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Ed DunhamAdministrator
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Initial Outlook for the 2011 Atlantic Season
      #90093 - Sun Nov 28 2010 10:48 AM

As the current season draws to a close, its time for a look ahead to the expected level of tropical storm and hurricane activity for 2011 in the Atlantic basin. La Nina is firmly in place in the eastern Pacific ENSO regions and it has the potential to remain in place throughout most of 2011. The biggest change from 2010 to 2011 is that SSTs in the eastern tropical Atlantic are expected to be cooler than normal during the 2011 hurricane season. The cooler sea surface temperatures will mean that the uncommonly high storm activity of 2010 will not continue into the 2011 season. The best analog years for 2011 seem to be 1989, 1974, 1999 and 1971 (in that order).

My initial 2011 outlook for the Atlantic basin is for 13 named storms with 7 hurricanes and 3 of those becoming major hurricanes - which would still be a slightly above average year. This thread will eventually transfer into the Storm Forum for next season, but feel free to add your own thoughts and numbers for the 2011 season. There will be plenty of time to adjust your seasonal totals before next June.

(Edit: Corrected Storm Total error and added 1971 as an additional analog year.)

Edited by Ed Dunham (Thu Dec 09 2010 07:10 PM)

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Re: Initial Outlook for the 2011 Atlantic Season [Re: Ed Dunham]
      #90095 - Tue Nov 30 2010 03:00 AM

Though nearly "burnt' out" from the busy year we are now concluding, I'll go ahead and stick out my ostrich neck out and guess that next year will start with an uncommon April or May T.S. Furthermore, will also speculate that Northern Gulf Coast regions will see a good deal more activity over all. Not really sure how E. Atlantic SST's will impact the overall season, but suffice it to say that assuming favorable conditions from about 60 degrees and westward exist, this could yield more undeveloped waves cross the Atlantic, only to potentially form "closer to home". This said, and with the addition of La Nina ( or at minimum waning Moderate La Nina ) conditions, I am a little more "bullish" in my early projection and will guess 2011 to have 15 named storms, of which 9 will reach hurricane intensity ( 3 of which will be major ).

Though next year could prove to have less overall intense storms, I am more concerned as to the overall number of storms that may ultimately impact the U.S. The other normal questions we can only speculate on. Such as what will the long wave pattern be or what may the upper air conditions be like. Finally, there is one other wild card that could end up impacting the later half of next years season. Will our strong La Nina simply fade to neutral conditions or possibly swing into an El Nino pattern?

Hmmm, so many questions. Fortunately for me, I'll soon have a number of 50 degree South Florida nights to help me kick back and ponder over it all. Nothin' like a good cigar and a glass of wine outside by the soft glow of the Chiminea's fire, to help come up with all the answers! Most of them likely wrong, but thats okay too.......

To those who actively post their thoughts and observations here, the site's administrators, and the many more who simply choose to "keep tabs" on developing events.....Best Wishes and may you all have a peaceful and safe holiday season.

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Ed DunhamAdministrator
Meteorologist & CFHC Forum Moderator

Reged: Sun
Posts: 2565
Loc: Melbourne, FL
Re: Initial Outlook for the 2011 Atlantic Season [Re: Ed Dunham]
      #90101 - Thu Dec 09 2010 10:25 PM

On Dec 6th, TSR issued its seasonal forecast for 2011: 16/8/4, and on Dec 8th CSU called for 17/9/5. Both lower than their forecast for 2010, but both still quiet high, i.e., they expect a very active Atlantic tropical cyclone season. One comment in the CSU forecast is rather significant: “At this point, we are uncertain whether La Niña conditions or neutral conditions are more likely for the 2011 hurricane season.” The latest (Dec 5th) NCEP ENSO outlook predicts that a moderate La Nina will persist through the 2011 Summer. There is a good chance that the current La Nina will persist through the entire 2011 year with the potential for a multi-year event extending into 2012 – and this is important from a climatological and seasonal forecasting standpoint.

First, some comments from a couple of 2007 posts (that have been updated to include recent seasons of high storm totals):

“About a month ago I did a little research from a slightly different angle. Since ENSO conditions are only available from 1950, I decided to check El Nino Region 3.4 anomalies against all of the very active seasons since 1950. I defined an active season as 14 named storms or more (there have been 13 of these) and ENSO neutral conditions as anything from +0.5C to -0.5C. I used the average sea surface temperature anomaly for the three month period of May, June and July (figuring that a three month lag was reasonable between Pacific ENSO conditions and Atlantic activity). The results coincide nicely with the findings of Ostro & Lyons.

1953...14 storms...+0.4 anomaly
1969...17 storms...+0.4 anomaly
1990...14 storms...+0.3 anomaly
1995...19 storms...+0.1 anomaly
1998...14 storms...+0.1 anomaly
2000...14 storms...-0.5 anomaly (weakening La Nina)*
2001...15 storms...+0.1 anomaly
2003...15 storms.....0.0 anomaly
2004...15 storms...+0.4 anomaly
2005...28 storms...+0.3 anomaly
2007...15 storms...-0.1 anomaly
2008...16 storms...-0.4 anomaly
2010...19 storms...-0.2 anomaly
*Note that since the original 2007 post, the 2000 MJJ SST anomaly has been adjusted by NCEP to -0.5 vice -0.6 .

Conclusion: Although the dataset is limited, it suggests that very active seasons occur under initially 'neutral' ENSO conditions. A strong La Nina doesn't really enhance activity, but a strong El Nino (1992, 1997, 2006) will limit activity. When the M/J/J average SST anomaly is +0.6 or greater, 92% of the time the season storm total will be 8 named storms or less. When that average is -0.6 or greater, 100% of the time the season storm total will be 13 named storms or less (and 83% of the time the season storm total will be 9 to 13 named storms, i.e., a slightly below normal to slightly above normal season. Note that a normal season, because of the increased activity since 1995, is now 11 named storms). A strong pre-season La Nina (anomaly of -1.2 or colder) has never resulted in a high activity storm season. Since 1950, all 13 previous high activity seasons have occurred under ENSO neutral pre-season conditions.”

Since 1950 there have been 12 seasons with a MJJ SST anomaly of -0.6 (or colder). Those 12 seasons (with storm totals and MJJ ENSO 3.4 anomalies) are as follows:

1950 13/11/8 -1.1
1954 11/8/2 -0.7
1955 12/9/6 -1.0
1956 8/4/2 -0.6
1964 12/6/6 -0.8
1971 13/6/1 -0.8
1973 8/4/1 -0.9
1974 11/4/2 -0.8
1975 9/6/3 -1.1
1985 11/7/3 -0.6
1988 12/5/3 -1.2
1999 12/8/5 -0.8

All of the above helps to illustrate why the CSU comment is significant. If the 2011 MJJ SST anomaly drops to a neutral ENSO state (-0.5 up to +0.5) then a high activity season is possible, but if its -0.6 (or colder) then a high activity season is not likely. At the moment I’m inclined to believe that 13 named storms is a realistic total for 2011 – but that’s just my viewpoint on next season.

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