Sunday, April 19, 2015

My First Thoughts On The 2015 Atlantic Basin Hurricane Season.

When I did my winter and the spring/summer outlooks..... I came up with two seasons that matched up well to the 1977-1978 and  2004-2005 that matched up well with the current pattern, Sea surface temperatures (SST).

But several seasons involved the late 1950's into the early 60's.  Those years saw several hits along the Gulf and Southeast Coast.

The Modoki El Nino and the AMO had a huge role in how Winter 2014-2015 and the spring so far have behaved.  And they will play a huge role in this year's tropical season.

The blue (cold) south of Greenland and North of Spain, in the northern and central Atlantic. The warmer yellow/orange shade coming out of the Gulf and Caribbean, and then the Blue (colder) in the southern Atlantic west of Africa.... is the signature of a negative (cold) AMO. During the cool phases of the AMO, the number of tropical storms that mature into severe hurricanes is less than during the warm phases. . During cool phases of the AMO, the numbers of tropical storms that mature into severe hurricanes is less than during warm phases. This is because, when the tropical waves move off the western African Coast, the cool waters interfere with tropical cyclone development. 

If you read my 2015 spring/summer outlook; you know 1977-1978, 1997-1998 and 2004-2005  matched up the closest of my Analog years, with  1977-1978  being an almost exact match.
Both of these analog seasons were Modoki El Nino years. The  past winter and the winter of 1977-1978, behaved very similarity. One of the main reasons is the  Modoki El Nino.  El Nino is a warming of  Sea Surface Temperatures (SST) in the eastern Pacific, where as Modoki El Nino is a warming of the central Pacific. This little difference might not seem like much....but it can make a big difference for weather in the Mid Atlantic and Northeast.  When one goes back to study past years, you see a pattern.  On average the Northeast and Mid Atlantic during Modoki El Nino tend to be colder and wetter than during their El Nino cousin.  There is no doubt that this past winter was cold and snowy. Another  Modoki El Nino  year was 2010, which was a very snowy year.

But as is the case with all weather events, no two El Nino Southern Oscillations (ENSO) are quite the same.

When it comes to tropical activity 1977 -1978, 1997-1998, and 2004-2005 were quite interesting....especially in this fact..... 1977 - 1978, and  were at the lower end of the of the scale when it came to activity, and 2004 and 2005 where at the very top. So clearly there is something else going on.

When trying to get a handle on the tropical season in the Atlantic; one thing Myself and many others look at is a thing called Accumulated cyclone energy (ACE).

ACE is used to  express the activity and destructive potential of  not only individual tropical cyclones, but also for  entire tropical cyclone seasons. ACE is calculated as the square of the wind speed every 6 hours, and is then scaled by a factor of 10,000 for usability. The ACE of a season is the sum of the ACE for each storm and takes into account the number, strength, and duration of all the tropical storms in the season. The random variation of ACE is determined by two sources: the random variation of the number of tropical cyclones and the random variation in the ACE for individual tropical cyclones. There is a large variation in the total ACE from year to year. As you can see ACE is a very complicated subject.

How do the ACE analog years stack up?

 1978 had a ACE value of  62.

The 1978 season had 24 tropical cyclones that developed, twelve tropical storms, five hurricanes two of them major.

1977 had an ACE value of 25  

The 1977 season had six tropical cyclones that developed, five tropical storms, five hurricanes one of them major.

The 1997 season had 8 total that developed, 3 hurricanes, 1 major. That year saw all the activity in the western Atlantic, Caribbean, and Gulf.  

1997 ACE value of 41
1957 and 1958 were two other analog years that did well in the matchup.

1957 ACE value of 84

The 1957 season had 8 tropical storms, 3 hurricanes, which two became major.

1958 ACE value of 121 ACE value of 225
Ten tropical cyclones, seven of full hurricane intensity, five reached major hurricane status, Including Category 5 hurricane Cleo. 

2004  ACE value of 225

The 2004 Atlantic hurricane season Total storms 15, Hurricanes 9, Major hurricanes 6

2005 ACE value of 250
The 2005 Atlantic hurricane season was the most active Atlantic hurricane season in recorded history.


My thoughts so far for this year's Atlantic tropical season.

This year the ACE is looking to be in the 50-60 range. But the final calculation hasn't been done yet. So this could change.

I've already gone over the ENSO. But, normally, El Nino results in diminished hurricanes in the Atlantic. But when an El Nino Modoki forms in the Central Pacific, rather than the Eastern Pacific as the typical El Nino event does. There is on average there is  a higher storm frequency and a greater potential for making landfall along the coast of Central America, Gulf coast and the Southeast U.S.

I said in my long range outlook that I felt the current El Nino Modoki, will strengthen and become an eastern based EL Nino later this year.. Most likely at least moderate to quite possibly strong ..then weaken as we head into fall and winter.

If I'm right, this summer into Fall would see more  El Nino like conditions in the tropical Atlantic. Those being increased upper-level winds over the tropical Atlantic creating hostile wind shear. As well as dry and dusty air in the eastern Atlantic.  But then we would see some late season tropical activity.

On the SST chart you can see how the AMO and the  has the Gulf of Mexico  very warm right now.  The Modoki El Nino will also increase the odds for Gulf, western Caribbean, and along the Southeast coast tropical activity.

Here are the tropical weather charts for 1977-1978,2004-2005, and 1957-1958. You can see there is more  tropical cyclone activity in the Gulf and Caribbean, than in the tropical Atlantic.  With tropical systems having a better shot closer to the US Mainland....the odds of land-falling systems does increase a little.



While the Gulf Coast, Florida, up to South Carolina is at a higher risk....... we can't rule out possible problems from tropical systems in the Mid Atlantic and Northeast.  I also can't rule out an early season storm in the Gulf, due to the very warm SSTs..

Right now, I thinking a below average tropical season, with the total number of Named Atlantic Basin storms 8-10 , Hurricanes 3-5, of which 1-2 will be major.  I also think two maybe three systems will make a landfall on the U.S.

Well I've explained some of the climatology that I put into my tropical outlooks...... I will post a final tropical outlook in the 20-27 May time frame.

If you want to look at some of the data I used..... 

ACE Data. 
Modoki El Nino Weekly.

Modoki El Nino Monthly.

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