Friday, August 29, 2008

Gustav Grows, Hanna Confounds

Today's early morning NHC discussion has worrisome news. Gustav is growing in size -- and the steering currents are growing even more complicated.
  • Gustav has grown in size.
  • Upper-level steering currents that have been edging it westward are expected to "weaken" today.
  • After passing Jamaica today, Gustav could strengthen "quickly" to a Category 3 hurricane.
  • Complicated interactions among various upper-level North American wind patterns -- the "mid-level ridge" over Florida, an expected "low"over the Southeast United States, a possible "weakness" in the Bermuda high," and another anticipated "high over the Ohio valley" -- leave the experts scratching their heads over just where along the Gulf Coast Gustav is likely to head after passing Cuba.
  • As a result, the latest computer-generated forecasts show "large changes" and increasing disagreement about the storm's projected path.
The one near certainty, blares the Hurricane Center in the usual capital letters:
As for T.S. Hanna, interactions among some of the same upper-level wind patterns leads the hurricane experts to conclude, for now, that Hanna will continue heading northwest for a time, then take a "rare, but not unique" southwesterly track while it fluctuates in strength for a couple of days.
Most of the global models are carving a large trough over the Central Atlantic and developing a large ridge over the eastern United states. This pattern should force Hanna on a slow Southwesterly track beyond three days... but at the same time the upper-level winds should weaken the cyclone.
Speaking of "rare but not unique," NHC forecaster Avila finds the picture so complicated he openly confesses, "I prefer to wait for more model runs" before making a forecast.

When even the savants at the National Hurricane Center decline to predict a storm path, you know things are truly up in the air.

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