NOAA Hurricane Outlook to be Revised Lower?
UPDATE, 11:45 a.m.: The Colorado State tropical prediction experts lowered their outlook for this season's Atlantic tropical activity for the third time according to a report released this morning. They are now calling for 10 named storms down from 11 in their June outlook, 12 in their April outlook, and 14 in their December outlook.
In May, the National Oceanic and Atmospheric Administration issued its 2009 Atlantic Hurricane Season Outlook which called for a 50% chance of a near-normal season with nine to 14 named storms and four to seven hurricanes. The outlook also indicates a 25% chance of an above-normal season and a 25% chance of a below-normal season. A revised outlook, scheduled for release on August 6, will likely shift the odds towards the below normal category, largely due to the influence of El Niño.
So what's the big deal?? I'll get to that, but first....
It is well-known that that El Niño tends to reduce hurricane activity in the Atlantic Basin (here) due to increased vertical wind shear (stronger winds aloft than near the surface) that can tear apart a developing storm. At the time of the May outlook, there was considerable uncertainty regarding the possible development of El Niño. By July, however, it became clear that El Niño had arrived and is expected to continue developing during the next several months, with further strengthening possible.
As reported by the Miami Herald, Gerry Bell, NOAA's lead seasonal hurricane forecaster, wouldn't say how or if El Niño might change NOAA's updated outlook. "El Niño isn't the only factor in the game," he said.
However, the Director of NOAA's Office of Atmospheric Research, Dr. Richard Spinrad, testified at a hearing of the Senate Commerce Committee (here, about 68 minutes into video) that the revised outlook "will accommodate the consequences of what is clearly now an El Niño signal". This testimony was in response to a question asking Dr. Spinrad what he sees for the balance of the hurricane season given the tendency for El Niño to suppress hurricane activity.
So what is the big deal?? Does this mean it will be a relatively benign hurricane season?? Hardly!! Dr. Spinrad added - rightly so - that the relationship between El Niño and Atlantic hurricane activity is only statistical in nature. Over many, many years on average hurricane activity tends to be less during El Niño years, but this most certainly does not guarantee that any given year will be relatively inactive. And, even if were less active than normal when El Niño conditions existed, all it takes is one major hurricane to wreak havoc, as was the case with Hurricane Andrew in 1992.
Finally, we should not become complacent this year given there have been no named storms to date. On average, the most active part of the hurricane season is between the beginning of August and end of October. Andrew, the first storm of 1992 ("A" storm) did not achieve named status until August 17. The latest first storm on record was Hurricane Arlene in 1967 which did not appear on the scene until August 28th. It was followed by an additional seven named storms that year.
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