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  2. Cyclone George May Have Been a Category 4...or Not

Cyclone George May Have Been a Category 4...or Not

By cmooney on March 12, 2007.

i-98fbd88d9d6564cecf238436740b7e0d-donga_1_m1363514.jpg

Over at Wikipedia, the storm that caused the damage pictured at left is currently classified as a Category 3 hurricane (albeit one with a very low minimum sea level pressure of 910 millibars). The maximum intensity estimate from the Joint Typhoon Warning Center also corresponds to Category 3. But our very valuable (if fairly technical) dialogue in the comments section on a previous post distinctly suggests that George may have been a Category 4 on the Saffir-Simpson scale--and, if so, the year's third such storm.

We don't really know, of course, and quite possibly we never will. At the end of the year, when people tally up how many Category 4 and 5 storms there have been and feed that conclusion into the ongoing hurricane-global warming debate, George will, accordingly, pose yet another data problem of the sort that has continually stymied resolution of this issue.

Meanwhile, pressure is falling in another storm system in the South Indian:

i-71b55c515a42d1f88091a5606af84a3d-globeMarch12am.jpg

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The BOM and the JTWC rate storms differently. Yes, they both use the Dvorak method, but it's subjective, it's a statistical relationship between satellite appearance and wind speed, and therefor dependent on the database of observations used to calibrate it, which vary between agencies, and the JTWC appears to ignore environmental factors in estimating MSLP, at least for southern hemisphere storms.

So it's as if trying to decide whether to measure something in meters or yards, but not knowing the conversion ratio. Changning metrics could introduce spurious abnormalities, and confuse things (Review the Landsea & Emanuel exchange in nature). So it's import to pick either the BOM lane or the JTWC lane and stay in it.

Overall I really like the wikipedia TC articles. But they sometimes treat numbers from different agencies as interchangeable, and they are often unclear about the differences in estimating TC properties, and how this can distort statistics. (On the other hand, I've seen very few TC for layman pieces of any kind, that handle these issues any better than wikipedia. And I will admit I don't myself understand the issues well enough to know the 'right' fix to apply to the wikipedia articles.)

Llewelly,
My approach, to standardize these things, has been to listen to JTWC except in the Atlantic and NE Pacific where I listen (obviously) to the National Hurricane Center. It does add consistency, if nothing else.