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Azores #96L fails to complete transition into a Sub-Tropical Storm. Elsewhere, weak low pressure in Caribbean may linger into next week.
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General Discussion >> Hurricane Ask/Tell

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Ed DunhamAdministrator
Former Meteorologist & CFHC Forum Moderator (Ed Passed Away on May 14, 2017)


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La Nina Still Expected
      #74722 - Thu May 10 2007 08:43 AM

Just a note that the latest CPC 6-month SST Forecast was issued this morning - and it still anticipates a respectable La Nina from June through October and the prediction still cools the tropical Atlantic starting in August.
ED


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Ed DunhamAdministrator
Former Meteorologist & CFHC Forum Moderator (Ed Passed Away on May 14, 2017)


Reged: Sun
Posts: 2565
Loc: Melbourne, FL
Re: La Nina Still Expected [Re: Ed Dunham]
      #75505 - Mon Jun 11 2007 09:12 PM

Monthly update was issued today. Not much change from last month. Eastern Atlantic still expected to be on the cool side through September, followed by slightly warmer than normal in October and November. If this thing comes close to verifying it could make for a wierd Cape Verde season with some uncommon late season storms in that region. Here is the link:

6 Month SST Forecast

Cheers,
ED


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cieldumortModerator
Moderator


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Re: La Nina Still Expected [Re: Ed Dunham]
      #75510 - Mon Jun 11 2007 11:21 PM

If it plays out that way perhaps the states get off lucky and watch as the cape verde storms run into all kinds of pain before they ever get this far - that might be nifty, for a change of pace

Speaking of ENSO, if anyone hasn't already had a chance to read it, Stu Ostro & Dr. Lyons took a good look over the history of La Ninas as they related to any increase in hurricane activity, and in their estimation it wasn't necessarily the presence of the La Nina that was favorable for active Atlantic basin seasons, as much as it was just the lack of an El Nino. Stu Ostro blogged about it a while back if anyone wants to give it a read. (Link)


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LoisCane
Veteran Storm Chaser


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Re: La Nina Still Expected-stu ostro [Re: cieldumort]
      #75512 - Tue Jun 12 2007 08:32 AM

Thanks for the link to his blog.

Stu Ostro is a very good writer. He is very grounded, cautious, doesn't hype nor does he rush to conclusions.

I've read other things he wrote and they are also enjoyable to read and I learn a lot.

And, I think what he says is true.. it is not the strength of the La Nina as much as the lack of El Nino.

And, I would add La Nina perhaps plays a bigger part in the track tropical systems will take once they do form.

--------------------
http://hurricaneharbor.blogspot.com/


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Ed DunhamAdministrator
Former Meteorologist & CFHC Forum Moderator (Ed Passed Away on May 14, 2017)


Reged: Sun
Posts: 2565
Loc: Melbourne, FL
Re: La Nina Still Expected [Re: cieldumort]
      #75514 - Tue Jun 12 2007 10:07 AM

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 10 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...-0.6 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

Conclusion: Although the dataset is limited, it appears that very active seasons generally 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.
Cheers,
ED


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cieldumortModerator
Moderator


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Re: La Nina Still Expected [Re: Ed Dunham]
      #75515 - Tue Jun 12 2007 12:58 PM

Wow, Ed. Thanks for reposting that! While the dataset is limited, and other factors notwithstanding, the signal strikes me as crystal clear (active seasons, as reasonably defined, seem to -prefer- initially neutral ENSO conditions) as you conclude. I can't read that any other way.

I am curious as to some more of the finer points.. perhaps you could refer me to if you have them listed elsewhere, or could repost them here sometime?

Here are the other questions your review brings up:

How many of the initially neutral conditions also coincided with seasons that were:
about normal
below normal

and what then is the percentage of seasons with initially neutral conditions that were below, about, and above normal activity in the Atlantic?

Having gotten that far, were there possibly any other clues in any of the tea leaves that you were able to catch that may have offered an explanation as to why some of these initially neutral seasons went on to become which of the three final results?

Thanks


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Ed DunhamAdministrator
Former Meteorologist & CFHC Forum Moderator (Ed Passed Away on May 14, 2017)


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Posts: 2565
Loc: Melbourne, FL
Re: La Nina Still Expected [Re: cieldumort]
      #75558 - Fri Jun 15 2007 12:51 PM

I'll start with your last question first - there were really no other clues in the ENSO analysis of pre-season conditions that would indicate which way a season would ultimately go. Too many other variables influence the final result, e.g., windshear, dust and upper level lows (or the lack thereof). Of course post season analysis can be helpful with this - but that offers no help in determining the expected activity for a season (or even the next season). However, it can be of some help in the initial identification of analog years if you are able to make a reasonable expectation of what the ENSO conditions are likely to be during the season.

Definitions / Number of Events / Percentage:
ENSO Neutral: SST anomaly from -0.5 to +0.5 (33 seasons since 1950) 58%
Moderate El Nino: +0.6 to +0.9 (10 seasons) 18%
Strong El Nino: +1.0 or greater (2 seasons) 3%
Moderate La Nina: -0.6 to -0.9 (8 seasons) 14%
Strong La Nina: -1.0 or greater (4 seasons) 7%
Low activity: 8 named storms or less (20 seasons) 35%
Normal activity: 9 to 13 named storms (27 seasons) 47%
High activity: 14 named storms or more (10 seasons) 18%

The Region 3.4 SST pre-season aggregate average anomaly period: May/June/July. The strongest El Nino pre-season average anomaly for this period was +1.4 in 1997. The strongest La Nina pre-season average anomaly for this period was -1.2 in 1950 and 1988.

Neutral pre-season anomaly vs season totals:
7 low activity seasons / 21% of all Neutral seasons
17 normal activity seasons / 52%
9 high activity seasons / 27%

Moderate pre-season El Nino vs season totals:
9 low activity seasons / 90%
1 normal activity season / 10%
no high activity seasons

Strong pre-season El Nino vs season totals:
2 low activity seasons / 100%
no normal or high activity seasons

Moderate pre-season La Nina vs season totals:
2 low activity seasons / 25%
5 normal activity seasons / 63%
1 high activity season / 12%

Strong pre-season La Nina vs season totals:
no low activity seasons
4 normal activity seasons / 100%
no high activity seasons

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, 92% of the time the season storm total will be 13 named storms or less (and 75% of the time the season storm total will be 9 to 13 named storms, i.e., a 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 has never resulted in a high activity storm season. Ninety percent of high activity seasons occur under ENSO neutral pre-season conditions.

The M/J/J SST anomaly for this year will probably be around -0.5 - but if it comes in at -0.6, a lot of high pre-season storm total predictions are in trouble.

ADDED: Current and anticipated ENSO conditions for a moderate La Nina along with similar upper air patterns suggest that 1964 might be the best analog for this season. The 1964 season had 12 named storms and 6 hurricanes - and quite interesting that all of the hurricanes that season were major ones.
Cheers,
ED

Edited by Ed Dunham (Sat Jun 16 2007 12:32 AM)


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ClarkModerator
Meteorologist


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Re: La Nina Still Expected [Re: Ed Dunham]
      #75574 - Sun Jun 17 2007 09:24 PM

Quote:

ADDED: Current and anticipated ENSO conditions for a moderate La Nina along with similar upper air patterns suggest that 1964 might be the best analog for this season. The 1964 season had 12 named storms and 6 hurricanes - and quite interesting that all of the hurricanes that season were major ones.
Cheers,
ED




I've also heard that 1964 analog from another source or two, making it a tad more intriguing. For the most part, 1964 was a Florida/recurve year with about equal frequencies of both. One major storm, Hilda, impacted the central Louisiana coast, but Isbell, Dora, and Cleo were all significant Florida impacts.

As an aside...the first storm in 1964 was a lot like Barry this year -- weak, first week of the season storms that impacted the upper west Florida coastline. Not that it means anything, of course, but an interesting coincidence.

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Current Tropical Model Output Plots
(or view them on the main page for any active Atlantic storms!)


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Hurricane29
Weather Guru


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Posts: 148
Loc: Miami Florida 25.77N 80.25W
Re: La Nina Still Expected [Re: Clark]
      #75575 - Mon Jun 18 2007 02:22 PM

The tune has changed with CPC as there now predicting Neutral conditions across the atlantic basin for the next 3 months.

june 18th CPC update in PDF fromat

I think this is significant news!


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HURRICANELONNY
Weather Guru


Reged: Sat
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Loc: HOLLYWOOD,FL.
Re: THE BRITS [Re: Ed Dunham]
      #75595 - Fri Jun 22 2007 07:43 AM

I heard something yesterday on the weather channel that the brits and I don't know what research team it is,said the Atlantic will be below normal this season. Anyone know where this site might be?

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