A Peek into Hurricane Season

By: Levi32 , 9:08 PM GMT on February 11, 2007

Hurricane Season 2007 is rapidly approaching, and there are many things to keep track of when trying to forecast how active a season we are to have in the Atlantic. Probably the most important variable to consider is the ENSO (El Nino Southern Oscillation).

What is El Nino?

El Nino is a reversal of the normal trade wind flow over the equatorial Pacific. When conditions are normal, trade winds flow from east to west. This usually sets up high pressure over northwestern South America, and low pressure in the western Pacific near Australia. A normal rainfall pattern with moist in Australia and dry in the eastern Pacific and South America is the result.

However when El Nino pops up, those trade winds can be reversed or greatly slowed down. The flow is then from west to east, which sets up the low pressure over NW South America and the high pressure over Australia. This is the total opposite of normal conditions. If El Nino sticks around for several months, Australia experiences severe droughts, and NW South America experiences heavy tropical rains. SSTs in the eastern equatorial Pacific are warmer than normal because no upwelling is occurring due to the reversed trade winds. Upwelling is brining up colder water from the deeper ocean to the surface. When the trade winds are from the east like normal, they "push" the ocean water westward from the coast of South America. As the warm surface water is pushed westward, the cold water from deep down moves up to replace it in response. But when the trade winds are reversed, upwelling is shut down, and the SSTs near the South American coast are warmed greatly. Warming of the SSTs near the equator is one of the first signs of an El nino, and is an easy signature to recognize on an SST anomaly map. El Nino is also known to cause global weather pattern changes which can be very severe. Where I live in Alaska, El Nino causes winters to be extremely mild and rainy, and summers to be very hot and dry. The affects are different for different parts of the world.

El Nino also has a large impact on the Atlantic and eastern Pacific Hurricane seasons. Warming of the SSTs in the eastern equatorial Pacific tends to be counter-acted by a cooling of the SSTs in the Gulf of Mexico, the Caribbean, and the western Atlantic. It also tends to increase wind shear. This lowers the average intensity and number of hurricanes. A classic example is last year, when even a weak El Nino greatly reduced the number and strength of hurricanes. The affects of El Nino can reduce the number of U.S. hurricane landfalls as well. When low pressure sets up over NW South America, high pressure sets up over the Caribbean, which directs tropical waves south and west over South America. These waves then pop out on the other side in the eastern Pacific, where they have a much better chance to develop. This results in a much more active eastern Pacific hurricane season. Therefore El Nino decreases hurricane activity in the Atlantic, and increases activity in the eastern Pacific.

La Nina is the opposite of El Nino, and is simply an intensification of normal conditions. Easterly trade winds are stronger, which causes more upwelling of colder deeper water in the eastern equatorial Pacific. SSTs are colder than normal, which is the signature of a La Nina on an SST anomaly map. Rainfall in Australia is increased, and NW South America experiences very dry conditions. La Nina, like El Nino, also has major impacts on weather patterns across the globe, though usually the opposite of El Nino. Likewise the affects on the eastern Pacific and Atlantic hurricane seasons are opposite. Strong high pressure builds in the eastern equatorial Pacific, which results in low pressure over the Caribbean. Tropical waves in the Atlantic are steered northwest towards the U.S. and Mexican coasts, increasing the number of storm landfalls. The cooling of the SSTs in the equatorial Pacific also tends to warm the SSTs in the western Atlantic. Wind shear is also decreased. This results in a more active Atlantic hurricane season. On the other end the eastern Pacific sees very little tropical activity, as SSTs are lowered and few tropical waves make it across into the pacific basin.

Current Conditions:

Right now there are strong signs that El Nino is weakening, and we are currently on our way into a neutral phase of the ENSO. I believe that a La Nina is possible by the time hurricane season starts. Evidence of this is shown in these two charts:



In the top image you can see the cold water bulging upward towards the surface. This is further shown in the bottom anomaly image by a large cold area near 125w at 100 meters. This spot has been migrating towards the surface over the last month or so. If this were to surface the SST anomalies would go down dramatically.

Model analogs
have been showing many La Nina years and very few El Nino years lately. This could also be evidence of a developing La Nina. Also this January was very warm in the eastern U.S., unlike the cool fall season. This is also evidence of a weakening El Nino. Further more, if this pattern continues to develop, a ridge in the east would mean more hurricane landfalls in the U.S. this season.

MJO (Madden-Julian Oscillation)

Not much is known about this fascinating oscillation, but there is a lot being learned about it all the time. What it is basically, is a fluctuation of upward motion, convection, and precipitation near the equator all around the globe. Areas of more or less convection migrate west to east across the tropics, and can enhance or decrease tropical development. A chart of the MJO phase over the last 90 days can be found here. Each phase is a different part of the world, and this chart shows which phase the MJO is in right now, where it has been over the past 3 months, and its strength. For example right now the MJO isn't very strong, but it appears to be in phase 6. This means that you can probably find above normal convection in the Western Pacific. Eventually this convection will move eastward. A good site for monitoring the MJO is here. The MJO won't become very useful until hurricane season is actually in progress, but we can still draw patterns from it in correlation with the upper air patterns and El Nino.



The above image shows the vertical velocity anomalies at 200mb for the world. Areas under green lines have above normal convection or convection potential. Areas under brown lines have below normal convection. When the MJO is pronounced (right now it is very weak), you can see a main area of convection which migrates west to east with time. This becomes very important during hurricane season because when that area moves over the Atlantic chances for hurricane development are greatly increased.

Models:

Global models are forecasting above normal precipitation in the ITCZ over the Atlantic this summer, along with very dry conditions over the eastern equatorial Pacific. The dry Pacific indicates La Nina, and the wet ITCZ obviously points to more TC formations.



This is the average forecast of the 6 models. The same models are forecasting at least a small La Nina during the summer.





The first image is the average of the 6 models, where you can see a weak La Nina is forecast. The second image is an individual model which is forecasting a very strong La Nina to develop. Other models are also forecasting the same thing, along with above normal heights over the western Atlantic, indicating a more western position of the Bermuda High.

Right now I see a more active year than last year shaping up, with a La Nina instead of El Nino. The big key this year will be where the Bermuda High sets up. Right now global models are showing a chance that it will set up pretty far west close the eastern seaboard, which wouldn't be good news. If that does happen there will be a corridor leading every storm towards the US. The SSTs in the Caribbean and off the eastern Seaboard should also be warmer this year than they were last season. In short: Be ready for a ride!



We shall see what happens!

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Reader Comments

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123. Levi32
3:26 PM GMT on February 21, 2007
Yes ma'am! Lol ok I will try to convince my parents to let me take pictures, but no guarantees here! lol. Thanks you have a great Wednesday as well.
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121. OGal
3:20 PM GMT on February 21, 2007
Ok Levi, you chore for the year is to get a digital camera and start taking pictures of Homer, the Spit, and the beautiful surrounding area. You are in the perfect place to share God's beauty with all of us. Go down to Land's End and take those gorgeous mountains. This is an order! Have a terrific Wednesday.
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120. Levi32
3:13 PM GMT on February 21, 2007
Thanks Red you too!
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119. Redhead
4:00 AM GMT on February 20, 2007

Mardi Gras Images @ Bopmyspace.com
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118. Levi32
3:40 PM GMT on February 19, 2007
The track map shows a nice gradual curve I'm not sure what's weird about that.



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117. Thunderstorm2
3:37 PM GMT on February 19, 2007
TC Favio looped around Madagascar without making landfall on the island. I think thats weird what about you?
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116. Levi32
3:21 PM GMT on February 19, 2007
TC Favio is now at hurricane strength. It's forecast track now takes it towards a landfall in Mozambique, Africa. Now I have little to no experience with the tropical cyclones of the southern hemisphere, so I have no idea when the last time was that a TC hit southeastern Africa. Seems like a fairly rare occurance to me, but I could be wrong.

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115. Tazmanian
1:33 AM GMT on February 15, 2007
yes time will tell
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114. Levi32
1:29 AM GMT on February 15, 2007
Hi David. Time will tell, hopefully it won't be bad.
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113. Tazmanian
1:29 AM GMT on February 15, 2007
hello i see its not looking good this year
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112. Levi32
1:27 AM GMT on February 15, 2007
Thank you C'lady! Happy Valentine's Day to you too!

Kris he really sent that? Holy cow that's disgusting lol.
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111. Tazmanian
1:20 AM GMT on February 15, 2007
hello STL and evere one
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110. weatherboykris
1:14 AM GMT on February 15, 2007
disgusting.I can't believe STL would send that.
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109. weatherboykris
1:14 AM GMT on February 15, 2007
It's literally crap in a hot dog bun.
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108. weatherboykris
1:13 AM GMT on February 15, 2007
I've seen what STL sent him before.
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107. charlestonlady
1:13 AM GMT on February 15, 2007
interupting the weather levi to say happy valenitnes day!
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106. Levi32
1:07 AM GMT on February 15, 2007
LOL Michael did you really send him stuff as bad as he said? "vulgar language" and pictures as disgusting as he described? lol
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105. Levi32
1:07 AM GMT on February 15, 2007
Nice little CDO forming with 14S.

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104. weatherboykris
10:45 PM GMT on February 14, 2007
check out their timer to their forecast.
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103. Tazmanian
10:45 PM GMT on February 14, 2007
run for your lives run for the hills
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101. Tazmanian
10:38 PM GMT on February 14, 2007
this look like i may be makeing up my lost time from last year not wishing a hurricane on any one but i this love to see TWC and cnn out in them i love recding hirrcanes when they make land fall
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100. Tazmanian
10:36 PM GMT on February 14, 2007
the Bermuda High sets up. Right now global models are showing a chance that it will set up pretty far west close the eastern seaboard, which wouldn't be good news. If that does happen there will be a corridor leading every storm towards the US. The SSTs in the Caribbean and off the eastern Seaboard should also be warmer this year than they were last season. In short: Be ready for a ride!



un oh the Bermuda High more W this year and all most evere hurricane will hit the usa
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99. 1900hurricane
10:32 PM GMT on February 14, 2007
... you could see the cloud tops and the lightening - a good 100 miles or so away from us but just amazingly brilliant...

A similar event has happened to me almost two years ago. My family was driving from Houston to Austin when we ran into a very intense squall line about half-way there. There was hail almost 3 inches in diameter and tons of lightning. However, because we were moving at each other and the squall line wasn't very thick, we passed through very fast. Even when we arrived at our destination, the tops of the T-storms and flashes of lightning were still visible. It was awesome.
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98. Levi32
10:25 PM GMT on February 14, 2007
Yeah those storms popped up out of no where and intensified very quickly. Montgomery was lucky not to see a tornado. The storm that passed over them had already spawned several twisters before it hit. That's neat that you got to see them from a distance in a setting like that. It must have been so beautiful.

I have to go now our dog needs to be played with and there's wood to be chopped. Nice talking with you! Have a great day :)
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97. ryang
10:23 PM GMT on February 14, 2007
Thanks Levi.
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95. Levi32
10:21 PM GMT on February 14, 2007
Even after it was over nobody could get a word out of him about the event until I came along and forced him to spill it lol.
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94. Levi32
10:19 PM GMT on February 14, 2007
Saddle - As I said, you saved his neck lol! I tried to warn him, but he was only listening to you so he didn't even see me lol. Apparently no tornadoes touched down in his area. He said a big oak and some dead pine were down across some roads along with a few power lines but he said that's all he saw, so I guess everything's pretty much ok where he is thankfully.
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92. Levi32
10:17 PM GMT on February 14, 2007
Ryan, read up a few comments and you'll see what saddle said. Pat was out there helping to find people after Katrina hit.
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91. Levi32
10:16 PM GMT on February 14, 2007
Yeah the tropics are never quiet are they.
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90. Levi32
10:15 PM GMT on February 14, 2007
After all saddle wasn't it you who saved Auburn's neck when you told him about the tornado coming to his house? LOL
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89. ryang
10:15 PM GMT on February 14, 2007
Yeah goodwatt,you're very lucky Patrap 'ain't here.


Why?
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88. Levi32
10:14 PM GMT on February 14, 2007
Oh saddle give yourself some credit you were there with all the rest of the "village", and contributed just as much as anyone else. We greatly appreciated you being there :)

Thanks so much!
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87. weatherboykris
10:14 PM GMT on February 14, 2007
Yeah goodwatt,you're very lucky Patrap 'ain't here.
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85. Levi32
10:12 PM GMT on February 14, 2007
By the way, tropical cyclone 14S is taking shape, and could pass close to some French islands southeast of Madagascar in a few days.

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83. Levi32
10:08 PM GMT on February 14, 2007
Thank you saddle! You did an equally fantastic job yesterday.
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80. Levi32
10:02 PM GMT on February 14, 2007
Goodwatt, I for one can't believe MichaelSTL would send you that sort of stuff. Now you have a right to believe what you want to, but think about this for a moment. Go to New Orleans yourself and see the destruction. Go to any part of southern Louisiana and Mississippi and tell me what you see. It's bad man it's really bad and it's not deniable. And the government of the United States of America wouldn't deliberately destroy property and KILL people! It's the worst thought I can think of, and you should be ashamed to suggest that our government would do that. Those people suffered and died down there because of a bad storm. It's unthinkable that you could deny what happened. Many people lost loved ones and property that they can't bring back. Do you really think all of that could have been a fake? You may think that I can't prove that Katrina was not fabricated, but neither can you prove at all that you're right either. There's a ton of evidence on our side and NONE on yours, so please stop talking about this it makes me sick and you shouldn't be posting stuff like this here. I'm asking you to please stop posting this in my blog.
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78. Goodwatt
9:56 PM GMT on February 14, 2007
Levi32,

no doubt there was a hurricane but was it as bad as they reported it to be? maybe the event was a fabrication gone wrong resulting in many people suffering. that is even worse. except for the media which loves disasters that grow worse. some people still think the landings on the moon are hoaxed. who is to say they are wrong? you would have to fly to the moon to see the junk they left behind to believe it. i think we did land on the moon, but i also think some people tried to worsen the events during Katrina and it went far worse. i am sorry if you disagree but i think thats what happened. maybe you can be mature like MichaelSTL and call me names with pictures of feces on bread in an Email like he did. ill gladly Email anyone the disgusting pictures and vulgar messages MichaelSTL sent me.
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77. Levi32
9:44 PM GMT on February 14, 2007
Hey guys I'm back. I see you had a little run in with that "nut" lol. I'll straighten him out.

Thanks OGal and Aqua! Happy Valentine's Day to both of you!

Goodwatt - You do have a right to your own opinion, however what you are proposing is absolutely ridiculous. It's like saying our president isn't really president but just a puppet of the real president in hiding. If you're so stubborn to argue this issue, then I'll lay it out for you:

If all of what you're saying is true, then the government, FEMA, the Red Cross, all the media outlets, all the local networks across the nation would all have to be lying. All the residents that lived in New Orleans would also have to be lying about what happened. That's hundreds of thousands of people we're talking about that would have to lie about this to keep it secret. Also like Michael said those satellite images clearly indicate a major hurricane at landfall. And if you would go as far as to say that those images were also fabricated, then that means the National Hurricane Center, the hurricane hunters, and every weather service from every country in the WORLD would have to lie about this and be part of the conspiracy. That's because the Navy aren't the only ones broadcasting satellite images of Katrina. Many many different places and people work with satellite images from GOES-10 and GOES-12. They'd all have to be part of this conspiracy. Think about it Goodwatt, it's absolutely ridiculous to think that all these people and companies and governments would all be lying about a stupid hurricane. It's unthinkable!

Now I'm going to have to ask you to stop posting this stuff in my blog and getting us worked up over you and your ideas. If anyone is responsible for planting these lies into your head then shame on that person for doing it.

Now that my rant is over we can move on lol.
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76. weatherboykris
8:15 PM GMT on February 14, 2007
hi Skye
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75. Skyepony (Mod)
8:13 PM GMT on February 14, 2007
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74. aquak9
7:33 PM GMT on February 14, 2007
Excellent blog as usual, Levi. I'm really happy to see you back here with us again. I hope you'll be able to be here for Season™, as your input is not only highly regarded, but written in such a way that even I can understand it. Thank you.
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73. weatherboykris
7:19 PM GMT on February 14, 2007

Oh come on goodwatt.If the Navy was doctoring images of the storm,they could've done it better than that.
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About Levi32

Masters student in tropical meteorology at FSU. Raised in Alaskan blizzards, but drawn toward tropical cyclones by their superior PGF.

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