2007 Atlantic Hurricane Season Outlook

By: Dr. Jeff Masters , 4:24 PM GMT on April 19, 2007

Share this Blog
4
+

It's too soon to find many clues about what the upcoming hurricane season might be like, since we are facing the famed "April Predictability Barrier". The atmosphere is not predictable enough to make a skillful forecast of seasonal hurricane activity in April (this changes by late May, when skillful predictions of the upcoming hurricane season CAN be made). Thus, we should put little faith in the predictions by the Klotzback/Gray group and TSR made in April, calling for 17 named storms, 9 hurricanes, and 4 or 5 intense hurricanes. However, there are a few indicators we can start looking at. I covered these in a talk I gave last week at Eckerd College in St. Petersburg that many of you asked to hear about, so here goes!


Figure 1. Sea Surface Temperature (SST) difference between March 2007 and 2005. Cool colors are regions where the SST was colder in 2007, and yellows and greens where SSTs were warmer in 2007. Image credit: NOAA/ESRL.

Sea Surface Temperature (SST) Outlook
Sea Surface temperatures are at the heart of any attempt to analyze seasonal hurricane activity, since SSTs change slowly and have a major impact on both the number of storms that form and their intensity. For example, the record-breaking Hurricane Season of 2005 had the warmest SSTs ever observed in the tropical Atlantic. Comparing the SSTs in March of 2007 with March of 2005 (Figure 1), we see that SSTs were more than 1 degree C cooler in 2007 over a large portion of the Atlantic west of the Lesser Antilles Islands. This is a key portion of the "Main Development Region" (MDR) for hurricanes (red box in Figure 1). The MDR is where 85% of all major hurricane form. Note, though, that the regions where Katrina, Rita, and Wilma formed--the Bahamas to the Western Caribbean--have SSTs warmer this year than in 2005. Overall, SSTs are well above average across most of the tropical Atlantic this year, continuing the pattern we have seen since 1995, when the current active Atlantic hurricane period began. We can expect this year's SSTs to support a more active than usual hurricane season, although there is still time for a significant cooling to occur if we get a major increase in the speed of the trade winds over the next few months.


Figure 2. Sea Surface Temperature (SST) departure from average in the region 120°W-170°W, 5°S-5°N (called the Niņo 3.4 region) for 2006 and 2007. Temperatures +0.5ēC above average in this region indicate an El Niņo episode; temperatures -0.5ēC below average indicate an La Niņa. Note that EL Niņo peaked in December, then rapidly decayed to neutral conditions in early February. Image credit:NOAA Climate Prediction Center.

El Niņo/La Niņa Outlook
Obviously, SSTs don't tell the whole story, since the second highest SSTs in the tropical Atlantic since the 1870s occurred last year. To our great relief, we had a very normal year with 10 named storms, 5 hurricanes, and 2 intense hurricanes. As we see in Figure 2, that was in part because 2006 was an El Niņo year. El Niņo events usually suppress Atlantic hurricane activity, by bringing increased wind shear and dryer, sinking air over the Atlantic. This is not always the case--recall 2004? El Niņo conditions were even stronger that year (as measured by SST departures from average in the Equatorial Pacific), yet that year saw 15 named storms, 9 hurricanes, and 6 intense hurricanes in the Atlantic. Florida got walloped with four hurricanes.


Figure 3. Sea Surface Temperature (SST) departure from average (left) and wind shear departure from average (right) from the April 10, 2007 run of NOAA's CFS model. The forecasts are for the 3-month period August-October spanning the most active part of hurricane season. Note the long tongue of cooler than average waters forecast to extend from the South American coast along the Equatorial Pacific--the telltale sign of a La Niņa episode. Image credit:NOAA Climate Prediction Center.

Regardless, El Niņo is gone this year, and SSTs have been nearly average across the Equatorial Pacific since mid-February. Is El Niņo likely to come back, or will its evil twin, La Niņa strike this year? Well, according the early April run of NOAA's Climate Forecast System (CFS) model (Figure 3), we can expect a weak to moderate La Niņa event during hurricane season (August-October). This should bring below average values of wind shear over the Atlantic, which should enhance hurricane activity. Other forecast models predict neutral conditions for hurricane season, and very few models foresee a return to El Niņo conditions this year. NOAA's April 5 El Niņo discussion indicates that the current pattern of ocean temperatures observed over the Equatorial Pacific is consistent with a developing La Niņa event. The International Research Institute for Climate and Society is forecasting only a 10% chance of El Niņo conditions during hurricane season in 2007. The chances of La Niņa are put at 50%, and 40% for neutral conditions. What is the skill of these forecasts in April for an upcoming hurricane season? IRI doesn't tell us, but it's not good. Last year's April forecasts failed to predict the arrival of El Niņo during hurricane season, leading to a large overestimation of hurricane activity. Still, the best information we have at this time says that El Niņo is unlikely to occur during hurricane season, Since the active period of hurricane activity that we are in began in 1995, both La Niņa and neutral years have seen very high levels of hurricane activity (Figure 4). In fact, calling La Niņa an "evil twin" is not fair, since neutral years have had even higher hurricane activity than La Niņa years (thanks in great measure to the Hurricane Season of 2005).


Figure 4. Observed numbers of named storms, hurricanes, and intense hurricanes (Category 3 and higher) for the 12-year period beginning in 1995. Background image is of Australia's Tropical Cyclone Monica, the most intense storm of 2006.

African dust outlook
African dust is thought to suppress Atlantic hurricane activity, although its role is not well understood. As I explained in a blog last year, research shows that the presence of drought conditions in the Sahel region of Africa the previous year will increase the amount of dust wafting over the Atlantic during hurricane season. This occurs because drought-damaged soil takes about a year to dry up and create lots of dust to be blown away. Last year saw average to above-average rains during the rainy season (June-September) over the Sahel (Figure 5). This was also the case in 2005, so in theory, two straight years of good rains in the Sahel should act to keep African dust levels over the Atlantic no higher than average this hurricane season. The last significant drought years in the Sahel were 2001 and 2002.

Figure 5. Departure of precipitation from average in Africa for August 2006. The region in the red box is the Sahel region of Africa that accounts for most of the year-to-year variability in dust transport over the Atlantic Ocean. Image credit: NOAA Climate Prediction Center.

The outlook for the 2007 Atlantic hurricane season
If the forecasts of above normal sea surface temperatures, no El Niņo, and below average African dust come true, the 2007 Atlantic hurricane season should be very active. However, since our skill in predicting these things in April is low, the most reasonable forecast to make is a post-1995 climatology forecast: 15 named storms, 8 hurricanes, and 4 intense hurricanes. (The 100-year climatology is 10 named storms, 6 hurricanes, and 2 intense hurricanes). By May, the atmosphere and ocean begin to give us significant clues about the upcoming hurricane season. Tune into the late May seasonal forecasts issued by NOAA, the Klotzback/Gray group, TSR, and Cuba's meteorological service!

My next blog will be Earth Day--Sunday, April 22. Next week, I also plan to review an article published today that hypothesizes that global warming should cause a significant increase in wind shear over the Atlantic and Eastern Pacific, inhibiting hurricanes.

Jeff Masters

Reader Comments

Comments will take a few seconds to appear.

Post Your Comments

Please sign in to post comments.

or Join

Not only will you be able to leave comments on this blog, but you'll also have the ability to upload and share your photos in our Wunder Photos section.

Display: 0, 50, 100, 200 Sort: Newest First - Order Posted

Viewing: 731 - 681

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15Blog Index

731. weatherboykris
10:19 PM GMT on April 22, 2007
really?
Member Since: December 9, 2006 Posts: 125 Comments: 11346
729. chessrascal
10:06 PM GMT on April 22, 2007
image

can somone tell me what all that activity off of Africa is??
728. chessrascal
7:40 PM GMT on April 22, 2007
.
727. chessrascal
7:38 PM GMT on April 22, 2007
everyones having a siesta!
726. chessrascal
5:12 PM GMT on April 22, 2007
any1 know when the NHC will issue its predictions for this season?

END OF MAY
725. Bamatracker
4:27 PM GMT on April 22, 2007
skypony so if I understand your post correctly the author is saying the indications are that this years pressure may stay lower than normal...like in 2005?
Member Since: May 17, 2006 Posts: 6 Comments: 1367
724. HurricaneRoman
3:33 PM GMT on April 22, 2007
any1 know when the NHC will issue its predictions for this season?
Member Since: February 25, 2006 Posts: 2 Comments: 959
723. Skyepony (Mod)
2:57 PM GMT on April 22, 2007
One reason 2005 was so bad for the Atlantic was the overall lower sea level pressure...the high wasn't so strong.

EH2R had a most interesting update recently. For those that hadn't followed his freakishly accuarte predictions, simply put, he takes pictures of the sun setting & compared the size & what not to determine many facters about the atmosphere currently & for the next season. Here's his latest update..

First some news: North American weather especially the US Northeast Coast eerily similar to 2005, as I recall cooler at this time of the year.

WD April 18, 2007

The following graph and caption helped synthesize 2007 Northern Hemisphere temperature projection

Click on image for a bigger version


Member Since: August 10, 2005 Posts: 163 Comments: 37852
722. StormJunkie
2:57 PM GMT on April 22, 2007
Just my two cent on this...

If a response to a person is with in a few posts and depending on how fast the blog is moving a "Taz-" can do the trick. Otherwise reposting quotes works well...
Member Since: August 17, 2005 Posts: 26 Comments: 16605
720. weatherboykris
2:48 PM GMT on April 22, 2007
Why'd you repost what Taz said?
Member Since: December 9, 2006 Posts: 125 Comments: 11346
718. weatherboykris
2:30 PM GMT on April 22, 2007
Anyone here?
Member Since: December 9, 2006 Posts: 125 Comments: 11346
717. weatherboykris
2:23 PM GMT on April 22, 2007
Isn't it funny though,that that would've been a typical season in the western north Pacific?
Member Since: December 9, 2006 Posts: 125 Comments: 11346
716. weatherboykris
2:21 PM GMT on April 22, 2007
It could always feel that way.Unforgettable year,that was.
Member Since: December 9, 2006 Posts: 125 Comments: 11346
715. HurricaneRoman
2:20 PM GMT on April 22, 2007
Good Morning everyone....Hard to believe hurricane season is almost a month away.... the 05 season feels like it just happened a couple months ago
Member Since: February 25, 2006 Posts: 2 Comments: 959
714. weatherboykris
2:19 PM GMT on April 22, 2007
A "Mod" on Day 3?This should be serious.

Member Since: December 9, 2006 Posts: 125 Comments: 11346
713. weatherboykris
2:11 PM GMT on April 22, 2007
Wait a month Taz.Then we'll have a much better idea.
Member Since: December 9, 2006 Posts: 125 Comments: 11346
712. weatherboykris
2:11 PM GMT on April 22, 2007
Mail for Adrian.
Member Since: December 9, 2006 Posts: 125 Comments: 11346
710. Tazmanian
2:03 PM GMT on April 22, 2007
cool stronger La Niņa means more rain for me this winter this winter is has been so dry this is my last strom of the winter it looks like


well in 2005 we had a 28 name storms and 4 cat 5 and i had a vary wet winter that year this year we olny saw 10 name storms and i had a all most bone dry winter with with vary little rain this winter this wait in tell june


i hop this stronger La Niņa gives me a lot of rain this winter
Member Since: May 21, 2006 Posts: 5091 Comments: 115125
709. hurricane23
1:59 PM GMT on April 22, 2007
Posted By: Tazmanian at 9:57 AM EDT on April 22, 2007.

and 23 that is bad news too that will take a hurricane right in too FL like it did in 2004

Taz i cant answer that right now but some of the long range models due indicate a stronger high this year.Once we get into mid-may we will get a better idea.
Member Since: May 14, 2006 Posts: 8 Comments: 13793
708. StormJunkie
1:57 PM GMT on April 22, 2007
La Niņa is being forecast for this season Taz. It looks like it may get stronger later in the season.

As for the high and east coast troughs and ULLs, it is wait and see.
Member Since: August 17, 2005 Posts: 26 Comments: 16605
707. Tazmanian
1:57 PM GMT on April 22, 2007
and 23 that is bad news too that will take a hurricane right in too FL like it did in 2004
Member Since: May 21, 2006 Posts: 5091 Comments: 115125
706. weathermanwannabe
1:56 PM GMT on April 22, 2007
This is most helpful; thank you...I'm off to Church...See everyone tommorow..
Member Since: August 8, 2006 Posts: 0 Comments: 9134
705. Tazmanian
1:56 PM GMT on April 22, 2007
you no the navy site and the last name storm at 31L that year why did we not see 31 name storms?
Member Since: May 21, 2006 Posts: 5091 Comments: 115125
703. Tazmanian
1:54 PM GMT on April 22, 2007
thanks



do you think we will see some in like that this year?
Member Since: May 21, 2006 Posts: 5091 Comments: 115125
702. hurricane23
1:54 PM GMT on April 22, 2007
Posted By: weathermanwannabe at 9:49 AM EDT on April 22, 2007.

23...So if I am reading these two links correctly; there is no BH in place yet off the coast?

Yes its right of the coast bringing florida this extremely dry weather which infact looks to stay dry around here for atleast the next 5-7 days with no relief insight.
Member Since: May 14, 2006 Posts: 8 Comments: 13793
701. StormJunkie
1:53 PM GMT on April 22, 2007
wmw, that shows there are actuall two highs right now. One on the left and one on the right.

This is one of the best pages for viewing models, IMHO because you get several of the best models. Just set to sea level pressure and hit the submit button.
Member Since: August 17, 2005 Posts: 26 Comments: 16605
700. StormJunkie
1:51 PM GMT on April 22, 2007
Taz, I think some of the thinking is that weak La Niņa to enso neutral conditions actually create a better environment for systems to form, as opposed to strong La Niņa.
Member Since: August 17, 2005 Posts: 26 Comments: 16605
699. hurricane23
1:51 PM GMT on April 22, 2007
Posted By: Tazmanian at 9:46 AM EDT on April 22, 2007.

so if we had neutral in 2005 why did we see 28 name storms that year ?

2 of a few factors the made 2005 an extreme event.

The atlantic basin saw the warmest SST'S ever recorded in its history and also very favorable conditions in place which ive never seen as they were when wilma went threw here incredible intensification.
Member Since: May 14, 2006 Posts: 8 Comments: 13793
698. weathermanwannabe
1:49 PM GMT on April 22, 2007
23...So if I am reading these two links correctly; there is no BH in place yet off the coast?
Member Since: August 8, 2006 Posts: 0 Comments: 9134
697. Tazmanian
1:47 PM GMT on April 22, 2007
+ 4 cat 5
Member Since: May 21, 2006 Posts: 5091 Comments: 115125
696. Tazmanian
1:46 PM GMT on April 22, 2007
so if we had neutral in 2005 why did we see 28 name storms that year ?
Member Since: May 21, 2006 Posts: 5091 Comments: 115125
695. hurricane23
1:46 PM GMT on April 22, 2007
Here are a few links i use to moniter the highs location.

1-GFS from unisys
2-GFS from weather underground

For more models visit my model page at my website.SEE HERE
Member Since: May 14, 2006 Posts: 8 Comments: 13793
694. weathermanwannabe
1:45 PM GMT on April 22, 2007
Thanks.........
Member Since: August 8, 2006 Posts: 0 Comments: 9134
693. Tazmanian
1:44 PM GMT on April 22, 2007
weathermanwannabe dont no where a good link would be at if i new where to find one



yawn LOL
Member Since: May 21, 2006 Posts: 5091 Comments: 115125
692. StormJunkie
1:42 PM GMT on April 22, 2007
Morning wmw,

There are quite a few good link all organized on one page here. Forecast models, imagery, marine data, wind data and more.

Member Since: August 17, 2005 Posts: 26 Comments: 16605
691. Patrap
1:40 PM GMT on April 22, 2007
StormJunkie..some Food for thought and some history in one read...Link notice the date of the story. And note the author. Many need to know,.so goes SE Louisiana.So goes the nation.
Member Since: July 3, 2005 Posts: 424 Comments: 128344
690. weathermanwannabe
1:39 PM GMT on April 22, 2007
Taz; true, the BH location in a few months will play a big factor in US vernerability as the season progresses.....Problem is, pursuant to your question, what are the best "links" which we can access for the daily location?
Member Since: August 8, 2006 Posts: 0 Comments: 9134
689. StormJunkie
1:31 PM GMT on April 22, 2007
Morning all.

Interesting read Pat...

7 to 10 year approval process...lmao...I live in a great country, but sometimes we are pretty damn stupid...

Either we are staying in NO or not...If we stay then these projects should already have funding. If we are not, then the funding for the moving of a city should already be approved...

It makes you wonder...
Member Since: August 17, 2005 Posts: 26 Comments: 16605
688. hurricane23
1:30 PM GMT on April 22, 2007
Posted By: Tazmanian at 9:24 AM EDT on April 22, 2007.

what the Bermuda high is doing right now??? and where it is and how strong it is right now????

Taz the bermuda high is something that cannot be predicted to weeks out so thoughts on were it might be during the heart of the season is pure speculation.In a few weeks we should begin to get some ideas on how things are setting up.Adrian
Member Since: May 14, 2006 Posts: 8 Comments: 13793
687. weathermanwannabe
1:29 PM GMT on April 22, 2007
Good Morning All.........
Member Since: August 8, 2006 Posts: 0 Comments: 9134
686. hurricane23
1:27 PM GMT on April 22, 2007
Here is a good read on a new hurricane rating system written by Matt Rogers.

Here is the PDF version
Member Since: May 14, 2006 Posts: 8 Comments: 13793
685. Tazmanian
1:24 PM GMT on April 22, 2007
what the Bermuda high is doing right now??? and where it is and how strong it is right now????
Member Since: May 21, 2006 Posts: 5091 Comments: 115125
684. hurricane23
1:20 PM GMT on April 22, 2007
Morning all...

Kris check your mail.
Member Since: May 14, 2006 Posts: 8 Comments: 13793
683. Patrap
1:07 PM GMT on April 22, 2007
Happy Earth Day to yall..3
Member Since: July 3, 2005 Posts: 424 Comments: 128344
682. weatherboykris
1:03 PM GMT on April 22, 2007
good morning,BTW.
Member Since: December 9, 2006 Posts: 125 Comments: 11346
681. weatherboykris
1:01 PM GMT on April 22, 2007
I know,I'm just joking.
Member Since: December 9, 2006 Posts: 125 Comments: 11346

Viewing: 731 - 681

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15Blog Index

Top of Page

About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.