NOAA has issued their last pre-season projection for the 2010 Atlantic hurricane season. In short, a very active season is possible. Here are the highlights:
We estimate a 70% probability for each of the following ranges of activity this season:
14-23 Named Storms, 8-14 Hurricanes 3-7 Major Hurricanes An ACE range of 155%-270% of the median.
The seasonal activity is expected to fall within these ranges in 7 out of 10 seasons with similar climate conditions and uncertainties to those expected this year. They do not represent the total possible ranges of activity seen in past similar years.
I like to see numbers in context. I’ll start with the 14-23 named storms. On average, 11 storms are named every year. The most active Atlantic hurricane season on record was 2005 – the same year of Katrina, Rita and Wilma – when there were 31 named storms. The first storm formed on the 8th of June and the last storm dissipated on the 6th of January, 2006! For those unfamiliar with hurricane naming conventions in the Atlantic, see this page. The set available this year are the same as those used in 2004. So if there are 14 named storms, Nicole will be the last of 2010. If there are 23, then just like 2005, the list of names will be exhausted. In 2005, storms after Wima were assigned Greek alphabet names. That convention could be used again this year if things get really ramped up.
There were 15 hurricanes in 2005. So this season’s projection calls for fewer hurricanes (tropical storm systems that attain 74mph sustained winds) than 2005. Last season, there were only 3 hurricanes. 2008 saw 8 hurricanes form – so this year could be more similar to that year. The average number of hurricanes per year is 6.
3-7 major hurricanes – those are big numbers. The average number of major hurricanes per year is 2. A major hurricane is one that reaches Category 3 strength on the Saffir-Simpson hurricane scale. Storms typically have a minimum of 111mph sustained winds. Of those 8 hurricanes in 2008, 5 reached major hurricane status: Bertha, Gustav, Ike, Omar and Poloma. Of the 15 hurricanes in 2005, 7 reached major hurricane strength. The difference between 2005 and 2008 in terms of number of major storms then was only 2. A lot of factors determine how strong hurricanes get. So the difference between 2 major hurricanes and 3 is a lot more than just a number.
The ACE measurement is a relatively new one. It is the Accumulated Cycle Energy, used to measure individual storms as well as entire tropical seasons. The ACE is calculated by squaring the the estimated maximum sustained wind velocity of each cyclone with sustained winds over 35 knots (tropical storm strength) every six hours. Those values are then added together over the life-cycle of the storm. The ACE values for every year since 1851 has been calculated by Chris Landea at NOAA’s National Hurricane Center. A projected ACE of 155%-270% of the median is obviously indicative of a very active season.
One of the factors that has a big influence on how strong tropical systems that enter the Gulf of Mexico can get is the position and strength of the Gulf Loop Current. This is the same current being discussed in relation to the oil volcano currently erupting off the Louisiana coast. The good news for the potential future spread of oil away from the Gulf of Mexico is an eddy has broken off the Loop Current. Oil within the eddy will more likely stay in the Gulf rather than be transported out of it, as Dr. Jeff Masters explains in this blog post. The last Loop eddy that broke off is still in the western Gulf off the coast of Mexico, having traveled 3-5km per day since it broke off the main current back in July 2009.
Unfortunately, what’s good for limiting the spread of oil can be bad for tropical systems entering the Gulf. The eddy maintains very warm sea temperatures to great depths, making high energy available to passing storm systems. Hurricane Katrina is a perfect example of this. She crossed the Florida peninsula on 26Aug2005 with 75mph sustained winds. One day later, as she passed north of the western side of Cuba, she had strengthened to 115mph winds (a Category 3). She stayed at that strength for another day while she passed over the northern edge of the Loop Current. Then, she encountered a loop eddy. Four hours later, her sustained winds jumped from 115mph to 144mph, becoming a Category 4 storm. 12 hours later, her winds were 161mph, becoming a Category 5 storm. 16 hours later, they had rocketed all the way up to 173mph. In just over half a day, Hurricane Katrina went from a weak Category 3 storm to a Category 5 monster – mostly because she passed directly over the warmest core of the Loop Current eddy. Thankfully for the residents of the Gulf Coast, that eddy was still in the middle of the Gulf. If it had been closer to land, Katrina would have been even stronger at landfall. In fact, Hurricane Rita passed over that same eddy later in 2005, rapidly strengthening just like Katrina did. Rita’s path took her over even more water before landfall than did Katrina’s. Rita still caused Houston to be partially evacuated and did plenty of damage after landfall.
So conditions are prime for another above-average hurricane season. Individual storms will of course form where they will and little can be confidently said about their potential impacts on the Caribbean or Mexico or the U.S. Potentially dangerous storms can quickly come together with all of the conditions that presently exist. 2010 could be another infamous season.
Cross-posted at SquareState.