Blogtrek

Isabel and the GFS

It's late summer and early autumn, so it's hurricane time. And sure enough, there are two hurricanes and two tropical depressions out there. Hurricanes are rather unpredictable creatures. For example, take Fabian. It looked like it was going to curve to the north and go out to sea, and so not harm any land areas. Well that it did, but it unexpectedly gave Bermuda a direct hit, and now they are cleaning up the mess there. It's gone but there is another storm out there, Isabel. It is following the path of Fabian. So where is Izzy going?

It is way to the east of the Leeward islands, and so it will take several days even to get there. After then, will it go out to sea or will it hit the US or somewhere else? This is way off in the future and so a weather prediction or model system is needed that will go out as far as possible. NOAA's Global Forecasting System or GFS goes out to a whopping 16 days! That is time enough to find out what happens to Isabel. For a while GFS was saying that it was going to go out to sea. Then Gary Gray pointed out that the 2003 September 7 12Z (Z means Greenwich Mean time or Universal time) run of GFS shows Isabel slamming into New England, creating a new version of the Great New England Hurricane of 1938. This would happen about two weeks from now, around September 21. Gary Gray points out that he has no confidence in this forecast, because it is so way out in the future.

Indeed, future runs show other things. The 2003 September 7 18Z run shows Isabel once again going out to sea, and the 2003 September 8 0Z run shows it slamming into Nova Scotia and Newfoundland. The 6Z run today says it will go to Ft Lauderdale, Florida, then head into Tennessee, join up with an ordinary low, and create the biggest floods this country has seen since Agnes in 1972. The 12Z run shows it hitting midway between Massachusetts and Maine, and the latest run, 18Z, is even more horrendous. First it heads into the Delmarva Peninsula, right into Baltimore's inner harbor. Then it goes up the Delaware River, into Pennsylvania and New Jersey, giving New York City a big whack. Then it curves into New England. If this happens it will be the most destructive hurricane in history, because this area is heavily populated with a lot of development.

The point here is that the forecast is all over the place. It could hit Florida, it could hit Virginia, it could hit New England or Nova Scotia, it could go out to sea or even hit Bermuda again. That is why we don't see this on the TV weather report. The TV weatherman's job is to predict, and watching a model go from here to there as newer editions go out is not predicting, which requires saying definitely where it will go.

But nevertheless it is interesting to watch the forecasts. In a sense there is a virtual storm out there, hanging in the future, hitting all these places as time goes by, and as the storm gets closer, its variations will damp out and become more consistent. Then we will know where the real storm will hit. Further, you can get some idea of where it will hit from these forecasts. The runs seem to center around the New England and New York City area, so I think this area is the most likely to get hit. Further, it is not coming in at a usual angle in any of these runs, except those that take it to sea. It looks like it goes out to sea, then it bends to the west or northwest. This makes striking Delmarva, New Jersey, or New York more likely than usual. This is therefore a storm to watch. By the end of the week, we may know just who Isabel is going to visit.