts: 407 Comments: 19076
1198. StormJunkie
3:38 PM GMT on September 16, 2006
Ok, y'all I am out. I will see y'all later.
Member Since: August 17, 2005 Posts: 26 Comments: 17164
1197. StoryOfTheHurricane
3:37 PM GMT on September 16, 2006
lets just drop this, its a stupid argument, i never said anything that you are claiming i said and its all blown out of proportion, i simply stated there is a small possibility at the forecast being further west, and the possibility of that spelling trouble, and i still stand by this belief, however, i do believe that it will be a fish storm, but with a possibility of something different occurring, ENOUGH SAID!!!!!!!!!!!!!!!!!!!!!
1196. StormJunkie
3:36 PM GMT on September 16, 2006
lol Story.
Member Since: August 17, 2005 Posts: 26 Comments: 17164
1195. ihave27windows
3:36 PM GMT on September 16, 2006
Not lowering myself to your level. Goodbye.
Member Since: July 19, 2005 Posts: 108 Comments: 14952
1193. StormJunkie
3:35 PM GMT on September 16, 2006
That is something Mel. Amazing the stucture is holding together so well so close to land.
Member Since: August 17, 2005 Posts: 26 Comments: 17164
1192. StoryOfTheHurricane
3:35 PM GMT on September 16, 2006
ihave27windows you must not have been reading all of the attacks against me that led to these comments, i wouldnt have said them if they werent called for, and any person with any common sense would agree with me there.
1191. Cavin Rawlins
3:34 PM GMT on September 16, 2006
Hurricane Helene:

Member Since: July 24, 2005 Posts: 407 Comments: 19076
1190. kenscanes
3:34 PM GMT on September 16, 2006
Thanks Junkie...I'll stay tuned

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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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