Dr. Jeff Masters' WunderBlog

La Ni�a is gone

Posted by: Dr. Jeff Masters, 03:13 PM GMT del 11 Maggio 2006

The La Ni�a of 2006 proved to be short-lived. Sea Surface Temperatures (SSTs) in the eastern Pacific near the Equator have returned to near-normal values over the past month, according to the latest El Ni�o advisory issued today by the Climate Prediction Center (CPC). We are now in what is characterized as ENSO-neutral conditions (or El Ni�o-neutral conditions), which means that there is neither an El Ni�o nor a La Ni�a occurring. This is the case about 45% of the time, and was true for March through December of 2005. The CPC expects El Ni�o-neutral conditions to continue for at least the next 3-6 months, which means for all of hurricane season. The 2006 La Ni�a was an unusual one, because it started very late--no La Ni�a of similar magnitude has ever formed in the middle of winter, as this one did. However, the demise of this year's La Ni�a came at the usual time such events end--April and May are the typical months for the demise of both La Ni�a and El Ni�o.

How will this affect the hurricane season of 2006?
So, what does all this portend for the upcoming hurricane season? It is well-known that the presence of a La Ni�a usually means more Atlantic hurricanes, and stronger hurricanes, too. This is because the large-scale wind circulation that develops during a La Ni�a keeps wind shear levels relatively low over the main development region for hurricanes in the tropical Atlantic. So, the demise of La Ni�a is good news for those of you living in Hurricane Alley. However, before we get too cheerful about this, it is worth remembering that the unbelievable Hurricane Season of 2005 occurred in El Ni�o-neutral conditions, and El Ni�o-neutral conditions are expected for this hurricane season, too. So, let's look at some other factors that will influence this year's hurricane season.

Figure 1. Comparison of this year's May SST anomalies with last year's. Image credit: NOAA.

SST comparison--this year vs. last year
Let's compare last year's SST anomalies (the difference in temperature between observed and normal) with this year's, to see how things have changed (Figure 1). The key things to look at are the SSTs in the Caribbean and the tropical Atlantic between Africa and the Antilles Islands, since this is where 85% of all major hurricanes form. While SSTs are .5 to 1.5 degrees above normal--which is a lot!--SSTs are a full degree Centigrade cooler this year than last year at this time. This reduction in SSTs should keep this year's hurricane season from producing early major hurricanes, like Dennis and Emily of July 2005. However, once we enter the prime hurricane months of August through October, expect another above normal year for hurricanes and intense hurricanes. My worst-case scenario for 2006 is a year similar to 2004, which was awful, but modest compared to 2005. My best-case scenario is a year like 1995, which was still very active, but the Bermuda High set up much farther east and recurved most storms before they hit land. Of course, this would be bad for the northeastern Leeward Islands, which got pounded in 1995.

The Gulf of Mexico SSTs are much warmer this year than last, due in part to the record warm temperatures the U.S. experienced in January and April. This may allow for more intense that normal June systems to develop in the Gulf this year. However, remember that systems that develop in the Gulf usually only last a day or two, which doesn't give them much time to strengthen before they hit land. There has only ever been one major hurricane in June (Audrey of 1957).

The other item of interest is that the pattern of SSTs over the eastern Pacific is much different this year versus last year. Waters near the Equator were much warmer last year, thanks to the lingering effect of the El Ni�o event early in the year. There is also a much warmer pool of water north of Hawaii this year. These differences may end up having a significant influence on this year's jet stream pattern, and where the Bermuda high ultimately sets up camp. The jet stream and Bermuda high determine how hurricanes are steered, but unfortunately we don't know enough about long-range influences of unusual SST patterns on the weather to be able to predict where this year's hurricanes are likely to be steered. The bottom line is that SSTs are cooler and have a much different pattern this year compared to last year, and thus we should not expect a continuation of last year's ridiculously hyperactive, once-in-a-lifetime hurricane season.

Outlook for the rest of May
SSTs are already warm enough to support hurricane formation in the Gulf of Mexico, and the entire tropical Atlantic. What is saving us are the strong upper level winds of the jet stream, which has been dipping far to the south and creating lots of wind shear. The jet stream is forecast to remain active and fairly far south for at least the next two weeks, which should maintain unfavorable levels of wind shear over the Atlantic for the remainder of May. As long as we're talking about tornado outbreaks in the southern U.S., such as we've experienced this week, we don't have to worry about hurricane formation in the Gulf of Mexico. Tornado outbreaks require a stong jet stream, which is the bane of a hurricane trying to form.

The other missing ingredient--at least in the Caribbean and tropical Atlantic--has been the lack of an initial disturbance to get a hurricane started. Africa has just begun to produce its usual summer parade of tropical waves, which frequently serve as the nucleus for a tropical storm. These tropical waves are coming off of Africa at about 2 degrees North Latitude, which is too close to the Equator to allow a hurricane to spin up. I'm not expecting any tropical development for the rest of May in the Atlantic due to high wind shear and the lack of proper initial disturbances.

It's another story in the Eastern Pacific, where wind shear is less and the remains of an old cold front coming off of North America could serve to trigger tropical storm formation as early as next week. The hurricane specialists at the National Hurricane Center begin rotating shift work on Monday May 15, which marks the official beginning of the Eastern Pacific hurricane season.

My next blog will be on Monday. I'll talk about air pollution some next week, since May marks the beginning of air pollution season, and next week is EPA's Air Pollution Awareness Week.

Jeff Masters

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552. StormJunkie 09:30 PM GMT del 14 Maggio 2006
I just realized that the NOAA Sat all update every 15min now. It use to only be the floaters that updated taht often. Nice. SJ Member Since: Agosto 17, 2005 Posts: 26 Comments: 15218

553. Levi32 09:34 PM GMT del 14 Maggio 2006
Rich I am going to punch up the landfall intensity to 125 knots. I just don't see how the outflow is going to be less than suitable. Despite the SSTs and heat content, I think this storm will be a Cat 4 at least. Member Since: novembre 24, 2005 Posts: 586 Comments: 25450

554. Levi32 09:35 PM GMT del 14 Maggio 2006
This water vapor loop shows that Chanchu has temperarily stalled. This may mark the beginning of the northward turn. Also outflow continues to rapidly expand and improve. Member Since: novembre 24, 2005 Posts: 586 Comments: 25450

555. squeak 09:42 PM GMT del 14 Maggio 2006
Levi check out the CIMSS upper level wind analyses. They showed that an outflow channel was setting up even after the 14/1500Z JTWC prog said that intensity would likely be capped due to limited outflow: "INTENSIFICATION WILL BE SLIGHTLY LESS THAN CLIMOTOLOGY AS THE SYSTEM ALREADY IS VERY INTENSE AND WILL HAVE TROUBLE MAINTAINING STRENGTH PAST 135 KNOTS FOR EXTENDED PERIODS DUE TO LACK OF A DEFINED OUTFLOW CHANNEL. UPPER LEVEL OUTFLOW IS RADIAL, BUT LINKAGE WITH A TROPICAL UPPER TROPOSPHERIC TROUGH CELL TO THE NORTH-EAST IS NOT EXPECTED." Probably why the intensity forecasts are up. She is such a plate right now http://www.ssd.noaa.gov/mtsat/wpac/rb-l.jpg and continuing with very cold cloud tops. Can't belive this but the graphic and prog from #25 still not up on their web site, would like to see if they mention the outflow.

556. turtlehurricane 09:43 PM GMT del 14 Maggio 2006
i hav updated my blog Member Since: Luglio 22, 2005 Posts: 227 Comments: 466

557. turtlehurricane 09:44 PM GMT del 14 Maggio 2006
this chanchu looks disastrous Member Since: Luglio 22, 2005 Posts: 227 Comments: 466

558. turtlehurricane 09:45 PM GMT del 14 Maggio 2006
how do u guys post pictures? Member Since: Luglio 22, 2005 Posts: 227 Comments: 466

559. Levi32 09:47 PM GMT del 14 Maggio 2006
She really looks good despite having no eye squeak. The CDO is very nice and has finished forming. I wonder why the JTWC keeps forecasting outflow difficulties. They should have learned after what happened with Monica. Her outflow channel looks quite healthy too. I just don't understand the tropical forecast centers the last few years. Member Since: novembre 24, 2005 Posts: 586 Comments: 25450

561. Levi32 09:49 PM GMT del 14 Maggio 2006
Turtle here is how you post a picture. img src="image url" replace the two s with greater than and lesser than signs. Member Since:* novembre 24, 2005 Posts: 586 Comments: 25450

562. StormJunkie 09:49 PM GMT del 14 Maggio 2006
Turtle, go to a website that has just an image, like a single radar image. the img src= but I think you have to use >. Member Since: Agosto 17, 2005 Posts: 26 Comments: 15218

563. turtlehurricane 09:50 PM GMT del 14 Maggio 2006
i see restriction in the north quadrant Member Since: Luglio 22, 2005 Posts: 227 Comments: 466

564. Cavin Rawlins 09:50 PM GMT del 14 Maggio 2006
Is Chanchu a Super typhoon? Member Since: Luglio 24, 2005 Posts: 407 Comments: 19076

565. turtlehurricane 09:50 PM GMT del 14 Maggio 2006
o ok, just html Member Since: Luglio 22, 2005 Posts: 227 Comments: 466

566. turtlehurricane 09:51 PM GMT del 14 Maggio 2006
thanks storm and levi Member Since: Luglio 22, 2005 Posts: 227 Comments: 466

567. Levi32 09:52 PM GMT del 14 Maggio 2006
Weather456 a super typhoon has sustained winds of over 150 M.P.H. Chanchu has winds of 150 so she is basically a super typhoon but until she reaches 155 they won't lable her as such. Member Since: novembre 24, 2005 Posts: 586 Comments: 25450

568. StormJunkie 09:53 PM GMT del 14 Maggio 2006
well that did not work. and levi beat me to it with a much simplier explination then I was going to give. This system over the US is impressive. Spurred hail storm in my area. Imagine if it got over warm water and low shear, then changed over. Ouch. Not that this could or will happen, just something I thought about. SJ Member Since: Agosto 17, 2005 Posts: 26 Comments: 15218

569. turtlehurricane 09:55 PM GMT del 14 Maggio 2006
The Joint Typhoon Warning Center has set the initial intensity at 130 KNOTS as of Warning #25. Based on JTWC's intensity, Chanchu is now a SUPERtyphoon.-----courtsey of independentwx Member Since: Luglio 22, 2005 Posts: 227 Comments: 466

570. Cavin Rawlins 09:55 PM GMT del 14 Maggio 2006
MANILA, Philippines (Reuters) -- The death toll from Typhoon Chanchu rose to 32 in the Philippines on Sunday, after more bodies were found from a capsized boat, and officials said the storm had affected or displaced more than 42,000 people. Cnn Member Since: Luglio 24, 2005 Posts: 407 Comments: 19076

571. Levi32 09:56 PM GMT del 14 Maggio 2006
Yeah SJ I see what you mean. If that tail end of the cold front was over the gulf with low shear and touched off that convection, we might be looking at something tropical. Member Since: novembre 24, 2005 Posts: 586 Comments: 25450

572. Alec 09:57 PM GMT del 14 Maggio 2006
so turtle, you still have your "hissing" turtles?lol

573. turtlehurricane 09:57 PM GMT del 14 Maggio 2006
did any of u guys see taht discovery channel thing about wat if hong kong was hit? this whole situation seems eerily similar to the show Member Since: Luglio 22, 2005 Posts: 227 Comments: 466

574. turtlehurricane 09:58 PM GMT del 14 Maggio 2006
lol, yup. no hissing yet this season though Member Since: Luglio 22, 2005 Posts: 227 Comments: 466

575. Levi32 09:59 PM GMT del 14 Maggio 2006
Just imagine what it would be like if Chanchu was forecast to be strengthening upon landfall. I don't want to think about it. Member Since: novembre 24, 2005 Posts: 586 Comments: 25450

576. StormJunkie 10:00 PM GMT del 14 Maggio 2006
Levi, I was actually talking about the whole system. The Great Lakes system. SJ Member Since: Agosto 17, 2005 Posts: 26 Comments: 15218

577. Alec 10:01 PM GMT del 14 Maggio 2006
I bet they were doing a bit more than just "hissing" when Wilma was threatening S FL...

578. Levi32 10:02 PM GMT del 14 Maggio 2006
Oh ok SJ sorry. That could be nasty if it was over tropical waters. Member Since: novembre 24, 2005 Posts: 586 Comments: 25450

579. turtlehurricane 10:03 PM GMT del 14 Maggio 2006
ya, they burrowed in deep. Member Since: Luglio 22, 2005 Posts: 227 Comments: 466

580. Alec 10:05 PM GMT del 14 Maggio 2006
lol turtle...I would have hated to hear they went out to sea!

581. StormJunkie 10:07 PM GMT del 14 Maggio 2006
Yea Levi, especially if it had looked as good as it did when it was over the lakes. Just can't help thinking about it with that well defined spin. Could that system, with a little different conditions, have pushed due south and in to the Gulf or SE and out ove the Gulf Stream SJ Member Since: Agosto 17, 2005 Posts: 26 Comments: 15218

582. Levi32 10:12 PM GMT del 14 Maggio 2006
Yep with that spin and look it had a couple days ago, it wouldn't have taken much time to turn warm core and then we would have been in trouble. Only I don't think there would be any way for it to get into the gulf in the middle of summer. Maybe the gulf stream but the trough would still have to dig pretty far south to get a system like that over water. Member Since: novembre 24, 2005 Posts: 586 Comments: 25450

583. Levi32 10:15 PM GMT del 14 Maggio 2006
Central Atlantic visible loop shows that our little wave approaching the Caribbean still has a little spinning feature associated with it. It could still be something to watch if it gets some convection going when it enters a low shear environment. I have to run for an hour or so. I'll be back then! Member Since: novembre 24, 2005 Posts: 586 Comments: 25450

584. ForecasterColby 10:21 PM GMT del 14 Maggio 2006
On IR/Visible imagery, Chanchu's eye looks small, but it's actually rather large. I'd estimate 11-12nmi from this image.

585. ForecasterColby 10:32 PM GMT del 14 Maggio 2006
Oooookay, that wasn't the image I was trying to post. More like 5-6nmi from that one.

586. tornadoty 10:51 PM GMT del 14 Maggio 2006
It's size and structure quite remind me of Hurricane Floyd.

587. hurricane23 10:52 PM GMT del 14 Maggio 2006
hey guys whats up iam new here! Member Since: Maggio 14, 2006 Posts: 8 Comments: 13276

588. RL3AO 10:54 PM GMT del 14 Maggio 2006
Hello hurricane23.

589. tornadoty 10:56 PM GMT del 14 Maggio 2006
I think that Chanchu will probably a) Start or be going through an ERC or b) Weakening due to dry air entrainment at landfall. I expect a 115kt landfall, but with an expanding windfield, much like Katrina, that could produce a massive storm surge that could devastate Hong Kong.

590. hurricane23 10:57 PM GMT del 14 Maggio 2006
hey guys iam trying to post but it wont let me. Member Since: Maggio 14, 2006 Posts: 8 Comments: 13276

592. RL3AO 11:03 PM GMT del 14 Maggio 2006
57 minutes until the start of the East Pacific Hurricane Season!

594. ForecasterColby 11:05 PM GMT del 14 Maggio 2006
I think Chanchu might be able to hold its eyewall. It certainly doesn't look too bad ATM.

595. RL3AO 11:05 PM GMT del 14 Maggio 2006
I'm not sure when the first TWO is issued.

596. hurricane23 11:07 PM GMT del 14 Maggio 2006
hey guys ive also been tracking this incredible typhoon on the pacific...here the forcast from hurricane alley! [url=http://img3.freeimagehosting.net/image.php?32bc7e064e.jpg][img]http://img3.freeimagehosting.net/uploads/th.32bc7e064e.jpg[/img][/url] Member Since: Maggio 14, 2006 Posts: 8 Comments: 13276

598. squeak 11:23 PM GMT del 14 Maggio 2006
Regarding the windfield, it has has been steadily expanding all day.

599. LemonAromatique 11:31 PM GMT del 14 Maggio 2006
Hmm. That is a rather interesting GFS for it. Yea, the weather channel is beginning to run some brief segments on it, which usually means they find it pretty significant (of course, it is).

600. turtlehurricane 11:35 PM GMT del 14 Maggio 2006
im looking at all the models now and theres a large cone of error from taiwan to hainan Member Since: Luglio 22, 2005 Posts: 227 Comments: 466

601. TampaSteve 11:44 PM GMT del 14 Maggio 2006
Chanchu will landfall as at least a solid Cat 4. Hong Kong better get ready!

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