Report 7: Isabel surprises
Just as it seems the models are in agreement and Isabel is headed right up the Chesapeake Bay straight towards the Washington Monument with 120 mph winds, Isabel pulls some surprises. They were talking about some shear affecting her progress. Today she got clobbered by it and her winds, despite an incredible tornado-like 236 mph gust in the clouds, dropped from 145 mph to 125 mph. Her huge eye, as if it suddenly looked into the bright sun, shrunk and shrunk until it vanished. She is predicted to hit another shear tomorrow and become even weaker, but she may grow stronger over the warm Atlantic, but then she may get weaker in coastal waters. It's a "good news, bad news" game. And now she has pulled another surprise tonight. The GFS, ETA, and all of the "SHIPS" runs now show Isabel hitting further south in North Carolina, like at Morehead City, then heading northwestward into western Virginia, Tennessee, and West Virginia. The Canadian GEM still shows her shooting up the Chesapeake but not as severe as before.
So what does it mean? Maybe Washington, Baltimore, and especially Hampton Roads are off the hook. It would be headed straight for Richmond, but go south of there and because of crossing over all that land, it weakens to tropical storm force with some hurricane winds over water. There would be no major catastrophic storm; as Gary Gray says, the Atlantic Coast won't fall off into the sea.
But keep alert, because more surprises may be coming. She may head to New England. She may hit South Carolina and produce floods there. She may even get into western Virginia, wheel around, and head back to Philadelphia and New York. Hurricanes are notoriously unpredictable and we should keep alert. Gov Warner was right in calling a state of emergency in Virginia. Hope he can deal with this emergency without the National Guard troops that can't help because they are in Iraq.
A Journey through Blogrealm
Blogtrek
Blogtrek
2003/09/15
Predictable/Unpredictable
With situations of the kind that hurricanes posed, it seems that things are either in fine agreement or they are haywire all over the place. There is no middle ground. With Isabel, the first few runs were all over the place: sea, Florida, Baltimore, New England, Nova Scotia. But then after a few days they consistently pointed a finger at North Carolina and Virginia. There was no mildly unpredictable phase. It is either precise enough to predict accurately or you can say absolutely nothing about it.
Similar situations happen in mathematical systems. For example, in estimating a quantity, such as the length of the tropical year in solar days, 365.2422, the first three decimals are just about absolutely accurate. The fourth one is about right, the 2, but it is fuzzy and I have heard estimates that begin with 365.2421. After that the digits are totally unpredictable and depend on the irregular rotation of the earth. Another example would be to observe that if x is the square root of 2, then x = 1 + 1/(1+x) so if one guesses a value for x, substitute it into 1 + 1/(1+x) and make that your revised value of x, one may hope to obtain sqrt(2). If you set x = sqrt(2) you get sqrt(2) back, but if you are off by a little bit, say x = 1.414213562373, then the next few approximations are about this value but they lose a decimal place of accuracy each iteration. Still, it is good enough for practical purposes. When this gets back to the units digits, the whole thing becomes unpredictable. Try it out on a spreadsheet and you see what I mean.
Why does this happen? Both the hurricane and the iteration formula are unstable equilibria. If you are right on the money, you remain so, but if you are not, you eventually get thrown off the track. And that is what happened to the first few predictions for Isabel, 12 days ago.
With situations of the kind that hurricanes posed, it seems that things are either in fine agreement or they are haywire all over the place. There is no middle ground. With Isabel, the first few runs were all over the place: sea, Florida, Baltimore, New England, Nova Scotia. But then after a few days they consistently pointed a finger at North Carolina and Virginia. There was no mildly unpredictable phase. It is either precise enough to predict accurately or you can say absolutely nothing about it.
Similar situations happen in mathematical systems. For example, in estimating a quantity, such as the length of the tropical year in solar days, 365.2422, the first three decimals are just about absolutely accurate. The fourth one is about right, the 2, but it is fuzzy and I have heard estimates that begin with 365.2421. After that the digits are totally unpredictable and depend on the irregular rotation of the earth. Another example would be to observe that if x is the square root of 2, then x = 1 + 1/(1+x) so if one guesses a value for x, substitute it into 1 + 1/(1+x) and make that your revised value of x, one may hope to obtain sqrt(2). If you set x = sqrt(2) you get sqrt(2) back, but if you are off by a little bit, say x = 1.414213562373, then the next few approximations are about this value but they lose a decimal place of accuracy each iteration. Still, it is good enough for practical purposes. When this gets back to the units digits, the whole thing becomes unpredictable. Try it out on a spreadsheet and you see what I mean.
Why does this happen? Both the hurricane and the iteration formula are unstable equilibria. If you are right on the money, you remain so, but if you are not, you eventually get thrown off the track. And that is what happened to the first few predictions for Isabel, 12 days ago.
2003/09/14
Isabel Report 6: National Guard Shortage
I have seen all of the runs of GFS today and they all say pretty much the same thing: Isabel is going to just miss the Outer Banks, come ashore somewhere around Norfolk, ride up the Chesapeake to Baltimore, then head straight for Rochester, NY. The population potentially affected by hurricane force winds is huge: Washington, DC, Baltimore, Philadelphia, maybe even New York, and then the upstate New York State cities, especially Rochester.
It is apparently not losing its maximum wind speed much, now about 155 mph. The weather forecast seems to say it will be 120 mph at landfall - a Category 3 hurricane. I am not sure what this will mean to places on the periphery of its clouds; I can't find the maps that show predicted wind speeds out to whichever radius. But they are powerful. If they hit the Outer Banks that powerful, it may redraw the geography. It may destroy the Oregon Inlet Bridge, but it may also fill in the inlet, meaning that they would simply pave an at-ground road instead of building a bridge. But another inlet will open up elsewhere, requiring the bridge there, perhaps somewhere on Pea or Hatteras island. That was open before at Pea Island and there is an abandoned bridge there which crossed that inlet.
After the hurricane, rebuilding will need to take place, and usually the National Guard is called out to help. But when we call on the National Guard this time, there may be no Guard we can call on, or inadequate Guard, because these troops are all in Iraq. They may have to borrow from Guards in other states, even though they are short too. It seems to me that we didn't need to pile all those troops in Iraq - they are needed in the states at times.
I have seen all of the runs of GFS today and they all say pretty much the same thing: Isabel is going to just miss the Outer Banks, come ashore somewhere around Norfolk, ride up the Chesapeake to Baltimore, then head straight for Rochester, NY. The population potentially affected by hurricane force winds is huge: Washington, DC, Baltimore, Philadelphia, maybe even New York, and then the upstate New York State cities, especially Rochester.
It is apparently not losing its maximum wind speed much, now about 155 mph. The weather forecast seems to say it will be 120 mph at landfall - a Category 3 hurricane. I am not sure what this will mean to places on the periphery of its clouds; I can't find the maps that show predicted wind speeds out to whichever radius. But they are powerful. If they hit the Outer Banks that powerful, it may redraw the geography. It may destroy the Oregon Inlet Bridge, but it may also fill in the inlet, meaning that they would simply pave an at-ground road instead of building a bridge. But another inlet will open up elsewhere, requiring the bridge there, perhaps somewhere on Pea or Hatteras island. That was open before at Pea Island and there is an abandoned bridge there which crossed that inlet.
After the hurricane, rebuilding will need to take place, and usually the National Guard is called out to help. But when we call on the National Guard this time, there may be no Guard we can call on, or inadequate Guard, because these troops are all in Iraq. They may have to borrow from Guards in other states, even though they are short too. It seems to me that we didn't need to pile all those troops in Iraq - they are needed in the states at times.
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