The Intersection

Yet another of these perennial data issues has come up with the latest tropical cyclone, Jaya, which is currently tracking mercilessly towards Madagascar. (As if they need another storm this season.) As is obvious from the image below, the storm has weakened considerably in comparison with how strong it was yesterday.


But the question is, how strong was Jaya at its peak? Both the Joint Typhoon Warning Center and Tropical Storm Risk (which uses JTWC’s data) consider the storm to have peaked at Category 3. But the Cooperative Institute for Meteorological Satellite Studies at the University of Wisconsin, which assesses storm strength from satellite images every half hour, suggests that Jaya peaked at around 120 knot winds (sustained for one minute) and a minimum sea level pressure of 924 millibars. That sounds like a Category 4 storm.

And then there’s Meteo-France, which says the storm peaked at 930 millibars and 100 knot winds sustained over 10 minutes. If you convert that to one minute sustained winds–and I don’t have the conversion factor handy at the moment–it might again imply that Jaya was a Category 4 storm.

So, in short, just as was the case with Cyclone George, there may be a legitimate dispute over whether Jaya was a Category 3 or 4. The more I blog about hurricanes and their intensities, the more I realize how murky it all really is.

Meanwhile, in other news, it looks like we’ll soon have our first Northwest Pacific typhoon of 2007. Kong-Rey, pictured below, is projected to steadily intensify on its way towards Guam and the Northern Mariana Islands:



  1. #1 Adrian Clement
    April 1, 2007

    This video suposedly “debunks” the notion that carbon dioxide emissions are responsible for global warming. Some guy brought it up on my xanga. I wanted to know your opinion on the video.

  2. #2 llewelly
    April 1, 2007

    I don’t have references handy, but I recall that for Dvorak-based estimation of TC intensity, 10-minute wind is either 1-minute wind * 0.9 , or 1-minute wind * 0.88 , depending on the weather agency. After the reduction factor is applied, the wind speed is rounded to the nearest 5 kts.

    Additionally, meteo France’s Dvorak estimate for Jaya was 6.0 3
    advisory periods in a row. A Dvorak estimate of 6.0 indicates 115
    kt 1-minute winds, or just above the cat 4 boundary. (See here) NOAA’s
    SSD also estimated Jaya to have a Dvorak number of 6.0 3 times in a row .

    I don’t know why JTWC’s Dvorak estimates stayed at 5.5, but 0.5 or 1.0
    difference in Dvorak estimates is normal as far as I know.

  3. #3 Adrian Clement
    April 2, 2007

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