Tropical storm formation requires three things. (1) A tropical distrubance (a storm). (2) Low upper wind shear, to allow deep convection (the eye). (3) An SST >= 26C, to power the system.
I was just thinking, that in effect one of these conditions is now almost always true, namely (3). So, where before we used to have a sort of boolean function like (TS & LW & SST), we now have just (TS & LW & "true"). In that sense, it's not too surprising that we see a significant storm activity increase. It's almost like we're working with an effective marginal probability, where one out of three conditions has been integrated out. And marginals are always more dense than joint distributions.
All that aside, I can't help thinking about a couple of last years storms. One of them survived for something like two days in 50mph wind shear. That's not supposed to happen. Another one formed over waters colder than 26C, and also in unfavorable wind shear. Events like that suggest the possibility of completely new effects emerging. Effects that are completely outside our models.
Or, maybe I'm just being melodramatic.
June is normally the least active month of hurricane season (Figure 1). There have been 32 named storms in June since reliable records began in the Atlantic in 1944--an average of one every two years. There have been 10 June hurricanes (one every six years), and only two June major hurricanes. One of these major hurricanes was the notorious Hurricane Audrey, a Category 4 monster that killed 550 when it slammed into the Texas/Louisiana border on June 27, 1957. The only other June major hurricane was Hurricane Alma, which struck Cuba on June 8, 1966. Alma moved just offshore Florida's west coast as a Category 3 hurricane before weakening to a Category 2 hurricane and striking the Big Bend region of Florida's Panhandle. Alma killed 90.
Last year June was 4 times more active than normal (...)
High wind shear is going to be a severe impediment to tropical storm formation for at least the first two weeks of June. The jet stream has split into two branches--the polar jet, located over the northern U.S., and the subtropical jet, which is blowing over the Gulf of Mexico. As long as the subtropical jet is blowing over the Gulf of Mexico with 30 - 50 knots of wind like it is now, no tropical storm formation is likely in the Gulf. If we do get Tropical Storm Alberto in the next two weeks, it will have to form in the western Caribbean south of Cuba. Steering currents would then likely take the storm north across Cuba and then northeastward across the Bahamas and out to sea. The Gulf Coast from Texas to the Florida Panhandle will be protected from any tropical storms by the strong subtropical jet steam. I'm predicting only a 10% chance of a tropical storm in the Atlantic by June 15 this year.
(...)
Given that the next two weeks are likely to be the quietest time in what promises otherwise to be another long and busy hurricane season, I'm outta here. This will be my final "live" blog until June 13, as I'm taking my main summer vacation early. I plan to spend some time at Cape Hatteras before any hurricanes threaten! I've prepared a series of "canned" blogs, mainly Q and A from a newspaper interview I did last Sunday for a Florida newspaper. If Alberto does surprise us while I'm gone, the other meteorologists at wunderground will post the latest analysis here for you.
http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=365&tstamp=200606
Printer-friendly format
Email this thread to a friend
Bookmark this thread
(1000+ posts)
Send PM |
Profile |
Ignore
