Notice Anything?

The Associated Press is reporting that the National Oceanic and Atmospheric Administration is predicting that the "La Nina" phenomenon will not form this year. The report says that means that there should "generally" be a less severe hurricane season (which is not at all what the NOAA website says that La Nina usually brings - but we digress). But we'll let the AP report:

MIAMI - The National Oceanic and Atmospheric Administration has predicted that La Nina — a cooling of Pacific Ocean waters that generally brings a more active Atlantic hurricane season — will be absent for the next two months.

The absence of La Nina doesn't necessarily herald a tame summer for tropical storms and hurricanes, said Dennis Feltgen, meteorologist and spokesman for NOAA in Miami.

"There are so many other ingredients that contribute to the development of tropical cyclones, it's not just the fact that we don't have a La Nina that comes into play here," Feltgen said.

Hurricane season 2005 was a textbook example of this. La Nina wasn't around, but the season managed to break records, with 28 named storms, including 15 hurricanes, seven of which were major.

La Nina is the counterpart to the better known El Nino, a warming of Pacific waters near the equator that creates a less conducive environment for tropical cyclones in the Atlantic. Both ocean conditions are hard to predict long-term and don't follow regular patterns.

This year, forecasters have predicted an above-average hurricane season, which runs June 1 through November. They believe there will be 13 to 17 named storms, with seven to 10 of them becoming hurricanes and three to five of those reaching at least Category 3 strength.

All of which is interesting. But buried at the bottom of the story is something that suddenly struck me as odd. There has not been a single named Atlantic storm since June 1st. Not one. That would be six weeks with no storms worth noting. That, I think, is unusual for this time of year, isn't it? There is no guarantee that there will not be a lot of storms in the next few weeks or months, of course. And La Nina actually does not, according to NOAA, form all that often anyway. But six weeks without a named storm? 13 to 17 predicted storms would average out to more than two per month over the season. (Yes, I know these things do not actually average out, it still seems very quiet.)

UPDATE: Well, I found the historical data for hurricanes, and it isn't really unusual not to have any storms through the first six weeks - there is no real pattern to any of that. (I did not check every year they have records posted for, of course, just a random sample). Some years there are several through the early part of the season, some years they all hit late in the year. Take a look at 1933 if you get a chance, though. It would have been a crappy year to go for a Caribbean cruise.

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  By chuck, Saturday, 14 July , 2007 @ 10:14 pm

  If the storms are evenly distributed over the time from June 1 through November, and they probably aren’t, then they would follow a Poisson distribution. The probability of k storms in a given period would then be

  exp(-L)*L^k/k!,

  where L is the average number of storms expected in that period. For example, if two storms were the average expected during the six weeks from June 1 to mid July, then the probability of zero storms (k = 0) is about exp(-2) ~= .135. Small, but not terribly small, about the same as getting three heads in a row flipping a coin.

  This approximation breaks down for large k because you can ‘overlap’ storms and have hundreds a day. Differently said, storms are forced to keep a certain distance from each other in time and space. Anyway, the same formula would also apply in the absence of trends for the yearly average of the number of storms in that period over a number of years. If el Nino and el Nina do affect the number of storms, then there are trends, so it all goes to H*ll

  Sorry for the blather, but you tickled my thoughts.

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