Ed Dunham
Former Meteorologist & CFHC Forum Moderator (Ed Passed Away on May 14, 2017)
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Posts: 2565
Loc: Melbourne, FL
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Initial Outlook for the 2008 Season
Sun Jan 13 2008 01:11 PM
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It is time once again to take a look at expectations for tropical cyclone activity in the Atlantic basin for 2008. I'll start with an excerpt from an article in the CFHC Hurricane Ask/Tell Forum that I posted last year:
"Definitions / Number of Events / Percentage:
ENSO Neutral: SST anomaly from -0.5C to +0.5C (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 +1.4C in 1997. The strongest La Nina pre-season average anomaly for this period was -1.2C in 1950 and 1988 (under a revised tabulation method, NCEP now records 1988 as -1.3C for M/J/J).
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 +0.6C or greater, 92% of the time the season storm total will be 8 named storms or less. When that average is -0.6C 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. Added: Since the start of the satellite era, the past 43 seasons in the Atlantic basin have averaged 11 named storms of which 6 became hurricanes and 2 of those became major hurricanes with sustained winds of at least 111mph.) 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 latest NCEP 6-Month SST Forecast calls for the strong La Nina currently in place in the eastern Pacific to continue (although weakening) through the aggregate pre-season anomaly period of May/June/July with an anticipated value of about -1.0C. The forecast indicates slightly above normal SST anomalies for the Gulf of Mexico and for the area off the west coast of Africa with slightly below normal sea surface temperature anomalies for the central tropical North Atlantic ocean.
Based on ENSO Climatology, the best analog years (in priority order), with the storm totals for those years, seem to be 1971 (13/6/1), 1985 (11/7/3), 1950 (13/11/8), 1974 (11/4/2) and 1999 (12/8/5). These years were selected because they had a strong winter La Nina (generally declining or holding steady) often with an El Nino in the previous year and a pre-season SST anomaly of at least -0.6C. From the tables above, there were 12 years with either a moderate or strong pre-season La Nina and only once did these early season conditions produce a high activity season of 14 or more named storms.
The initial outlook from CSU is for 13/7/3 and from TSR its 15/8/4. If the SST anomalies hold as forecast (or are at least close to what actually happens), my initial outlook is for 12 named storms of which 7 will be hurricanes and 3 of these will be major hurricanes. Confidence level for this forecast is high.
Major threat areas for the United States based on the analog years would suggest the Gulf coast from Louisiana to Florida, and the east coast areas of Florida, eastern North Carolina and southern New England. With regard to timeframe, I anticipate a normal season with 3 storms in August, 5 storms in September and 4 storms in October. Probably a good number of Cape Verde tropical waves during the season, but with the prospect of a cooler than normal central Atlantic, I suspect that many of them will not develop much until they travel west of 55W Longitude.
Now its your turn. If you wish, post your own totals for the upcoming season in this thread. Rationale is not required, although your thoughts are always welcomed. We'll summarize at the end of the year and see how close we came to the actuals.
Cheers,
ED
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Initial Outlook for the 2008 Season
