The Intersection

Flummoxed by Flossie

Overnight and up through this morning, Hurricane Flossie in the Northeast Pacific–having started out as a category 1 storm–rapidly intensified into a weak Category 4 with a well defined eye, as you can see in the infrared image below:

i-11f602621b12f142c75bee584287697c-flossie cat 4.jpg

I think it’s fair to say Flossie’s behavior took everyone by surprise. The National Hurricane Center forecasters were not predicting it, or anything close. Neither were the models. This is yet another indication of how bad we still are at forecasting hurricane intensity.

But you can’t blame the forecasters, really. I’m looking at some of the same data they did, and I’m just scratching my head. Typically, in order to rapidly intensify a hurricane needs deep warm water. But look at the figures below, first the Northeast Pacific sea surface temperatures as of August 10, and then the tropical cyclone heat potential as of the same date. (Click the images for higher resolution.)


As best I can tell, Flossie rapidly intensified between 135 and 140 W Longitude and 10 and 15 N Latitude. The SSTs in the area were warm enough to support a hurricane, of course, as the figure above shows. But as you can see from the next image (tropical cyclone heat potential), there was hardly a hurricane bullseye in this area in terms of a deep patch of warm water of the sort that one might expect:


So what the heck was Flossie doing? Beats me…perhaps this has something to do with the fact that Flossie is a very small storm as hurricanes go. Or perhaps there were very cold temperatures aloft in the storm outflow region, increasing the potential intensity that Flossie could achieve. But those are just guesses, I honestly don’t have a clue. I wonder what the forecasters think, but am not really getting any sense from reading their discussions.

In any event, Flossie has now passed 140 W and has become the responsibility of the Central Pacific Hurricane Center, based in Honolulu. Let’s hope the storm doesn’t continue to frustrate expectations–if it does, we may find ourselves contemplating possibility of a significant hurricane landfall on the islands. For now, though, Flossie is still far from Hawaii and expected to weaken as it gets closer…


  1. #1 bloomingpol
    August 11, 2007

    Any idea why the hurricane season has been relatively quiet in the Atlantic this summer? Is it just too early? What are the water temps like?
    I just finished your book Storm World, thank you for writing it, I plan to give it to my brother for his birthday very shortly.

  2. #2 llewelly
    August 11, 2007


    Any idea why the hurricane season has been relatively quiet in the Atlantic this summer? Is it just too early? What are the water temps like?

    In the west Atlantic, The water has been plenty warm since June or so. However – there was a great deal of African dust, dry air, and the shear was a little too high. Those all inhibit tropical development, and are normal throughout June, July, and the first half of August. So yes, it’s just too early. For more, please see the typical progression of an Atlantic hurricane season. In particular, note table 1, which shows that an ‘average’ Atlantic hurricane season will have 3 tropical storms by August 20. This year, the third tropical storm, Chantal, reached tropical storm strength on July 31st , about 20 days early.

  3. #3 ChrisC
    August 12, 2007

    Flossie is really representaitve of the way the whole eastern Pacific has been misbehaving this year. The season was predicted to have a 70% chance of being below average according to NOAA:

    While the season started slowly, it appears to have kicked off recently, with several named storms in the last few weeks, which was unexpected.

    Still, 2-4 hurricanes are expected, with 6-12 named storms, so we’re well on track to meet this prediction… if things don’t continue to charge on as they have in the last few weeks.

  4. #4 llewelly
    August 13, 2007

    As you can see here , despite La – Nina like conditions along the equator, most of the Eastern Pacific is anomalously warm (although Flossie is well out of the large warm region, and has been for a few days), and as you can see here , the Eastern Pacific has been anomalously warm for most of the year. Finally – you can see here that although the tropical heat potential was not high, waters exceeding 26C reached quite deep in the area where Flossie intensified. Nonetheless – the Epac has been surprising recently – but this is the normal time of year for peak Epac activity.

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