Dr Masters Wonders
Jeff Masters outlines some unanswered questions about Isaac and I want to talk about one of them:
2. What’s the deal with these super-sized Category 1 and 2 hurricanes that have been hitting the U.S.? The past three landfalling hurricanes in the U.S.–Isaac (2012), Irene (2011), and Ike (2008)–have all been exceptionally large, among the top ten on record for horizontal extent of tropical storm-force winds. Each of these storms had an unusually low pressure characteristic of a storm one full Saffir-Simpson category stronger. Is this the new normal for U.S. hurricanes?
I said that Isaac was weird, this is really what I was talking about. The inability to establish an accurate track for the storm is related, but not the real issue.
The minimum pressure is an indicator of what the storm will do, which is why you may notice that there may be an up or down arrow after the pressure. If the arrow points up, indicating that the pressure is rising, you can expect that it is weakening and the wind speed will drop.
If you look at the 10PM Day 7 for Issac, it was a Tropical Storm with 70mph winds and a pressure of 979mb. Compare that to the 10PM Day 3 for Kirk which was a Category 2 with 100mph winds and a pressure of 980mb. This should not happen.
This was the problem with the tracking models. Isaac’s pressure said it should have been affected by the trough building in from the East, but that didn’t happen. That’s why the track kept moving West, because Isaac was totally ignoring the trough.
Kirk, OTOH, was pulled out into the Atlantic and away from land as the result of being pulled by a trough, and it looks like Leslie will follow, but Isaac only seem to respond to ridges of high pressure.
I didn’t remember the two earlier storms that were mentioned, probably because they didn’t directly affect me, but Isaac did. Dr Masters did notice that all of the storms had names beginning with “I” and wondered if they would also be the only storms to hit the US.
2 comments
Ike had an incredible span. And trust me… it hit hard enough, lasted forever, and knocked out more power around Houston than any storm I can remember: you could watch the horizon if you dared; the flashes occurred every few minutes for a couple of hours. Ike caused more wind damage in my neighborhood (knocked-over brick walls, bent 100′ posts under signs, signs themselves of various materials blown out, etc. But the really scary time was not the noisy middle of Ike (though I admit that whatever occasionally vibrated Stella’s apt. door was pretty bad) but the aftermath: traffic lights out for a couple weeks, some of them dangling in the middle of the road, drivers crazy at lightless intersections, glass everywhere, stinking rotten food in dumpsters, damned few grocery stores able to open, no internet access within our reach, etc., etc. I don’t want any more storms like Ike.
I remember Ike and the pictures you posted, Steve, I just didn’t remember it in this context because it got its wind field the old fashioned way, by spinning up to Category 4. It was very normal in its development, as that is what Cat 4 storms do – push a lot of atmosphere. Isaac didn’t spin up. I saw that I commented that Ike had the potential of rapid intensification at any point in the Gulf.
Going back in my archives and looking at the numbers, I now see what Dr Masters was talking about, because it still had a 944mb pressure after the max winds slowed, and it was acting resistant to the effect of a trough in the Gulf. This may be the new normal for storms in the Gulf – slow moving, huge wind fields, super-low pressure, but lower than expected max winds, and resistance to steering influences.
I know what you mean about the traffic lights. They were down for weeks after Opal, but they replaced the old ones with a new type rated for 200mph with a separate power system of some kind.
The storms of my youth lasted hours, not days.