So what happened to the 2007 hurricane season?

Lots of experts are weighing in as the Atlantic hurricane season comes to an end (today). One of my favs, Jeff Masters, summarizes it this way:

The Atlantic hurricane season of 2007 is over, and it was a strange one. For the second straight year, we had a near average season, despite pre-season predictions of a very active season.


Before going further, I should point out that hurricane forecasting experts tend to be on the wild side. The dean of forecasters, Bill Gray, has become a cranky global warming denier — you can read his detailed explanation of the 2007 season here. Masters, on the other hand, flew into hurricanes, of his own free will, for four years (!), sans parachutes (!!), until he was nearly killed flying into Hurricane Hugo, in “the most harrowing flight ever conducted by the NOAA hurricane hunters”.

On the more normal side, Chris Mooney, science writer and author of a good recent book on hurricanes and global warming, has his post mortem here.

Now the 2007 season did set a lot of records, as Masters notes:

1) Hurricane Felix set the Atlantic record for fastest intensification from the first advisory to a Category 5 hurricane. It took Felix just 54 hours to accomplish the feat.

2) Hurricane Humberto set the Atlantic record for fastest intensification from first advisory issued to hurricane strength–18 hours. (Actually, Humberto did the feat in 14 1/4 hours, but this will get rounded off to 18 hours in the final data base, which stores points every six hours). There have been six storms that accomplished the feat in 24 hours.

3) Hurricane Lorenzo tied the Atlantic record for fastest intensification from a tropical depression to a Category 1 hurricane–twelve hours.

4) With the occurrence of Dean and Felix, there have now been eight Category 5 storms in the past five years–the highest total ever observed over such a short time span.

5) Dean and Felix both made landfall at Category 5 strength, the first time two storms have done that in a single year.

But why were the pre-season forecasts so wrong? Masters explains:

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.

The 2007 hurricane season provides no evidence against the theory of human-caused global warming. As we return to normal dust years, expect above-normal hurricane seasons to return.

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10 Responses to So what happened to the 2007 hurricane season?

  1. David says:

    “Hurricane Felix set the Atlantic record for fastest intensification from the first advisory to a Category 5 hurricane. It took Felix just 54 hours to accomplish the feat.”

    Of course you fail to mention that part of the reason is that comparing Felix to past category 5 hurricanes is an apples to oranges comparison:

    When forecasters upgraded Hurricane Felix to a category 5 storm, it had a minimum pressure of 939 millibars. That’s nearly 20 millibars higher than the old Saffir Simpson scale which included designations for central pressure in addition to wind speeds. Frank: “We would have never called that a category 5 hurricane.”


  2. Joe says:

    Interesting, but hardly earth-shattering.

  3. Paul K says:

    Good post. There is disagreement in meteorology about possible trends in hurricanes and the connection, if any, to global warming. It seems statistical analysis and nomenclature is having a hard time keeping up with ever increasing measurement capabilities. As you have pointed out, meteorology and climatology are very different sciences with often different conclusions.

  4. paul m says:

    With hotter/drier seasons we should get more dust – this will mean more chaotic patterns for hurricane activity. However, because of the hotter surface temps there will probably be very intense storms around.

  5. Gary Herstein says:

    A couple of question sets, actually:

    My first constellation of questions: are there any predictors — either in place or in the pipeline — for dust effects on the Atlantic? I am guessing the answer is “no,” since if they were even partially in place they would be providing input into the hurricane precitions. (Alternatively, are there acurate dust predictors, albeit on a shorter time scale than that required by the seasonal hurricane predictions, such that one could not know in July, but could tell by early September, that the dust effects were taking control of the overall pattern?)

    A second and related question set is this: are the dust factors principally from the Sahara (and hence, presumably related to the Levant &/or Sciroco) or are there other factors? If others, from which directions & sources do they typically flow? Or is this something that is itself genuinely global in character? (For example, dust from drought areas around the world, “Spanning the Globe”?)


  6. TAR says:

    With the Northern hemisphere tropical cyclone activity ACE index steadily decreasing since 2004 does that mean the dust from africa has been blowing for that long a period?

  7. beefeater says:

    “So what happened to the 2007 hurricane season?”

    Easy answer, it was unpredictable just like always. What happened to “Global Cooling” from the 70’s? Same thing. What will happen with “Global Climate Change”? Nobody knows for sure except that it will change, usually does, always has. So what’s the problem? That doesn’t sell books or get study grants.

  8. Jay Alt says:

    Gary Herstein writes:
    “are there any predictors — either in place or in the pipeline — for dust effects on the Atlantic? I am guessing the answer is “no,”

    Dust is a new research focus that requires some patience. In 2006 NASA research aircraft from French bases in W. Africa showed a link between dust and a quiet period.

    NASA review of 2006 season –

    For the 2007 season the flights and research were expanded. Predicting the occurance and extent of dust storms months in advance has never been done. Give them time to work on the problem.


  9. Ron says:

    The science is in its infancy and Gaia is a complex system. Give the scientists time to work.

  10. Gary Herstein says:

    Thanks for the dust info — which sounds like a snide phrase, but really isn’t. And I’m happy to give scientists time to work; I just knew that I did not know how much work had been done.

    For example, one misunderstanding I had: I assumed knowledge about the link between dust and quiet periods in the atlantic basin was older than the data mentioned above.