Senior meteorologist at The Weather Channel. Proud to be a weather-obsessed weather geek. Would be a DJ if not a meteorologist.
By: Stu Ostro , 2:57 AM GMT on August 29, 2012
Isaac has had two characteristics that have been a constant throughout its life: its struggles to strengthen, and its big size. The latter unfortunately more than compensates for the former. Isaac is a large and dangerous tropical cyclone and represents about as serious a threat as one will ever see from a low-end Category 1 hurricane in this location.
But what about the former? Here are a current map and time series graphs of vertical instability in the atmosphere relative to average, showing it being much less than average over the Gulf and Caribbean. I'm not sure to what extent this is dry air vs. something else going on in the atmosphere, but it is consistent with the difficulty Isaac has had in having and maintaining deep, symmetric convection.
Images credit: Regional and Mesoscale Meteorology Branch (RAMMB)
If instability had been above average, Isaac may very well have become a higher, perhaps a much higher category of hurricane. Which is scary, given its size and how dangerous it is as it is. The wind will be relentless, and result in widespread power outages continuing to accumulate and create adverse conditions for crews trying to restore power quickly. A long-duration strong onshore flow onto this very surge-prone coastline will cause the storm surge to be much higher compared to that from a small Category 1. The size and slowing movement of Isaac will produce excessive rainfall amounts, and flooding of that nature in addition to storm surge flooding.
And, having said that about Isaac's struggles, it is, alas, at the last minute the healthiest it has been. Look at the difference in symmetry between 24 hours ago last night (top image below) and tonight (top image), and the central pressure is down to 968 millibars... It's going to be a long night and a long couple of days ...
Images credit: NOAA/NESDIS
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