TreeFrog
12-01-2007, 10:22 AM
This is from yesterday, full text still on www.wunderground.com/tropical as this is posted.
Why did the pre-season hurricane forecasts do so poorly?
In June, forecasters gave several reasons to expect a very active season in 2007:
1) A continuation of conditions since 1995 that have put us in an active hurricane period (in particular, the fact that sea surface temperatures in the Atlantic Main Development Region for hurricanes were about 0.6° C above normal.
2) The strong likelihood of either neutral or La Nina conditions in the tropical Pacific Ocean, leading to average to below average wind shear conditions.
Well, La Nina conditions did develop, and wind shear gradually declined during the season. Wind shear was slightly above average in August, near average in September, and below average in October over the main development region for hurricane formation. However, sea surface temperatures declined to near average levels by July and August, thanks to a major incursion of African dust. According to the excellent write up of this hurricane season's activity posted by Phil Klotzbach and Bill Gray, 2007 was the dustiest year over the tropical Atlantic since 1999. All this dust acted to block sunlight from reaching the ocean surface, and sea surface temperatures were not able to maintain their above average state. We don't have the ability to predict major dust outbreaks from Africa more than a few days in advance, and this inability will continue to confound efforts at seasonal hurricane prediction for years to come.
So last year wind shear was our friend. This year's honors go to African dust. Either way, it works for us.
Why did the pre-season hurricane forecasts do so poorly?
In June, forecasters gave several reasons to expect a very active season in 2007:
1) A continuation of conditions since 1995 that have put us in an active hurricane period (in particular, the fact that sea surface temperatures in the Atlantic Main Development Region for hurricanes were about 0.6° C above normal.
2) The strong likelihood of either neutral or La Nina conditions in the tropical Pacific Ocean, leading to average to below average wind shear conditions.
Well, La Nina conditions did develop, and wind shear gradually declined during the season. Wind shear was slightly above average in August, near average in September, and below average in October over the main development region for hurricane formation. However, sea surface temperatures declined to near average levels by July and August, thanks to a major incursion of African dust. According to the excellent write up of this hurricane season's activity posted by Phil Klotzbach and Bill Gray, 2007 was the dustiest year over the tropical Atlantic since 1999. All this dust acted to block sunlight from reaching the ocean surface, and sea surface temperatures were not able to maintain their above average state. We don't have the ability to predict major dust outbreaks from Africa more than a few days in advance, and this inability will continue to confound efforts at seasonal hurricane prediction for years to come.
So last year wind shear was our friend. This year's honors go to African dust. Either way, it works for us.